The AM Forum

Regular unsealed relays can get a coating of oxide or dirt on the contacts, enough to stop very tiny signals from getting through it.

For switching 1uV signals, Reed relays may be an option being small and sealed, but there is contact bounce.

I have used mercury wetted contact relays for audio stuff and never had any issues whatsoever even with older used relays as long as they were good.

The mercury wetting would seem to make the contact more reliable and it eliminates noises caused by bouncing.

What about receiver RF input switching on the HF bands? These miniature pcb-mount 1KV ones are available. Usually they are rated lower voltages but this is interesting.

GI Clare Mercury Wetted Relay
type CUP P001A505 1-form-A one
NO 2A 1000V
coil-5V

Don't care about the mercury. It's not getting out of these things.  If it were used as the receiver-to-antenna part fo the TR switch, wonder if it would do for HF?

Has anyone tried this kind of relay?

Plating relays and contractors with Cool Amp really helps with any residual resistance build up.

It also helps with lowering contact resistance to very low levels.

Plate liberally.

--Shane
KD6VXI

My trick has been to use a DPDT relay and wire the two poles in parallel. Not a perfect solution, but it works well enough. If your going to buy a relay, there those with bifurcated contacts that essentially do the same thing.


Don

I've done what Don has done as well without issue. 

hermetically sealed relay?  Yaesu had an issue with the FT-102 and had a fix with a new relay that was essentially  hermetically sealed and possibly bifurcated as well. Not a 100% sure though on this.

Bifurcated are the cat's meow!

Did try some non-hermetic large bifurcated leaf ones before and had the problem but they were very old. Maybe I put bad parts in my TR switch to start with.
Got boxes of old relays including some surplus telephone company ones, all way tarnished. If some have the soft contacts like Gold I should try one. Some have double contacts on one arm, like bifurcated but with bump-type contacts fitted on them. Have not tried any of those, so dirty I guess it put me off.

The question about the mercury-wetted and regular-type reed relays is more about having excessive capacitance in the receive antenna circuit since the conductor in both kinds goes right through the middle of a coil.

Just Learned that mercury-wetted relays including the 'octal' plug-in types have the glass ampoule sealed containing hydrogen under high pressure. A reason not to bust them! Also, Hydrogen will leak out through the glass wall of a pressurized containment over time.

May be time to put frugality aside for this one thing, go hermetic and bifurcated..

Pretty simple to test for the "excess" capacitance, I would think.
The other thing would be to test for isolation between contacts...

There seems to be in the back of my mind some reason or other that mercury wetted
relays are contraindicated for low level signals. Of course it may be the other way around.

Another option is just reed relays. No oxygen to make the contacts get nasty.

Telco contacts often were designed to be "self cleaning" via a wiping motion.
Especially those that had the contacts that were at 90 deg to each other...

I know this stuff has been covered somewhere... in books or online.

                          _-_-

I remember, somewhere in the foggy past, something about applying a fraction of a volt of DC with a mil or two of current load would help keep the contacts in good condition.   

Those that wipe would be the best bet I'd think.

 

I've thought about wiping. When I worked for Alcatel, we had a line length simulator instrument. Inside were many boards filled with dozens of relays and hundreds of resistors.
It had a self cleaning function which would run every time a new line length was selected. The thing would rattle and buzz operating the relays many times to make sure they were exercized. We use to say 'exorcized' because of the racket going on for 20 seconds or so.

There is an article including intermittent receiving issues:
https://www.w8ji.com/relay_cleaning_and_life.htm

Some technical advantages of mercury wetted contacts that seem to apply to contact problems are on page 2of this PDF file:
http://bunkerofdoom.com/relay/pb/JM_MERCURY.pdf

Just seems to me that a sealed unit is best for the tiny signals, and the above PDF seems to say that mercury wetting eliminates the wear and contact resistance issues.

If no one has tried this kind of relay then it's for me to measure the thing and see how it works.

Perhaps more data/info in this (yet to read it):
http://www.ni.com/product-documentation/4199/en/ (http://www.ni.com/product-documentation/4199/en/)
and:
https://www.eevblog.com/forum/beginners/signal-relays-(1khz-1mhz)/ (https://www.eevblog.com/forum/beginners/signal-relays-(1khz-1mhz)/)

Teledyne used to offer relays like these, but in what looked like metal transistor/early IC packages"
https://www.te.com/usa-en/products/relays-contactors-switches/relays/mil-aero-relays/high-frequency-relays.html?tab=pgp-story (https://www.te.com/usa-en/products/relays-contactors-switches/relays/mil-aero-relays/high-frequency-relays.html?tab=pgp-story)

see attached too.

There was a problem with the relays in the Kenwood TS-430S going intermittent on receive (ask me how I know). Kenwood issued a repair and modification.

The mod put a small maintenance current through the relays to keep them working.

https://www.qsl.net/wb4kdi/Kenwood/TS-430S/Service%20Bulletins/asb0902.html (https://www.qsl.net/wb4kdi/Kenwood/TS-430S/Service%20Bulletins/asb0902.html)

Edit: The idea of this is to provide a DC current for the relay to switch that creates a small arc which refreshes the contacts every time it switches. The input and output must be DC blocked by capacitors, which is easy enough to do for a receiver, if it isn't already. By using this method, probably just about any general purpose relay would suffice for a T/R application.


Don

In my earlier post, I couldn't remember the particulars but it seems KW found the same ancient fix keeps the relay contacts bright.

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Those relays were used quite a lot during the 60s and 70s in military equipment.   They drew a lot of current but could withstand fairly high "G" shock load and vibration.

(https://photos.smugmug.com/Miscelaneous-/BIGGIES/i-Hn3VzPX/0/3b9dfeb6/L/P1010014-L.jpg)

Yeah Mike!
That's one of those Teledyne relays! :D

Those are some snazzy relays! so tiny. Is that a TO-5 can?
In almost every way, at some time, we get to see a particular pinnacle or zenith of technical evolution. That's what those look like.

Yep, TO-5.   I've had maybe 20 of those things for at least a decade or so, and maybe used ...1!

Surprisingly they are still made and also offered on the auction site.

Cool-Amp? How is it I've lived as long as I have and never heard of this stuff. Is this the right product: https://www.cool-amp.com/conducto-lube