The popularity of the nanovna with new users has led to a lot of ‘beginners’ seeking advice of the online experts.
A recent question and the responses exposes some common misunderstanding / woolly thinking.
A beginner in search of wisdom asked if
there an easy way to measure balun loss?
One of the responses was…
Measure the return loss of the balun with the balun shorted. The return loss should be about twice the balun loss. This is similar to measuring the loss of a shorted or open piece of cable.
This was expanded by others, basically supporting the concept. Continue reading Transformer loss from half return loss
I have a nanoVNA-H which has had many hardware problems, some designed in,but mostly sub-standard / faulty components.
Above, the latest repair. A new battery socket to replace the original that crumbled apart… sub-standard plastic from all appearances. This was from a reputable supplier, so it is probably a genuine Molex Picoblade part rather than some cheap Chinese knock off.
The blue wire is part of a mod to invoke the bootloader on power up, R5 was also changed to something small, 1k IIRC.
PS: a word of warning… always check polarity when fitting a battery, there is not rigid standardisation of connectors on LIPO batteries.
At nanoVNA-H – Port 2 attenuator for improved Return Loss I explained the reasons for essentially permanent attachment of a 10dB attenuator to Port 2 (Ch 1 in nanoVNA speak).
Above, the 10dB attenuator is semi permanently attached to Port 2 principally to improve the Return Loss (or impedance match) of Port 2, a parameter that becomes quite important when testing some types of networks than depend on proper termination (eg many filters). I should remind readers that the improvement in Port 2 Return Loss comes at a cost, the dynamic range of Port 2 is reduced by 10dB. Continue reading nanoVNA-H – Port 1 attenuator for improved what???
Articles describing how to make a Return Loss Bridge are pretty common, but they don’t often spell out component values that are critical to accuracy.
Above is a schematic for discussion. It is somewhat simplified, but it is complete and will work. Continue reading Return Loss Bridge – some important details
A friend wrote saying “I thought the nanoVNA display was smaller than this”.
I make the index finger nail width exactly the same as the round part of the SMA nut which is 7.6mm. That is a very tiny hand… or the image is a composite fraudulently not to scale. Continue reading nanoVNA – promotion by cheats
There is little doubt that the nanoVNA has made VNAs very popular in the ham community, possibly more so that any other device.
Eager owners are trying to apply them to solve lots of problems, often without sufficient knowledge or experience to properly inform the measurements.
An example that has a appeared a few times on online forums in the last weeks is measuring the matched line loss (MLL) of a section of RG6 coax… to inform a decision to discard it or keep it.
The common approach is to use a measurement of |s11| and to calculate Return Loss and infer the MLL.
For discussion, lets consider an example of 30′ of Belden 1694A RG6 solved in Simsmith. We should note that unlike most RG6 in the market today, this uses a solid copper centre conductor.
Short circuit termination
Some authors insist that the half return loss method is to be performed using a short circuit test section. Bird does this in their Bird 43 manual.
Above is a plot of calculated |s11| (-ReturnLoss) from 1 to 20MHz for the test section. The three plots are of |s11| wrt 50Ω, 75Ω and frequency dependent actual Zo (as calculated for the model). The cursor shows that the actual |s11| is -0.37474dB (ReturnLoss=0.37474dB). Using the half return loss method MLL=ReturnLoss/2=0.37474=0.187dB/m. Continue reading nanoVNA-H – woolly thinking on MLL measurement
A question was asked in an online forum specific to nanoVNA as to how the use the nanoVNA to
check the attenuation loss in some old & weathered RG-6 (75 ohm) cables for the TV signal frequencies. Excuse the term
attenuation loss, lets assume the poster is asking for matched line loss (MLL).
The assembled experts are offering solutions to transform the ports to 75Ω and make a measurement, deducting the loss of the transformation (minimum loss pads were suggested).
There is a very simple solution that should be quite practical for the scenario described. Let’s work through two examples using 35.5m of unbranded quad shield RG6 with CCS centre conductor (of unknown quality) for the DUT. Continue reading nanoVNA-H – thinking laterally
There are often times when it would be useful to transform measurements made looking into a feed line to the other end of the feed line.
Common advice given by online ham experts include:
- it just cannot be done, the best (only) point to measure an antenna is at the feed point;
- it can be done, but only with an integral number of half waves of feed line;
- use the port extension facility in your software;
- use software package x;
- do an OSL cal with the feed line being part of the fixture.
Continue reading nanoVNA-H – de-embedding the feed line in remote measurement
nanoVNA-H – measure 40m low pass filter for WSPRlite flex describes measurement of the response of a filter.
The filter is of a type that depends on its source and termination impedance for as designed performance.
The article mentioned the use of a 10dB attenuator on the nanovna-h Port 2 for the purpose of improving the accuracy of the load impedance for the filter.
Like most low end vnas, the nanoVNA Port 2 VSWR or Return Loss is not wonderful, not as good as needed for some types of measurement. Return Loss can be improved by placing an attenuator ahead of the port. The nanoVNA-H v3.3 already includes an attenuator on the PCB, and the nanovha-H v3.4 increased that attenuation by about 5dB to improve Return Loss by about 10dB.
In my own case, I am using a nanoVNA-H and upon measurement of |s11| (-ReturnLoss) I determined that it needed to be improved by 20dB for my use so I purchased and installed a 10dB attenuator semi permanently on the Port 2 connector.
Above, the 10dB attenuator is semi permanently attached to Port 2 and also serves the purpose of a connector saver. There is a connector saver semi permanently attached to Port 1. Continue reading nanoVNA-H – Port 2 attenuator for improved Return Loss
This article describes a common mode choke intended to reduce RF interference with a VDSL service.
The MDF is located where the underground cable enters the building. From here it rises vertically and travels some 25m across the ceiling to the VDSL modem. Continue reading A common mode choke for a VDSL pair – LF1260 core