[hpsdr] Help with Hermes VNA

[Helmut Oeller]

Martin, thanks for your post.

It's John, W0GN, who is suffering from connection problems between 
HERMES and VNA software after switching from win7 to win 10, not me. 
Hermes VNA 1.6.0  as well as HamVNA 1.1 works fine on my win 10 machine.

Maybe it can be in the interest of others to reply on your further comments:

Of course you have to use HERMES exclusively with direct access to the 
SMA ports for VNA operation. Moreover I would recommend to connect 10 dB 
SMA pads to the port. A precise calibration set for open, short and 50 
ohms and a good reflection bridge is essential for serious measurements. 
Crosstalk or leakage is not so bad as you mentioned. Acceptable and 
repeatable values are between 80 dB and 90 dB. That's far more than a 
ham needs.

The 900 Mhz-NanoVNA and the new 3 Ghz-NanaVNA2 show approx. 30 dB less 
dynamic range than HERMES! But they have a huge frequeny range and you 
can't compare them directly. These cheap Chinese stuff - employing 
western chips of AD and ST - are really nice tools for hamradio apps, 
but not for higher standards.

73, Helmut, DC6NY


Am 07.12.2020 um 10:10 schrieb Martin Emmerson:
> ***** High Performance Software Defined Radio Discussion List *****
>
>
> I am not sure what version of the VNA software for Hermes is causing 
> your problem but a
> long time ago around 2013 I did some work on the original VNA code for 
> Hermes as it had
> problems connecting.
> I did this in conjunction with Phil Harman and I ported some code from 
> the "KISS Konsole"  and
> with the addition of repeated tries to connect I got it working 
> reliably and I think this version
> was published and had my callsign on the about box.
> Then I found this version:
> http://www.dxatlas.com/hamvna/ <http://www.dxatlas.com/hamvna/>
> Which worked reliably with the Hermes and had no problems with 
> connecting but the remaining
> problem is that while the Hermes is an excellent SDR transceiver it is 
> not a very good VNA!
> This is because leakage between the TX and RX terminals, limiting its 
> dynamic range.
> Made worse if you have the necessary RX/TX switching connected. Direct 
> connection to the
> Hermes SMA connections, it is just acceptable.
> I was so impressed with HamVNA that I modified the code to also work 
> with my dedicated N2PK
> VNA.
> Then I found NanoVNA available on eBay for less than £50 which goes 
> right up to 900MHz and that
> is now my VNA of choice.
> Just my view on the VNA for what it is worth.
>
> 73's
>
> Martin G3OQD.
>
>
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