[TenTec] TT and the rest of us...

Charles Harpole k4vud at hotmail.com
Thu May 21 00:03:09 PDT 2009


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 at hotmail.com   




> Date: Thu, 21 May 2009 01:19:46 -0400
> From: jruing at ameritech.net
> To: geraldj at storm.weather.net; tentec at 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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