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Author Topic: Audio jacks/plugs as QRP RF wire quick connects  (Read 28200 times)

Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #15 on: June 20, 2019, 1627 UTC »
Even modern AM/FM/SW portables have 3.5mm audio jacks as their antenna connection. 

Yes, my pl-880 has this as well.  However, my concern is whether they could handle even modest TX powers.

Offline R4002

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #16 on: June 20, 2019, 1907 UTC »
Probably depends on how you define "modest" - are we talking less than 1 watt QRP or 4 watt carrier CB power levels or QRPP/Part 15 power levels?   If those emergency CB radios mentioned by Kage used RCA jacks then probably.  I remember I used to have a late 70s vintage Radio Shack (Realistic) handheld CB with a massive center telescopic whip antenna and it had connectors on the side for external microphone, speaker, 12VDC power and antenna...and the external antenna connection was a RCA connector.  The handheld CB was wither 2 watts or 4 watts transmit power rated, that's with a fresh set of batteries or an external 12 volt power supply though. 

Did I ever actually connect an external antenna to the handheld CB?  Nope.  But as mentioned by Kage, there were other radios sold with these connectors so they must work to some degree or another.  I imagine that the emergency CBs aren't designed for absolute maximum range but the antennas still need to present a workable impedance and SWR to the transmitter.
« Last Edit: June 20, 2019, 1913 UTC by R4002 »
U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers

Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #17 on: June 21, 2019, 1413 UTC »
Probably depends on how you define "modest" - are we talking less than 1 watt QRP or 4 watt carrier CB power levels or QRPP/Part 15 power levels?

In my case, I'm looking at 15 watt PEP SSB at most.

I'm not clear on what the dangers are.  Is it a concern of an arc between conductors at higher voltages?  Impedance problems?  Overheating due to too little conductor for applied wattage?

Offline syfr

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #18 on: July 12, 2019, 2326 UTC »
Much of the 100W heath gear of the 70's and 80's used RCA jacks. They're fine RF connectors with an excellent impedance match even at the 100W plus power level.
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Offline ChrisSmolinski

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #19 on: July 13, 2019, 1220 UTC »
I ran the test here the other day on 20 and 40 meters, about 125 watts SSB through some RCA connectors on my antenna patch board. Worked fine.
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Offline Pigmeat

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #20 on: July 13, 2019, 1949 UTC »
I used it when I made up patch cords for my vintage Drake receivers from the "Twin Series" of TX/RX's. It's what they were set up to take for RX from the factory. RG-9 is the 75 ohms mini coax that I prefer. A crimp-on RCA male plug and you're rocking with an antenna that matches a dipole at the feed point. It's about as easy as it gets.

I knew a pirate that used either RG-6 or RG-9 feedline for a TX in the power ranges you're talking about with a 1:1 balun for years. He would occasionally add an amp and run roughly 150 watts of AM through the stuff, no problems.

I've used Dollar Store speaker wire for both feedline and the antenna, using a tuner. and had good results. That RF has to go somewhere.

Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #21 on: July 15, 2019, 1405 UTC »
I ran the test here the other day on 20 and 40 meters, about 125 watts SSB through some RCA connectors on my antenna patch board. Worked fine.

For some follow up I used RCA connectors and have been running 100 watts PEP SSB, and 50W/30W FM VHF/UHF as well with no noticeable ill effects.

Online Josh

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #22 on: July 16, 2019, 0353 UTC »
On speaker wire as transmission line, some is very lossy on hf and above.
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Offline Pigmeat

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #23 on: July 16, 2019, 1844 UTC »
It is when it gets twisted. That's when it got split and turned into general low profile antenna wire. Those 100 ft. "Dollar Store" rolls of the stuff were much less bulky to carry into the woods than coax. 65'-67' ft. length for the feed, 33-34' for the dipole all for a buck and change.

They lasted about 5-7 tx'es, which was fine for my needs. When I split some of them I'd string them through a hayfield as a BOG which worked great or used them just to experiment with Made a nice MW mag loop out of the stuff about 20 years ago until a late tomcat got tangled up in it.