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