Alexanderson alternator in the SAQ Grimeton VLF transmitter.
Sweden’s Alexanderson alternator station SAQ has planned a Christmas Eve transmission on 17.2 kHz. The transmitter will be tuned up starting at around 0730 UTC, and a message will be transmitted at 0800 UTC. The 200 kW Alexanderson alternator is an electromechanical transmitter dating back to 1924.
The event will be streamed live on the Alexanderson site YouTube Channel. Listener reports are invited via email or direct to Radiostationen Grimeton 72, SE-432 98 Grimeton, Sweden. Amateur Radio station SK6SAQ will be active on Christmas Eve on 7,035 and 14,035 kHz on CW, or on 3,755 kHz on SSB. Two stations will be on the air most of the time.
Many thanks to SWLing Post contributor, Gary DeBock, for sharing the following guest post:
Supercharging the XHDATA D-808
Installation of High Performance AM and LW Loopsticks
By Gary DeBock, Puyallup, WA, USA, September 2018
As a stock receiver the Chinese-made D-808 AM-LW-FM-SW-AIR portable is a very capable performer, with AM reception superior to that of any current Ultralight model, and impressive FM reception as well. The radio was certainly “inspired” (to use a generous term) by the C.Crane Skywave SSB model, which coincidentally was manufactured in the same part of China by C.Crane’s Redsun partner—with the first units going out the door a few months before the D-808 came into existence.
Because foreign intellectual property is routinely copied in China with no punishment from the government, XHDATA essentially had the chance to copy all the good points in the Skywave SSB design and improve upon its weak points as well. The only precaution that XHDATA took after this wholesale design appropriation was to forbid direct shipments of the D-808 from China to North America—presumably to avoid a copyright lawsuit by C.Crane. As such, the first D-808 models were sold to the rest of the world around January of 2018 at a price about half that of the Skywave SSB, while North American DXers were told that since the model couldn’t be shipped to the USA or Canada, they were out of luck.
Of course some D-808 models did make it into North America, where it was found to be a very capable portable with astonishing value for the price. Finally around March, an enterprising Chinese eBay seller came up with a plan to ship the model to North America through Israel, thereby skirting around XHDATA’s direct shipment prohibition. As of late August this eBay seller (harelan ecommerce) has already sold 62 of the D-808 models this way, even though he charges a premium for shipment to North America. Whether this single supply source will continue to serve North American customers is currently unknown, but out of the 7 models that I have purchased from him there hasn’t been a single D-808 model with any issues– despite the apparent lack of any manufacturer’s warranty offered on the radio.
Despite the D-808’s rather dubious design pedigree there is no doubt that the Chinese engineers (or reverse engineers?) did a superb job in creating an awesome radio for the money. Besides directly copying the Skywave’s SSB design and controls, XHDATA also made significant improvements, including a longer loopstick (providing clearly superior AM sensitivity), a much more powerful audio amplifier (correcting a serious shortcoming in the Skywave SSB) and a much lower price (about half that of the $169.99 Skywave SSB, for models shipped outside North America). Another great advantage for someone wishing to perform this loopstick upgrade are the perfectly located, highly accessible Litz wire connections on the RF circuit board—apparently used by the Chinese engineers to conveniently test out various loopsticks, and retained in the final product. The radio’s high quality construction and survivability in adverse conditions were proven repeatedly over the summer here, with the model surviving accidental exposure to a 104 degree (43 degrees C) car trunk temperature, exposure to moderate rain, repeated travel bumps, and use as the main receiver during a 9-day DXpedition to a plunging ocean side cliff in Oregon state. The 3.7v lithium-ion rechargeable battery provides superior run time for extended DXing sessions, and is included in the D-808 shipping package, along with a USB cord to charge the battery, a plug-in wire antenna (for FM,SW and AIR), a vinyl carrying case, and a pretty basic English instruction manual.
One thing you will NOT find supplied with the D-808 is a warranty card– either in the shipping box, or online. This is pretty standard practice in China, incidentally, where concepts like refunds and warranties aren’t generally part of customers’ expectations. This doesn’t necessarily mean that XHDATA won’t repair obvious problems in a new D-808, but it does mean that they aren’t assuming the obligation to do so. I have heard from one North American purchaser who received a new D-808 with a defective speaker, and he is still waiting for the model to be repaired (after paying the shipping charge to send it back to China). Each individual purchaser must decide whether or not this lack of any warranty is a deal breaker. But if you are looking for a final reason to perform this loopstick transplant, why not consider the fact that you will not be violating any manufacturer’s warranty by doing so??
Although this 7.5” loopstick upgrade will certainly make your D-808 far more sensitive than the stock model on Medium Wave or Longwave, it is not designed to compete with large (2’ sided or larger) inductively coupled box loops, or any of the new FSL antennas. The sensitivity upgrade will boost the D-808’s MW band weak-signal performance up to the level of classic portables like the ICF-2010 and RF-2200; however, and since the D-808’s DSP-enhanced selectivity will generally exceed that offered by these classic portables, the overall DXing capability in the AM mode could be considered slightly greater. The D-808 does have SSB capability, although it lacks the SSB tuning convenience offered by the ICF-2010 and RF-2200. It also lacks the ICF-2010’s superb Synch detector, a big advantage in weak signal DXing. But in portability, versatility and DXing value for the price, the “Supercharged” D-808 is a real winner.
