[SCCC] VHF Antenna Switch

[Steve]

At 07:30 PM 12/3/2021, Tree wrote:
>Switches or relays?
>
>The old school Dow Key switches are pretty good although I can't verify
>that they will handle that much power on 2 meters.

If it's for T/R purposes, it'd need to have isolation on the order of 
a minimum of 53 dB to keep the leakage power into the RX port below 
10 milliwatts (+10 dBm) and preferably more like 63+ dB (+63 dBm = 
2000 watts). One way to achieve that is to use a low-isolation, but 
high-power handling switch/relay (such as a DowKey) on the TX/antenna 
side and another, smaller, lower-power relay on the RX port which 
grounds the RX input on transmit.

But IIRC, DowKeys have poor SWR at 144 MHz and are lossy, to boot. 
 From what Dennis says, I suspect this fellow is having trouble 
keeping switches/relays alive after a full minute of keydown at full 
legal power; either the contacts, or the connectors (go look at the 
power ratings of type N connectors at 150 MHz) burn up after a short 
time. I've burned and lost the tension of the leaf "spring" on 
DowKeys at 1500 watts just with CW on HF.

I suspect what this guy is gonna need is one of those thousand-bux 
military switches with HN or larger connectors and weighs 25 - 30 lbs 
(and also shakes the whole operating table and makes great big 
KER-CHUNK sounds when it switches). Or the Europeans probably have 
something... I hear there's lots of them running well over 1.5 kW 
output power on 144 (although I dunno about continuous duty...).

Another alternative would be using Pin diodes. However, this would 
require an engineering project both to design and build a successful 
unit. Some years ago, Leif Ericsen (an SM5... can't remember his call 
now) and I corresponded at length about Pin diode switches for use at 
multi-kW power levels on 144 and 432 MHz. Quite a bit of engineering 
was involved in our designs; they weren't something you could throw 
together in an afternoon. I eventually did build one that I used 
successfully in my HSMS CW skeds with W8WN but I only had 500 watts.

SteveH, K0XP