[hpsdr] Hermes design thoughts

[Phil Harman]

Hi Steve,

Thanks for your interesting feedback.


> preamp, etc. I also looked at a QS1F front end discussion. My conceptual
> design would have used a 1.6MHz high pass filter (always in) to eliminate
> strong AM broadcasts if you happen to live near one) followed by a 60MHz
> high pass filter (always in) followed by a programmable 0-31.5db HMC472
> Hittite attenuator which allows 0.5dB attenuation steps followed by a
> mini-circuits GALI-74+ preamp (always in) followed by a 6dB resistive pad
> attenuator to cut the gain down some on the high gain preamp.  This would
> eliminate any relay switching, provide finer control of RF attenuation
> while
> trading off maximization of IP3 (would need additional FPGA I/O and
> associated firmware).  I would not add any other filters,  to minimize
> complexity and to depend on the inherent filtering of the antenna itself.
> I

This is something we will look at. I'm not so sure about the 1.6MHz HPF
since I use my Hermes to monitor NDBs and I'm sure there are others who
would like to monitor the MW bands.

I prefer balanced preamps to assist with IP2 issue - particularly since we
open up the front end to the entire HF spectrum.

The HMC472 looks interesting assuming that the IP3 is acceptable.

73's Phil...VK6APH


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