This construction article will provide the builder with step-by-step instructions to upgrade the XHDATA D-808’s loopstick to a much more sensitive, externally-mounted 7.5” Medium Wave or Longwave loopstick replacement. Both the Medium Wave and Longwave 7.5” loopstick designs have been thoroughly tested and proven effective in actual DXing by hobbyists other than the author, and as long as the instructions are followed carefully, this relatively inexpensive modification will provide a major improvement in the D-808’s weak-signal reception capability.
This modification project involves close-order soldering on the D-808’s circuit board, and should only be attempted by builders with reasonably good eyesight, good hand coordination and soldering experience. The project also calls for the use of a precut plastic loopstick frame to attach the antenna to the top of the D-808’s top back cabinet surface, and the construction of this precut plastic frame requires either the use of a 12” (or larger) power miter saw, or some rather lengthy cutting with a hacksaw. Use of a power miter saw SHOULD NOT be attempted by those without serious power tool experience! The author assumes that only qualified power tool operators will attempt to use a 12” miter saw to cut these frames quickly, and that other builders who wish to construct them will use a hacksaw. As such, only basic cutting instructions are provided for the 12” power miter saw users, while detailed instructions are provided for the hacksaw users. To assist builders who are not qualified to use power tools, the author has prepared a LIMITED number of these precut plastic loopstick frames on a power miter saw, which will be offered at cost to these builders on a first come, first served basis.
A final warning is in order concerning the step of gluing the precut plastic loopstick frame to the D-808’s top back cabinet surface. Although this step is not dangerous, it is pretty tricky. Since the superglue “grips” very rapidly, you will only get one chance to ensure that the frame is straight, and centered on the D-808’s top cabinet surface. Do yourself a favor, and make multiple “dry runs” to practice this important step before applying the glue! Failure to take this step seriously will probably result in a crooked loopstick frame—which will hold the antenna just fine for DXing purposes, but which will be an eternal reminder to the DXer (and everyone else) of the hazards of haste.
Construction Parts Required
This 7.5” loopstick D-808 construction article will guide you through the assembly of either a 7.5” Medium Wave loopstick D-808 or a 7.5” Longwave loopstick D-808, so make sure that you order the parts necessary for construction of your chosen model. The picture above shows the parts that will be necessary for construction of either model, but the Litz wire and 7.5” ferrite rod components differ according to whether you are building the Medium Wave or Longwave model.
Miscellaneous: One packet of Duro Super Glue (.07 ounce size), solder, 25w (low heat) soldering iron, hacksaw (or power miter saw), screwdriver set, sandpaper, needle nose pliers, diagonal cutters
D-808 Radio Preparation
Before starting the modification give the radio a thorough test on all bands, ensuring that all the stock model functions work properly, and that there are no issues with the display, speaker, headphone jack, battery or charging system. It’s also a good idea to run a daytime DX band scan on the AM or Longwave band (for whichever band you plan to construct an upgrade loopstick) and document the results—to use as a benchmark for the upgrade loopstick’s performance.
Antenna Frame and 7.5 inch Loopstick Preparation
1) Refer to the photo below. Using the “Supercharging the Tecsun PL-380” article (posted at http://www.mediafire.com/file/du3sr5cd9thqvau/7.5inch-LS-PL380.doc/file or available directly from the author) carefully prepare the orange loopstick antenna frame according to construction steps 1-9, EXCEPT note that the lower (glue surface) edge of the antenna frame should be cut to a length of 5 3/4” (147mm), NOT 5” (127mm) as described in the PL-380 transplant article. Pay close attention to the safety precautions concerning power tool usage, and DO NOT attempt to use a power miter saw unless you have SERIOUS power tool experience!
2) If you are constructing an AM (Medium Wave) loopstick, follow construction steps 10-16 in the PL-380 transplant article to construct the antenna. If you are constructing a Longwave loopstick, follow construction steps 10a-16a in the PL-380 transplant article to construct the antenna. If you are constructing both loopsticks, MAKE SURE that the ferrite rod and Litz wire are only used in the antennas for which they were designed. Mixing up these items is very easy, and such a mistake will make both loopsticks perform like clunkers.
3) After construction of either the AM or Longwave loopstick, follow the instructions in steps 29 and 30 of the PL-380 transplant article to install a piece of 3 1/8” (79mm) shrink tubing, EXCEPT note that this length is slightly longer than the 3” (76mm) length called for in the PL-380 article.
4) Refer to the photo below for the following three steps. [NOTE: Although this photo shows the AM (Medium Wave) loopstick, the procedures in this step are the same for the Longwave loopstick, although the position of the rubber hose lengths and clear vinyl inserts will be closer to the ends of the ferrite rod]. Carefully slide the length of 3 1/8” shrink tubing into the position shown, ensuring that there are no Litz wire kinks or bends inside the shrink tubing.
