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Show all reviews of the MFJ-225 GRAPHICAL ANTENNA ANALYZER
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of the MFJ-225 GRAPHICAL ANTENNA ANALYZER.
Dec 19, 2013 13:36
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Has a few issues
Time owned: 0 to 3 months
I purchased the MFJ-225 from a UK Ham Radio equipment supplier (Martin Lynch & Sons Ltd). On unpacking it I noticed that the rotary encoder knob had quite a bit of lateral movement.
The power ON/OFF push button and the power source selection push button are mounted to far back inside the unit. This results in them having a tendancy to stick in the down position against the front panel.
On taking the cover off to fit the batteries noticed that the thin grey coax from the DDS RF Source was touching the inner connection of the SO259 output socket.
Whilst this cable is insulated I found that its proximity to the centre pin affected the SWR reading on the higher frequencies by its capacitive shunt effect to ground.
This was easily fixed by moving the coax.
The lateral movement (wobble) of the rotatary encoder is due to the encoder not being secured to the side panel with a nut on its threaded bush. It is only secured by the soldered connections to the main PCB. As there is a gap between the encoder body and the side panel I fitted a 1/4" washer to take up the gap and secured the encoder to the side panel with a 1/4" thin nut. Having resolved these two issues I then decided to check its performance in more detail.
Whilst the MFJ-225 cannot be considered as a lab quality instrument I found that its performance in terms of SWR/Return Loss accuracy falls away rapidly after 130MHz which gave me concern. This is mainly due to the DDS RF output source rapidly reducing in level which limits the dynamic range of SWR/Return Loss measurement at the higher frequencies.
Here are the results:
BATTERY VOLTAGE: 4.77v
RF LEVEL MEASURING INSTRUMENT:
RACAL-DANA 9301A TRUE RMS RF MILLIVOLTMETER
USING ITS INTERNAL 50 OHM LOAD.
MANUFACTURES RF OUTPUT SPEC: -5dBm
FREQ O/P Level DISPLAYED
MHz dBm SWR
1 -3.2 1.10
2 -2.8 1.08
10 -2.5 1.07
20 -2.5 1.07
30 -2.8 1.07
40 -3.0 1.08
50 -3.0 1.08
60 -3.0 1.08
70 -3.0 1.11
80 -3.0 1.12
90 -3.2 1.15
100 -3.6 1.18
110 -3.8 1.19
120 -3.9 1.20
130 -4.1 1.20
140 -5.1 1.19
150 -6.5 1.19
160 -7.0 1.20
170 -15.2 1.39
171 -16.6 1.46
172 -18.0 1.56
173 -19.0 1.65
174 -20.3 1.76
175 -21.5 1.91
176 -22.8 2.13
177 -23.9 2.41
178 -25.0 2.72
179 -26.0 3.17
180 -27.4 3.66
At this point I wondered if I had a faulty MFJ-225 as I expected the RF output to be stable within +/- 1dB across its measuring range like the MFJ 259B which I also have. I contacted Martin Lynch & Sons Ltd who checked the three of the units they had in stock and confirmed my test results and reported their findings to MFJ.
However, it appears that this is how the all current production units will be until MFJ fix this issue.
Maybe MFJ will sort out this design defect in the "B" model together with the other mechanical issues mentioned above!
I also checked the frequency accuracy of the DDS RF source:
FREQUENCY ERROR AT 1MHz = +8Hz
FREQUENCY ERROR AT 90MHz = +632Hz
FREQUENCY ERROR AT 145MHz = +1.01KHz
FREQUENCY ERROR AT 180MHz = +1.3KHz
The link in the manual to the IG-miniVNA software no longer exists. I eventually found it at:
I like the MFJ-225 with its flexability to use as a stand alone VNA when working outside on antennas together with its ability to connect to the IG-miniVNA software but it needs a bit more work done on the product design before I could give it a higher rating.
Things that need fixing by MFJ:
1. Fix the Rotatary encoder to the side panel to stop the wobble!
2. Make sure that the DDS RF Source output coax is routed away from the SO259 socket.
3. Reposition the Power ON/OFF and Power Source selection buttons further out when they are in the "IN" position.
4. Redesign the DDS RF output levelling amplifer to make it as good as the MFJ-259B RF output level stability. (My MFJ-259B measures 8dBm flat +/-0.6dB across the frequency range).
Product is in production.
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