Transmit performance of 2m hand held transceivers – absolute gain estimates

Transmit performance of 2m hand held transceivers reported relative field strength measurements for some transceiver / antenna combinations.

This article documents a more careful measurement of the absolute field strength of one combination, and application of that knowledge to the other results.

Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.

RFPM1-10

Above, the RFPM1 RF power meter.

VhfUhfLoopAbove is the small loop used for field strength measurement. It is 2mm hard drawn round copper wire formed into a circle 185mm in circumference, and a common mode choke is used to connect the loop to the RFPM1 power sensor. The common mode choke is 0.6m of RG58C/U with 0.5m of ferrite sleeves over it and its loss is accounted for in the “Other Loss” item.
Continue reading Transmit performance of 2m hand held transceivers – absolute gain estimates

Accuracy of AIMuhf system – AIM910A vs several recent versions on a ferrite cored inductor

AIMuhf

Yet another release of AIM software is available, 910A at the time of writing. I have downloaded and tested 8 versions this year, most have been wanting. Again, there is very little detail on what has changed and likely impact on historical measurments.

Inductor1

A quick set of measurements was made on my test inductor pictured above. Continue reading Accuracy of AIMuhf system – AIM910A vs several recent versions on a ferrite cored inductor

Transmit performance of 2m hand held transceivers

This article documents measurements of transmit performance of three hand held 2m radio with several antennas.

Measurements of field strength were done with Lou Destefano’s (VK3AQZ) VK3AQZ RF power meter (RFPM1) and a small loop antenna.

RFPM1-VhfLoop

Above, the field strength meter, a RFPM1 with small loop antenna oriented for max gain in the direction of the DUT.  The instrument reads -73.5dBm with no signal, -69.5dBm with the strongest transmitter with the loop removed, and around -30dBm for the various transmitters with the loop in place… so the meter reading is predominantly due to the loop mode pickup.

All three transmitters have different power. The table below reports power into a 50Ω load and does not take account of mismatch with the various antennas.

Screenshot - 06_07_2015 , 12_53_56

Above a comparison of the configurations on a field strength test at 1λ. The relative column factors the different transmitter power and FS to obtain  a comparative figure independent of power. Mismatch is almost certainly a significant part of the explanation of different performance, but it is quite difficult to measure in this sort of application without disrupting the DUT.

BoafengINF641Antenna

It is interesting that there is little difference observed with the Baofeng on two different antennas, when the Boafeng antenna is clearly inefficient, see the thermograph above.

 

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

A walk through of a practical application of AIMuhf/AIM900A #2

I mentioned at A walk through of a practical application of AIMuhf/AIM900 that I wasn’t all together happy with feed point R at resonance, at 40Ω it was perhaps a touch high for a 2m quarter wave ground plane on a largish vehicle roof.

AIMuhfRepeated measurement of the DC resistance from the coax plug sheild to car body yielded unstable resistance ranging from 1 to 10Ω. If stable low DC resistance is not achieved, this feed line won’t work properly for RF. Continue reading A walk through of a practical application of AIMuhf/AIM900A #2

A walk through of a practical application of AIMuhf/AIM900

This article describes the use of the Array Solutions AIMuhf/AIM900 to test a mobile antenna installation, a quarter wave whip for 2m with about 4m of RG58 cable which has been previously installed and tuned.AIMuhf

 

The exercise is motivated by a perception that the antenna is not working as well as it should.

Screenshot - 16_05_2015 , 14_38_07

Above is a scan of the VSWR. It indicates problems, there should be a main VSWR dip around the high end of the 2m band (147MHz), but instead the minimum is nearer 160MHz. Clearly there is an antenna connected to the far end of the line in some form (ie the inner conductor is not simply broken), but there could be a high resistance in the inner conductor or shield connection (the latter is common issue with this type of antenna base). Continue reading A walk through of a practical application of AIMuhf/AIM900

Accuracy of AIMuhf system – AIM865A vs AIM885Gx on a ferrite cored inductor

AIMuhfAt Accuracy of AIMuhf system – AIM865A vs AIM882 vs AIM885 on a ferrite cored inductor I compared measurement of a small ferrite cored inductor on three ‘production’ releases of the AIM program.

Since then, AIM885A was released and it had problems as mentioned at AIM 885A produces internally inconsistent results.

Since then, AIM882, AIM885, and AIM885A have been pulled.

The developer advised on his support forum I’m sorry but version 885A has some problems. I’m working an update. In the meantime use the mature version AIM_865A.

Today, he posted a link to AIM885Gx (a declared beta release which presumably fixes problems in the pulled versions AIM882, AIM885, and AIM885A). Continue reading Accuracy of AIMuhf system – AIM865A vs AIM885Gx on a ferrite cored inductor

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

Accuracy of AIMuhf system – AIM865A vs AIM882 vs AIM885 on a ferrite cored inductor

AIMuhfThis article builds on Accuracy of AIMuhf system – AIM865A vs AIM882 on a ferrite cored inductor by adding a measurement using AIM885 of the same test inductor.

 

Inductor1

Above is the test inductor. It comprises 6 turns of 0.5mm PVC insulated wire wound on a BN-43-202 binocular balun core. Continue reading Accuracy of AIMuhf system – AIM865A vs AIM882 vs AIM885 on a ferrite cored inductor