Category Archives: Radio Modifications

Gary pulls apart and examines the XHDATA D-808


Many thanks to SWLing Post contributor, Gary DeBock, who shares the following report of the XHDATA D-808:


XHDATA D-808 AM-LW-FM-SW-AIR Portable- Tech Report

by Gary DeBock

The XHDATA D-808 portable is an AM-LW-FM-SW-SSB-AIR band model which has already been the subject of many excellent reviews. Until recently the model was not marketed to North American purchasers, but recently a couple of Chinese sellers have started soliciting North American buyers via eBay listings.

My own interest in the model was in comparing its AM Band performance to that of the best performing Ultralight radios– specifically the CC Skywave and Skywave SSB models. Although the D-808 is slightly larger than the 20 cubic inch limit for Ultralight radios, its size and weight make it very convenient to take along as a “travel portable,” specifically as an SSB-enhanced model capable of checking transoceanic station carrier strength on exotic ocean beaches. The Skywave SSB model can also do that– but at a $169.99 list price, compared to the $112.86 (plus $10 shipping) cost of the D-808. In addition, none of the published D-808 reviews seemed to have any information about internal components like the loopstick, or Si4735 DSP chip.

My first test was to compare the stock Skywave SSB model with the D-808 in fringe AM station reception. The Skywave SSB model has a reputation of being one of the most sensitive Ultralight radios, but the D-808 clearly outperformed it on both low band fringe station (550-KARI) and high band fringe station (1700-City of Auburn TIS) reception. The D-808 couldn’t quite hang with a 7.5″ loopstick Skywave model, but that only made me curious about how the same modification could enhance the D-808. So… it was time to disassemble the D-808, and find out why its loopstick was such a superior performer.

The D-808’s 3 7/8″ (98mm) loopstick is shown adjacent to the 2 3/4″ (70mm) loopstick of the CC Skywave models. The D-808 is much easier to disassemble than the CC Skywave models, though, so enhanced loopstick transplants should prove to be quite popular in the D-808.

The D-808 loopstick is 3.7/8″ (98mm) long, while that of the CC Skywave SSB model is only 2 3/4″ (70mm) long. Other reviewers have noted the excellent performance of the D-808 on the AM band, and this is probably one of the main reasons. The SSB mode operates very similar to that of the Skywave SSB in providing a quick check of carrier strength on weak AM band targets– the LSB mode can be set to +55, and the radio tuned to different frequencies to check fringe station carrier strength. This can provide a real-time check of propagation changes during time-limited propagation openings for live ocean beach DXing with Ultralight radios or other portables (or with the D-808 itself, if desired).

The D-808’s Si4735 DSP chip was initially used in the Eton Traveler III Ultralight radio model, which was fully reviewed in the 2015 Ultralight Radio Shootout (where it won top honors for MW sensitivity). The D-808 augments that capability with a significantly longer loopstick, plus multiple DSP filtering selections. As such, the D-808 in stock form should be a very superb performer.

The Si4735 DSP chip has markings of “3560, DCUL, .738” and provides a wide range of AM bandwidth choices for the Medium Wave DXer (6K, 4K, 3K, 2.5K, 2K, 1.8K and 1K). These perform very well, and as with the other DSP-enhanced portables, the narrowest bandwidth (1K) provides the most sensitive AM band reception.

In construction very similar to that of the CC Skywave, the D-808 separates into two main circuit boards, connected together by a plug-in ribbon cable. One strange quirk is that the Si4735 DSP chip is located on the RF board (close to the center right edge). The Si4735 DSP chip is also used in the Eton Traveler III Ultralight radio, and although that model lacks the multiple DSP filter selections of the D-808, is has been the subject of highly successful 7.5″ loopstick transplant modifications– proving that such enhanced Medium Wave and Longwave loopsticks will perform very well in the new, Si4735 chip- powered D-808.

Disassembly of the D-808 model is fairly straightforward in comparison to the CC Skywave models, and the technician doesn’t need to memorize a detailed reassembly protocol in order to perform a routine loopstick transplant operation. Neither C.Crane nor XHDATA are likely to show any sympathy to someone botching up an antenna transplant, so you need to be confident that that your skills are superior to those of the company technicians before taking the plunge. In the CC Skywave and CC Skywave SSB models various parts fit together like a puzzle, but the D-808 isn’t like that. It should prove to be a fairly popular model for enhanced MW and LW loopsticks.

Those considering a purchase of the D-808 should be advised that its type 18650 Li-ion 3.7v battery is not commonly available at most stores, and that Postal regulations supposedly forbid shipping these batteries through the mail. One of the eBay sellers (harelan ecommerce) did manage to ship me two of the standard XHDATA type 18650 batteries through the mail (along with two new D-808 models) but if your seller won’t do this, you can still purchase the batteries on eBay. Some of the 18650 batteries sold on eBay have a flat positive terminal which won’t contact the D-808 cabinet’s positive battery connector terminal, but in such a case you can simply insert a #8 lockwasher in between the two, and the arrangement will be very secure. From that point on you can simply recharge the battery with a USB terminal connector.


Thank you for sharing this technical overview of the XHDATA D-808, Gary! I’m looking forward to the antenna mods you’ll no doubt make to this compact DX machine!

Click here to read other posts about the XHDATA D-808 and here to read posts by Gary DeBock.

