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Author Topic: Drawbacks to the Differential Tuners?  (Read 2360 times)
W6NFL
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Posts: 17




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« on: August 31, 2007, 02:30:05 PM »

   Im in the market for a new manual hf tuner and have narrowed it down to either the Palstar AT1500DT or the AT1500CV. The DT version uses the differential type tuning which uses just two controls for the tuning. The CV version uses the more conventional 3 controls for tuning. There must be drawbacks to the 2 control version right? Would love to hear hams who have used both types with positive and negatives takes from these.
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WD8PTB
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« Reply #1 on: August 31, 2007, 02:41:10 PM »

I have both. Both have been reliable. It's a little easier to tune the differential and so far I have always been able to get 1:1 swr. Most of my antennas are resonant so the most swr I need to tune out is typicaly 2:1 or 3:1 at worst.  73 Don WD8PTB
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N3JBH
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« Reply #2 on: August 31, 2007, 03:10:48 PM »

i had and used the good old heathkit 2060A tuner and it as you may know is a  3 knob tuner. i replaced it with the Palstar AT1KP a 2 knob Differential Tuner.

and i can tell you i am really happy i did. now the ole HeathKit did a yomans job allright. but this new palstar beats it hands down. tunes faster much simpler
and far better range.

I too was kind of concerned by the Differential Capicator in it and was not sure what to think. now in hind sight i can say good rideness to the ole 2060A.

i know i did not answer your question here about the tuners of your choice but i did explain how i feel about the 2 differant types. Jeff
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K0BG
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« Reply #3 on: August 31, 2007, 03:28:04 PM »

Personally, I like the AT-Auto. No fuss, no bother, no nothing, it just makes the match for you, and in well under 5 seconds most of the time.

Alan, KØBG
www.k0bg.com
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W8JI
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« Reply #4 on: August 31, 2007, 04:55:31 PM »

The actual difference between the tuners, and make no mistake there is a difference, is the differential tuner for the SAME components handles less power on low bands.

It is easier to tune, but it always handles less power on the low bands than the same components would in a conventional T.

(This assumes you know how to tune a regular T network properly.)

If you are running near the limit of the tuner or if you have a low impedance load on 160, 80, or 40  you will be able to run perhaps twice the power into a regular T with the caps set near maximum C.

Other than that the only difference is operating ease. The differential is easier, but does sometimes need more adjustment than a regular T.

73 Tom

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WB6BYU
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« Reply #5 on: August 31, 2007, 08:50:11 PM »

For the same reason, a differential tuner with the same sized capacitors
will be somewhat less efficient when matching low impedances on the
lower frequency bands.

You can get a sense of the difference running the W9CF Tuner Simulator
Applet at http://fermi.la.asu.edu/w9cf/tuner/tuner.html

For example, using 250pf capacitors to match a 10 ohm load on 4MHz
and using the AUTOTUNE feature, the loss is 20%.  Now if you manually
adjust the tuner so the sum of the capacitance values is 250pf (a
reasonable approximation of a differential capacitor) I got around 29% loss.
You'll see more difference on 160m and less on 40m.

Doesn't mean the tuner won't match the load, just that it may not be
as efficient.  If you don't stress your tuner much on the lower bands
with high power and/or low impedance loads, the convenience may be
worthwhile.  It's a personal decision.
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K0CWO
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Posts: 416




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« Reply #6 on: September 01, 2007, 12:43:11 AM »

Hello all.

Antenna tuners.  What an interesting subject. Differential T versus conventional T type tuner?  Good question. I am not smart enough to give an answer.  Theoretically, specs will show one to be more efficient than another.  I would be "smart" to say: "It all depends on what antenna is part of the system".

I am a fan of the standard doublet.  I have used differential T, conventional T, link coupled, balanced L, and conventional L tuners with a variety of baluns on the input and output side of some of the types.

Given a reasonable antenna, resonant or not, I have worked regular nets (mainly on 160, 75, and 40) interchanging the different types during the duration of the net or round table rag chew.  On the receive end, nobody ever noticed that I changed from the theoretical efficient tuner to the theoretical "less" efficient tuner.

I think that commercially made tuners are devices that attempt to match a wide variety of antennas to a wide range of frequencies.  In my situation hard to do with a “low” 230 foot doublet from 160 through 10 running 1.5 KW without arcing and sparking Smiley.  I am looking for a tuner (coupler) that does it all efficiently.  I’m afraid that is not going to happen.

I think it is safe to say that any matching or coupling device will have its advantages and disadvantages depending on the antenna, frequency range, and power we plan on using.

At the end of the day, after discussing apples and oranges, we end up using what works best, given our particular operating environment.

Long story short, buy or build a matching device that suits your needs.  I question amateurs who spend $3000 on a transceiver and $50 on a tuner.  My operating experience shows that $50 transceiver works better on $3000 tuner than the other way around.  I’m not implying one should spend $3000 on coupling systems. For most of us, paying more attention to this part of our antenna system would be money well spent.

73,  B.J.


   
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SSB
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« Reply #7 on: September 01, 2007, 04:15:38 AM »

Consider this.  Take a T tuner, put a timing belt and pulley between the caps at differencial position, and you have a DT tuner which can easily be put back.

Alex....
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