Signal distribution at SWL camps: The new JK-1000 HF distributor
by Joachim von Geisau (DH4JG)
The Friends of Radio NRW – an independent group of shortwave listeners and radio amateurs in Germany – have been organizing 2-3 SWL camps per year for a number of years, where they meet as far away as possible from electrical noise in order to listen to shortwave together.
To distribute antenna signals, we have previously used an RFT AVV01 antenna distributor.
At an SWL camp there are high demands on signal distribution. Both very weak and strong signals should be distributed well, un-distorted, without noise and other interference. The signal levels are approximately between 0.2 ?V (S1) to over 5 mV (S9 + 40 dB), with a frequency range of at least from 150 kHz to 30 MHz, thus broadcast bands from LW to SW are covered, also all amateur radio bands from 160 m to 10 m.
Popular among listeners are RFT AVV01 RF distributors from the former GDR, at least 30 years old. However, the use of an AVV01 has several disadvantages: high power consumption, difficulties in getting spare parts, high upkeep with corroded contacts and the like. In addition, the transmission of the LW/MW range drops, which is a disadvantage especially for MW listeners. The NV-14 system from Rohde & Schwarz from the late 1960s has the same weaknesses.
Two years ago, the desire arose to develop a concept for the replacement of the RFT system.
The following aspects were important:
- Frequency range at least 100 kHz – 30 MHz, as linear as possible
- frequencies below or above desirable
- Running on 12 V DC or integrated noise-free power supply
- Remote power supply for active antennas
- Robust structure
- Hobby friendly budget
The amateur radio market offers several products for RF signal distribution (e.g., ELAD, Bonito et al.), but no solution to distribute 6-8 antennas to 10-12 receivers. It was clear from the beginning that DIY development was inevitable.
The starting point of the considerations was to integrate remote power supply for active antennas, an amplifier stage and a distribution network.
Such a distributor is able to distribute an antenna signal to several receivers; several antennas require several such distributors, which led to the decision to implement the project in plug-in technology.
With OM Frank Wornast DD3ZE (www.dd3ze.de), known e.g. for his converters, filters and the like, a well-known RF developer could be won, who took over the implementation of the concept based on the detailed specifications. OM Wornast first produced a prototype without remote power supply, which already did an excellent job of RF signal distribution.
A “hardness test” at an SWL camp showed that this distribution module easily fulfilled our requirements: Frequency range 10 kHz – 50 MHz (also usable with a few dB loss above 50 MHz). Supplemented by a switchable remote power supply and a 90V gas discharger at the antenna socket, the final PCB layout was created, representing the core of the new HF distribution system of Radio Freunde NRW
The distribution block consists of the following components:
- Input with 90V arrester & 100 kOhm MOX resistor to dissipate static interference
- Remote power supply, switchable, 10-14 V, max. 350 mA
- Amplifier stage with 14-14.5 dB
- Resistor network for distribution
The device is characterized by a very smooth frequency response and has a very low inherent noise. It offers the possibility of using levels of -120dBm with very good SNR
to process up to strong levels of up to + 14dBm. In addition, the reception on VLF is now possible, which did not work with the previous system.
The PCB is designed in a very practical way: series resistors for LEDs are integrated as well as fixing points for coaxial cables. The remote power supply can be switched separately, but can also be used permanently by means of a jumper.
With this concept, the distribution block can be used universally: use on an active or passive antenna with distribution to several receivers, by means of a step switch in front of it also for several antennas; if you leave the remote feed path unconnected, the block can also be used as a simple distributor, so it is almost universal for hobby purposes.
For use on SWL camps, we decided to install them in 19 “rack-mount technology. A standard rack can thus accommodate 4 distributors and a power supply, allowing distribution of 4 antennas to 12 outputs each. An example of the installation is shown in the following picture: Parallel to the input is another BNC socket, which is connected via a C 100 nF where the input signal can be used DC-free for measurement purposes or the like. The distribution unit is installed in a transport case. The components themselves are mounted in slide-in housings which are provided with a corresponding front panel: Such front panels might be obtained from CNC manufacturers.
