r/AntennaDesign

I have a project where I would like to track down a pair of decommissioned communication parabolic dishes. I a in the Seattle area, but would be will to drive some ways. Has anyone has any luck just calling the communications contractors? I've been searching cragslist, ebay, ham classifieds, etc for local sources. I'm looking for a simple round prime focus dish rather than the widely available oval TV satellite dishes to make feed horn design easier. I also want matching dishes to make mounting identical so I don't have to solve the same problem twice.

Prefer 4 foot (1.2 meters) for transport, but might consider 6 footers if anyone thinks I can haul them on a Subaru WIlderness Outback with factory rails? These will be in a noisy environment so I want solid dishes to keep the back lobes down. Any advice on f/D (relative depth of the dish)? Sat dishes are relatively flat, but comm dishes are often deep at f/D 0.3 or so. I assume that I am facing the same problems as the backhaul microwave comm folks, but a short focal distance seems to imply a splash plate rather than a simple horn to handle 120 degree feed? What's a fair price to pay?

Appreciate any advice -73s

I am looking for the manual for a 690D-1 antenna loading coil, coupler seen in the attached picture. This thing is painted green so there is a high chance there is an army field manual , parts breakdown, or maintenance manual. I am guessing that while it is labeled 690D-1 the army in its infinite wisdom calls it an M25/arc B -6 or something equally as helpful any assistance would be greatly appreciated

https://preview.redd.it/82y1y229tc0h1.jpg?width=1200&format=pjpg&auto=webp&s=4a942920c76f78edebd5a5072226f3b4fd74bcd6

Thanks

I’ve finally deployed my first take on a homebrew 80m EFHW today. The SWR results aren’t what I was hoping for.
My homebrew 2m antenna (variation of a slimjim) is much easier to tune. Very good results.

The 80m build is 14AWG for the main element and counterpoise.
The 49:1 unun is using solid 18AWG “bifilar” with 82pF cap across the primary. Ferrite 31 as the toroid type.
A compensation coil with 6 wraps is 78 inches from the feed point.

I bench tested the unun with a 2.2k ohm resistor as the dummy antenna and the NanoVNA suggest a 82pF cap had the best matching.

The deployed testing was in a sloped configuration, where the unun was 2m off the ground then inclining to 20m. This was the best height I could manage and easily test the modifications.

I tried changing the cap valve and even removing it.
My next action is to rewind the unun with different wire, possibly matching wire size. Although, I’m uncertain if this will help.

With my slimjim build there are knobs which dial it in: overall length, matching stub length, feed point, cap gap width, parallel gap width.
Are there other knobs to consider with this EFHW?

Also the full length of the counterpoise at 14ft was never fully utilized, but with or without, the NanoVNA did not indicate matching changes.

Apologies for the screen glare. It was a beautiful sunny day.

73

I have a Fosi Audio BT20a Pro amplifier. If bluetooth is detected, it plays audio from that, otherwise, it plays audio from the RCA connectors on the back. I never use bluetooth, so never attached the external antenna.

My new elderly neighbor has a device that auto-connects to my bluetooth first thing every morning and blasts something out of my speakers. I've taken to turning it off at night, but am looking for a more comprehensive solution.

Is there an easy way to disable the antenna? Will an "Direct Termination Cap" do that? I tried opening it up, but could only get it open about an inch before having to do a lot more work. I found a tiny coax cable going from the circuit board to the exterior antenna connector. It was connected with a friction fit and a dot of hot glue, so I carefully disconnected it with a tiny screwdriver, rolled it up and tried again. It seemed to connect to bluetooth even faster that way! So confused.

I tried dropping the whole thing in a cooking pot, but that didn't seem to work. Stacking a collection of pots on top if it may have worked sometimes. IDK.

Is there a simple solution to disable this? If it's going to be a big project, I already have my eye on a better non-bluetooth stereo amplifier, but I wanted to ask first and maybe save money and learn something without losing a whole day on another project.