[TowerTalk] Antenna switch isolation?

[n8de at thepoint.net]

One trick is to use 3PDT relays with the two OUTER poles continuously  
grounded on each relay and all poles grounded on unused relays.
Orienting the relays in a 'circle' so mutual coupling is minimized works, too.
Depending on the number of antennas to be switched, the internal  
arrangement for isolation can be further improved by putting small  
'shields' between the relays, but that's overkill.
73
Don
N8DE

Quoting Pete Smith <n4zr at contesting.com>:

> Another trick to consider is arranging the relays so that there are two
> sets of open contacts between ports.
>
> BTW, it is quite amazing how little relay capacity is really required
> for a legal limit antenna switchbox - Top Ten, for example, uses a NAiS
> relay that costs about $2 a pop.  I have tried to break these running
> really high SWRs at 1200 watts - without success.
>
> 73, Pete N4ZR
>
> The World Contest Station Database, updated daily at www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com
>
>
> On 6/5/2010 8:02 AM, n8de at thepoint.net wrote:
>> Martin,
>> With careful orientation of the relays and grounding of unused
>> contacts, 60db of isolation is possible.
>>
>> The amount of 'internal coupling' between relays is the major
>> difficulty when trying to get very good isolation.
>>
>> 73
>> Don
>> N8DE
>>
>> Quoting Martin Sole<msole at loxinfo.co.th>:
>>
>>
>>> How much isolation should I be aiming for in a remote relay switch box. I
>>> have some 30A rated relays that look as if they will handle a fair  
>>>  amount of
>>> power. I can see only about 40dB of isolation across the open contact. I
>>> don't need it to go above 30MHz and 2kW handling should be fine. Antenna
>>> connections will be all low impedance. So 1kw into the common port  
>>>  will give
>>> me about 10mW at the open port, enough?
>>>
>>>
>>>
>>> Martin, HS0ZED
>>>
>>>
>>>
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>>
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