[FARC] Antenna Tuner

[Bob Moroney]

Kirk,
 From the sound of it, you could have a screwed-up tuner, you could have 
a screwed-up antenna, you could have some station grounding problems, 
you could simply not be using the tuner quite as it's meant to be used, 
or you could have some combination of the above. 

Does that make you feel any better?  Probably not. 

Basically, you need to deal with one problem at a time, starting with 
the antenna and feedline.  If that system isn't behaving as it should, 
you might as well be beating your head against the wall.  Have you or 
anyone else put an antenna analyzer on the end of the coax that goes 
into your transceiver?   That alone will tell you a lot about your 
antenna and feedline; e.g., what its impedance is at various frequencies 
and where it's naturally resonant.

Is your station's grounding system solidly bonded to a real earth 
ground, and is all your station equipment solidly tied into that 
system?  An ohmmeter will help answer that question.

Are all your coax connectors "good" and fully seated into one another?  
Another job for the ohmmeter, at least as a start.

I didn't know it until today, but I too have one of these tuners; I just 
never fully assimilated the make or model number.  To me it was simply 
the somewhat cheap manual tuner I bought maybe ten years ago from some 
mail order place (Radio Works?).  It's an OK tuner as far as it goes, 
but it's definitely nothing special.  I can't say that I've ever looked 
at the manual.  Although I bought this tuner ten or more years ago, I 
would doubt that the manual I have is any different or better than 
yours, so loaning you my manual probably won't help.

On the tuner, one thing I would say right off the bat is that the knobs 
on the front panel (other than the "Output Select" knob) have no stops.  
As you suggest, they will turn forever.  So just picture what they do.  
Matter of fact, it wouldn't hurt to unscrew the cover from the tuner and 
view what lies beneath to help you visualize. 

You'll see two variable capacitors and a coil.  The two variable caps, 
one "transmitter" and one "antenna" are just plates that twirl around, 
interleaving (or not) to various degrees, depending on how much they've 
been twirled, then start it all over again.  The "inductor" (coil) has 
taps off of it that are connected to the "inductor" switch.  You can 
turn this switch forever as well, but in reality you are just cycling 
through the same tap points over and over, adjusting the impedance of a 
capacitance/inductance bridge in various combinations until the antenna 
is "tuned".  Unfortunately, though, an antenna can't really be "tuned" 
without increasing or reducing the length of its radiating elements to 
match the frequency desired.

So the idea of an "antenna tuner" is to achieve a reasonable impedance 
between whatever radiating contraption you hooked up to the "tuner" and 
the transmitter, so you don't wind up releasing the smoke from your 
transmitter's output transistors.  The transmitter finals are happiest 
when they sense a 50-ohm impedance on their output; thus you need to 
fiddle with the tuner controls until the radiating contraption 
(antenna)  "matches" what the finals want to see.  So you could view a 
tuner as a "pacifier" for your transmitter finals, more than anything 
else.   It may or may not really increase the power that winds up going 
to the antenna, but it will help to keep the transmitter output stage 
happy and smoke-free.

Put the inductor switch into the position recommended by the "manual" 
for a given band, then tweak the transmitter and antenna variable 
capacitors within their range, until SWR is minimized.  Make sure you've 
got the "Output Select" switch set to the "Tuned" segment so you're 
getting the correct meter readings, and make sure you've got the 
"Peak/Avg" push button "out", so that you're getting average readings 
instead of peaks that depend on your voice modulation.  Also, if you can 
get your transmitter to key in CW mode, do that instead of using SSB, 
which as you note, various according to the volume of your voice.  I 
don't know your rig, so I don't have any suggestions there, other than 
plugging in a key.

Well, I'm tired of typing, and I've got to make some cole slaw for 
supper, so hopefully all these words may help you a little.  Feel free 
to write or call if they don't, or whatever.

73, Bob K9CMR
======================
Kirk Talbott wrote:
> I recently bought a Vectronics VC300DLP antenna tuner and I am using it with 
> an ICOM 718 transceiver. My antenna is a hy-gain model 18 AVT/WB-S vertical. 
> I bought an antenna tuner based on a consensus of other experienced hams 
> that if I used the ICOM 718 I would probably need an antenna tuner 
> regardless of what antenna used.
>
> I am new to ham radio, HF, and antenna tuners in general and that is mostly 
> the problem,   however I am having specific problems with the tuner and am 
> ready to pitch it into the street!
>
> The instruction manual for the tuner is essentially useless due to many 
> typos and obvious errors in English translation.  I was able to divine how 
> to hook it up to the transceiver and to set the defaults for the 
> transmitter, antenna, and inductance controls on the tuner for a particular 
> band.  Since the labels on the tuner's controls didn't match the labels in 
> the manual, it's a toss-up as to whether I had things set right from the 
> get-go.
>
> Now to transmitting.  Do I have it tuned?  Probably not.  Both the forward 
> and reflected power needles dance back and forth wildly to the lows and 
> highs of my voice during SSB transmission, making it nearly impossible to 
> read the SWR at the intersection of both needles. The tuner has a dummy load 
> built-in which is convenient, but remember, there is no carrier in SSB 
> transmission, so you can't just hold the PTT switch down while you 
> simultaneously fiddle with the three tuner controls.
>
> Put the transceiver in FM or AM mode so you have a continuous carrier you 
> say?  Nope, I tried that.  The transceiver has no FM, and using AM pegs both 
> needles to their stops on the tuner with some erroneous indication.
>
> After much fumbling I was able to finally coordinate mike, talking, and 
> twiddling the controls but to no avail, adjusting the controls did nothing 
> to change tuner meter needle indications.  As a matter of fact, the controls 
> on this tuner will turn past their stops  infinitely, giving you what tuner 
> setting as a result?  One ham said, "After you tune, write down the 
> settings."  So I would write down, 20 turns to the right past "6" on the 
> antenna knob?  Or 5 turns to the left past "1" on the transmitter knob? 
> This can't possibly be the way it works.
>
> Now, fortunately the transceiver has an SWR meter so I could use that maybe 
> as an indicator of getting close to doing something right, and not burn up a 
> transmitter in the process.  Nope again. The transceiver's SWR meter varied 
> between 1:1 to 9:1 depending on the highs and lows of my voice during 
> transmission.  If I spoke softly, it would read 1:1 all the time.  Raise 
> your voice, and it would peak out at 9:1 then drop back to 1:1.
>
> Anyone up for some antenna tuner 101?  Or better yet, would someone like to 
> purchase an antenna tuner, cheap, that is before I reduce it to its 
> elemental parts with a sledgehammer? You don't have much time.
>
> Plodding along blind
> KB3ONM
> Kirk 
>
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