[TenTec] OMNI-C on 17 meters concern

[Steve Ellington N4LQ]

Being concerned about out of band signals on my Omni-C, I have performed the
following experiments.

1. Connected Omni C to 50 ohm dummy load.

2. Connected scope to coax Tee at dummy load.

3. Measured voltage at 7, 14 and 18mhz with drive control set for 0.

Here are the results:

1. RMS voltages at 7 and 14 mhz were .35v or .0025 watts
2. RMS voltage at 18mhz was 7.07v or 1 watt.

This indicates that at 18mhz, the Omni C produces 400 times more power than
on the other two bands. Now the question is, what frequency is this power
being generated?
Not having a spectrum analyzer, I was forced to use crude methods of
testing.

1. Inserted the TenTec 238 antenna tuner between dummy load and Omni C.
Tuned for
   best match. Results showed no additional attenuation of the 18mhz signal
on the scope.

>From this, I gathered that if other frequencies were being generated, some
attenuation would have be obvious on the scope.

2. Using a monitor receiver, IC-706, I measured the signal strength of the
Omni C (drive set for zero) at 7, 14 and 18mhz. The signal on 18mhz was
about 25db stronger than the other two bands.

Conclusion:

With the bandswitch set for 18mhz and the drive control fully
counterclockwise, the Omni C produces 1 watt of power. 10v peak X .707 = 7v
RMS.  7squared divided by 50 ohms = .999698 watts,

On other bands the Omni C produces only 2.5mw, making it an excellent QRPp
rig for any band except 17 meters where it can become a QRP rig.

I no longer fear using my Omni C on 17 meters since most if not all
measurable power is radiated on the correct band.

73 Steve N4LQ


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