Now after raising
>to 160 feet it checks 2.5 to 1 at 7.200 mhz, with no real match
>anywhere near forty meters. Now it has been taken down and checked
>from elbow to you know where and it is still at the correct settings for
>the book and checked good on the same MFJ meter. Then it went
>backup to 160 feet and you guessed it it now is at 2.5 to 1 and doesn't
>show a big dip on the meter.
Sounds like classical overload of the MFJ from local AM stations. The
readings on my 4L M-squared are completely trashed by a small 5KW
AM station over 10 miles away. If you tune in the AM station and
watch the MFJ meter you can see it wiggle in time to the modulation on
the station.
Three solutions:
1) You can make a quarter wave shorted line of coax and Tee it at
the MFJ. (22 ft 10.5 in for RG-8/213/58). This will be an open circuit
at 7 MHz and not affect the MFJ reading but it will be a relatively lower
impedance at the AM broadcast band and usually reduces the
strength of the AM signals enough so that the don't cause the problem.
2) Try using the SWR meter in your transceiver. Its sensitivity may be
low enough (since it works with 100 watts instead of milliwatts like the
MFJ) to be immune to the AM overload.
3) Use a real Bird wattmeter to measure Forward and Reflected power.
If you still have problems then your antenna may need work but I will bet
it is just a limiteation that all of the low-power SWR bridges have--AEA,
Autek, MFJ.
Good luck.
John W0UN
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