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Well, I had intended to post something, but on using a better 50-ohm load, and revisiting the calibration procedure a number of times, I now have short-open-load displaying at their expected positions on the Smith chart with the nanoVNA 10 kHz-1500 MHz firmware (sweeping 50 kHz-900 MHz.).

One thing which was confusing me was also using the 1-3000 MHz RF Bridge. I somehow had it in my mind that when the bridge had short or open loads it too would show 100% transmitted power. Of course, this cannot be the case as some of the power will be lost in the resistive divider.

Thanks for making me think (a little)!

Cheers,
David
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David

I have two NanoVNAs and two 1-3000 MHz RF bridges. I get identical results with all four. The VNAs are calibrated with one set of supplied OSL terminations. When I use the bridge with the NanoVNA I connect Port 1 to the Input of the bridge, Port 2 to the output, and terminate the REF port with the NanoVNA 50 ohm load. I then calibrate the VNA for "Through" only with the DUT terminal open. This sets the CH1 Logmag return loss to zero. From this point forward calibrated NanoVNAs give identical readings to the RF Bridge down to reasonable levels. Once Return Loss hits 30 dB and beyond I pay no attention to discrepancies because they are meaningless for the most part.

I use a similar setup when using the RF Bridge with my Rigol Spectrum Analyzer. Tracking generator output to RF Bridge Input, RF bridge output to spectrum analyzer input, NanoVNA reference load on the REF port and the DUT port open. I then normalize the spectrum analyzer to zero, connect the DUT, and read the return loss directly from the screen.

Up to 30 dB or so of return loss all four devices produce reasonably identical readings through 750 MHz plus or minus one dB.

WA8TOD

David

I have two NanoVNAs and two 1-3000 MHz RF bridges. I get identical results with all four. The VNAs are calibrated with one set of supplied OSL terminations. When I use the bridge with the NanoVNA I connect Port 1 to the Input of the bridge, Port 2 to the output, and terminate the REF port with the NanoVNA 50 ohm load. I then calibrate the VNA for "Through" only with the DUT terminal open. This sets the CH1 Logmag return loss to zero. From this point forward calibrated NanoVNAs give identical readings to the RF Bridge down to reasonable levels. Once Return Loss hits 30 dB and beyond I pay no attention to discrepancies because they are meaningless for the most part.

I use a similar setup when using the RF Bridge with my Rigol Spectrum Analyzer. Tracking generator output to RF Bridge Input, RF bridge output to spectrum analyzer input, NanoVNA reference load on the REF port and the DUT port open. I then normalize the spectrum analyzer to zero, connect the DUT, and read the return loss directly from the screen.

Up to 30 dB or so of return loss all four devices produce reasonably identical readings through 750 MHz plus or minus one dB.

WA8TOD
===============================

Thanks, Warren, your explanation helped a lot.

I think there were two issues.

- First I wasn't including the bridge in the SA normalise - hence the dB loss I was seeing even for open or short. Beginner's error.

- Secondly I guess I was expecting higher quality than this bridge actually is. It's not HP quality (or whatever they're called today), but it's not HP price! Fine for indicating resonances.

For resonance out in the field taking the Rigol is not the most convenient (!), and something like the FA-VA5 which covers up to 600 MHz is a robust and well-boxed unit.



73,
David GM8ARV
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SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

David

I too initially questioned the quality of the RF Bridge, primarily due to the price. I did the same with the Nanovna and for the same reason. In both cases, overcoming the learning curve and careful calibration have led to results that put those concerns to rest. I use the devices for hobby work as well as in my business and I do not need 0.1 dB accuracy in either case.

Now I take the Nanovna by itself onto job sites instead of lugging the Rigol/RF Bridge/cable kit. The internal power supply alone makes field setups a snap. The Nanovna is in daily used here........ no time or need for firmware upgrades and research. It has become perhaps my most valued tool.

I would be curious to know what deficiencies you see with the RF Bridge versus the HP bridge but that is probably OT here.

Best regards,
WA8TOD
===========================================

Warren,

I think that at the time I bought the bridge more as a learning tool, and it was less than the price of a reasonable meal out. With now having the nanoVNA I see no use for the bridge. As you say, having the portability of both the nanoVNA and the FA-VA5 is the "deal-breaker", although I still use the Rigol SA/TG and the support and documentation on my DG8SAQ VNWA is second to none - this matters. For higher frequency work I have the AAI N1201SA which covers up to 2.7 GHz, so useful for QO-100.

All hobby use as I'm nominally retired.

I don't have an HP bridge - it was just a generic quality comparison term!

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

Warren,

Where can I purchase the 1-3000 MHz RF bridges?

Thanks,

Mike N2MS

google defective?

Hi Warren -

When I use the bridge with the NanoVNA I connect Port 1 to the Input of the
bridge, Port 2 to the output, and terminate the REF port with the NanoVNA 50
ohm load. I then calibrate the VNA for "Through" only with the DUT terminal
open. This sets the CH1 Logmag return loss to zero. From this point forward
calibrated NanoVNAs give identical readings to the RF Bridge down to
reasonable levels.

On recent firmware, this works up to the point of trying to display CH1 in SMITH format.
Small horizontal excursion to OSL occurs for SCALE 1x but becomes only vertical for e.g. SCALE .2x

Adding a firmware option to OSL calibrate CH1 with an external bridge would be neat...

I too initially questioned the quality of the RF Bridge, primarily due to the price.

A transverters-store clone from eBay seller seller25812 was substantially defective:
* one of each 100 Ohm pair was disconnected at the balun end
* center conductor of the balun reference coax was shorted to shield at both ends
* labels for DUT and REF are reversed, relative to schematic for Ukraine version

It works OK after correcting...