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Author Topic: ATR-15 Advice Requested  (Read 1635 times)

Posts: 13

« on: October 23, 2004, 08:07:03 AM »

I recently bought a used ATR-15 tuner (pre-MFJ-buyout).  Unit looks to be in excellent condition inside and out.  However, I’m green about using it.  I’d appreciate some pointers.  Here’s my dilemma.  I put up a 0.64 wavelength (i.e., 0.64 wavelength for each “dipole” half, designed around 18.11 Mhz) EDZ (extended “dipole” Zepp) as described in Walter Maxwell’s (W2DU) Reflections book, chapter 20, Sec. 20.5, and p. 20-15.  (This would essentially equate to a 42 m, conventional ½ wave dipole in reality, if my calculations and understanding are correct).  My intent was to possibly obtain the purported 3-db gain, broadside, Mr. Maxwell describes.  Anyway… I fed the EDZ w/ 450 ohm LL, connecting to the “Balanced Line” terminals off the back of the ATR-15.  If I remember correctly from taking the cover off of the ATR-15, the internal balun is indeed currently wired as a 1:1 current balun, rather than the 4:1 voltage balun.  I had very high expectations of this setup based on Mr. Maxwell’s writings above; but no matter what band I choose or what Transmitter/Antenna settings on the tuner I choose, I cannot get the SWR down to satisfy myself that I am “tuned” to the antenna.  I’ve even disregarded the attempt to work the antenna as an EDZ at 18.11 Mhz and actually attempted to tune it to 40 m and make it work as a conventional ½ wave dipole.  I’ve got the ATR-15 manual, but, by the way, I’ve yet to understand what the “SWR Set” knob and adjustment is about and when I am to move it off of full clockwise position.  The only reference I’ve found in the manual regarding this “SWR Set” function is operational step #2 which says, “Set the SWR SET control to the full clockwise position . . .”.  The manual then proceeds to describe how the TRANSMITTER and ANTENNA controls are to be used to adjust to minimum SWR in the REF (reflected) position.  Herein is where I begin to get lost as I’m hardly ever able to get the (“REF”) SWR reading out of the red zone (i.e., less than 3:1).  In fact, I actually can reach approximately a 12 o’clock position with the TRANSMITTER adjustment that causes the reflected SWR reading to rapidly peg out full scale.  I’ve been told to “tune slowly”; having done so, and still not being able to get the above described system below 3+:1, I’m at a loss.  I’d truly love to get the hang of this purportedly fine tuner so as to use it with the AL-80B that’s not even been fired up since I bought it.  I want to get familiar with the tuner, barefoot first, before trying it on the linear.  Any and all comments would be welcome and appreciated.


Posts: 1

« Reply #1 on: October 23, 2004, 08:47:56 AM »

As far as the "set" knob, you apparently don't have a basic understanding of typical SWR bridge operation.  Just about any swr bridge (generally) operates so:

To get the "cart before the horse", once you think you are tuned up, you put in "some" carrier, any stable amount, say, 100 watts.  it does not matter, as long as it is not MORE than what the SWR bridge is rated for (you may not want to put 1.5kw through  some "cheap" cb type bridges)   and you want "enough" that the bridge can give you a useable reading.

So, with "some" carrier transmitted, PUT THE BRIDGE in the FORWARD   function, and adjust the SET knob for full scale reading at the meter.  NOW,  switch the bridge function to REFLECTED, and now you can read accurately the SWR.  This reading is ONLY accurate at this power setting and ONLY with the set knob at this position.  You will have to change it each time.

Now, to get  the horse back in front of the cart,  What the instructions are probably referring to is this:  If you put the sensitivity control ALL THE WAY  to the right, this makes the meter VERY sensitive, and allows you to see the CHANGE on the reading with LOW power settings from the transmitter.

This does a couple of things:

Low power is easier on the tuner components during the time that it is "out of tune"--less chance of arcing.

Low power negates the problem some tranceivers have--high swr at the tranceiver causes the PA protection circuit to "cut back" the transceiver power--which can make it tough  to tell what the tuner/swr is actually doing.

Low power of course reduces possible QRM to hams near your frequency as you tune up

As far as trouble matching a given load, you can certainly reach some combination of antenna/feedline/impedance that can be tough or impossible to match.

GENERALLY--"tune" these tuners with a LOT of capacitance and LESSER amounts of inductance.

Be careful you don't get into a "false" tuning situation--where the tuner inductor is absorbing power, indicated by heating of the inductor.

It may be helpful, until you learn to use this, to tune up a few times with the cover off, so you can SEE what the caps and inductor are doing.

It might be helpful to "practice" into a dummy load or light bulb.

Generally, start with the caps at 1/2 or 70 percent (roughly) and tune the inductance,  STARTING FROM MINIMUM  inductance, or the "10 meter end"  for some noise in your receiver.  Then tune the caps for min. swr.  You will have to go back and forth with the adjustments.   After you get "some dip"  move on or the other cap ONE WAY  just a little, and retune the opposite cap.  If the swr went down further, you went the right direction,  if not, not.  

Once you have the caps  "jiggled" this way, and depending on how the inductor switch--or if roller, you may need to move the inductor some.  ALWAYS TRY DECREASING the L setting first, to see if the "dip" gets better.

THIS DOES TAKE PRACTICE.  Some antennas are much, much fussier than others.  Might be helpful to find a "local" if possible.

There was another thread recently posted on eham about this very thing, you might do some searching, and I'll see if I can find it.  Don't remember the heading it was under.

Posts: 13

« Reply #2 on: October 23, 2004, 10:39:52 AM »

Thanks for the comments.  I'm still learning.  I'll try your suggestions.
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