Re: LF: Receiver protection

[N1BUG <paul@n1bug.com>]

Hi Stefan,

I did not yet measure the voltage across the diodes. When I finish
the power supply and put my LF TX back on line I will make some
measurements like voltage across the diodes while TXing, and RF
voltage coming from the RX antenna into a 50 ohm load when TXing.

I think there is no worry here about the diodes conducting during
receiving. We don't have very strong signals (like DFC39) near
either the LF or MF band. The preamps are preceded by reasonably
good band pass filters which keeps away strong signals far removed
from the band of interest. Oh, and there are no LF or MF amateur
stations within a few hundred km.

73,
Paul



On 07/10/2018 04:49 PM, DK7FC wrote:
> Hi Paul,
> 
> Looks not critical for me. Just for interest, did you measure the 
> voltage across the diodes during TXing on the TX antenna?
> 
> I would leave it as it is. It is just fine i think.
> 
> But beware of conducting diodes during receiving! This can happen with 
> strong local transmitters at any band. The diodes become conductive at 
> much lower voltages, maybe 0.5V. If this level is reached there will be 
> much distortion, i.e. QRM.
> 
> 73, Stefan