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Author Topic: Amplifier output and antenna tuner issues  (Read 12532 times)
WA9UAA
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« on: September 11, 2012, 04:55:35 PM »

Good Day,
I am running a THP 1.2 Kfx The amplifier is fine into a dummy load. Here is the issue, I run tuned feeders, 18 ga ladder line ~~ 137 ft., via a Palstar AT2K and a DX Engineering 1:1 balun on the output. The balun is connected to the tuner by about 6" of RG-8 size cable. What I find is that even with the tuner showing a 1:1 match (also on my MFJ 259B) the amplifier output is reduced by 200 watts or so, it varies from band to band, as read on the tuner metering. If the antenna is resonant at that frequency the power output is higher. This condition is most noticeable on 80M and 40M. I have pruned the antennas and just gotten the resonant point in the 80M band at 3.540. The VSWR being above 8:1 at the top end of the band, I'd like to shift the resonant point to the center of the band or a bit below.

So, I have two issues, can I shorten the ladder line a bit to raise to resonant point rather than continue to trim, (shorten) the antenna? Why is the power reduced when the amplifier should be seeing 50 ohms (J0)?

Thanks es 73,
Rob WA9UAA
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WX7G
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« Reply #1 on: September 11, 2012, 05:35:34 PM »

What does the THP 1.2 Kfx report for power into the dummy load and into the antenna (fwd pwr minus reflected pwr)?

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WA9UAA
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« Reply #2 on: September 11, 2012, 06:52:11 PM »

Thanks for the question, The 1.2k fx will put out 650 to 700 watts through the tuner tuned (1:1) to the dummy load. Depends upon how hard I drive it. When the output is low, as with the antenna system, additional drive does not improve the situation. My dummy load is a little light so I can't drive it too hard or to long.
73,
Rob
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WA9UAA
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« Reply #3 on: September 12, 2012, 05:02:47 AM »

Additional info.
All readings through the tuner matched to 1:1

Rig at 3550 Khz................................................................3950 Khz
Output to DL 83W maximum.............................................82W to Ant.
Antenna  82W to DL..........................................................80W to Ant.
Amplifier 600W to DL.......................................................480W to Ant.

Amplifier
Meter      580W to DL........................................................590W to Ant.

Metering issues ? I have seen this on another tuner but with a different antenna.
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KC4MOP
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« Reply #4 on: September 12, 2012, 08:57:08 AM »

The 1:1 balun may not be a good choice and providing a questionable load to the amp.
What is the distance between the wires for your Ladder line? 6 inches?? You probably have between 300-600 ohms on the ladder line.
Your tuner does not offer balanced lines output.
The ones that do, usually have a 4:1 balun to match the tuner's internal circuit to ladder line.
Window line is around 450 ohms dry.
The good ole stuff mentioned above is more stable wet/dry.

From the manual for your Palstar tuner...........................
Balanced Output 4:1 current type balun EXTERNAL-OPTIONAL

Fred
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WA9UAA
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« Reply #5 on: September 12, 2012, 11:12:18 AM »

Hi Fred,
Yes I am running window line. The antennas are 80M and 40M dipoles that show in band resonance via the 1:1 balun though the 80 meter resonant point could be a little higher. It's resonant at 3.540 or so. I decided to go with resonance on these two antennas and let the chips fall where they may on the higher frequencies. One antenna question I have is whether or not I could trim the ladder line to bring the 80M antenna closer to the center of the band? I took 5 feet off each side and that brought it up 140 Khz. Cut by the book it should have been resonant at 3750. All this to provide a more reasonable match for the tuner. The amplifier question is why do I get 600W output at the low end of the band and only (sic) 480W at 3950 where the tuner shows a 1:1 match and the uncorrected VSWR is ~~ 8:1?
73,
Rob WA9UAA
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W8JI
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« Reply #6 on: September 12, 2012, 12:51:14 PM »

4:1 baluns have less impedance and balancing range, for the same cost and size, than a 1:1.
1:1 is the preferred balun by far for use with a tuner. Besides, if the balun was somehow not allowing a tuner match, the SWR at the rig and amp would be high, and not tune down with the tuner.

Where are your meters? You don't have a meter after the tuner do you?

If the meter on the amplifier side of the tuner shows a low SWR, the power from the amplifier should be exactly the same as a dummy load. What is after the tuner for a load makes no difference at all so long as the tuner input is matched.

If the tuner is adjusted to a good match and the THP is low on power only into the antenna, you have one of the following:

1.) The amplifier is unstable and oscillating into the high-Q load from the tuner. This can happen with solid state amplifiers.