The AirSpy HF+ R3 bypass modification

After SWling Post contributor, Guy Atkins, posted the survey results of his excellent Elad FDM-S2  vs AirSpy HF+ weak signal comparison, I received a few questions about the AirSpy HF+  “R3 Bypass” modification Guy mentioned in his post.

Guy has not yet performed the modification on his HF+–neither have I–but he points out that others have noted it: “significantly boosts sensitivity of the HF+ from longwave up to about 15 MHz, without any noted overload issues.”

I reached out to AirSpy president, Youssef Touil, for a little more insight about this modification. Youssef replied:

During the early phases of the design R3 was a place holder for a 0 ohms resistor that allows experimenters to customize the input impedance. For example:

  • A 300 pF capacitor will naturally filter the LW/MW bands for better performance in the HAM bands
  • A 10µH inductor would allow the use of electrically short antennas (E-Field probes) for MW and LW
  • A short (or high value capacitor) would get you the nominal 50 ohms impedance over the entire band, but then it’s the responsibility of the user to make sure his antenna has the right gain at the right band
  • A custom filter can also be inserted between the SMA and the tuner block if so desired.

Click to enlarge. (Photo source: RTL-S1DR.com)

R3 and the nearby resistors have been intentionally left outside of the RF shield, and their size was picked to be big enough to allow anyone to play with them. You will notice the size difference with the rest of the components.

In general, unless one knows what he’s doing, it’s not recommended to alter a working system. “If it’s working, don’t fix it”. But, we are hobbyists, and not doing so leaves an uncomfortable feeling of something unachieved. Most brands addressing the hobby market leave some tweaks and even label them in the PCB.

The main purpose of the HF+ is the best possible performance on HF at an affordable price. This is to incite HAMs to get started with this wonderful technology while using an SDR that isn’t worse than their existing analog rig.

The MW/LW/VLF crowd may have slightly different requirements, but that can be addressed by shorting a resistor.

Regards,

Youssef Touil

Thank you, Youssef, for replying to my inquiry so quickly and thoroughly.

No doubt, I too will eventually modify R3–it’s very difficult not to experiment, especially when a product was designed with the experimenter in mind.

I really feel like AirSpy has knocked it out of the ballpark with the HF+. For those of us primarily concerned with HF performance, this SDR is very hard to beat–especially at its $199 price point!

Video: How to calibrate the Tecsun PL-660 frequency offset

Many thanks to SWLing Post contributor, Mike Mander, who writes:

I’ve recently really been enjoying swling.com. Thanks for having such a great resource online with shortwave radio and hardware reviews, tips and more! I started listening to shortwave on an old Philips portable receiver back in the late 70’s as a teenager. Recently, after decades of not listening to shortwave, I decided to buy an Eton ‘Grundig Edition’ Satellit radio and in no time at all, I had also acquired a C.Crane Skywave SSB and now, within the last week, a Tecsun PL-660.

[…]I thought I’d record a video showing how one can calibrate AM, FM, SW wide-bandwidth as well as SW narrow-bandwidth independently, and how to reset those calibrations back to factory default. I have not heard it mentioned anywhere that one can calibrate both wide and narrow bandwidth SW modes independently.

Online, I have read about many people being disappointed in their PL-660’s wide-bandwidth frequency calibration, where often being on-station results in the frequency being up to 5 kHz too low, and it seems many simply return their radios as defective, not realizing how easy it is to recalibrate. This is the first “instructional” video of this sort that I’ve ever posted online, so you’ll have to pardon if I am perhaps not explaining things clearly enough:

Click here to view on YouTube.

Excellent video, Mike! You’ve done a fine job making the explanation clear and easy to follow. Thank you for sharing!

A $25 upgrade for the Elecraft KX2

Many of you know I’m quite a fan of the Elecraft KX2. I take this little transceiver along almost any time I travel. Not only is it a full-featured ham radio transceiver, but it’s also an exceptional shortwave broadcast receiver.

The KX2 is a quality US-built rig (like all of Elecraft’s gear) but I’ve never been a fan of its plastic encoder knob. It lacks a finger dimple and feels cheap compared to the rest of the radio. Don’t get me wrong: the stock encoder knob gets the job done, but it’s not nearly as nice as the one on the slightly larger Elecraft KX3.

Comparing the Elecraft KX3 (top) and KX2 (bottom) at Elecraft’s Dayton Hamvention booth.

Two weeks ago, I ran into another Elecraft KX2 owner and happened to notice that his KX2 had a solid aluminium encoder knob with a finger dimple. Turns out, he purchased the knob from a ham radio operator (W1JH) in Maine who manufactures and sells this knob on eBay.

The price was $24.95 US shipped. I didn’t hesitate to place an order.

You might think $24.95 is a lot to pay for such a small item, but third party Elecraft vendors tend to charge much more for comparable items. I’ve also considered adding a heatsink to my KX3, for example, but those can total upwards of $100!

My new encoder knob arrived in only a couple of days via the USPS–installing it was a breeze.

It took me all of thirty seconds to pull the plastic knob off of the KX2 and replace it with the new aluminium one. The seller even includes an Allen wrench to secure the new knob.

The new knob is slightly larger in outer diameter, but fits the KX2 like a glove. The slightly larger size makes the finger dimple a practical addition for smooth band-scanning.

If you own an Elecraft KX2 (or the Elecraft KX1) I highly recommend this simple encoder/VFO knob upgrade!

Click here to order on eBay.