[TenTec] Tuning Amp on 17 meters

[Lee WA3FIY]

When operating barefoot and with the tuner in line, you have a near perfect match as 
expected.  The O VII sees the tuner directly.  When you insert the Centurion in line, the O VII 
sees the input impedance of the amplifier (cathode circuit) and the amplifier is now seeing 
the tuner directly.  In other words, the amplifier is seeing a near perfect match and the 
transceiver is seeing the amplifier input impedance whatever that may be.    No real surprise 
since you have selected the 15 meter band on the amp which inserts a 15 meter low pass 
filter in line when you are operating.  It works but is not optimum as you see.   I doubt there is 
any real issue at low power at 2.1 : 1  SWR.      

I rarely use my antenna tuner here on any of my TT rigs unless the SWR exceeds 2.5 : 1 and 
I am running at or near full power.   YMMV    :-)

73,

-Lee-

WA3FIY 



On 17 Apr 2013 at 15:52, Richards wrote:

> Greetings TT Mavens.
> 
> Background -
> 
> I rarely work 17 meters SSB with my Omni VII.  Today, I reworked my 10
> meter vertical ground plane antenna into a 17 meter ground plane which
> measures about 1.3:1 SWR at around 42-45 ohms both in the back yard 
> and inside the shack using a RigExpert AA-230 analyzer.
> 
> I also have a TenTec Centurion and a TenTec 238C  and/or a Palstar
> AT-auto matchbox in line, which I alternate using at my whim on other
> antennas.  I generally put them in bypass mode when working a resonant
> dipole or vertical.
> 
> For 17 meters, I set the Centurion to the 15m Band, and set the LOAD
> and TUNE controls according to the chart in the user manual, and then
> fine tune for most power out with the TUNE knob.
> 
>  Sidebar: This seems to be a very forgiving amp...
>  I can set the LOAD wide to either side of the
>  recommended LOAD setting and it has no apparent
>  effect, while the TUNE control is quite response
>  and it is easy to tune to highest power out with
>  very little movement.  The Plate Meter almost
>  never changes no matter what I do.  I have never
>  heard it arc or make any odd noises... he said
>  knocking on wood...
> 
> When I briefly transmit a CW tone barefoot on 17 m, the rig meter says
> it sees 1.2 SWR, but when I put the amp in line, and run exciter power
> (maybe only 2-30w) I get 2.1:1 SWR.  I have not tried it on higher
> power.   I am sorry I don't recall what it did into my dummy load, and
> I cannot test that again right now because a humongous thunder storm
> is rolling in off Lake Michigan and ...well... you understand my
> reticence to be operating while that is brewing in the neighborhood.
> 
> The Inevitable Questions -
> 
> *   So... why does this happen?
> *   Is this a normal occurrence?
> *   Does this have anything to do with working 17m
>  opposed to another band?  The radio usually
>  reports SWR close to the antenna's inherent
>  measurements on the other main bands like 40m
>  20m, 15m, and 10m.  I have not tested for this
>  on 12m or 30m.)
> *   Using the auto tuner does not change this dichotomy
>  of SWR reports.  I did not think it would, but
>  I tried it anyway.
> 
> So... any thoughts?
> 
> ----------------------  K8JHR -------------------------
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