Using the AIM to measure matched line loss

A correspondent wrote seeking explanation of difficulty he was having measuring line loss using the advice given in the AIM manual using a scan with either O/C or S/C termination:

Note the one-way cable loss is numerically equal to one-half of the return loss. The return loss is the loss that the signal experiences in two passes, down and back along the open cable.

Because my correspondent was using one of the versions of AIM that I know to be unreliable, I have repeated the measurements on a cable at hand using AIM_900B to demonstrate the situation.

The test cable I have used is 10m of RG58C/U which I expect should have matched line loss (MLL) of 0.26dB, but I expect this to be a little worse as it is a budget grade cable that I have measured worse in the past. Continue reading Using the AIM to measure matched line loss

AIM 885A produces internally inconsistent results

 

AIMuhfFurther to AIM 885 produces internally inconsistent results

A new release, AIM885A appeared recently.

In the common theme of one step forward, two steps backwards, this version produces error popups when started.

Screenshot - 15_04_2015 , 17_41_08

The above popup appears twice when starting AIM885A. Just another symptom to undermine confidence in the system. It doesn’t make sense to me, and the program appears to otherwise start and run. Continue reading AIM 885A produces internally inconsistent results

Speaker wire is so popular as an RF transmission line

I received a sample of speaker wire from a correspondent who asked me to characterise it.

Even if I had the time, a 50mm sample isn’t sufficient to characterise in a meaningful way… but let’s have an abbreviated look which will highlight the pitfalls of this stuff.

SpeakerMicrometer

First thing to do is measure the conductors, stranding and diameter. There are 14 strands and several measurements fall just below 0.15mm diameter. This is probably nominal 0.15mm with new drawing dies which are a little undersize. Continue reading Speaker wire is so popular as an RF transmission line

Feeding at a current maximum, and three other options

Feeding at a current maximum visited the common practice of designing to feed a multi band dipole with open wire feed at or very near to a current maximum.

I explained that feeding at the current maximum may provide sub-optimal performance on the popular T-match ATU as its losses tend to be worst with low R loads, aggravated by the use of 4:1 baluns for even lower R.

On the other hand, feeding at a voltage maximum might exceed the ATU’s voltage capacity, or perhaps be outside of the matching range of the ATU.

Well if neither of these is optimal in all cases, what about half way between. It has been done, the odd eighths wave feed line on an 80m half wave is another of the recipes you will hear.

Lets explore the options of a half wave dipole at 3.6MHz with four different feed line lengths (Wireman 551). Continue reading Feeding at a current maximum, and three other options

LP-100A manual advice on VSWR measurement

At Where is the best place to measure feed point VSWR I discussed location of the VSWR meter and projection of its reading to another point on a known transmission line.

A correspondent has taken me to task and citing Telepost’s LP-100A manual: Continue reading LP-100A manual advice on VSWR measurement

Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2

This is a follow up to Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites.

Steve saw the above article and revisited the FT240-52 measurements which he apparently did, and found them wanting: Continue reading Attempting to reconcile W5DXP & G3TXQ’s comparison of K and 52 mix ferrites #2