[Lowfer] WM and SIW in South Carolina

[John Hamer]

Below is the link to the full Argo screen

http://jwhamer.me/grabber/WM_SIW_FULL_12_2_2020.PNG

Regards,
John Hamer

On Wed, Dec 2, 2020 at 10:57 AM John Hamer <wilbur0611 at gmail.com> wrote:

> I have been working on my loop antenna/receive setup over the past few
> weeks trying to tackle noise issues. Below is what I found if anyone is
> interested. I have been using WM as a goal and last night I had the best
> capture yet. as I bonus, I have a positive SIW capture also. I have
> attached it. The time is in EST.
>
> The first thing I found was my computer's power supply was dumping
> inverter noise into my ground. I was able to reduce the noise on my radio
> by using an ungrounded isolation transformer, but as soon as I plug in the
> audio cable for argo, the noise would reappear into my radio. I next tried
> an audio transformer on the audio cable, but it didn't even touch the noise
> (capacitively coupled through the transformer?). I didn't like the idea of
> using an ungrounded isolation transformer on my radio, so I decided to find
> a computer with a quieter power supply. I do have a ground rod outside the
> house, but It didn't help.
>
> I have a few older computers. The first one I tried was much better, but
> unfortunately I couldn't get it to boot. The second one, which was the last
> desktop I had, worked really well and is what I am using now. It is a
> little slow, but I am only using it for this purpose so it is ok. All my
> laptops did fine, but I wanted a dedicated desktop computer for this.
>
> Next I found my lights produce a lot of noise. They are LED with a dimmer,
> so I guess thats obvious, but I keep them off when I'm trying to capture
> lowfers.
>
> Now onto the loop. I built my unbalanced loop 5 years ago and used K0LR's
> unbalanced preamp design with remote tuning. I know making a balanced loop
> would be the best solution, but it would be a complete redesign. I had 11
> turns inside 3/4 inch conduit and I couldn't tell where the center was to
> make a tap. 11 turns was all I could fit.
>
> The first thing I did years ago was to make an isolation transformer
> between the  pre-amp to the coax. My thinking was this would isolate the
> loop from ground to cut down on it acting like a short monopole. This
> seemed to work and I captured TH, but he is in South Carolina, so that
> wasn't that impressive. But a success nonetheless.
>
> So, I tried making a "shielded loop" as it seems to be called on the
> internet. It seems to me like it's just a way to balance a loop by coupling
> it to a center grounded dipole type antenna. I wrapped the whole antenna
> except a few inches at the top with aluminum duct tape. Next I grounded the
> center at the bottom. After playing around with grounding, I received my
> first capture of WM. It was faint, but definitely WM.
>
> After a few days of faint WM captures I decided I wasn't happy with the
> results. I removed the aluminum duct tape, pulled 6 turns out of my loop
> and made a center tap. Then I put 5 of them back in. This took a few hours
> and was not fun. So, now my loop is only 10 turns. To compensate for this I
> have to put a capacitor in parallel with the tuning diodes to get to the
> lowfer range. This isn't a big deal, but it reduces my full range. I tried
> grounding the center of the loop with the ends of the loop run into the
> unbalanced preamp. I was thinking this would work since the unbalanced
> preamp was floating (battery operated), but all I managed to do was create
> a noise generator. Disappointed I gave up for the night.
>
> The next night, last night, I realized what I had done wrong. I isolated
> the tuning diodes from the preamp so the ends of the loop were only run to
> the tuning diodes. Then I connected one end of the loop and the grounded
> center tap from the loop to the unbalanced preamp. I also removed the
> isolation transformer from the output of the preamp since it was referenced
> to ground now. I immediately started receiving WM including the graphics!
>
> I did a lot of other things with ground rods and coax grounding, but this
> is already long enough. I know it doesn't really make a lot of sense to
> have all the wires in the tube from an electrical standpoint, especially
> since I'm trying to have a balanced antenna. But, it's working so I'm happy.
>
> Regards,
> John Hamer
>
>
>