[RTTY] SO2R Problem

[Jay WS7I]

Icom 751's had it right in the old days they have a simple transistor 
that protects everything.  We got so that we installed a transistor 
socket and had a handy supply in the old M/S days without band change 
rules.  Ran out once!



On 2/14/2012 9:16 AM, Joe Subich, W4TV wrote:
>   >  What is the most I can tolerate? I don't know, but I assume it would
>   >  take more than a half volt to punch through the typical SS devices in
>   >  the rx front end.
>
> It's not typically voltage punch through to the active devices that
> kills front ends ... except for switching diodes that can be damaged
> will less than 1/4 volt depending on type and how they are biased.
> The more common failure is burned resistors and chokes which can be
> damaged with 100 mW or less.
>
> 200 mV is slightly less than 100 mW ... uncomfortably close in my
> opinion.  I would prefer to see levels of 10 mW or less *before*
> any bandpass filters with levels after bandpass filters no greater
> than -33 dBm - particularly with "transceivers" that have blocking
> thresholds less than 120 dB.
>
> 73,
>
>      ... Joe, W4TV
>
>
> On 2/14/2012 11:45 AM, Jerry Flanders wrote:
>> At 09:30 AM 2/14/2012, Tom Martin wrote:
>>>     Excessive RF took out the front end of the FT-1000MP after 2 hours.
>>>                             Lost 10 meters on the PRO II on
>>> Sunday.  As of Monday morning, no receive or transmit with  the PRO
>>> II on any band.
>>
>> When I first tried SO2R I was concerned about high RF levels from the
>> tx antenna coming back down the rx stn line and zapping the receiver
>> on the other band(s), so I rigged up a simple RF voltmeter and
>> actually measured voltages presented to the rx.
>>
>> A combination of stubs and filters got it down to<50mV on most
>> bands, a max of 200 mv on only one.
>>
>> This worked for me with pairs of IC756, 756P3, Elecraft K3, and now
>> Flexes - I have never had any front end damage from SO2R at 1KW from
>> Quadras. My antenna separation is typically 100 ft or so.
>>
>> What is the most I can tolerate? I don't know, but I assume it would
>> take more than a half volt to punch through the typical SS devices in
>> the rx front end.
>>
>> Jerry W4UK
>>
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