Michael Black schrieb:
Volker Tonn ) writes:
...
This one diode with 0.7 volts could make you think your S-meter reading
is going nuts as it will never show more than S9+10dB or so. Even the
1.4 volts of 2 diodes in series will only give you addtional 3dBs.
Just a thought....


But there are very few cases where one would be receiving more than 0.7volts.

If you're in such a strong field that those diodes are conducting, you may
have plenty of distortion from one of the active devices. If the field
is strong enough for the diodes to conduct, the radio likely was overloading
anyway. We're talking close to an actual transmitter.

I'm living in Berlin/ Germany and I have a FD-antenna (42mtrs) in the
attic. Strongest singnal readings on my NRD-525 are S9+60dB.
When transmitting with my CB-Rig there is more than S9+80dBs.
The NRD-525 does not overload even on this signal.
When using occasionally my Sony 2001D on this antenna I always use the
Yaesu FRT7700 (preselector/ attenuator)in line. I also use the FRT7700
when connecting this antenna to the PCR1000.

The diodes are there for protection from really strong local signals, and
I suppose even before that, in an attempt to protect from static generated
locally. Under normal use they will never conduct.

For sur not with the Whip antenna :-)


Wait, I suppose it depends on where those diodes are. If they are just
across the antenna jack, the above applies.

They are across the antenna input.
If they are put at a high
impedance point, like the secondary of a tuned circuit right at the antenna,
perhaps there would be enough step-up for a weaker signal to start being
significant voltage at that point.

The blown FET is with broad impedance input for impedance matching on
the HF preamplifier stage.

Volker