Re: Wanted Tohtsu CX600NC relay
Same here no matter what I always, under advice from G3XDY/G4DDK and the VHF/UHF DX book, use an isolating relay...... however the tiny SMD relay in my HA8ET 70cm pre-amp has so far enabled the device to survive, used last night in the 70cm UKAC with 250w.
Colin de G8LBS.
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From: ian hope (2E0IJH)
Sent: 09 September 2020 15:07
Subject: Re: [UKMicrowaves] Wanted Tohtsu CX600NC relay
I always use preamps that have internal bypass relays, even if they are only on the RX line and drop the power to those before switching the mast head relay, we use either cx520's or Cx600's depending on application, But as Ian says the older versions of both the cx600 and the cx520 had a different design.
Sent: Wednesday, September 09, 2020 at 2:47 PM
By having the common port pointing the opposite way from the other two, the CX520D saves a lot of space inside a preamp box. I wish there was a wider choice of relays with that connector layout, and at a similar price point (which rules out the big, expensive EME relays) but I have never found even one alternative.
However, the problems with poor isolation and poor power handling are surprising. I used the same CX520D in the 70cm EME preamp for many years, handling 1kW CW and connected directly to the GaAsFET preamp, all with no damage. So does the performance really fall over a cliff between 432MHz and 1296MHz?
A possible explanation for poor isolation is that there have been at least two versions of that relay, sold under the same model number. In the modern ones, the isolated contacts are grounded onto gold-plated contacts that are screwed into the body. The older ones relied on grounding onto the body itself, which is a poorer contact and also less reliable... bearing in mind that the relay will be operated tens or hundreds of thousands of times, but preamp only has to be unlucky once.
Yet another thought is about the settings of the moving arms and the actuator plungers. These settings are quite critical to achieve the correct contact pressures, and the TohTsu relays aren't exactly built like Swiss watches.
As I said, I do wish there were other relays with that highly practical port layout and at a similar price point.
73 from Ian GM3SEK
On 09/09/2020 13:29, Colin Ranson wrote: