[hpsdr] [OT] Hermes VNA calibration

[Alfred Green]

On 10/10/2014 6:49 AM, AA8K73 GMail wrote:
>
>
> What is a good 50 ohm termination to use for Hermes VNA calibration?
>
> The open and shorted ones are easy.  When I calibrate with a 50 ohm 
> load and then measure other 50 ohm loads, I get variation.
>
> I've tried a Decibel DB4303B, Relm T44100, Bird Termaline, and 
> various, small BNC terminators.
>
> Where can I find a 50 ohm precision terminator that will be flat on HF 
> to 50 MHz?
>
How accurate do you need? Finding a good load up to 50MHz is easy.
Using my HP8505 vna and HP8503 test set the worst of my collection of 
loads was a 47ohm resistor in a BNC plug, and that gave >30dB return loss.
Most of the SMA and N loads were >38dB RL, with the best being near the 
bridge limit of ~45dB, and the BNCs were >35dB. 'Waggling' the BNCs gave 
a couple of dB variation, but they were still quite acceptable for such 
a low frequency range.

I built a return-loss bridge for when I use my Hermes as a VNA, and it 
was simple to get >30dB from 0.5 to 60MHz using one of my HP precision 
loads as a reference. If you need better than that a different topology 
is probably needed.

Finding a good load up through 10Gigs is more of a challenge!

GL & 73,  Alf  NU8I
Phoenix  AZ  DN33xo

 1412962466.0