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In article , Marc Teugels
writes
Thanks Tim,
it is an AR3201 Becker,

what happens is this :
during the VHF annual check, the lower freq turn out to be weak.
My friends hear me sometimes , sometimes not.
Distance does not seam to play a big role here, sometimes they hear
me (123,8) from quite far off.

An antenna will only perform at it's best at as specific frequency
(except for some special types of composite antenna). This frequency is
determined by the length of the antenna element(s).

A fin-mounted antenna is usually a dipole.

If the elements are shorter, the optimum performance will be at a higher
frequency and if the elements are longer, the optimum performance will
be at a lower frequency.

As you report the lower frequencies to be weak, it may be that the
antenna elements are too short. Sometimes with Fin antennas this is a
physical limitation on the length the fin can accommodate.

The best way to check this is with an antenna analyser, but if you do
not have one available you can use a VSWR meter and plot a curve of SWR
against Frequency.

Using the headset (with a small ampli) seems better than with the swan mike

This may be because the headset and amplifier is presenting a stronger
audio signal to the radio and the result is a better depth of
modulation.

I am not sure about the AR3201, but with the AE4201 the depth of
modulation can be set by using the Service Mode selection. However be
sure that you know what you are doing before attempting this yourself. A
modulation meter is highly to check the results of any adjustment.

Your problem could be a combination of both these factors.

Best regards.

Tim Newport-Peace

"Indecision is the Key to Flexibility."