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Author Topic: Audio jacks/plugs as QRP RF wire quick connects  (Read 28342 times)

Offline i_hear_you

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Audio jacks/plugs as QRP RF wire quick connects
« on: June 19, 2019, 1540 UTC »
Are 1/4" or 1/8" audio jacks and plugs contraindicated for field-swappable connections between coax connector and antenna terminals, or between coax connector, the coax ends of a toroid-wound choke and antenna terminals at QRP?  I'm looking for a way to quickly and easily swap or remove different chokes/baluns/isolators into the watertight junction box feedpoint of a vertical.

EDIT:

Same as above but with RCA?
« Last Edit: June 19, 2019, 1625 UTC by i_hear_you »

Offline ChrisSmolinski

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #1 on: June 19, 2019, 1638 UTC »
I have no experience using 1/4" or 1/8" plugs, but lots of old ham gear used RCA plugs, I recall them being used to connect external VFOs to transmitters, for example.
Chris Smolinski
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Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #2 on: June 19, 2019, 1658 UTC »
Thanks for the input.  It sounds like RCA is the way forward.

Offline ChrisSmolinski

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #3 on: June 19, 2019, 1718 UTC »
My original antenna/radio patch board used BNC connectors, but I got tired of the short lifetime. I have since switched to F connectors. Now I think I maybe want to try RCA  :)   I may look for some deals on cheap F to RCA adapters and plug those in to the existing F connectors vs ripping everything apart (again).  I have some pictures of the patchboard here on the HFU: https://www.hfunderground.com/board/index.php/topic,47530.0.html
Chris Smolinski
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Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #4 on: June 19, 2019, 1756 UTC »
My original antenna/radio patch board used BNC connectors, but I got tired of the short lifetime. I have since switched to F connectors.

Could you elaborate on this?  Is BNC prone to relatively short mean time-to-failure?  I've started using ground-isolated BNC jacks for I/O to Altoids tins that house DC-isolation transformers, and BNC-to-wireforks for connecting to the terminals on the back of several receivers.  It's been working well, although the plastic threads and nut on the isolated jacks don't have much mechanical strength.  I'm considering super glueing them so the jack doesn't spin while attaching/detaching cable.

I had briefly considered using BNC for connections inside the junction box, but space is tight.  The RCA connectors will work perfectly.  I'm sourcing solder types for the coax connector and radiator/radial connections, and compression types for the coax ends of my chokes/transformers.

Offline ChrisSmolinski

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #5 on: June 19, 2019, 1814 UTC »
Yeah, depending on the connector you can easily start getting loose connections after a few hundred cycles - I did. You can get there very quickly if you switch antennas around a few times a day to check things out.

Not sure what the lifetime of RCA connectors is. In my case I will be putting adapters on the existing F connectors, so if one were to fail, I could easily replace it. As long as I don't have to do THAT more than a few hundred times I should be OK.

The adapters themselves are cheap and easy to find on eBay, but I have yet to find a short for some decent short RCA patch cables. I might need to check out some of my cable sources vs eBay.
Chris Smolinski
Westminster, MD
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Offline Josh

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #6 on: June 19, 2019, 1857 UTC »
I have no experience using 1/4" or 1/8" plugs, but lots of old ham gear used RCA plugs, I recall them being used to connect external VFOs to transmitters, for example.

Collins did testing on RCA jacks and found them to be low loss at the rf freqs they tested them at. Not very environment proof however.
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Offline ChrisSmolinski

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #7 on: June 19, 2019, 1912 UTC »
Collins did testing on RCA jacks and found them to be low loss at the rf freqs they tested them at. Not very environment proof however.

