[RTTY] SO2R Problem

[Joe Subich, W4TV]

 > 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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