Omni VII T/R Relay Noise Mod

From the Ten-Tec Omni VII Yahoo Group August 18, 2007

Some of you may have noticed that the Omni VII T/R relay is slightly noisy. I say "some of you" because the degree of noise is a function of the individual relay and stiffness of the wire used to connect the T/R daughterboard to the mating PCB. In other words, some radios may sound noisier – or quieter than others.

In the Omni VII, Ten Tec designed an ingenious T/R relay mounting scheme by inverting the T/R relay daughterboard and suspending it with foam against the main PCB. In my case, I could not adequately decouple the relay noise. Part of the problem is that the relay is soldered right up against the the T/R daughterboard and functions much like an acoustical sound board on a piano or violin, thereby amplifying the "ticking" of the T/R relay.

I decided to slightly revamp the mounting scheme, and use an Aromat/Matsushita RF reed relay. The Aromat relay is a genuine RF relay. Moreover, when operating, this relay exhibits almost no acoustical noise on its own, but care must still be taken to acoustically de-couple it from its wiring.

I began by placing an order for ultra-flexible 22 AWG wire from a robotics dealer. The Aromat relay was ordered through Rich Measures, AG6K. The wire uses a silicone jacket, much like HV wiring. In fact, the wire has a HV rating, owing to its use of silicone so it's an ideal candidate for switching RF, provided small lengths are used.

I completely removed the T/R daughterboard and mounted the new relay on weather-stripping material from Home Depot. The new stripping is 1/2" wide as is much more flexible than the type used by Ten-Tec. In order to ensure long adhesive life, I used Loctite gelled Superglue on both sides of the weather-stripping. The connecting relay wire was formed into "C" like loops. Flexible wire formed this way adds to the acoustical isolation.

The new relay, silicone wiring, and mounting configuration results in no perceptible "ticking" noise when the T/R relay activates. Total time on the bench was about 45 minutes. While I doubt many of you will be interested in such a mod, some of us are always in pursuit of the cleanest QSK switching possible and with the least amount of acoustical noise.

Paul, W9AC

August 19, 2007

I received several private replies concerning this mod. First, previous Omni transceivers also used nearly-silent reed relays for T/R switching – in addition to the loud amplifier PTT key line relay. You may have thought your Omni used solid-state T/R switching, but if you were to listen closely, you would hear the slight "ticking" of the reed relay during T/R transitions.

The Omni VII uses a HV transistor for amplifier switching, leaving only a small signaling relay for the T/R switching function. But this relay is a bit noisier than RF reed relays I've used in the past.

The Aromat/Matsushita relay I purchased for the project is a model RSD-12V. There's a guy on the popular Internet auction site that sells them for about $11 each. Also, AG6K sells them. These are superb RF relays that switch in ~ 1.0 ms without the addition of an accelerator circuit.

The 22 AWG flexible silicone wire was purchased from Trossen Robotics.

Paul, W9AC

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