[TenTec] Pegasus Internal SWR

[Mark Erbaugh]

I have been having trouble getting good SWR readings on my Pegasus when
using the PT-11 intenal tuner. Especially on the higher HF bands, when the
tuner would finish tuning, the Pegasus SWR meter would still show SWR's
close to 2:1.

I have spoken with TT and LDG (makers of the PT-11 for TT). The consensus is
that the SWR bridge in the Pegasus is not that good and that the tuner is
actually working properly.

I ran a test to see if I could figure anything out.  I hooked up my Pegasus
to a manual antenna tuner and put a dummy load on the output. I made sure
that the internal PT-11 tuner was bypassed. For frequencies at the center of
each of the bands 160 - 10, using my MFJ 259 antenna analyzer, I adjusted
the SWR of the dummy load and antenna tuner to 1.0, 1.2, 1.5, 2.0 and 3.0. I
then recorded the forward and reflected power according to the Pegasus when
applying full power into the antenna tuner / dummy load, and calculated the
SWR using the formula:

rho = sqrt( reflected / forward ).
SWR = (1 + rho) / (1 - rho)

I've listed the results below. Hopfeully, they are viewable if you select a
fixed pitch font. If not, let me know, and I can email you the Excel
spreadsheet. The columns, in order are Frequency, SWR according the the MFJ
analyzer, R according to the MFJ, X according to the MFJ, Forward power on
the Pegasus, Reflected power on the Pegasus and calculated SWR from the
Pegasus values.

For 160 and 80, the Pegasus tracks well.
For 40, it got 1.2 for the 1.0 test, but tracked the other SWRs okay
For 30, it seemed to register high for all but the 3.0 SWR
On 20, it tracked well for low SWRs but read low for the higher SWRs
On 17, it actually read a high SWR (1.6) for the 1.0 test and then read 1.0
for the 1.2 and 1.5 tests and then was low for the 2.0 and 3.0 tests
On 15, 12 and 10 the Pegasus was consistently high, reading 1.8 to 2.0 for
the 1.0 SWR test and going up from there.

If anyone else would like to run a similar test on their Pegasus, I'd be
interested in seeing the results.

One of my (paramoid) concerns is based on the fact that I installed the
PT-11 upgrade myself. I wonder if these problems could be caused by
something I did wrong in the upgrade, pehaps a cold solder joint (my
nemesis).

73,
Mark, N8ME


FREQ SWR-M R X F R SWR-P
MHz  OHM OHM
1.900 1 55 0 104 0 1.0
 1.2 45 10 103 2 1.3
 1.5 39 17 104 7 1.7
 2 33 24 104 13 2.1
 3 26 33 104 23 2.8

3.750 1 50 0 104 0 1.0
 1.2 39 0 104 1 1.2
 1.5 32 0 104 6 1.6
 2 25 4 104 13 2.1
 3 17 11 104 24 2.8

7.150 1 53 0 104 1 1.2
 1.2 51 12 103 1 1.2
 1.5 44 20 103 5 1.6
 2 35 25 103 10 1.9
 3 21 25 103 22 2.7

10.125 1 55 0 103 2 1.3
 1.2 62 0 103 5 1.6
 1.5 77 0 103 10 1.9
 2 97 10 103 17 2.4
 3 104 56 103 26 3.0

14.175 1 48 0 103 0 1.0
 1.2 41 5 103 0 1.0
 1.5 34 11 103 2 1.2
 2 29 17 103 7 1.7
 3 22 25 103 17 2.4

18.118 1 51 0 103 5 1.6
 1.2 39 2 103 0 1.0
 1.5 32 0 103 0 1.0
 2 24 1 103 2 1.3
 3 17 7 95 9 1.9

21.225 1 54 0 108 8 1.8
 1.2 51 10 103 10 1.9
 1.5 43 19 103 12 2.0
 2 32 33 103 17 2.4
 3 21 22 103 22 2.7

24.940 1 53 0 102 11 2.0
 1.2 59 10 102 14 2.2
 1.5 53 21 102 19 2.5
 2 43 33 101 24 2.9
 3 29 37 98 30 3.5

28.850 1.1 59 0 102 12 2.0
 1.2 60 0 102 12 2.0
 1.5 78 0 102 17 2.4
 2 101 5 103 23 2.8
 3 172 52 103 32 3.5