5) Take the two 3/4” (19mm) clear vinyl inserts and slide them onto the ferrite rod ends, twisting them up against the border of the Scotch “Extreme” tape ends to lock the tape in place under the vinyl inserts. Ensure that the clear vinyl inserts do not touch any Litz wire leads or coil turns.
6) Slide the 1” (25mm) lengths of rubber heater hose over the clear vinyl inserts until the appearance of the loopstick resembles the above photo. Ensure that the rubber hose sections also do not touch either the Litz wire leads or any coil turns. Finally, place the completed loopstick in a safe place until it is called for in Step .
7) Refer to the photo above for this step. Remove the battery from the radio, and using a Jeweler’s Phillips screwdriver of the correct size, remove the six identical screws in the positions shown (NOTE: These screws have a tendency to stick inside their slots, even when the slots are turned upside down. If you cannot remove all six screws it’s not a major problem, but at least ensure that the screws are completely loose in their slots, and that you don’t lose any of them during the remaining steps). Grasp the tuning knob, and pull it out horizontally in a completely straight manner to remove it from the radio. Ensure that the battery, tuning knob and all removed screws are placed in a safe place until the radio is reassembled.
8) Carefully separate the front and back cabinet sections and place them down in the position shown in the photo below. Note that the front and back sections of the radio are connected by a ribbon wire plug-in system– ensure that this plug remains securely inside its slot at all times, and that no great stress is placed on the speaker wires.
9) Refer to the close up photo below, and note the position of the two Litz wire soldering points on the circuit board (in the lower right corner of the photo). Using diagonal cutters, cut the two Litz wire leads at the position shown, UNLESS you wish to salvage this stock loopstick for other projects—in which case you should desolder the entire lengths of the Litz wire leads from the circuit board at the positions shown in the lower right corner (NOTE: The stock loopstick is of a fairly good design, and has an inductance that would be compatible with any DSP-chip Ultralight radio, providing an AM sensitivity boost in the process).
10) Refer to the photo below. Using a flat Jeweler’s screwdriver with a 1/16” blade, carefully probe around all four sides of the stock loopstick to break all of the glue bonds. Work slowly and carefully around the perimeter of the ferrite rod, including the plastic covers on each end. Once most of the glue bonds have been broken the ferrite rod will begin to shift around as you break up the few remaining bonds, but until this point work slowly and patiently to break up the glue.
11) Refer to the photo below. Using the flat Jeweler’s screwdriver, once all of the glue bonds have been broken and the ferrite rod is loose in its slot, lift the ferrite rod out of its slot on one side by prying up under the plastic cover on the end of the ferrite rod. Ensure that the Litz wire leads have either been cut or desoldered from the circuit board, then grasp the ferrite rod with your fingers and pull it completely out of the slot with a slight twisting motion.
12) Remove the wrist strap, and refer to the photo below. Carefully pick up the two sides of the radio and place the back section in a vertical position as shown, with a heavy flat weight (barbell, or other heavy flat item) pressing up against the back cabinet section to keep it in a vertical position. Ensure that there is adequate, even lighting on the top cabinet section for the gluing process in the next step, and that the back cabinet surface will not shift around as you make the gluing “dry runs,” and perform the actual gluing of the loopstick frame to the top of the cabinet.
13) Take the previously prepared orange plastic loopstick frame, and ensure that its bottom glue surface is completely smooth and flat, with no uneven ridges on the edges of the glue surface (remove these with fine sandpaper, but ONLY on the ridges, and not on the rest of the flat glue surface). Using a damp paper towel, wipe the top cabinet glue surface and the loopstick frame glue surface to remove any dust or debris, then wipe them again with a dry, clean paper towel to ensure that they are both completely dry.
Take the loopstick frame and gently slide the frame over the top cabinet surface to ensure that both surfaces are smooth and flat. Refer to the photo at the top of the next page. Ensure that there is even, bright lighting on the top cabinet surface, and make several “dry runs” to place the loopstick frame in the exact center of the top cabinet surface (with 1/16”, or 1.5mm of space between the frame ends to the cabinet ends), and also 1/16” (1.5mm) of overhang above the front edge of the cabinet’s glue surface (NOTE: if you wish to simplify the process by lining up the front edge of the loopstick frame with the front edge of the cabinet’s glue surface it will still provide an acceptable result, but you will need to do some minor sanding of the whip antenna’s plastic slot post, as shown in the photo below. In either case, make repeated “dry runs” with the loopstick frame to practice placing it in the exact center of the top cabinet’s glue surface, since you will only get one chance to place it in the proper center position once the superglue is applied.
NOTE: The back of the loopstick frame has a beveled surface to permit full operation of the radio’s whip antenna after the frame is glued on the top of the cabinet surface. If the loopstick frame is glued with a 1/16” (1.5mm) overhang in front of the front edge of the cabinet surface then the whip antenna should have enough space for free operation. The alternative is to glue the two front edges lined up with each other to simplify the gluing process, in which case minor sanding may be required on the whip antenna slot post, as shown in the photo below.
