Friday, July 24, 2009

What's wrong with RCA connectors?

Why are BNC connectors "the standard" for QRP HF radio use? Who decided, and why?

My QRP connector of choice is the RCA (more commonly known in the UK as "phono") connector. They are cheap, small, and easy to assemble, and one size can be used with standard RG-58 or miniature RG-174 cable. MFJ uses one in the small Cub transceiver, and I seem to remember that Heathkit used them at frequencies up to 145MHz and powers of up to 100W. You can get gold plated ones if you want to be flash, or want to minimize losses. If you're a cheapskate, you can salvage them from old audio equipment.

The use of BNC connectors and other types designed for use at UHF where losses can be significant is completely unnecessary at HF. QRP is supposed to be about "doing more with less" and I think using RCA connectors fits that description admirably.

4 comments:

M0PZT said...

I personally think the phono connector shouldn't be used to carry RF, not because of the losses (or purist views) but because they are mainly used as "accessory" connectors for things like PTT-switching and audio signals.

Would you use a 3-pin mains plug instead of an XLR connector ?! It's far safer to use the right type of connector for a specific job - and it makes interfacing much easier, eg: "now, is that phono carrying my RX audio, 12v DC or is the lead from the ATU?"

g4ilo said...

That's a fair point, but perhaps I didn't make it clear enough that I was thinking mainly of simple, usually homebrew QRP equipment. Such gear typically doesn't have anything other than connectors for power, antenna, key and headphones.

The standard barrel connectors are normally used for power, while jack sockets are generally used for key, mic and headphones. There is usually only one coaxial socket required, so there is little scope for confusion, especially where the constructor will also be the user. If space is at a premium - such as a transceiver built into an Altoids tin - then phono connectors have the additional benefit of small size.

Larry W2LJ said...

Julian,

I agree. Seems everything I owned and built that was Heathkit used them. If they were good enough back then, they're good enough now. Only problem I remember having with them, is that they could lose their tension and get loose quite easily. They also seemed to build up a coat of oxidization or "tarnish" quite easily, too. But on the good side, they are inexpensive, easy to work with and are pretty easy to find.

g4ilo said...

Yes, I can remember that happening with the Heathkit ones. You had to clean them now and then to get a good contact. The modern ones are plated (you can even get gold plated ones) which should avoid that problem.