On the back + 12V DC must be supplied as operating voltage. For the power supply units, we opted for linear power supplies because we have made the best experience with these without interference. For a distribution unit with 4 slots, a power supply with 12V 1A is sufficient – each distribution block takes about 55 mA, an active antenna up to 150 mA, so even with “full load” a power supply with 1 A is sufficient. The distributor was tested with various well-known active and passive antennas, including a PA0RDT MiniWhip, active loops, long wires and T2FD.
Due to the wide input voltage range, the module can handle nearly any antenna. The cost for a distributor for 4 antennas amounts (depending on the version: housing, sockets, switches, power supply, etc.) to about 700-1000 €. That may seem a lot at first glance. However, taking into account that a simple 5-gang distributor from mass production costs already around 250 ¬, the cost of the distribution of 4 antennas to each up to 12 outputs are not that much. The Friends of Radio NRW use two of these distribution units for SWL camps.
Wow! What a beautifully engineered antenna distribution solution, Joachim! I love how you worked together to sort out all of the requirements for your system then build it for ultimate performance and flexibility. No doubt, you and your colleagues at Radiofreunde NRW posses a lot of design and engineering skills! Simply amazing and thank you for sharing your design with the radio community!
Many thanks to SWLing Post contributor, Mario Filippi (N2HUN), who shares the following guest post:
Recently we had a remodeling job performed at the home QTH and the workers used telescoping poles to form a dust barrier. When the job ended, they said I could have the telescoping poles, a product called ZIPWALL10, which when collapsed are four feet long but extend to ten feet. This got me pondering about how handy these could be in the radio shack, especially for indoor impromptu antennas.
Indoor antennas, especially wire antennas usually have to be secured to a wall somehow, and should be as high as possible in the room. That requires using adhesive tape to attach the wire and a ladder (most ceilings are eight feet), but using the ZIPWALL10 poles it’s easier and safer. Below is a temporary random wire antenna in my shack using 26 gauge insulated wire strung between the two poles.
What’s nice about these poles is they have rubber feet to grip the floor and plastic pads on top to avoid damage to the ceiling. The top section is spring loaded to assure a tight fit. The ZIPWALL10 model extends to ten feet in three telescopic sections. No tools are needed to set these up, and they conveniently collapse for storage.
These poles just happened my way due to a remodeling job, but surely other types are available on the market for those wanting to experiment with indoor antennas. The price for a ZIPWALL10 pair on Amazon is around eighty dollars. Thanks for reading.
What a great use for ZipWall poles, Mario! I’ve spent the past few days at an ocean front condo and could have used two of those supports to suspend a small, lightweight passive loop antenna safely on the balcony. That’s fantastic your contractors simply gave you those poles!
Thanks for the tip!
As you mention, Amazon sells a full line of ZipWall options (links below support the SWLing Post) but these can also be found at most home improvement stores.
To begin, for reference, check out this post where The Professor reviews the RFA200. Also, check out the following video from the replies of that post:
Both the RFL-200 and the Q-Stick came in today.
But Gerry says he’s going to close RadioPlus early next year so-presumably-
that will leave just the RFL-200 and its REA-200 sibling.
The “200” no doubt comes from the length, 200mm or 8 inches…the Q-stick
uses a 7-3/4 inch ferrite bar which is probably why the similar performance.
There is one thing: the small tuning knob is not hard to turn on the RFL-200
as it was on the REA-200 tested earlier but a bigger knob would be nice.
But the tuning cap uses a 1/8th inch shaft so finding a larger knob is too
much bother, most are for 1/4 inch shafts.
By comparison the Q-Stick has a nice big knob and is quite easy to tune.
So for now the Q-Stick would be the better buy, but don’t tarry.