14) After making multiple “dry runs” and becoming familiar with accurate placement of the loopstick frame on top of the cabinet, refer to the photo at the top of the next page. After once again ensuring that the back cabinet section will not shift around during the gluing process, take the Duro superglue packet and apply a thin (1/8”, or 3mm) bead of glue along the center of the cabinet’s glue surface, extending it 5 1/4” (133mm)long, with equal spaces on both ends (as shown). While sighting the two sides place the loopstick frame carefully down in the correct center position as practiced previously, with the 1/16” overhang if desired. If satisfied with the position, press down on the frame to lock the two surfaces together securely. Usually the frame may be shifted around slightly within 1 or 2 seconds of placing it on the superglue, so use this brief time to promptly shift the frame to a straight position, if necessary. After a couple of seconds, though, you will need to be satisfied with whatever position the frame has ended up with (regardless, it will still hold the loopstick just fine, for DXing purposes).
15) After the loopstick frame is securely placed and locked on top of the D-808’s cabinet surface, place downward pressure on the loopstick frame along its length in order to ensure a tight glue bond throughout the entire top cabinet surface. Continue this process for about one minute, and sight both ends of the loopstick frame to ensure that they are both completely flat against the D-808 cabinet.
16) Inspect the front and back edges of the loopstick frame’s border with the D-808 cabinet for any glue seepage, and if any is found, remove it promptly with the 1/16” flat Jeweler’s screwdriver blade. Glue should not be allowed to run past the frame edges. This completes the process of gluing the frame to the D-808 cabinet.
7.5” Loopstick Installation
17) [NOTE: The installation procedures of the Medium Wave (AM) and Longwave loopsticks are identical, except that the plastic tie wraps and rubber hose sections are closer to the ends of the ferrite rod in the Longwave version. The following photos are for the Medium Wave (AM) version, but Longwave loopstick builders should follow the same steps, while referring to the Longwave model photo in the “Operation” section as a guide]
Refer to the photo below. Carefully take the previously prepared 7.5” loopstick and hold it in the position shown—in its slot, centered in the middle of the orange antenna frame, with the shrink tubing and Litz wire leads running down to the left. Take the two plastic tie wraps and install them in the position shown, centered over the rubber hose sections on the loopstick, while ensuring that no Litz wires or shrink tubing is bound under the plastic tie wraps.
18) Refer to the photo below. Lay the two cabinet sections down flat as shown, ensuring that the Litz wire shrink tubing is in the exact position shown (if it isn’t, carefully slide it along both Litz wires until it is in this exact position). Carefully thread one Litz wire end through the empty wrist strap hole, then thread the other Litz wire end through the hole, as shown. Finally pull on the two Litz wires together from the right while guiding the end of the shrink tubing into the empty wrist strap hole, and pull a short section of the shrink tubing through the hole (as shown) to protect the Litz wire insulation from friction damage.
19) Refer to the photo below. Using the previous procedure to install shrink tubing (which is described in the PL-380 transplant article) install a 2.5” (63mm) length of shrink tubing over the two Litz wire ends, and shift the shrink tubing into the position shown in the photo. After this is done cut the two Litz wire leads to the lengths shown in the photo (NOTE: make sure that the ends of both Litz wires are cleanly cut, not frayed and at the minimum diameter before attempting to insert them into the shrink tubing. The process is much easier when the Litz wires pass smoothly through the shrink tubing).
20) Refer to the close up photo below. Using a low heat (25w) pencil-type soldering iron, remove the two stock Litz wire leads at the positions shown, taking care not to use excessive heat, or touch the adjacent components. Ensure that the new Litz wire leads are at the length shown when the leads are in a horizontal position throughout the cabinet, and cut them to this length if they are not.
21) NOTE: When tinning the 250/46 Litz wire it is essential that all of the individual Litz wire strands be completely soldered together for a length of at least 1/4” (6mm), with bright, shiny solder around the circumference of the Litz wire ends for this minimum (1/4”) length. The Litz wire must be heated with a clean, hot soldering iron around its circumference in order to melt the solder properly for this step]
Refer to the photo above. Pull the Litz wires up out of the previous position, and place a clean rag underneath them (on top of the circuit board) to completely protect the circuit board from any solder which might accidentally drop down during the tinning process. Using your hot 25w soldering iron melt a generous amount of solder on its tip, and work the soldering iron tip slowly and patiently around the circumference of each Litz wire end until there is a bright, shiny solder length of at least 1/4” (6mm) in a cylindrical pattern at the end of each Litz wire. When doing this, take great care not to allow any solder to drip down onto the circuit board below (i.e., make sure that your rag completely covers the circuit board). The final appearance of your Litz wire lead ends should resemble those in the photo.
22) When your Litz wire lead ends resemble the photo above, cut the soldered portion down to a length of 3/16” (5mm) and observe the appearance of the end of the Litz wire. It should have a bright, solid circular shape, with no gaps or individual Litz wires showing. If not, reheat the end of the Litz wire while adding some solder, and repeat this step.