2.) There is a feeder balance, feeder routing, or station wiring problem causing troublesome levels of RF to get back into some piece of equipment that is sensitive to external RF. Maybe a power supply, maybe the radio.

3.) A meter is on the wrong side of the tuner, on the antenna side.

4.) The amplifier has no harmonic filtering. Since you have a ham-band amp, it should not have this issue unless something is wrong inside.

This is something special or unusual. None of what you are saying makes any sense. You should be able to add or remove modest amounts of length from the feedline or antenna and it should have absolutely no effect on the system. All that should be necessary is a slight retouch of tuner settings.

The changes you see with antenna length changes should not occur with a tuner in line. Neither should the power level changes.


73 Tom
« Last Edit: September 12, 2012, 12:53:14 PM by W8JI » Logged
KC4MOP
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« Reply #7 on: September 12, 2012, 03:28:56 PM »

Trimming the actual antenna length will change tuning. We are assuming now that this is a non-resonant length of wire (137feet) fed by window line.
This part of your original post is confusing. Do you have a resonant antenna for 40M and you are trying to tune to 80M?

A meter on the output of his tuner will be extremely inaccurate even with a 1:1 balun, as there is not 50 ohms on the output side of the tuner. His explanation of the antenna is not clear to me.

The tuner satisfies the rig/amp. What's going on the output side is not measurable.

Your amp is a no-tune solid state.Huh

The MFJ 259 is not going to show the bad stuff that may be driving that solid state amp crazy. The MFJ269 shows the reactance Xs.
This should be interesting.

fred
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W8JI
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« Reply #8 on: September 13, 2012, 02:01:31 PM »

Trimming the actual antenna length will change tuning. We are assuming now that this is a non-resonant length of wire (137feet) fed by window line.

People, from the start of this, seem to have missed or ignored the fact he says he has a tuner in line.

Changing antenna length or feeder length will change tuning on the TUNER he says he is using...... but antenna and feedline  changes will NOT change tuning on the amplifier unless he has a system wiring problem or the tuner is not matching.

As I read this he seems to be saying when he changes the antenna length or feeder length a little bit it changes the amplifier, even though the tuner is adjusted for 1:1. We all know, or should know, that is impossible without a problem in the metering or equipment, or a mistake in how he has things connected.

If the amplifier REALLY is seeing a 1:1 from the tuner, it doesn't matter if the antenna is a bed spring, an old wet noodle, or a mile high 90 element Yagi. The amplifier sees a 1:1, it sees a 1:1.

The fact he keeps saying the amplifier is sensitive to antenna length indictes a problem not related to the antenna.

73 Tom

 
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KC4MOP
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« Reply #9 on: September 13, 2012, 05:25:25 PM »

Trimming the actual antenna length will change tuning. We are assuming now that this is a non-resonant length of wire (137feet) fed by window line.

People, from the start of this, seem to have missed or ignored the fact he says he has a tuner in line.

Changing antenna length or feeder length will change tuning on the TUNER he says he is using...... but antenna and feedline  changes will NOT change tuning on the amplifier unless he has a system wiring problem or the tuner is not matching.

As I read this he seems to be saying when he changes the antenna length or feeder length a little bit it changes the amplifier, even though the tuner is adjusted for 1:1. We all know, or should know, that is impossible without a problem in the metering or equipment, or a mistake in how he has things connected.

If the amplifier REALLY is seeing a 1:1 from the tuner, it doesn't matter if the antenna is a bed spring, an old wet noodle, or a mile high 90 element Yagi. The amplifier sees a 1:1, it sees a 1:1.

The fact he keeps saying the amplifier is sensitive to antenna length indictes a problem not related to the antenna.

73 Tom

 
Hi Tom I keep reading it over and over also. The tuner tells me that the antenna is not resonant for the band or frequency he is attempting to use.
Also he has not replied, to my googling his amp, that it is a no tune SS amplifer. If reactances are really screwy the amplifier will respond with different output readings.
Is this really the OP's amp?Huh?
http://www.tokyohypower.com/hl-1_2kfx.html


I quoted, in one of my replies, from the manufacturer of his tuner, that if using a balanced line, Window line or open ladder, whatever spacing between conductors, that a 4:1 balun was recommended.
PLS read Pg 6
http://www.palstar.com/manual_at2k.pdf

I have a 4:1 balun in my Dentron 3KA tuner (balanced out) and handles a 240' long dipole with 120 foot long OWL with no problems from 160-15M.
My Ameritron AL1500 went wild one day having a fit on a freq I was trying to use and my MFJ269 read almost 1:1. I took a shot at re-tuning and got another dip that wasn't 1:1, more like 1.7:1 and the amp was perfectly happy to make 2500 watts.

