The Great Relay Race...or What IS THAT?

Howdy All:

A few days ago I discussed the AN-762 Amplifier.  Not exceedingly difficult to home brew.

Before I go further, I may ask you, what is this?

Let's see, it has two metal thingies, and it is on some kind of circuit board. Hmm.  It has little labels.

Here's the back of it:

Well, not to keep you in suspense, this is a homemade relay board for the AN-762 amplifier.  Just to briefly explain the basics, the AN-762 Amplifier is designed to take 5 watts and give you 140watts output.  In order for that to happen, you need an exciter (in my case an Elecraft K2 transceiver).  I also want to receive using the K2, but because of the tremendous attenuation of the amplifier board,  I need to bypass the amp when in receive.  That means 2 relays.  One to bypass the amp in, and one to bypass the amp out.  When you key the Elecraft, the relays switch to allow the rf from the K2 to go through the amp, giving you 140w out..less insertion losses, etc.

My original amp relay circuit has two loud and clickity-clack relays that have a life expectancy of 50,000 switches.  That is not a lot if you consider that you may be sending CW quite often, and if it fails, when it fails, then that RF might be going into your finals or elsewhere and POOF.

So, I was looking for a nice elegant solution, and that is when I came upon the idea of high-speed (1 to 2 ms) relays that have long lifespan and don't make noise.  That led me to using wetted mercury relays, and that is what you are seeing  in the first photo. These relays have a lifespan of 1,000,000,000 throws before failure.  My friends, that is a lot of Dits and Dahs, even for those speed demons working at 35 wpm.  As far as quiet; you can barely hear these things switch.

Cutting the traces on a little shop milling machine

The downside is that they contain mercury, and that is not even allowed in a large number of states in the USA.  They also MUST be positioned vertically, and will not work otherwise.  They are also a lot more money than your standard mechanical relay.

However, once installed in whatever ham radio device you are using, they will last.  As far as full QSK, no problem, have at it.  My existing relays have an electrolytic capacitor / resistor combo to create a delay so that I can operate at 20 or 22 wpm and not have the relays clicking on and off after every dit.  The wetted relays can run full QSK and you won't even hear them switching.

So, If you are in the mood to build an amp for your QRP transceiver, then this might be the Cadillac solution to your switching issues.

Next time we will be switching gears (not relays), when we discuss the amazing Zumspot digital hotspot.  It is an amazing little device and you might want one if you don't have one already.

Until then,  73, Mark 4x1ks