[TowerTalk] 6m QRO 2 Position Manual Antenna/Coax Switch

[Michael Tope]

I made some isolation measurements with a network analyzer on the Diawa 
CS-201 about 20 years ago when I was building an SO2R setup for the W6UE 
station. Most astonishingly, I found the test data. I did isolation from 
common to both the A and B ports with and without the unused port 
terminated into 50 ohms. Here is the worst-case:

30 MHz          -69 dB
144 MHz        -59 dB
220 MHz        -53 dB
432 MHz        -44 dB

The isolation decreases more or loss monotonically with increasing 
frequency (there is a flat spot around 300 MHz). Of course, remember 
this is a sample of one switch. YMMV.

In terms of reliability I had one switch stop working when one of the 
beryllium copper contacts rotated out of plane because the thingamajig 
holding it to the SO-239 center conductor became loose. I put some JB 
weld on it and never had any problems with it after that. We had 7 or 8 
of these in our SO2R setup, and aside from that one early failure, the 
rest worked flawlessly. The switches were used routinely at the legal 
limit level. Definitely good bang for the buck, IMO.

Unfortunately I didn't check VSWR while I was at it (I was mostly 
interested in isolation at HF frequencies).

BTW, I remember working Desecheo Island on 15 meters back in the mid-80s 
utilizing the poor isolation of a B&W rotary coax switch. I didn't 
realize that the switch was set to the dummy load position when I made 
the contact (I guess I was the dummy). Their signal really came up when 
I actually selected the antenna :-)

73 Mike W4EF................

On 7/22/2020 5:19 PM, John Simmons wrote:
> The spec on switches few look at is- isolation. This isn't terribly 
> important if you are switching antennas for a transceiver. It IS 
> terribly important if you are switching radios between an antenna- or 
> even more so if you are using an amp! Two relays in series will give 
> you up to 80 dB.
>
> If you are using an amp and switching to different antennas.... if the 
> antennas are on the same band that you are operating on, what is the 
> effect? If the switch has poor isolation then some of your 
> transmitting power will be radiated on the unselected antenna(s). 
> Interesting thought.
>
> -de John NI0K
>
> Jim Brown wrote on 7/22/2020 6:50 PM:
>> On 7/22/2020 10:03 AM, Wes wrote:
>>> I have not looked inside one of their switches, but based on 
>>> examination of some of their surge protectors, I would not recommend 
>>> Alpha Delta.
>>
>> I've used Alpha Delta switches for years,all 1x4s, mostly before 
>> replacing them with good coax relays and relay-switched boxes, but 
>> also on portable setups like FD and CQP. I HAVE looked inside, since 
>> I had one that was bad. It wasn't broken, it was MADE that way, with 
>> a part missing so that there was no way that position #4 was going to 
>> work. So much for final test. Electrically they're fine. The 1x2's 
>> are made the same way.
>>
>> I also have a few 1x2 Daiwa switches that seem pretty good. I haven't 
>> measured any of them, but their mechanical construction of all of 
>> these switches suggests that crosstalk/leakage should be very good.
>>
>> The only other Alpha Delta product I've seen was their dipole 
>> insulator, which includes a GDT. When it fries (shorted) on a 
>> lightning discharge or too much TX power, the antenna must be lowered 
>> to correct the problem. That can be a real PITA, depending on how the 
>> dipole is rigged. And, IMO, it's the wrong place for a GDT to protect 
>> the radio. This was one of a half-dozen dipole insulators I bought to 
>> figure out which were suitable for my needs.
>>
>> 73, Jim K9YC
>>
>>
>>
>>
>>
>>
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