[Icom] IC756 SWR meter compared with FC902 or DAIWA CN101

Sat, 22 Mar 2003 12:25:39 -0800

Hi Chris,

Just a note of caution - you should always disengage the internal autotuner
when attempting to match the load with an external tuner.

Tuning for maximum output is not the correct procedure; when using an
external tuner, it is essential to tune for minimum SWR as indicated on the
radio's SWR scale. The reason for this is that a tuning point which presents
a complex load to the transmitter will cause the internal reflectometer to
fold back the drive, so as to protect the PA. The maximum-output reading is
deceptive, as the meter reading cannot be trusted if the load presented to
the transmitter is anything other than 50 ohms. The complex load impedance
in your experiment caused high SWR readings on both meters.

In general, if your antennas are within a 2.5:1 SWR range on all bands, you
are best off using the internal autotuner and not even connecting an
external tuner. This minimises the possibility of mistakes.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of Chris BONDE
Sent: Saturday, March 22, 2003 11:06
To: [email protected]
Subject: Re: [Icom] IC756 SWR meter compared with FC902 or DAIWA CN101

My rig, IC756P  (old now) has a digital (bar) and analogue (needle meter),
both internal meters read very close to the same.  I use the bar as it is
easier to read from about 1 metre.  I have an external tuner with meter,
analogue.   The external meter is usually a little higher than the
internal.  But as one person said, "If the rig is happy, that is the way to
go".

Some one said to tune to max output.  I tried that and became
frightened.  I used both the rig output to max and the external tuner
output to max, then checked the SWR.  The SWR was higher than 3:1 on both
the internal and external meters.  So what is going on?

Chris opr VE7HCB

>Hi Juan,
>
>I would put my trust on the the CN101 (I own one and I'm very happy
>with it), the scaling on a good SWR meter will give you a better
>reading than the rig build in rig meter, especially if the rig uses a
>LCD bar display (my 706MKIIG uses one of these).
>
>73
>Demetre - SV1ENS

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