Print

[KT0DD]

Hello, I have a Ten Tec 238C tuner (Modified L-network) and a Palstar AT2KD (Differential) tuner. I mainly operate 75M to 15M. With my antenna system which is coax fed (an 80/40m dipole, and a 20M dipole) I rarely have to match over a 6 to 1 max mismatch at band edges (or on 17 meters). I mainly run a tuner for increasing the useable bandwidth of an antenna that doesn't quite cover the entire band (80-75M etc.) and to protect my linear amplifier at 700 watts. I am wondering how much difference in loss there is between the two tuners if the mismatch is the same? If I'm trying to match a 5 to 1 mismatch, will the loss difference between the Modified L- Network 238C and the (SINGLE) capacitor AT2KD be significant or hardly noticeable? I plan on selling the Ten Tec 238C since Ten Tec no longer sells or supports this tuner unless the efficiency of it is so much better that it's worth keeping. The 2KW power meter position quit working on the Ten Tec but the 200W position still reads ok. Rather than having it repaired at a 3rd party shop and paying repair fees and the shipping, I may just sell it to help fund the purchase of another AT2KD.  Any constructive replies are appreciated.

[K1VSK]

With that high a mismatch on your coax, the loss in a tuner is the last thing I’d be worried about.

[KT0DD]

With that high a mismatch on your coax, the loss in a tuner is the last thing I’d be worried about.

Most of the time the mismatch is not nearly that high. That is a worst-case scenario. I don't need a tuner for the part of the bands where the antennas are resonant or close. No antenna I know of gives a perfect 50-52 ohm 1:1 SWR across the entire band on several ham bands I use like 80-75 meters. If you know of one, please let me know! I rent and don't have the real estate for a resonant antenna for each band or resonant on every section of each band. Many hams like me have to compromise. Your comment did not provide any useful info but thank you anyway.   

[AE0Q]

If I'm trying to match a 5 to 1 mismatch, will the loss difference between the Modified L- Network 238C and the (SINGLE) capacitor AT2KD be significant or hardly noticeable?

Well, you could measure the loss of each and see.

But the Palstar is a T-match circuit, they are notorious for showing a good match at many combinations of C and L settings.  Some combinations are very inefficient with power being lost in the C and L circuit.  The operator has to be sure to use the one with the least inductance being used.

The L-match circuit only shows a good match at one combination of settings.  In theory there is no combination that shows a good match that is also highly inefficient.

I have melted the coil in a T-match tuner rated for 300w with a 100w transmitter, accidentally, of course.  I have never damaged my 125w rated L-match tuners with 100w and crappy antennas.

Glenn AE0Q

[KT0DD]

If I'm trying to match a 5 to 1 mismatch, will the loss difference between the Modified L- Network 238C and the (SINGLE) capacitor AT2KD be significant or hardly noticeable?

Well, you could measure the loss of each and see.

But the Palstar is a T-match circuit, they are notorious for showing a good match at many combinations of C and L settings.  Some combinations are very inefficient with power being lost in the C and L circuit.  The operator has to be sure to use the one with the least inductance being used.

The L-match circuit only shows a good match at one combination of settings.  In theory there is no combination that shows a good match that is also highly inefficient.

I have melted the coil in a T-match tuner rated for 300w with a 100w transmitter, accidentally, of course.  I have never damaged my 125w rated L-match tuners with 100w and crappy antennas.

Glenn AE0Q

I found this a DJ0IP's tuner site:
"At minimum SWR, the Differential-T is always operating at its most efficient tuning position."

I'll look inside the 238C tomorrow and see if I can find the damaged component for the 2KW section of the metering circuit. If I can fix it myself, I may keep it.

Todd - KT0DD

[WB6BYU]

That's a difficult question.

First, remember that tuners match impedance, not SWR.

With a 5 : 1 SWR, you might have an impedance of 10 ohms,
or 250 ohms, or 50 - j100 ohms, or some other value.  The
tuner efficiency will depend on the exact impedance:  some
tuners may be better at matching higher impedances than
lower ones, or vice versa.

What I did when I did a similar analysis was to put an RF
indicator (an SWR meter, power meter, or RF voltmeter
will work) on the output of the tuner and compare the
readings for each tuner.  That allows you to compare the
actual efficiency with your specific antenna.  In my case,
results varied by band, and were quite enlightening.

That's likely to give you a more realistic evaluation of
the difference in efficiency than any analysis on paper.

[N7EKU]

Hi,

I'd keep the Ten-Tec as it's a very good tuner.  Not much to go wrong with the metering circuit.  If the lower power ones work, the only things it could be on the 2kW circuit is the calibrating trimmer pot or switch.  I could just be that the trim pot contact is dirty.  Those can lose contact after sitting in one place for ages.  Mark the location and put a bit of Faderlube on it.