We'll see one day.
Hopefully the OP will return with more info so that we can help him figure this out.

Fred
« Last Edit: September 13, 2012, 05:31:47 PM by KC4MOP » Logged
WA9UAA
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« Reply #10 on: September 13, 2012, 06:08:50 PM »

Hi Tom and all,
Thanks for weighing in here. Yes there is a tuner in line between the amp and feed line. The length of ladder line to the antenna is 140 - 137 ft. No meters on the window line. Cheesy There are two issues here, one is the power level (TPO) changing even though the the amplifier is tuned to a 1:1 match.  The other is the fact that I seem to be having to trim large amounts of wire to achieve resonance where I want it frequency wise. The dipole was cut by the book for the middle of the band and showed resonance about 140 Khz below the band. After cutting 4 feet off each  end of the dipole and using a foot of wire for the wrap on each end I found resonance at ~~3540 Khz or so. It's raining here and resonance is again below the band edge.  Angry  I started checking the antenna and tuner using my MFJ 259B and have been setting the tuner up to pretty much 50 Ohms (J0) with as much capacitance as possible. I have seen the low power thing in the paging industry on PAs and later saw the PA was in oscillation, not often, but it happened. One thing I can try is to see if I can find a better match on the high end of 75M with more capacitance on the output of the tuner.   Shocked I just had an A-HA moment, I left out what may be an important detail. Having a ladder line fed antenna, it is switched to ground outside the shack with a large DPDT knife switch. In my interest in draining charges from the antenna system I installed a pair of Dale HL-50D6z 100 K Ohm 50 watt wire wound resistors from the high side of the ground switch to ground through about 5 feet of inch wide strap to the ground system.  Embarrassed I seem to remember a little extra capacitance adds to the stability of any system. I going to stop here and wait for feed back on the power resistors, they are always connected between the feed line and ground.
73,
Rob WA9UAA

p.s. Hi Fred Yes, it is a THP 1.2 Kfx. I am actually trying to make the antenna resonant mid band on 75-80 meters. There is a 40M dipole connected in parallel with the 80m antenna though I don't seem to have as much if any problem on 40 meters. The 1:1 current balun is correct in this instance as the antenna should show 50 Ohms on 80M. I am suspecting the 100K Ohm Wire wound resistors that are acting as current drains. (see above)

ETA. I just took the resistors out of the circuit and did a quick tune up on each end of the band. On the low end of the band ~~3550 I show a bit over 550 Watts at max drive. At the high end of the band above 3950 I see a bit over 400 watts out.  Huh

ETA 2 Tuning into the dummy load at the low end of the band I get 600W out and 550W at the high end of the band.  I guess the resistors can go back in later though I'll wait until the line drys out tomorrow.
« Last Edit: September 13, 2012, 06:53:20 PM by WA9UAA » Logged
W8JI
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« Reply #11 on: September 13, 2012, 07:14:09 PM »

Hi Tom and all,
Thanks for weighing in here. Yes there is a tuner in line between the amp and feed line. The length of ladder line to the antenna is 140 - 137 ft. No meters on the window line. Cheesy There are two issues here, one is the power level (TPO) changing even though the the amplifier is tuned to a 1:1 match.  

Here is what I said earlier:
If the meter on the amplifier side of the tuner shows a low SWR, the power from the amplifier should be exactly the same as a dummy load. What is after the tuner for a load makes no difference at all so long as the tuner input is matched.

If the tuner is adjusted to a good match and the THP is low on power only into the antenna, you have one of the following:

1.) The amplifier is unstable and oscillating into the high-Q load from the tuner. This can happen with solid state amplifiers.

2.) There is a feeder balance, feeder routing, or station wiring problem causing troublesome levels of RF to get back into some piece of equipment that is sensitive to external RF. Maybe a power supply, maybe the radio.

3.) A meter is on the wrong side of the tuner, on the antenna side.

4.) The amplifier has no harmonic filtering. Since you have a ham-band amp, it should not have this issue unless something is wrong inside.
 