It rarely rains inside my shack, so I should be OK  ;D

That reminded me, years ago one place I worked there was an older gentleman in the wire shop, he must have been in his late 60s or even 70s (this was in the late 1980s) who used to work for Collins. He had many stories to tell about Collins in general, and even Arthur Collins himself. He did some of our best wiring work on chassis, as you can probably imagine, from his prior experience.
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eQSLs appreciated! csmolinski@blackcatsystems.com
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Offline ThaDood

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #8 on: June 19, 2019, 1927 UTC »
Heck, I had a Realistic DX-40 portable,   http://www.radioshackcatalogs.com/html/1978/h131.html     that had a 3/32" ANT connector. It worked, for what it was at the time. I certainly would not TX with a connector like that, even QRP.
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Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #9 on: June 19, 2019, 2002 UTC »
3/32" ANT connector

I'm having trouble finding info on this.

Offline JimIO

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #10 on: June 19, 2019, 2008 UTC »
"I'm having trouble finding info on this."

AKA   2.5mm

Offline i_hear_you

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #11 on: June 19, 2019, 2017 UTC »
You mean the extra-small audio connector!?! Wild.

Offline NJQA

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #12 on: June 20, 2019, 1122 UTC »
Yeah, depending on the connector you can easily start getting loose connections after a few hundred cycles - I did. You can get there very quickly if you switch antennas around a few times a day to check things out.

The number of “mate cycles” a connector is rated can vary wildly.  Some precision connectors are rated for thousands:

https://www.keysight.com/main/editorial.jspx?ckey=632781&id=632781&nid=-11143.0.00&lc=eng&cc=US

Some cheap overseas connectors are seemingly rated for a number less than one.

Most connectors seem to have manufacturer ratings for mate cycles in terms of hundreds of cycles.  This doesn’t necessarily mean that the connector outright fails completely, it means that it doesn’t meet some specification any more (for example, the thickness of the gold plating).   The connector may still be perfectly useful for most applications.

If the connector is abused, all bets are off.  Most RF threaded connectors have torque specs, but you rarely see a torque wrench used.  Some connectors come in 50 ohm and 75 ohm variants.  They look similar, but internal pin diameters are different.  If you mix the two, you may damage one of them.

This article had some good points about connector mate cycles:
https://www.cirris.com/learning-center/product-articles/other-products/227-connector-life-cycles

When you buy hamfest connectors and adapters, who knows what you are getting.  “You pays your money and you takes your chance.”  I try to stay with well known brands like Amphenol, and avoid the ones that look like they have had a rough life.


Offline R4002

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #13 on: June 20, 2019, 1230 UTC »
"I'm having trouble finding info on this."

AKA   2.5mm

Even modern AM/FM/SW portables have 3.5mm audio jacks as their antenna connection.  I know my Grundig G3 uses a 3.5mm jack for the roll-up wire antenna connection, and I believe my Tecsun PL-660 does as well. 

For RX purposes I would feel better using a RCA plug over a 3.5mm plug, but for portables it makes sense to use a smaller size plug for form factor.  Plus, as others have mentioned, there's a huge amount of variability when it comes to the quality of the connectors/sockets themselves. 
U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers

Offline Kage

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Re: Audio jacks/plugs as QRP RF wire quick connects
« Reply #14 on: June 20, 2019, 1410 UTC »
Lots of those older emergency CB radio walkie talkies that were meant to be kept with a road kit used RCA jacks for the magmount antenna and they worked just fine for TX. I suspect because in emergencies they are one of the fastest connectors to plug in and most familiar to ordinary people.
I've also used RCA jacks for <30MHz without problem but wouldn't trust them for anything other than QRP since they can easily be yanked out and would cause a PA transistor to pop.

If you have some of the higher quality A/V RCA cables around and are like me and often split the audio cables from the video and toss the video (yellow) cable to the side often those video cables have better shielding and can be used well into the higher SW frequencies with low power since they are made to carry wideband composite video. Impedance may be unpredictable but at low power it's not much of an issue. I often keep the yellow video RCA cables around for mono only interconnects too for the same reason.

This reminds me that I found 50' of 5 connector A/V RCA cables (red/green/blue left/right) in the trash and should try to push some RF down one to a dummy and see what kind of SWR and power loss they have on 11m since I have RCA to PL259 adapters :P
« Last Edit: June 20, 2019, 1422 UTC by Kage »
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