[TenTec] Comments on "Repairs"

[Robert & Linda McGraw K4TAX]

Larry:

One concern that surfaced from the description of your station and grounding 
technique.  You indicated that you have a common ground connected to an 
outside driven ground.  Is this ground rod connected or bonded to the AC 
mains ground?  It should be in order to prevent a difference in voltage 
between the station ground and the AC mains ground.  Typically your radio is 
connected between these two and thus any current differences are flowing 
through the radio equipment.  Not good.

With balanced lines into the shack, if they are indeed balanced, then there 
should be NO circulating currents.  I would certainly question this aspect 
of the station.  Why would you have circulating currents or RF in the shack 
if the line is balanced?  It is normal for a small amount of imbalance to be 
in existence due to different ground conductivity under the legs of the 
antenna.  I find it acceptable to have current differences in each side of a 
balanced line to be less than 10% worst case.  More like 2% to 3% in my case 
in practice.

With the tuner and its internal SWR metering system you get good results. 
OK, I'll buy that.  However, what is the SWR the radio is seeing?  This must 
be measured at or in the radio.  Now to that end, with the ground system you 
describe I could easily suspect that one of the diodes D2 or D3 on the Low 
Pass Filter board could be defective thus caused by a nearby lightning 
strike and a step voltage between two different grounds.  With either diode 
at fault the radio ALC and power control system may be failing to protect or 
control the radio.  I've seen this before.  Others relate the same story.

Now I know this doesn't explain why the Yaesu works fine and the Tentec 
doesn't.  Could it be that the Tentec stays connected in the system all the 
time or most of the time and the Yaesu sits detached from the system most of 
the time?  A recent nearby lightning tap may have taken out D2 and or D3.

Regarding commercially made RG-213 jumpers.  OK good I'll buy that but I've 
seen new, commercially made jumpers in two way and broadcast equipment found 
to be defective out of the box.  Spin the shell off of the PL-259's and 
check to make sure the braid is soldered and the center pin is soldered.  A 
good check with an ohm meter is wise.  Better yet, a dummy load on one end 
of the cable with the MFJ bridge on the other end and do a wiggle and jiggle 
check. Any change in SWR is a bad cable or connector installation.  In my 
book, new and commercial does not automatically imply good.  I'm like a 
cat......always suspicious.  At one place I worked, a failure rate of  3% 
AQL {acceptable quality level}  or less was considered passing grade.  That 
says 30 out of 1000 cables could be bad and the company is happy with their 
quality.

You have made some very good choices on several points.  Your choice of 
Polyphaser and Wireman lightning protection equipment is as good as it gets 
in my experience.   Frankly, I don't care for the RM-35M power supply unless 
you have a 20A fast acting magnetic breaker between it and the radio.  It 
has the ability to instantly dump 35 amps of current into the PA which is 
only rated for about 26 amps max.  OK so it works with the Yaesu but they 
use a totally different over current protection scheme.  Tentec does not 
monitor or control emitter currents on the PA or driver stage.  They use the 
SWR and ALC circuit to control drive power.  This area could be the source 
of your evils.

More good dialogue please.  We'll solve the problem to component level if 
you wish.

73
Bob, K4TAX