Category: Amateur Radio

Rigexpert Antscope2 – v1.1.1

A new version of Antscope2 has been released.

Online posters are excited that it supports some versions of nanoVNA, and one thread attempts to answer the questions:

The SWR image shows that the SWR minimum is at the center phase angle as you would expect. My question is:

  1. what are the other points that look like resonance,

  2. and should I trim my antenna based on phase?

  3. If so which one?

They are interesting questions which hint the ham obsession with resonance as an optimisation tartget.

Properly interpreting VNA or analyser measurements starts with truly understanding the statistic being interpreted.

In this case, the statistics being discussed are Phase and VSWR, and their relationship.

What is the Phase being discussed?

Above is an Antscope2 phase plot for an archived antenna measurement. The measurements are of a 146MHz quarter wave mobile antenna looking into about 4m of RG58C/U cable. We will come back to this. Continue reading Rigexpert Antscope2 – v1.1.1

Last update: 14th June, 2020, 5:53 PM

Rigexpert AA-600 N connector dimensions

A recent post by David Knight described dimensional issues with the N connector on his AA-600 and problems with the seller in having it resolved.

Warned of a potential quality issue, I measured my own AA-600.

Above, the test of the inner pin forward surface distance from the reference plane on the N jack on the AA-600. The acceptable range on this gauge for the female connector is the red area, and it is comfortably within the red range.

Above is a table of critical dimensions for ‘ordinary’ (ie not precision) N type connectors from Amphenol.

This dimension is important, as if the centre pin protrudes too much, it may damage the mating connector.

Pleased to say mine is ok, FP at 0.192″.

I used a purpose made gauge to check this, but it can be done with care with a digital caliper (or dial caliper or vernier caliper), that is what I did for decades before acquiring the dial gauge above.

Last update: 12th June, 2020, 7:59 AM

AIM4170 – de-embedding the feed line in remote measurement – a simple match

At AIM4170 – de-embedding the feed line in remote measurement a set of measurements of a monoband antenna looking from the transmitter were analysed to de-embed the feed line and arrive at the indicated feed point impedance.

This article explores a simple series match to improve the load seen by the transmitter.

In the Simsmith model above, the estimated feed point impedance is imported into element L, then a series section of lossless 50Ω line to represent the coax in the common mode choke (balun), then a series section of lossless 75Ω to perform the impedance transformation, then a section of 50Ω lossless line to make up the required length to the transmitter. Continue reading AIM4170 – de-embedding the feed line in remote measurement – a simple match

Last update: 8th June, 2020, 7:14 AM

AIM4170 – de-embedding the feed line in remote measurement

At nanoVNA-H – de-embedding the feed line in remote measurement I recently wrote on a procedure that can be very useful to refer measurements made at the transmitter end of a feed line to the antenna feed point.

A correspondent recently shared an AIM 4170 scan file of his 40m half wave dipole antenna system taken from the transmitter end of the coax and maintaining the common mode current path by bonding the shield of the coax connector to normal connection point on the transmitter.

Above is his graphic of the measurement looking into around 23m of RG58 feed line.

It shows the VSWR curve is quite classic in shape, the frequency of minimum VSWR is a little low, and the minimum VSWR is 1.478 which is quite within expectations of such an antenna. Continue reading AIM4170 – de-embedding the feed line in remote measurement

Last update: 6th June, 2020, 10:45 AM

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

Last update: 11th February, 2021, 9:52 AM

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.

Last update: 1st December, 2020, 7:51 AM

SND implications of variations on the untuned small loop at MF/lowHF

Three recent articles developed an explanation of the YouLoop-2T at MF/lowHF:

The first and third articles explained the concept of signal/noise degradation (SND) statistic, and gave graphs of the behavior of the subject antennas.

This article draws together those SND plots for two antennas, and some variations to the configurations.

Configurations

Simple loop with transformer

Above, the “simple loop” with 0.5:1 ideal transformer. It could be implemented as a shielded loop (with transformer) with similar behavior (but improved common mode suppression). Continue reading SND implications of variations on the untuned small loop at MF/lowHF

Last update: 19th May, 2020, 9:11 AM

Towards understanding the YouLoop-2T at MF/lowHF

Small untuned loop for receiving – simple model with transformer gave a simple model for analysing a loop. If you haven’t already read it, you should. It provides a step towards understanding the YouLoop-2T at frequencies where is is a small loop (perimeter<λ/10).

Above is the Airspy Youloup-2T. Try to put the two turns thing out of your mind, it is misleading, panders to some common misunderstanding, and so does not help understanding.

This is somewhat similar to the simple loop, but now the transformer primary is connected to the loop gap terminals by two parallel sections of 50Ω transmission line, the combination being effectively a 100Ω with similar parameters to the component coax sections. Because of the series connection at the transformer and parallel connection at the loop gap, there is a 1:4 impedance transformation additional to that of the coax sections themselves. Continue reading Towards understanding the YouLoop-2T at MF/lowHF

Last update: 7th July, 2020, 8:03 AM

A transmission line 1:4 impedance transformer

This article explains the operation of a simple nominally 1:4 impedance transformer using transmission line (TL) elements.

Above is a diagram of the device. The currents shown are differential currents in the coax (ie wholly inside the coax), the current on the outside of the shield is not shown on the diagram.

At very low frequencies it may be intuitive that \(V_1\approx V_2\) and \(I_1\approx I_2\), but as frequency increases, a more exact solution is needed. Continue reading A transmission line 1:4 impedance transformer

Last update: 19th January, 2021, 10:35 AM