Antenna tuning (was RE: [Icom] 756 II Pro Questions)

Thu May 6 00:50:50 EDT 2004

The "antenna" is a closed triangular loop around
120' or so in length.  I never measured it, it just
fit.  About 40' along back wooden fence about
4.5 feet above ground with SGC-230 near the
center of that length.  The other 80' or so of
the loop form the other two sides of the triangle
with apex about 15' above ground.  No good
(read simple) way to change any wire lengths.
As I suggested, there are a few spot frequencies
within 80/75 meters that the SGC-230 won't
get the SWR down to 1:1 and I just use the
internal tuner to take SWR the rest of the way
down  AFTER  the SGC-230 has gotten a minimum.

Seems to work fairly well.  Of course, nothing like
the 60' tower, beams, wires, etc. I had before the
tornado took everything five years ago Monday.  Lot
at new house too small for much of anything.  The
wire is for 80 and 40 (plus 30-10), Force 12 Sigma V
for 20-10 & verticals for 6m, 2m, & 70cm.

73  ---  Mac, K2GKK/5

----Original Message Follows----
From: Adam Farson <[email protected]>
Reply-To: [email protected]
To: [email protected]
Subject: RE: [Icom] 756 II Pro questions
Date: Wed, 05 May 2004 15:59:53 -0700

Hi Mac,

It is possible that your antenna radiator is approaching a half-wave, or
multiple thereof, at the frequencies on which the SGC-230 will not match
down to VSWR < 1.5:1. You may be able to correct that by lengthening or
shortening the radiator.

Apart from the possibility of an "accident" when cascading two autotuners,
the additional insertion loss of the internal tuner is something it would be
nice to dispense with.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: [email protected] [mailto:[email protected]]On
Behalf Of D C Macdonald
Sent: Wednesday, May 05, 2004 10:13
To: [email protected]
Subject: RE: [Icom] 756 II Pro questions

I use an IC-746 feeding a "stealth" type antenna with an
SGC-230 autotuner.  At some frequencies, the SGC-230 can
not bring the VSWR down below a fold-back condition.  The
procedure I use is to set up the external SGC auto-tuner to
best match and then engage the internal IC-746 auto-tune.
It all works very well in this manner.

I agree that you should not try to get both auto-tuners to
search for match simultaneously.

73  ---  Mac, K2GKK/5

----Original Message Follows----
From: Adam Farson <[email protected]>
Reply-To: [email protected]
To: [email protected]
Subject: RE: [Icom] 756 II Pro questions
Date: Wed, 05 May 2004 09:46:56 -0700

Hi Mike,

Several friends of mine, and I, have had IC-756Pro II's in our stations for
2 to 3 years, without any problems whatsoever.

The IC-756Pro II Monitor is a sophisticated DSP-IF receiver. Here is a
description of it:

http://www.qsl.net/ab4oj/icom/ic756pro_notes.html#mon

I believe that the SWR foldback starts to reduce power at VSWR > 1.5:1. I
never experience this, as my ProII always drives a Yaesu Quadra amplifier
which has a flat input circuit. The Pro II autotuner will match loads up to
VSWR = 3:1 or slightly better; if load VSWR > 1.5:1, simply activate the
autotuner, but do not cascade it with an external tuner.

Neither my friends nor I have experienced any display problems with the Pro
II, or its predecessor, the IC-756Pro. Please check out my User Review:

http://www.qsl.net/ab4oj/icom/ic756pro_notes.html

Hope this will help you make a decision in favour of the Pro II. I feel that
it is without doubt the best HF transceiver I have ever owned.

Best 73,
Adam, VA7OJ/AB4OJ
North Vancouver, BC, Canada
http://www.qsl.net/ab4oj/
Icom FAQ site:
http://www.qsl.net/icom/

----
Your Moderator: Dick Flanagan K7VC, [email protected]
Icom Users Net: Sundays, 1700Z, 14.316 MHz
Icom FAQ: http://www.qsl.net/icom/

----
Your Moderator: Dick Flanagan K7VC, [email protected]
Icom Users Net: Sundays, 1700Z, 14.316 MHz
Icom FAQ: http://www.qsl.net/icom/