Direct Connection of Antennas to Ultralights: First Real Tests
John H. Bryant <bjohnorcas@...>
We have made our annual migration to Orcas Island, just south of Vancouver city and about 90 miles north of Seattle. I've gotten my two biggest antennas up and running.... formerly 70' x 100' EWEs at W and NW, now set up as Conti Super Loops. Yesterday and today, I spent several hours testing the performance of a covey of Ultralights. I have three Ultralights set up to receive direct connection to external antennas through coax lead-ins, just as my communications receivers interact with the same antennas. The one that has been posted is my National SRF-39 in the nice wooden cabinet. The other two are a DT-200VX and an E100.
In all three cases, I've used the technique of winding a coupling loop of 6 or so turns of insulated tie-wrap wire around the stock ferrite bar of the Ultralight radio. This coupling coil is connected directly to the incoming coax lead-in. When I first tried this technique, I thought that the coupling coil, while disconnected from the antenna, was inducing some weirdness or detuning the stock ferrite bar. However, I've had much more experience with this system now and I'm fairly certain that this supposed detuning is NOT happening. I cannot tell the difference between identical radios with or without the coupling coil in place.
In general, in near RF-free central OKlahoma, the directly connected antenna/Ultralight radio combination worked EXCELLENTLY. At night with my closest MW transmitters about 60 miles away and only three of them being 50 kW, all three radios performed well, with no strangeness of any sort noted. It was kind of magic, using the Wellbrook Array with the SRF-39 and looking four different directions per frequency.
Here on Orcas Island, the RF environment is ever so much different, with my antennas being awash in RF from Vancouver and Border Blasters serving that market from nearby Blaine, WA. Nearby Victoria also chips in with two 10 kW stations that put in huge signals, as well. The daytime RF environment looks like this :
The vertical scale lines are -dBm, the horizontal in 10ths of a MHz. This is a sweep of the entire MW band. The -30 dBM line corresponds to about 40 dB over S-9. People have been surprised that the WinRadio 313e would work well when connected to those huge loop antennas in this RF environment. Happily, it does and I've never noted overloading or other problems, EXCEPT that the signal on 600 kHz. is so powerful that it seems to partially desensitize the receiver for about 10 kHz. either way from 600, making hearing Tokyo 594 rather difficult.
Anyway, in this environment, I did not expect the Ultralights to be trouble free, when connected to the monster loops. I was correct. Both the Sangean DT200VX and the E100 overloaded massively. On every channel where there should be one strong or moderately strong station, there were two or three false stations and 1600, Blaine was on many of the channels at the tops of the dials. Basically, I ended up with a semi-tuneable tower of Babel. The National SRF-39, hooked to the same antennas behaved much more sedately. In fact, I couldn't find any false stations or stations overlaying other stations where they shouldn't be and the stronger stations were not distorted. What was unusual was hearing what I think are 10 kHz. heterodynes in quite a few places on the dial. I assume that the signals were so wide that they were QRMing each other??? It sure won't keep me from using the SRF-39 and the big loops for some TPs later in the season from here.... when the Asians start booming in (I hope!)
Interestingly, I also tested all three radios (substituting a stock SRF-39 for my National set-up) with a tuneable Booster Bar antenna, based on a .75 x 12" very large ferrite rod. I sort of expected some overloading problems with the big Booster Bar, too, but none were apparent. So, to the extent that I DX with Ultralights from here, it will be the National SRF-39 with the big loops and the DT-200VX and E100 will sit on the booster bar. I have some faint hope that the Wellbrook Array will work with all of the Ultralights in this RF environment. The gain of that antenna is less than the big loops, but the S/N and F/B ratios are better. I'll be putting it back up here after my first trip to Grayland.
In any case, directly connecting monster antennas to the Ultralights was done, largely, to be used at the coast at Grayland. In that much more forgiving environment, I really hope to see the directly connected Ultralights shine.
After that first trip to Grayland in a week or two, I'll be putting together an article with details and photos of the direct connection method. By the way, I'm happy enough with this approach that I'm going to be putting an antenna input port on my Kaito 1103 for use in traveling DXpeditions. That is a pretty wonderful receiver, the size of a paperback book, that has an antenna port, BUT ONLY FOR SW! BCB is limited to a ferrite bar. Soooo..
Hope everyone is having a fine early summer!
--- In ultralightdx@..., "John H. Bryant" <bjohnorcas@...>
The graphic, if that's what it was, didn't come through on my e-mail,
or on the groups page, John. Maybe it needs to be posted on the files