[TenTec] Pegasus Internal Tuner

[Mark Erbaugh]

I just installed the new internal antenna tuner in my Pegasus and thought I
would post my initial experience. I'd be interested in hearing what others
have found.

Installation:

You need to remove the LPF board to remove change the rf output routing to
go through the tuner.  While the instructions didn't call for it, I found
this task easier by first removing the back panel of the Pegasus (4 screws).

The instructions have you install a wire from the tuner to the DSP board as
the first step. They have you physically install the tuner board in the
radio as the last step. In the interim you have to juggle the tuner board
which is now connected to the radio (via a single solder connection and a
wire that isn't long enough to allow you to place the tuner board out of the
way) while trying to remove the LPF board and make connections to it.
Installing the tuner board into the radio doesn't interfere with any of the
following steps, and it makes it easier to work on the radio with not having
the tuner board flopping around.

Speaking of installing the tuner board. There are four screws that mount the
bracket that holds the tuner board. The bracket has captive nuts for machine
screws that you install through vent slots in the Pegasus chasis. The screw
holes line up perfectly, but I was unable to get two of the screws to thread
into the nuts. Currently my bracket is held in place by just two screws;
fortunately, one is on the top an one on the bottom so it still seems
secure.

Operation:

I'm a little disappointed with the operation of the tuner with the TenTec
software.

1) MAJOR DISAPPOINTMENT:  The tuning operation does not stop automatically.
You have to listen to the tuner (you hear the relays clicking) or watch the
SWR meter and click the Antenna Tune button again to stop TX. See my
discussion below about the radio / computer / tuner interfacing. Even with
the limitations, the software could monitor the SWR and wait for it to
settle and then shut down the RF.

2) I have an LDG AT 11 MP tuner, which uses similar circuitry. The cap up /
down, inductor up / down switches (which also provide tuner bypass and Hi-Z
/ Lo-Z reconfiguration). Are active regardless of Rx/Tx mode. On the Pegasus
version, the cap up / down and inductor up / down switches are only
available when RF is applied. The bypass control is a checkbox, but checking
or unchecking it doesn't cause anything to happen until you apply RF, and
then only after about 3 seconds. So to bypass the tuner, I have to click the
checkbox and TX for 3 seconds or so.  There is no control to provide Hi-Z /
Lo-Z reconfiguration (this switches the capacitor from input to output of
the tuner). I spoke with Duane at LDG and he confirmed that the Hi-Z / Lo-Z
feature is in the tuner and that there is no way to access it from the
Pegasus software.

Also with the AT 11 MP, there is a feature called auto tune. In this mode,
whenever the tuner senses an SWR greater than some limit, it will
automatically retune. It doesn't appear that this feature is available with
the Pegasus version.

Performance

It seems that the tuner usually seeks an SWR (indicated by the Pegasus
meter) that is low, but not as low as possible. Often, the tuner stops with
an SWR of 1.5:1 or so (even though during the tuning, I see 1.0:1). With a
couple of clicks of the L or C manual buttons, I can usually get the Pegaus
to read 1:1.  Similarly, if I click on the tune button with an SWR of 1:1,
the tuner will tune and end up with a higher SWR.  Duane said that this is
due to the fact that there are now two SWR sensors in the system (the one in
the tuner and the one in the radio) and they won't always agree. So the
question is, which one is right? Which is the best match?

My antenna has an SWR of 2.9:1 (92 R, 62 X) at 29.6 MHz according to my MFJ
analyzer. The Pegasus indicates about 3.4:1 with the tuner bypassed. The
best the tuner can do is about 2.4:1. The stated range of the tuner is 10:1,
so I would expect it to be able to do much (1:1) better. Even using the
manual L C buttons, I was unable to improve the match. According to Duane,
being able to switch Hi-Z / Lo-Z may help here, as it does seem that the
match is found near the limit of both the capacitor and inductor ranges.

Comments:

The interface between the Pegasus and the tuner is uni-directional. There is
a single wire that goes from Pin 3 ( Rx data) of the Pegasus serial port to
the tuner. Apparently, whenever RF is applied, the tuner listens for
commands from the computer over the serial port. There is no way for the
tuner to return information to either the radio or the computer. There is no
interaction between the DSP in the Pegasus and the tuner. All the interface
is between the computer and the tuner. However, it is nice having the tuner
and radio in one box.

Software enhancement suggestions

1) have the software monitor the SWR and stop the tuning after it has
settled.

2) while in tune mode have the meter automatically display SWR and then
return to whatever it was displaying when tuning is complete.

3) Add Antenna tune, capacitor / inductor manual tuning and bypass buttons
on the main radio screen.

4) Have the capacitor / inductor manual tuning and bypass buttons active all
the time. If the radio isn't in TX at the time the button is clicked, have
it apply the minimum amount of RF needed and send the command to the tuner
and then shut off the RF and return to RX.

73,
Mark, N8ME




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