[Icom] RE: antenna tuner

Sun, 27 Oct 2002 00:06:57 -0700

Hi Rolly,

The T-network in the IC-756Pro/Pro2 autotuner appears to be identical to
that of the original IC-756. On the HF bands, I have also found that the
tuner will match a load with a 5:1 SWR under certain conditions. Feedline
length will certainly play a role in such cases. I would be particularly
nervous about operating the tuner outside its design limits on 6 metres.

At a pinch, or in an emergency, one can operate with an SWR significantly
outside the specified matching range of the autotuner. It may be prudent to
turn the output down to 50W or so in such cases, to avoid stressing
capacitors in the T-network.

In my home station, an IC-756Pro drives a Yaesu Quadra amplifier; my antenna
is a Cushcraft R8. A reflectometer at the output of the Quadra autotuner
takes the amplifier off-line for load SWR > 3:1. That limit is a good match
for the antenna, which has a decent 2:1 SWR bandwidth on all bands. Even on
40m,  2:1 SWR BW > 150 kHz (in practice about 160 kHz). The radio's
autotuner is disengaged when driving the Quadra.

For CW operation at the bottom end of 40m (outside the 2:1 SWR limit of the
R8), I operate the Pro2 barefoot with the autotuner engaged.  The Pro2 meter
indicates SWR > 4:1, but the autotuner tunes this out without difficulty.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Note new e-mail address:
mailto:[email protected]

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of R Goodspeed (W7DGX)
Sent: October 26, 2002 23:11
To: [email protected]
Subject: Re: [Icom] RE: antenna tuner

Is the Automatic Antenna Tuners in the pro2 of similar design in the old
756??

If so, I have found the spec says it will tune SWR's of 3 to 1. In actual
practice it has handled SWR's in excess of 7 to 1 on many (but not all)
occasions. It has always handled SWR's of 5 to 1 except on one occasion on
10
meters. Moving a few 10's of KHz and it would tune it.

Like Specification on most items, they are limits that the unit is
guarenteed
to met without damaging itself. Operation outside those specifications is at
your own risk.

I also had an ICOM 737a and had similar performance with it's automatic
antenna
tuner. (Same antennas)

        Rolly  W7DGX

Adam Farson wrote:

> Hart,
>
> As per my previous message, the  IC-756Pro2 has an internal ,
> fully-integrated automatic antenna tuner which will match a maximum load
> VSWR of 3:1 on all HF bands, and 2.5:1 on 6m.  The tuner will match any
> antenna whose maximum VSWR falls within these limits.
>
> A good, inexpensive starter antenna is a resonant dipole for each band on
> which you intend to operate.
>
> Here is the link to Icom's IC-756Pro2 page. You can download the Pro2
> brochure there as well.
>
> http://www.icomamerica.com/amateur/hf/index.html#756pro2
>
> You referred to the 756. The original IC-756 has been discontinued for
some
> years now, and is available only on the second-hand market. The IC-756
uses
> analogue filters, but has some DSP functions. It also has a built-in
> auto-tuner.
>
> Best 73,
> Adam, VA7OJ/AB4OJ
> North Vancouver, BC, Canada
> http://www.qsl.net/ab4oj/
> Icom FAQ site:
> http://www.qsl.net/icom/
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Hart Engel
> Sent: Saturday, October 26, 2002 19:12
> To: [email protected]
> Subject: [Icom] RE: antenna tuner
>
> Does the 756 model come with a built in antenna tuner? If so, how low does
> it come down too? will tune any type of antenna? Or just certain types. If
> not, what would be a good external antenna to buy or look out for.
> Hart
>