nanoVNA-H – measure ferrite transformer – Noelec balun

At nanoVNA-H – measure ferrite transformer I gave an example of using a nanovna to measure loss of a ferrite cored transformer.

Noelec makes a small transformer, the Balun One Nine, pictured above and they offer a set of |s11| and |s12| curves in a back to back test. (Note: back to back tests are not a very reliable test.) Continue reading nanoVNA-H – measure ferrite transformer – Noelec balun

VSWR ripple

Having seen some recent discussion where the online experts opined that an example given of a VSWR plot that contained a fairly consistent ripple was quite normal, this article suggests there is an obvious possible explanation and that to treat it as quite normal may be to ignore the information presented.

Above is a partial simulation of a scenario using Rigexpert’s Antscope. It starts with an actual measurement of a Diamond X-50N around 146MHz with the actual feed line de-embedded. Then a 100m lossless feed line of VF=0.66 is simulated to produce the plot that contains a ripple apparently superimposed on an expected V shaped VSWR curve.

This is the type of ripple that the expert’s opine is quite normal. Continue reading VSWR ripple

Transformer loss from half return loss

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

nanoVNA-H – another hardware fail – battery socket

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.

nanoVNA-H – Port 1 attenuator for improved what???

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???

nanoVNA-H – woolly thinking on MLL measurement

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.

DUT

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

nanoVNA-H – thinking laterally

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

nanoVNA-H – de-embedding the feed line in remote measurement

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.

Ham lore

Common advice given by online ham experts include:

  1. it just cannot be done, the best (only) point to measure an antenna is at the feed point;
  2. it can be done, but only with an integral number of half waves of feed line;
  3. use the port extension facility in your software;
  4. use software package x;
  5. 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