James, what is your intended power output?
If less than 500 watts, go for an automatic
antenna tuner and forget all this other stuff.
73, de Dr. Charly
Charles Harpole
k4vud@hotmail.com
> Date: Thu, 21 May 2009 01:19:46 -0400
> From: jruing@ameritech.net
> To: geraldj@storm.weather.net; tentec@contesting.com
> Subject: Re: [TenTec] TT and the rest of us...
>
> Thank you for the further gloss on tuner performance... I must
> read it a dozen more times before I will get half of it. I am afraid
> that you have now jumped way over my level of comprehension.
>
> I have a doctorate degree, but in something other then electronics,
> and as new ham, I am teaching myself the requisite electronics.
>
> I do gather, however, that I need to learn the best radios of
> capacitance, reactance, and impedance.
>
> In my case, I have one of those big stick 43 foot vertical antennas,
> and I believe (from playing with my antenna analyzer) that the
> impedance is nearly ALWAYS higher than 50 ohms. In fact I just
> replaced the original 4:1 current balun with a 4:1 Un-Un, at the
> suggestion of DX-?Engineering, which said it will usually end up
> having a higher impedance, but that it is (they say) easier to bring
> impedance down to 50 ohms, than it is to raise it to that level.
>
> I believe your comments are consistent with that claim. Thus, I
> might be OK to run the input capacitor as far down as possible,
> and work the output capacitor higher - rather than try the other
> way around.
>
> I do find, in practice, that the antenna with the newer Un-Un is
> somewhat more difficult to tune, meaning it is more difficult to
> find the sweet spot, and that smaller variations in the input and
> output capacitor settings will cause larger changes in SWR than
> I saw on the former current balun - but that it does seem to give
> better resulting SWR when I am finished. Oddly, the Inductor
> settings are substantially lower with this newer transformer at
> the base of the big stick.
>
> I am also getting from your commentary, that other considerations
> apply, and perhaps a different pattern would be best if the subject
> antenna has a lower impedance than 50 ohms. Somehow that
> makes sense, as an odd sort of "inverse" rule to apply.
>
> I truly appreciate your comments and the time you took to spell
> it out. They will become part of my permanent files and I hope
> to someday read them with total comprehension.
>
> Unfortunately, your final comment eludes me - other than to
> realize you would rather build your own from scrap parts than
> spend the big money to end up no farther ahead. I, unfortunately,
> must spend the penny at this time, as I lack sufficient knowledge
> to follow your lead.
>
> Happy trails.
>
> ============== James Richards- K8JHR ============
>
> Dr. Gerald N. Johnson wrote:
> > On Wed, 2009-05-20 at 17:22 -0400, Richards wrote:
> >> Well... shoot, Jerry. Now I AM confused. I spoke with Paul
> >> Hrivnak and company at Dayton last Friday and that is what they
> >> told me to do... but now you are giving me somewhat different
> >> instructions. So... now I all conflicted...
> >>
> >> Is this reason to get a beer?
> >>
> >> Is there some way to reconcile the two methods?
> >>
> >> If so... is THAT reason to get a beer?
> >>
> >> Is it reason enough to get the TT tuner instead of the Palstar? or to
> >> justify getting the Palstar auto tuner (which I think I want) because it
> >> may work more like the TT tuner, and also be automatic for "just" a few
> >> hundred more?
> >>
> >>
> >> ========== Richards - K8JHR ===============
> >>
> >>
> >>
> > Well, I suppose one could run the input capacitor to minimum and adjust
> > only the output capacitor and the coil to get a match, nearly an L
> > match, But that's only for the case when the load Z is higher than the
> > input desired 50 ohms. That's just backwards when the load Z is lower,
> > like feeding an 8' whip on 75 meters. If you crank in minimum input C
> > but not the absolute minimum you deviate from that almost L. A pi is
> > sometimes analyzed as two L networks, but it works out for the
> > conventional PI, that the loaded Q of the network is closely
> > approximated by the ratio of source R and input C reactance (R/Xc) and
> > that ratio of the load R and output C reactance (R/Xc) is very close to
> > the same. You have to adjust the load C to compensate for the reactance
> > of the load. I assert that the network will have the lowest losses when
> > the reactance is largest, e.g. the capacitance smallest because that
> > corresponds to the lowest Q and so the least resonant circulating
> > current in the PI while still preserving the greater versatility of the
> > PI for matching Z both higher and lower than the feed Z without
> > reversing the network.
> >
> > However having the lowest loaded Q means having the least harmonic
> > rejection, and its conceivable that using lowest C means largest L and
> > more loss from the larger coil. But it seems to me that minimizing the
> > multiplication of the input current by keeping the Q low minimizes the
> > circuit losses.
> >
> > I'm one of those been around so long that a "few" hundred bucks was my
> > beginning salary before taxes and a Collins receiver only cost 2/3 that
> > with the employee discount. Makes it harder for me to pay a few hundred
> > bucks more for a tuner that may actually contain parts comparable to
> > those in my stash of good parts, and not be as capable as that tuner I
> > built out of a huge broadcast transmitter coil back in 1964 that runs
> > cold at all the power I've ever fed it, even with the output open or
> > shorted. In the last year, I've built two tuners out of parts on hand.
> > Neither will handle a KW but that 811 amp I bought 8 years ago, still
> > sets on the floor unused. I'm glad I didn't spend a few hundred bucks on
> > it.
> >
> > 73, Jerry, K0CQ
> >
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> >
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