73

[VR2AX]

The loss is the inevitable result of the matching process which is being performed. 'How much loss' depends on the circuit design (L, T, Pi or other), and the component values and Q. Most of the loss results from heat caused by high circulating rf current in the inductor.

Back in the 90s, an ARRL book that I got came with a super little program, which allowed one to calculate matching circuit loss (as well as individual component losses and peak rf current and voltage stresses). Came on a floppy disk and ran on DOS. Wish I still had that program, or could even remember its name.

I had a MFJ T match supposedly rated at 3KW, which I used to match a 160 quarter wave vertical. Lots of tripping of my ETO amp. Lifted the MFJ cover, key down for 30-60 sec, the coil turned red, then orange, then..flash..solder melted plus arcing!

Bought a new Ten Tea 238C. No problems. Very docile. Not as versatile, did not match everything, however none of the previous problems. Sold it around 18 years ago to another Hong Kong ham due to a QTH move...he contacted me a year or so back to say the tuner was still performing great.

[G4AON]

February 2003 QST has a review of the 238A (L match) and the Palstar AT1500CV (T match), plus others.

The AT2KD is reviewed in July 2013 QST, it has low loss but also a limited tuning range.

Both the AT1500 and 238A look OK to me with regard to loss in the review, although the Ten Tec has a wider matching range.

I have an AT1500CV and use it with an external 1:1 home wound “tuner” ferrite balun on a doublet. It works well.

Check the reviews for more info, assuming you are an ARRL member.

73 Dave

[AE5X]

If you have a nanoVNA you can measure the insertion loss of each tuner at any specific frequency:

https://ae5x.blogspot.com/2022/10/tuning-characteristics-of-atu-10-and.html

Tune your first antenna tuner, with antenna of choice connected, for a good match on your freq-of interest.
Disconnect it.
Repeat with 2nd tuner.
Disconnect it.

Feed the output port of the nanoVNA to the input of one tuner, then the input port of the VNA to the 'Antenna' connector of the tuner. Set up VNA to read S21 value. That's the loss through that tuner.
Repeat with next tuner.

Then do the same on other bands.

[K1VSK]

With that high a mismatch on your coax, the loss in a tuner is the last thing I’d be worried about.

Most of the time the mismatch is not nearly that high. That is a worst-case scenario. I don't need a tuner for the part of the bands where the antennas are resonant or close. No antenna I know of gives a perfect 50-52 ohm 1:1 SWR across the entire band on several ham bands I use like 80-75 meters. If you know of one, please let me know! I rent and don't have the real estate for a resonant antenna for each band or resonant on every section of each band. Many hams like me have to compromise. Your comment did not provide any useful info but thank you anyway.

Clearly, no antenna is infinitely broadbanded. When used to match impedance, the inherent loss of the tuner required to do so is far less than that on your coax making your concern trivial. Sorry you didn’t like the answer but rather than worry about trivial things, use open wire feed line if you want to actually minimize loss.

[WB6BYU]

...When used to match impedance, the inherent loss of the tuner required to do so is far less than that on your coax making your concern trivial...

That may be a dangerous generalization, as those who have
had the coil melt in their tuner when using balanced line
can attest to.

Each case (and each band) needs to be considered individually.
If the SWR is relatively low (say, less than 5 : 1 at the
antenna) then coax may not be a bad choice.  On the other
hand, with a long length of coax the losses may be high
enough that you never see an SWR over 5 : 1 even with the
far end of the cable open or shorted.

This is complicated by the fact that the losses for open wire
line published by ARRL for many years were too low - as if
they used the resistance of just one copper wire  rather than
two in their calculations.  And lines made of stranded
CopperWeld have higher losses, especially on the lower bands,
than any such calculations might suggest.

It also varies greatly with the type of tuner used, etc.
I measured more than a 3 dB difference among various
tuners when matching my doublet.


Fortunately we have tools that help us to calculate the
losses in such a system, including AC6LA's TLDetails
(runs on a PC), and Owen Duffy's Transmission Line
Loss Calculator (runs in a browser window).

Using such tools will help to understand the possible
losses in an antenna configuration to see how suitable
it is for each situation.

[W1VT]

An inexpensive IR cooking thermometer can be used to measure temperature rise in different parts of the the antenna system.
If everything is staying cool it is likely that the system is efficient.
When I designed my 80/160 system I had issues with choke baluns heating up, so I experimented with different configurations to eliminate that.
If heating is really bad you may see SWR drift.  You tune for a 1:1 SWR but if you transmit the SWR starts to rise.

Zak W1VT

[N2SR]

simple solution:  use a resonant antenna and eliminate the tuner

[WB6BYU]

simple solution:  use a resonant antenna and eliminate the tuner

Even resonant antennas may need an antenna tuner.

Lots of resonant antennas don’t have a 50 ohm
feedpoint impedance.

And, as at least partially the case here, the bandwidth
may not cover the whole band even if the antenna is
resonant in the band.