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50mhz TX antenna mod


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I recently picked up an old Airtronics Vision tx listed as not working, parts only, because it has a bnc connector on the top of the case where the stock antenna would have fit in, and I was interested in seeing how the bnc connector was installed. Turns out the tx does work - all the better. Inside the case it looks like whoever added the bnc connector just used a piece of hookup wire from the old antenna base mount up to the bnc connector at the top of the case. Seems this woud work ok if using an antenna with a bnc connector at the base.

My need is for an external antenna about ten feet from the tx  - the tx would be on my desk, and the antenna outside a window. Would it be better to use a piece of coax internal to the tx from the antenna connection up to the bnc at the top of the case? Only other post I've seen about using an external antenna suggested removing the transmit module, and locating it separate from the tx. In my case, the outside location would be more or less permanent, so not sure about the durability of the tx module with winter coming even if it is in a waterproof case.

My goal is to get a reliable signal about one mile away. More or less line of site except for a lot of trees. Tx antenna will be outside a second floor window, and the rx antenna will be about 15 - 18 feet above ground. I will provide more info on the project if needed.

Thanks, Mike


Edited by Oldtimer
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There shouldn't be any issue with installing a BNC or UHF connector on the R/C Tx. For best matching/efficiency don't use a single wire to the connector; You need both signal and shield.

After mounting the connector on the case, a short piece of 50 ohm coax would be used inside the Tx wired as follows: Shield soldered directly to the PCB's ground plane (near the RF signal pad). The coax's center conductor soldered to the RF signal pad.

Google for plans on how to build a vertical polarized 6-meter antenna your outdoor installation. For example: http://fedler.com/radio/6m_vertical.htm
Note: I haven't built the antenna example, it's just a random project found with google.

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Ok, thanks for the info. Adding the internal piece of coax will be a project for this weekend. Not sure about building an antenna at this time.  Might look at a mobile antenna for 6 meters for now, since I already have the mobile mount, and see how well it works just with the magnet base on a flat metal bar.

Another issue that came up in testing is rfi from the solar panel / battery setup at the rx location. Seems the cheap charge controller I was using created a lot of noise. Once I had the tx a far enough away from the rx, the rx wasn't responding. Didn't realize noise was the problem until I hooked the rx and control circuits directly to another battery. Have a Morningstar controller that I'm switching out in hopes that reduces any interference. Also, need to clean up the rats nest of wires between the rx and the control circuits. Next would be some chokes, but need to figure out values to use.

Thanks again for the help.


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