[TenTec] RFI Issues

[Jim Brown]

On 5/14/2012 5:53 AM, chacuff wrote:
> This comes at a time when I am trying to make sense of some problems with my
> station.  I'm a recent Ten-Tec convert having bought a used Orion II and
> Centurion amp.  Was using a Yaesu FT-1000MP MKV and a modified Clipperton L
> prior.  Since putting the Ten-Tec gear online my wife is complaining that I
> am coming through many different things in the house (shack is in a separate
> building) that I never had problems with before.  TV audio in two rooms
> mainly.  I get complaints from her even if I am only running the rig at 100W
> so I don't believe the amp is a contributor other than making the problem
> stronger.

Interference with ANY audio system is caused by the AUDIO equipment, 
NEVER the radio equipment. The most common cause of RFI within audio 
equipment is a Pin One Problem, and the easiest fix is a common mode 
choke formed by winding multiple turns of the audio cable that is 
connected to the Pin One Problem through a suitable ferrite core.  All 
wires act as receiving antennas, they pick up our transmitted signals, 
and Pin One Problems cause our signals to be coupled into that 
equipment. Chokes work by killing the antenna current.

The only equipment that any transmitter could POSSIBLY interfere with is 
a RADIO receiver (including the radio receiver that is part of a TV 
set), but it is VERY VERY unlikely that your ham gear could be 
interfering with it.

> When using the amp I drive it with 50 watts out of the rig and tune to 1KW
> peak out using CW dits as recommended by Ten-Tec.  Amps not pushed hard and
> neither is the rig.

Hmmm.  How did you choose 50W as the drive level?  How do you determine 
output power? Are you using ALC between the amp and the rig?  Do you 
work CW or SSB or both?  What does the interference sound like to your XYL?

The RIGHT way to set drive level to any power amp is to first start with 
a drive level a bit less than needed to get full power out, tune the amp 
for max out, increase (or back off) the drive until you get the desired 
output power, then retune the amp if you've changed the output power 
very much.

Ten Tec amps have peak-reading LEDs to show amplifier power output, as 
well as an analog meter driven by circuitry that may or may not catch 
peaks of power, and both of these indicators have an internal 
calibration pot that may or may not be properly adjusted. External power 
meters that CLAIM to read peak power may or may not do that very well.

> My grounding system is very robust...near commercial/cellular spec for
> lightning protection and all equipment is bonded to it.  Really nothing has
> changed in my station except the transceiver and amp.  Antennas are resonant
> on 10 thru 20 and 40.  (Force 12)

The only thing earth connection of your ham station has has  to do with 
RFI is that can change the way a long wire antenna works.  It's very 
important that it be grounded, and how it's grounding is critical, but 
it doesn't help or cause RFI with a transmitter feeding a transmission 
line.

> I plan to put my spectrum analyzer on the air next chance I get and see just
> what is going out.  I didn't expect this and am concerned about what the
> neighbors might be experiencing but haven't come knocking on my door as of
> yet.

That's a good thing to do to make sure you're not producing intermod 
trash on the ham bands, but it's very unlikely that anything you're 
doing besides producing more output power has anything to do with your 
RFI issues.

> Old rig was a 200W version of the MKV run at about 125 watts into the amp
> that was tuned up tight to about 900W out.  I was pushing it much harder.  I
> never ran the rig in Class A due to the heat and stress it created on the
> finals.

I don't think any of this has anything to do with your RFI.  Rather, I 
suspect that something has changed in your home entertainment setup 
between the time you ran the old setup and the new one.  Perhaps you 
added a connection between the TV and the audio system. Or perhaps you 
changed the cables connected to that system -- a new piece of equipment, 
a new cable box, a new outdoor or indoor antenna, etc. OR, perhaps the 
RFI happened when your beam was pointed to it and you didn't point it in 
that direction before at times the XYL was using the TV that way.

My RFI tutorial offers both a detailed discussion of how RFI occurs and 
detailed recommendations for fixing it.  
http://audiosystemsgroup.com/RFI-Ham.pdf

73, Jim Brown K9YC