23) NOTE: The Litz wire connection points on the circuit board are surrounded by other important components. It is important to avoid solder drips on these components, or solder bridges to their leads. Solder the Litz wire leads down at an angle to avoid these surrounding components, and use the minimum amount of heat and solder to ensure good electrical connections)
Refer to the close up photo above. Following the precautions described, solder the two Litz wire leads down onto the circuit board at an angle, as shown in the photo. After soldering, make a close visual inspection to ensure that there are no solder bridges across the Litz wire connections, or nearby components. The remaining length of the Litz wire leads should be routed in a horizontal manner to the wrist strap hole.
24) Carefully pick up the front and back cabinet sections, and hold the back cabinet section fairly close to the front section (as the radio would normally be oriented, when assembled). Refer to the photo below, and carefully insert the “Fine Tuning” control thumbwheel from the front cabinet section into its slot on the back cabinet section in a sideway movement. This will allow you to fully close the front and back cabinet sections in the next step.
25) Refer to the photo below. Pick up the two cabinet halves and carefully snap them together (this action should not require any great force). Place the radio face down in the position shown (with a soft surface underneath, for protection), and using the Jewelers Phillips screwdriver of the correct size, carefully screw in the six screws that were loosened previously, starting with the screw near the whip antenna post (you should pick up the radio temporarily and hold the two cabinet sections together tightly at this corner, as you do this).
After all six screws have been retightened take the Tuning control knob and press it back onto its shaft in a straight horizontal motion. Finally, reinstall the battery and battery compartment cover to finish up the reassembly.
TESTING AND OPERATION– MEDIUM WAVE MODEL
This 7.5” transplant loopstick is designed to provide a major boost in sensitivity from 530-1700 kHz, and if the antenna is working properly both the weak signal reception and the radio’s nulling capability should be greatly enhanced. It is normal for the antenna to receive more background noise on the low band frequencies, although the sensitivity boost should be substantial across the band.
The construction design of the orange antenna frame allows full usage of the whip antenna for checking SW parallels of MW-DX stations, although if you chose to glue the antenna frame flush with the front of the back cabinet surface to simplify the gluing process, you may need to sand the whip antenna slot post slightly to allow free movement of the whip antenna (see step #13).
In the photo above, some of the important controls for Medium DXing are highlighted. The AM Bandwidth control allows you to choose multiple DSP filtering selections to enhance selectivity as desired, with the narrowest filtering (1 kHz) providing both the sharpest selectivity and the best weak-signal sensitivity. However this 1 kHz setting also has the poorest audio fidelity, with the higher audio frequencies typically cut off by the DSP filtering. As such, for regular DXing far away from strong local pests, the other AM Bandwidth settings may be more suitable. The Direct Frequency Entry key allows you to manual enter in any MW frequency, to which the radio will shift once the numbers are pressed on the keypad. The Tuning knob has three different modes, which can be toggled by pressing the knob horizontally. The first mode is tuning in either 9 kHz or 10 kHz steps (depending on which of these step you have selected), while the second mode is tuning in 1 kHz steps. The third mode is to lock the frequency in place. Pressing the knob again will return the tuning to 9 or 10 kHz steps.
The XHDATA D-808 has multiple display functions, which can be toggled by the indicated key. The first option is the temperature in either Centigrade or Fahrenheit (depending on your pre-set preference), while the second option is the alarm time. The third option is the current time (which you need to set according whether you prefer UTC or local time), while the fourth option is the received signal strength in both dBu and dB.
The supplied 3.7v lithium ion battery has superior run time, and may be easily charged using the supplied USB cable to either a computer or AC outlet (with the appropriate adapter). As reported in various posts throughout this year, the D-808 model has rugged construction with an excellent record of survival under tough conditions, including hot summer days, moderate rain exposure and extended usage as the main receiver during a 9-day ocean cliff DXpedition in Oregon—performing flawlessly at all times.
It is the author’s sincere hope that this “Supercharged” D-808 model will bring you a lot of DXing fun during travel, as well as at other times. When conditions are good you should never underestimate this enhanced model’s potential of receiving awesome DX beyond your expectations—as an example, here is the stand-alone performance of a 7.5” loopstick D-808 in receiving 1017-A3Z in Nuku’alofa, Tonga (10 kW at 5,632 miles/ 9,063 km) on the ocean cliff near Manzanita, Oregon at 1301 UTC on August 8th of this year:
Not only Tonga is received, but even the Australian horse racing station 1017-2KY in Sydney (5 kW at 7,630 miles/ 12,280 km) is received as a weak co-channel in the middle of the recording. My hope is that you all will be so lucky with your new Supercharged D-808!
73 and Good DX,
Gary DeBock (in Puyallup, WA, USA)
Absolutely amazing! Thank you for taking the time to put this procedure together and describing the process in such fine detail, Gary! Hats off to you!
Click here to read all of Gary DeBock’s posts on the SWLing Post.
Many thanks to SWLing Post contributor, Ron, who notes that Hamcrafters appears to be planning a replacement for the Palomar VLF converter.
