Hey, Colin:

I have a quick question here, just for the record.

I agree totally on disabling the radio's internal tuner when tuning an 
antenna.  However, instead of also having to totally dis-connect the manual 
tuner to get an accurate SWR reading, couldn't you simply put the manual 
tuner in bypass mode if the tuner has such a feature as does my Tentec 238A?

Not trying to argue here or question what you have said, but just trying to 
consider one other possibility that might be easier as a means to get the 
antenna's true SWR.

73 from Tom Behler:  KB8TYJ

----- Original Message ----- 
From: "Colin McDonald" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 27, 2010 5:14 PM
Subject: Re: Question About TW 1 and readings


not a head scratcher at all.
the meter is expecting a 50 ohm load on the radio side.  the internal tuner
is altering that load to compensate for the impedance of the antenna system
and is therefore no longer 50ohms when it is activated.
so, the meter is seeing something other than 50ohms on the radio side and
gives inaccurate readings because of it.
That's why everyone keeps telling you to turn both the internal tuner, and
the other tuner off, take the external one right out of line actually, then
tune the antenna with the meter.
in fact, to be safe, disable the internal antenna tuner in the radio's menus
so you don't accidentally turn it on at some point.
Physically disconnect the external tuner from everything.
Then, make sure you have a counter poise of some kind for the antenna.
After that, you can start trimming or adding wire to your quarter wave
length radiator until you achieve a 1 to 1 match.
You won't hurt the radio if you use 5W to check the swr, no matter how high
the swr is.
You could key down all day long with no antenna connected at all with 5 w
and the radio wouldn't be hurt.
Remember, tune in CW mode.
Not AM or FM as the modulation will cause the power to fluctuate and could
alter your readings for SWR before you reach a 1 to 1, or close match.
As long as the antenna is 3 to 1 or below you will be fine...the internal
tuner will take care of anything from a 3 to 1 match down and make the radio
efficient.
73
Colin, V A6BKX

----- Original Message ----- 
From: "mark Torgerson" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 27, 2010 2:26 PM
Subject: Re: Question About TW 1 and readings


> Hi
>     The internal antenna tuner is simply to protect the radio. I want =
> to=20
> have the SWR meter reading the true value of the antenna system =
> including as=20
> much of the feed line as possible. Interestingly though, when I take the =
>
> internal tuner off line the SWR tends to jump about two units on the=20
> external meter. Now, there is a head scratcher.
>
> God bless,
> Mark Torgerson
> =20