[TenTec] TT 238B ?s...

[Ken Brown]

Hi John,

>>From what I understand, both the LDG and 238 are L-tuners, which means they
>have one optimum setting... is this right?
>
Since an L network has only two adjustable circuit elements (one L, and 
one C), and there are two antenna system characteristics (resistance and 
reactance) that you are adjusting the network to transform, there is 
only one possible set of coeficients (settings of L and C) in the 
equation that are a solution. So, yes this is right.

>But, is there a better way given
>that I can measure the antenna's capacitance and inductance directly?
>
Actually it is one or the other, not both, and the RF-1 doesn't know which.

>  Can I
>not 'dial out' these using the capacitor and inductor controls on the 238
>(obviously measuring with the analyzer)? 
>
If you calibrated the inductance and capacitance setting dials on the 
tuner so that you would would know what amount of capacitance you get at 
any setting of the knob and switch, and you knew what amount of 
inductance you get any setting of the inductor dial, then you could  use 
the measurements from the Autek and a little math (or graphical methods) 
to find out exactly where to set the knobs for a good match. 
Alternately, if you were  using it on just one frequency you could 
calibrate the dials in Capacitive Reactance and Inductive Reactance, 
instead of capacitance and inductance.  Even if you did this, I suspect 
that you would still need to fine tune it after you got it set to the 
calculated settings for the load you are matching to.

>I'm trying to understand antennas, and tuners, and the 238, and the RF-1 a
>little better.  Any help would be appreciated.
>
Something else you could try: Measure the Z of the antenna system with 
the RF-1 at the end of the coax that will be plugged into the antenna 
port of the tuner. Then connect a 50 ohm termination (a good 
noninductive dummy load) to the transceiver port on the tuner. Connect 
the RF-1 to the antenna port of the tuner and adjust the tuner so that 
you read the same Z. There will be two settings that get this Z. One 
will be positive X and the other with a negative X. Then remove the 
RF-1, connect the antenna, remove the termination and connect the RF-1 
to the transceiver port of the tuner. It should now read  Z = 50 ohms 
resistance and SWR = 1:1, if you picked the correct one of the two 
settings. Problem is that the RF-1 does not tell you whether the X part 
of Z is plus or minus. And when you push the C or L button it calculates 
how much capacitance or inductance it would take to make that reactance. 
Only one of them is correct, because the X is either + or - , not both.

>Also... has anyone had any experience with the new LDG 1000w PEP autotuner?
>Does anyone think there would be a market for a full-gallon autotuner that
>went for around $1200 or so?
>
I think there is a market for full power tuners, both manually tuned and 
auto tune. I don't know whether it would be a marketing success at that 
$. I sure wish that there was a standard for power ratings on tuners. 
Most of the "1500 and 3000 watt" tuners made lately, I would rate at 
about 300 watts.

Have fun,

Ken N6KB