Here’s the product description:
The Hamcrafters VLF Converter is based on the original Palomar design and converts 10 KHz – 500 KHz to 4.010 to 4.5 MHz. This allows use of your HF Receiver or Transceiver and all its filters, noise blankers, DSP, and memories while tuning the VLF band. Modern HF radios have poor sensitivity in the VLF range (by design). Using this converter with a simple wire antenna will allow receiving of navigational beacons, time signals, and other VLF signals.
The Palomar is well-known among longwave DXers but hasn’t been in production for some time. Indeed, Ron adds, “The last two original Palomars went for $343 and $260 on eBay. Is there a demand? You bet!”
Moments ago, I posted a press release from the UK-based software-defined radio manufacturer, SDRplay, announcing their latest product: the RSPduo: a 14-bit Dual Tuner SDR.
I should start with the disclaimer that, not only was I sent an RSPduo to review and evaluate, but SDRplay has been a supporter of the SWLing Post for a few years now. You’ve no doubt seen their ads in the upper right corner of our site. After I reviewed their first SDR (the RSP1) I discovered that SDRplay––all of their staff and supporters––welcome constructive criticism and even invite frank discussions. They’re a company with integrity. No doubt, this is why I agreed to alpha- and beta-test their SDRs. Fortunately, I’ve not been disappointed.
As a company, moreover, SDRplay breaks the mold––and in very good ways:
SDRplay is a small company that employs actual radio enthusiasts. Their designs and software cater to DXers, SWLs, hams, scanner enthusiasts, amateur astronomers, experimenters, and makers, among others.
SDRplay designs and builds their products in the United Kingdom. No doubt they could increase their profit margin by using manufacturing centers in China, but they choose not to do so, to the benefit of their products.
The quality of the company’s products is, at least to date, excellent.
SDRplay’s product pricing is nonetheless quite affordable
That last item, in particular, is a head-scratcher. Considering these facts, how does SDRplay still manage to keep their pricing so competitive? I only wish I knew. When the company released the RSP1A last year, I had already spent a few months with alpha and beta units, mulling over their respective merits (and there were many). So I was simply gobsmacked when they announced that the price would be just $99 US. I rather figured the company was leaving money on the table, although I was pleased to announce this price to my readers here.
Fast-forward to two weeks ago: I received the new RSPduo to review. And the price this time? $279 US. While this is currently the priciest product in the SDRplay line, let’s go over what makes this SDR special…and why I still think SDRplay may be leaving money on the table.
Introducing the SDRplay RSPduo
The RSPduo is unlike any other SDR in the SDRplay product line, and, indeed, unlike most of the budget SDRs currently on the market.
As “duo” implies, this RSP features dual independent tuners, both piped through a single high-speed USB 2.0 interface. With the RSPduo, you can explore two completely separate 2 MHz bands of spectrum anywhere between 1kHz and 2GHz.
SDRplay lays out several use-scenarios in their press release:
The ability to simultaneously receive on two totally independent 2 MHz spectrum windows anywhere between 1 kHz and 2 GHz
Simultaneous processing from 2 antennas enables direction-finding, diversity, and noise-reduction applications
Ideal for cross band full-duplex reception, e.g. HF + VHF, or VHF + UHF
Simultaneous Dump1090 and VHF ATC reception
Simultaneous monitoring and recording of 2 ISM bands
Use SDRuno to seamlessly control and manage the dual tuner in a single environment.
Externally, the RSPduo bears a strong resemblance to the RSP2pro. Internally, however, it’s quite different.
Besides featuring a second independently controlled tuner, the RSPduo also sports 14 bit ADCs and a completely re-designed RF front end, which enhances receiver selectivity and improves dynamic range.
In short, the RSPduo is like having two SDRs in one.
I received the RSPduo during a very busy time of the year: the build up to the Hamvention in Xenia, OH.
One of the first things I noticed about the RSPduo is its weight. When I picked up the package from SDRplay, I could tell it weighed at least twice that of the RSP1A. One reason for the extra heft is that the RSPduo, like the RSP2 Pro, has a metal enclosure. I’m willing to bet the RSPduo also has more shielding––adding even a little extra weight.
I’ve had the RSPduo on the air for more than a week now, and have checked out all of its major functions and begun to learn the nuances of navigating the dual receivers in the latest version of SDRuno.
SDRplay will, I feel sure, post a primer video on using the various dual tuner functions in the coming weeks.
Installation of the software, even in pre-production, was totally a “plug-and-play” experience. Simply install the SDRuno software package with the RSPduo disconnected from the USB port. Plug in the RSPduo, and wait for the USB driver to load, then open SDRuno. That’s it. You’re on the air!
As I’ve indicated, the RSPduo is really like having two RSP1As in a single RSP2 Pro package. One of these dual receivers––the master––can utilize either a standard 50 ohm SMA antenna port, or a Hi-Z port. The second receiver uses one 50 ohm SMA antenna port just like the RSP1A.
I much prefer using the Hi-Z port for everything longwave and mediumwave. I did hook up both antenna ports on the master receiver, however, and switched back and forth between the two. At least in my antenna setup, I feel like the Hi-Z option lends itself to improved sensitivity on these bands. It’s not a dramatic difference––indeed, looking at the spectrum display one barely notices the difference––but my ears told me the noise floor was lower and signal strength slightly better with the Hi-Z port. Above 2 MHz, the Hi-Z port is not prefered since it lacks the same level of RF pre-selection as the 50 ohm ports provide.
