Output Power Levels
The following measurements were done to compare the AIM4170, HP8753B, and MFJ-259.  Equipment used to make the measurements was an HP436A power meter with HP8481A sensor, an HP8591E spectrum analyzer, and various precision RF attenuators.
The tests were done over the range of 1 to 170 MHz

AIM4170: -17dBm to -21dBm with all spurious signals in the range of .1 to 500 MHz down at least 34dB.  In the HF range (2-30MHz) the spurious signal were down at least 40dB.

HP8753B: -11.8 to -12.2dBm with all spurious signals in the range of .1 to 500 MHz down at least 35dB.  In the HF range (2-30MHz) the spurious signal were worst but down at least 35dB.  The synthesizer in the HP8753B got much quieter in the VHF and above region. The output level of the HP8753B could be increased by up to 20dB. and could be decreased by up to 70dB. for making specialized measurements such as input impedances of low level amplifiers.

MFJ-269: +6 to +7dBm with all spurious signals in the range of .1 to 500 MHz down at least 27dB.

Conclusion: On average the HP8753B typically outputs 5 times more power (7dB) and the MFJ-269 outputs 350 times more power (25.5dB) than the AIM4170 to make measurements.  When running the HP8753B at max. power output, it outputs 500 times more power (27dB) than the AIM4170.  The signal produced by the AIM4170 (into a 50 ohm load) when making measurements is between 8 and 20uW and is extremely unlikely to cause any QRM.
Resistance to RF Overload
This test is important since one of the most common uses of the AIM4170 is to make impedance measurements of antennas requiring the analyzer to distinguish the test signal generated by the analyzer from all the other signals received through the air by the antenna.  Generally the problem is most prevalent when measuring 160m antennas in the presence of strong AM radio stations.

For the test, the interfering signal was placed at the top of the AM radio band at 1.700MHz and the analyzer measurement range was swept from 1 to 5MHz and from 1.6 to 1.8MHz to better measure the area of disruption.  The signal source was an IC-7000 (opened up to TX everywhere) running 100W (+50dBm) into a 10dB 100W Narda attenuator followed by a 12dB 20W Narda attenuator (yielding a +28dBm signal) which then was fed into a precision 0-70dB adjustable HP attenuator.  The output was a very accurate 50 load for the analyzer and still could inject an interfering signal from -42dbBm to+28dBm.  Since the AIM4170 does not have 50 ohm input (about 110 ohms) the actual voltages are higher by about 1.35x and no attempt was made to correct this since in the case of a 160m antenna the source impedance should be about 50 ohms if the antenna is for transmitting.

AIM4170:
: (the 1st value in each row is the magnitude of the disrupting signal at 1.700MHz)
: -20dBm: Area of msmt. disruption 5KHz,  all SWRs outside this area were <1.03:1*
: -15dBm: Area of msmt. disruption 6KHz,  all SWRs outside this area were <1.04:1*
: -10dBm: Area of msmt. disruption 20KHz, all SWRs outside this area were <1.04:1*
:  -5dBm: Area of msmt. disruption 22KHz, all SWRs outside this area were raised to 1.10:1
:   0dBm: Area of msmt. disruption 38KHz, all SWRs outside this area were raised to 1.28:1
:  +5dBm: Area of msmt. disruption 40KHz, all SWRs outside this area were raised to 2.25:1
: * There were a couple small ranges where SWR was slightly raised but otherwise SWR <1.01:1

HP8753B:
: (the 1st value in each row is the magnitude of the disrupting signal at 1.700MHz)
: -15dBm: Area of msmt. disruption 12KHz, all SWRs outside this area were <1.01:1
: -10dBm: Area of msmt. disruption 12KHz, all SWRs outside this area were <1.01:1
:  -5dBm: Area of msmt. disruption 12KHz, all SWRs outside this area were <1.01:1
:   0dBm: Area of msmt. disruption 12KHz, all SWRs outside this area were <1.01:1
:  +5dBm: Area of msmt. disruption 18KHz, all SWRs outside this area were <1.01:1
: +10dBm: Analyzer produced reflected power warning and disconnected source, no harm done.

MFJ-269:
: (the 1st value in each row is the magnitude of the disrupting signal at 1.700MHz)
: -25dBm: SWRs at all frequencies in the 160m band were unaffected
: -20dBm: SWRs at all frequencies in the 160m band were raised to <1.1:1
: -13dBm: SWRs at all frequencies in the 160m band were raised to <1.5:1

The MFJ-269 uses a broadband RF detector and does not discriminate between in band and out of band signals.  The AIM4170 and the HP8753B both have tracking receivers which allow in band and out of band signals to be separated.  The bottom line is that the AIM4170 produces accurate measurements (outside of the 1700 KHz disturbance area) until the interfering signal source gets to about -5dBm, while the HP8753B is totally accurate until about +8dBm, and the MFJ-269 is accurate until -20dBm.  With the default output settings the HP8753B can accept a 13dB larger interfering signal than the AIM4170 which is 15dB better than the MFJ-269.  Additionally the HP8753B, which cost 50 times as much as the AIM4170, is even more robust if the default output amplitude is increased and the receiver has internal attenuation inserted.  However both the AIM4170 and the HP8753B can be calibrated through an inline high pass filter which could attenuate AM radio signals before reaching the analyzer.  I understand that Array Solutions sells an inexpensive inline filter that increases the resistance to AM broadcast overload to a level where it isn't a problem for large 160m antennas with nearby AM radio stations.
More measurements continue on the next page.
Page content last updated Mar. 12, 2008
Copyright 2008 Larry Benko, W0QE

AIM4170 Page 2

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