Receiver Sensitivity down from a spike

[Mathew Quaife]

With sadness I think my multiband dipole antenna fed with ladder line has done it to me again, lost the front end of my receiver on the Hermes, so my question is, is there a protection circuit on the board that I can check it's death?  It still transmits just fine, and I can hear extremely strong signals, so I know it's just a protection circuit

Thank you!

Mathew 

N9LV 

[Steve Haynal]

Hi Mathew,

You can find the HL2 schematic here:

http://hermeslite.com/

Please examine D1 for damage. This TVS diode is present to protect against spikes. You can try removing it and seeing if your RX sensitivity is restored.

There have been problems with the TR relay K2 which result in low RX sensitivity. You might try flicking that with your finger to make sure it engages to RX. Also, try bypassing the TR relay and N2ADR board to eliminate them by connecting a receive antenna as seen here:

https://github.com/softerhardware/Hermes-Lite2/wiki/Hardware#rx-only-test-and-use

Ideally, if you have a signal generator, you can connect this to the RX input with low level/attenuator and trace the RX chain as seen in the schematic with an oscilloscope. You want to make sure that an appropriate signal reaches the AD9866 with little attenuation.

73,

Steve

kf7o

[Mathew Quaife]

Taking a long wire to the 5th pin did not give me any receive, tapped on K2, no luck.  I have looked all over trying to find D1, is it by change on the underside of the main

 board?

[mr.ri...@gmail.com]

Mathew, try looking here:

[Mathew Quaife]

Update, I pulled the one end of D1, that did not make any improvement, upon tracing the boards, I noticed the U2 on the IO Board looks blown, hence part of the carbon gone and burn marks around it, nothing looks odd on the main board, but after I pulled D1 and going to pin 5 with a long wire, I still did not hear any signals.  I have replaced the IO board, no damage is visible on the filter board to the naked eye, I can put it all together, change the S-ATT and hear signals that are super strong to me.  Any additional suggestions.   Unfortunately I don't have an oscilloscope or signal tracer.  Was hoping to save the $267 on a new board.

Thanks

Mathew 73 N9LV