Unlike the Hi-Z port with the RSP2, the RSPduo treats the Hi-Z port more like an auxiliary antenna port. When I employed the Hi-Z port in the HF bands, I did notice small spurious noises, but this might have been due to my antenna port configuration here in the shack (my Hi-Z connector is simply attached to the shield and center conductor of my coax).
Again, however, for anything above 2 MHz, SDRplay suggests using the 50 ohm ports.
How to set up dual receivers on one screen/monitor
Listening to the FM broadcast band on the main receiver and Voice of Greece shortwave on the second receiver.
One of the first things I was eager to do was to run the dual receiver functionality on one monitor. Although SDRplay makes this a pretty simple process in the latest version of SDRuno, I still stumbled a bit as I learned to navigate the controls.
Here’s a quick primer to get both receivers on the air on one monitor/screen:
First, open SDRuno in “single receiver mode” (the typical SDRuno default).
Next, click on the “RSPduo mode” button and select one of the modes. In this case, I’m not running the ADS-B application, so I’ll choose “DUAL (NORMAL)”.
Now, to format the “Master” receiver windows so they only use the top half of the monitor, click on the OPT button.
Select “Auto Layouts” and “RSPduo Master.”
If you’ve followed these steps with me, your screen should look something like this:
Now you’ll want to start the second receiver. Do this by opening the SDRuno application again (as if you were opening SDRuno for the first time). Make sure you’ve selected your RSPduo if you have more than one RSP connected.
The new instance of SDRuno will fill the entire screen by default, so you’ll need to format it to occupy the lower half of the screen.
Simply click on the OPT button again, select “Auto Layouts,” and “RSPduo Slave.”
Your full screen should now look something like this:
Now you can start using both receivers, but you’ll have to always start the “Master” receiver first. In fact, the “Master” receiver must always be active in order to operate the “Slave” receiver. You can always close the “Slave” receiver without affecting the “Master” receiver; however, if you close the “Master” receiver, you will effectively close both receivers.
Again, I fully expect SDRplay will soon produce a demonstration video showing how you can navigate SDRuno’s new dual-receiver functionality.
As I’ve mentioned in most previous SDR reviews, I do like to take a considerable amount of time to set up SDR comparisons.
Herein lies the difficulty of reviewing an SDR’s performance. Because the user has so much power to control variables and thus shape the receiver’s function, it’s actually quite hard to make an “apples-to-apples” comparison––insuring that all important filters, gain controls, DSP, etc., are as close to identical as possible.
One tool that helps me do this is SDR Console, since it can control a number of SDRs and receiver parameters can be set up identically. Unfortunately, the RSPduo is so new, SDR Console doesn’t yet support it.
I did use SDRuno to compare the RSPduo with the RSP1A. Fortunately, I could actually run two separate instances of SDRuno simultaneously (and on different monitors, in my case). Both were hooked up to the same antenna via my ELAD ASA15 antenna splitter amplifier.
The RSPduo’s improved dynamic range gives it an advantage in terms of noise floor, sensitivity, and selectivity.
The improved performance is not dramatic––but I understand it might be especially detectable to those who want a receiver with a more robust front end.
In fact, the RSPduo’s 50 ohm coaxial ports have quite an array of automatically configured front end filters:
2 MHz Band Pass
And an array of notch filters
FM Notch Filter:
>30dB 77 – 115MHz
>50dB 85 – 107MHz
>3dB 144 – 148MHz
MW Notch Filter:
>15dB 400 – 1650kHz
>30dB 500 – 1530kHz
>40dB 540 – 1490kHz
DAB Notch Filter:
>20dB 155 – 235MHz
>30dB 160 – 230MHz
The thing is, I live in an RF quiet area, so I can’t fully take advantage of the SDRuno’s more robust front end.
In head-to-head comparisons with the RSP1A, the RSPduo’s performance edge is discernible. Again, I suspect it would be a bit more obvious if I lived in an urban setting with blowtorch stations in the neighborhood. Using the Hi-Z antenna port in the mediumwave portions of the band, the RSPduo has a performance edge over the RSP1A, as well.
Should you grab the RSPduo?
The new SDRplay RSPduo
Anytime a new product hits the market, I ask myself if this is the sort of product that would tempt me to reach for my hard-earned cash.
The short answer? Absolutely! Take my money, please! There is no other sub-$300 SDR on the market currently that has the dual tuner functionality of the RSPduo. Thing is, I’ve only had the RSPdup a couple of weeks–there’s so much yet I want to explore here–especially diversity reception!
But what if you already have an SDRplay SDR? Afterall, the RSP1A was only released a few months ago, and the RSP2 series only a year before that.
Here’s my opinion: If you’re an RSP1A or RSP2 owner who is pleased with this SDR’s performance, I wouldn’t necessarily urge you to purchase the RSPduo simply for the modestly enhanced performance characteristics. SDRplay hasn’t retired the RSP2 and RSP1A designs because each model still holds its own, has a purpose, and obviously enjoys a healthy market.
