Re: Topband: Topband relays
On 12/11/2019 5:13 AM, Tim Shoppa wrote: Not relevant to my topband setup, but For the high-impedance (ladder line) side of my switching, I use open-frame relays with the contacts pried a little further apart than stock. Example part is the McMaster Carr 7384K14. N6RK outlines the process of widening the contacts in the May 2009 QST Hints and Kinks. Tim N3QE Postscript to my QST article from 10 years ago: Modifying relays this way increases the pull-in voltage. Depending on how much design margin the relay has, and depending on how much the contacts have been opened up, it may be necessary to boost the coil voltage momentarily. To implement this, you can repurpose a T/R relay "speed up" circuit, such as this one designed by Tony, K1KP and described by Bob, K6XX: http://www.k6xx.com/radio/fastrely.html The nice thing about this circuit is that it doesn't require an auxiliary power supply voltage that is higher than the normal relay coil drive voltage. Extremely elegant IMHO. Will this drive circuit, you have the luxury of overkilling the contact spacing so there is no concern about arcing. It is hard to say just how much contact spacing is "enough". Not mentioned in the write-up is that contact bounce will establish the ultimate limit as to how fast the relay can close, regardless of how much boost is applied to the relay coil. In any event, once the modified relay does pull in, the holding force is the same as it was before the relay was modified. Rick N6RK _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Topband: Topband relays
Continuing from N4ZR’s relay thread and Rob’s observation: For low impedance (50 ohm ballpark) side switching, I went to Struthers Dunn (now P) DPDT T92 relays with paralleled 30A contacts. I got a big boy legal-limit amp and have been COMPLETELY happy with these at legal limit. Several hundred thousand QSO's through these relays without a problem. These are the "low impedance" side of my tuner switching. Many vendors use PCB relays at legal limit “, and I’ve tried these, but I have found these to never survive legal limit RTTY contesting. They may be OK at CW or SSB duty cycles. What I ended up using was much beefier relays. I went to Struthers Dunn (now P) DPDT T92 relays with paralleled 30A contacts. I got a bigger legal-limit amp and have been COMPLETEY happy with these at legal limit. Over a hundred thousand QSO's through these new relays without a problem. These are the "low impedance" side of my tuner switching. Not relevant to my topband setup, but For the high-impedance (ladder line) side of my switching, I use open-frame relays with the contacts pried a little further apart than stock. Example part is the McMaster Carr 7384K14. N6RK outlines the process of widening the contacts in the May 2009 QST Hints and Kinks. Tim N3QE > On Dec 11, 2019, at 7:38 AM, Rob Atkinson wrote: > > Actually, if you have a quarter wave driven element and you are > disconnecting it at the feedpoint, your relay concern shouldn't be > voltage so much as current. Fast switching and large contact surface > is more important than voltage handling. > > 73 > Rob > K5UJ > _ > Searchable Archives: http://www.contesting.com/_topband - Topband Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