[One more note,] if you want the most bang for your buck, forget both of these, get
a PK Loop for $90.60 delivered (be sure to specify the 155-500 kHz model).
Thanks for sharing your thoughts, Ron!
Do you enjoy the SWLing Post?
Your support makes articles like this one possible. Thank you!
Many thanks to SWLing Post contributor, Grayhat, who writes:
Hi Thomas, was about to write you about some infos related to the NooElec balun when found that they now offer a v2 model:
The new balun has the same schematic as the previous one:
But it is slightly bigger, has a better connector for the antenna wires and (according to NooElec) uses a transformer which allows the tiny balun to work more efficiently from 0 to around 70 MHz (check out the charts found in the downloads section of this link).
The transformer used, judging from the pics, is a CoilCraft WB9-1, whose data can be found here:
As I wrote the reason for this was the fact that a friend of mine reported that he used the (v1) balun with a Loop On Ground (LoG) Antenna !
If you look at the schematic (above) you’ll notice that there’s a “jumper” labeled R1 (zero Ohm resistor). That tiny detail is important, see, leaving the balun as is, it will work fine with a longwire, one just connects contact #1 to the antenna and #2 to a counterpoise or ground system and there he goes, BUT there’s another way to use the balun, that is, CUT the “jumper” (ok, resistor) labeled “R1”. If you cut it, the balun will become a 9:1 isolation transformer and with such a modification will work just fine with the KK5JY “LoG”
According to what my friend reported, the balun works just fine, and although probably the ferrite core used in the V1 isn’t up to par with the original one used by KK5JY, the difference isn’t so huge.
Oh, and I also suspect that the modified balun may work fine with the KK5JY simpler passive loop http://www.kk5jy.net/rx-loop/ which may be a nice antenna for restricted spaces!
I think it may be of interest to people not knowing/willing to wind their own baluns, at that point one may just need an enclosure to protect the balun and putting up a receive antenna will be as easy as 1-2-3.
Thank you for sharing this! Readers: Grayhat has been encouraging me to deploy a LoG antenna at my home and I do plan to do so in the coming months. Please comment if you use a LoG similar to the KK5JY model and what your results have been.
Thank you again for the tip, Grayhat!
Many thanks to SWLing Post contributor, Marty, who shares this fascinating article from the IEEE Spectrum:
A new antenna that uses saltwater and plastic instead of metal to shape radio signals could make it easier to build networks that use VHF and UHF signals.
Being able to focus the energy of a radio signal towards a given receiver means you can increase the range and efficiency of transmissions. If you know the location of the receiver, and are sure that it’s going to stay put, you can simply use an antenna that is shaped to emit energy mostly in one direction and point it. But if the receiver’s location is uncertain, or if it’s moving, or if you’d like to switch to a different receiver, then things get tricky. In this case, engineers often fall back on a technique called beam-steering or beamforming, and doing it at at a large scale is one of the key underlying mechanisms behind the rollout of 5G networks.
Beam-steering lets you adjust the focus of antenna without having to move it around to point in different directions. It involves adjusting the relative phases of a set of radio waves at the antenna: these waves interfere constructively and destructively, cancelling out in unwanted directions and reinforcing the signal in the direction you want to send it. Different beam patterns, or states, are also possible—for example, you might want a broader beam if you are sending the same signal to multiple receivers in a given direction, or a tighter beam if you are talking to just one.[…]
Many thanks to SWLing Post contributor, Balázs Kovács, who shares the following video of a Swiss Army knife and tweezers being used as FM antennas:
Thanks for sharing this, Balázs. The video actually makes a good point: it takes so little to make an effective FM antenna to receive local stations. I’ve been with repair technicians when working on radios They’ll often use their precision screwdriver as an antenna to test the receiver before reassembly.
I also carry a couple cheap instrumentation patch cord with alligator clips on both ends to act as a short antenna or antenna extension when needed. Honestly, It’s amazing how often I reach for them!