The RSP1A is the affordable yet high performance entry model in the SDRplay product line. It’s really the best value in the radio world, in my humble opinion, at just $99 US. Som enjoy.
The RSP2 and RSP2pro provide excellent performance, three software-selectable antenna inputs, and clocking features, all of which lend it to amateur radio, industrial, scientific, and educational applications; it is a sweet SDR for $169 or $199 (Pro version). I know of no other SDRs with this set of features at this price point. If I liked the characteristics of the RSPduo, but didn’t really need a dual receiver for my application, I’d probably reach for the RSP2 Pro.
But if you have the original RSP, and like SDRuno and the SDRplay community, then I would certainly consider this an opportunity to upgrade. For $279, you’re getting a dual receiver SDR with excellent performance characteristics that will easily surpass the original RSP––considering that you’re essentially getting two very good SDRs in one.
And if you’re all over the spectrum (aren’t we all a bit––quite literally?) in terms of usage, the RSPduo is a fascinating machine for running, say, an ADS-B receiver while independently using the same SDR box to monitor other parts of the spectrum. Or one can listen for FM DX on one receiver while trying to snag elusive LW DX on the other.
Better yet, the RSPduo only uses one USB port––an important factor if you’re using a laptop or tablet. Of course, having two receivers on two different antennas, while sharing one data port, means syncing them for diversity reception is especially effective. This alone will sway many SDR experimenters in favor of this rig.
I have yet to compare the RSPduo with the brilliant little AirSpy HF+. The AirSpy HF+ is not a wideband receiver like the SDRplay RSP series; it only covers 9 kHz to 31 MHz and 60 to 260 MHz. But if your primary concern is HF performance, the HF+ and its excellent dynamic range will impress you, if you’re anything like me. It’s also a bargain at $199––very hard to beat!
The RSPduo is a good value, in my opinion––and an inexpensive upgrade to a proper dual receiver SDR––so if that’s the sort of thing you’d like to add to your shack, go ahead and bite the bullet!
In fact, I suspect SDRplay will quickly sell out of all of the units they bring to the 2018 Hamvention (SDRplay: pack some extras!). I’m happy to see the company continue to push the price and performance envelope to such exceptional ends. I’m also looking forward to the many applications SDRplay customers (and our readers) find for the RSPduo.
Stay tuned! I plan to post more comparisons in the future.
And if you acquire an RSPduo and find some new and fun applications for it, please share!
SDRplay announces the RSPduo – A 14-bit Dual Tuner SDR
Today at the Dayton Hamvention, SDRplay Limited is announcing the launch of a new Software Defined Radio product – the RSPduo.
The RSPduo is a radical new addition to the RSP line of SDR receivers from SDRplay. Architecturally, it is different from any previous RSP in that it features dual independent tuners, both piped through a single high-speed USB 2.0 interface.
The SDRplay RSPduo is a dual-tuner wideband full featured 14-bit SDR which covers the entire RF spectrum from 1kHz to 2GHz giving 10MHz of spectrum visibility. Initially using Windows based ‘SDRuno’ supplied by SDRplay, you can simultaneously monitor two completely separate 2MHz bands of spectrum anywhere between 1kHz and 2GHz.
Superficially the RSPduo looks identical to the highly popular RSP2pro and will be able to operate in a very similar way.
However, it also allows a completely new and exciting set of usage scenarios such as:
Simultaneous monitoring of two widely spaced bands – e.g. 40m (HF) and 2m (VHF)
Mixing and matching applications simultaneously – e.g. ADS-B and ATC scanning
Phase and time coherent demodulation of two receivers
Scenario 3 is very difficult to achieve with two separate USB devices because of the uncertainty of USB latency. The RSPduo overcomes this limitation because all traffic goes through a single USB interface, thus enabling the possibility of the development of various types of diversity demodulation such as: spatial, frequency and polarisation which can bring
huge benefits in terms of improved performance.
Jon Hudson, Marketing Director at SDRplay commented:
“As well as adding a second independently controlled tuner, which in itself, offers a whole new set of exciting usage possibilities, the SDRduo features 14bit ADCs and a completely re-designed RF front end. These changes provide better RF selectivity and even more dynamic range, offering outstanding performance under extremely challenging reception conditions. The combination of performance and features makes the RSPduo our highest spec RSP yet and sets a new benchmark in the sub $300 SDR market”
Due to its exceptional combination of performance and price, the RSP family of receivers have become very popular and the RSPduo provides the next level of functionality for both amateur radio enthusiasts as well as the scientific, educational and industrial SDR community.
As well as being demonstrated at Hamvention, the RSPduo is available direct from SDRplay or via SDRplay’s network of channel partners and resellers
The RSPduo is expected to retail at approximately $279 USD (excluding taxes) or £199 GBP (excluding taxes).
About SDRplay: SDRplay limited is a UK company and consists of a small group of engineers with strong connections to the UK Wireless semiconductor industry. SDRplay announced its first product, the RSP1 in August 2014
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