Rob said:
Quote
The other is the fact that I seem to be having to trim large amounts of wire to achieve resonance where I want it frequency wise. The dipole was cut by the book for the middle of the band and showed resonance about 140 Khz below the band. After cutting 4 feet off each  end of the dipole and using a foot of wire for the wrap on each end I found resonance at ~~3540 Khz or so. It's raining here and resonance is again below the band edge.  Angry  I started checking the antenna and tuner using my MFJ 259B and have been setting the tuner up to pretty much 50 Ohms (J0) with as much capacitance as possible.


I don't know why you are worrying about resonance, or how you are measuring it. You have an antenna tuner and ladder line. An antenna tuner with ladder line makes resonance, however you are measuring it, a moot point. 

Quote
I have seen the low power thing in the paging industry on PAs and later saw the PA was in oscillation, not often, but it happened. One thing I can try is to see if I can find a better match on the high end of 75M with more capacitance on the output of the tuner.   Shocked I just had an A-HA moment, I left out what may be an important detail. Having a ladder line fed antenna, it is switched to ground outside the shack with a large DPDT knife switch. In my interest in draining charges from the antenna system I installed a pair of Dale HL-50D6z 100 K Ohm 50 watt wire wound resistors from the high side of the ground switch to ground through about 5 feet of inch wide strap to the ground system.  Embarrassed I seem to remember a little extra capacitance adds to the stability of any system. I going to stop here and wait for feed back on the power resistors, they are always connected between the feed line and ground.


If you have a match on the input of the tuner, and the amplifier does not work like it does into a dummy load, you have one of the problems I mentioned earlier. It cannot be capacitor settings or anything else.

You might mess around and get it going, but you won't actually be fixing the real problem.

If the tuner is adjusted to a 1:1 SWR and the amplifier is not at full power, it has to be a problem on the radio side of the tuner.

73 Tom
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WA9UAA
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« Reply #12 on: September 13, 2012, 08:16:04 PM »

Hi Tom,
My reference to resonance is to say that the Amp is seeing a resistive load. I have been using a MFJ 259B, it seems to agree with the tuner on 1:1 match points. The line between the tuner and amplifier is a W2DU balun with my intent of keeping any R.F. on the outside of the tuner away from the amp. I don't have the tuner grounded to the system outside as I can't get past the idea of the chassis' on my gear lighting up to what ever charge might show up on the ground system. The ground is connected back to the house ground through a system of ground rods so it may be OK.

Quote W8JI,"I don't know why you are worrying about resonance, or how you are measuring it. You have an antenna tuner and ladder line. An antenna tuner with ladder line makes resonance, however you are measuring it, a moot point."  end quote

I had been operating under the perhaps mistaken notion that having the antenna at resonance some how made it easier for the tuner to pass the full power from the amplifier to the antenna as this seemed to reflect (pun intended) what I was seeing happen. Though for what now seem to be the wrong reasons. Shocked

I'd hope it is not the Amp, I probably do have some imbalance in the antenna system as I have a tree branch near one side the 80M dipole. Having just redone the antenna system, I did not have any tree branches near the antenna before.

I'd need to be reassured about grounding the station to the same place as the lightning ground and as you say it won't fix a balance problem related to the tree branch or not. I just have to get to the tree branch. Grin
I have not heard any RF in my audio but have no idea where the rig gets it's sample of audio for monitoring.

Considering RF in the shack as a source of the problem, the ladder line does not make a 'clean' path away from the balun. It's too close to the chassis. Conservatively speaking, running this antenna from 80m to 6M, how long can the coax between the tuner and the balun be, if the coax is well assembled, and not impact the performance?

Looking at your other points, I can put another SWR meter between the rig and amplifier to see if the rig or supply is folding back.

Thanks again Tom I have several things to look at, the length of coax between the balun and tuner is something I'll really need advice on. Is there any reason to believe that the longer the coax between the tuner and balun seems to decrease the amount of real 'R' seen by the tuner?
Time to back out of here before I become more incoherent.
73
Rob WA9UAA
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KE6EE
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« Reply #13 on: September 13, 2012, 09:03:36 PM »


Considering RF in the shack as a source of the problem...how long can the coax between the tuner and the balun be, if the coax is well assembled, and not impact the performance?

I have several things to look at, the length of coax between the balun and tuner is something I'll really need advice on. Is there any reason to believe that the longer the coax between the tuner and balun seems to decrease the amount of real 'R' seen by the tuner?
Time to back out of here before I become more incoherent.
73
Rob WA9UAA


I think your problem may be the length of coax between balun and tuner. I recall some (authoritative) advice to the effect that the coax length should be no more than about 15 ft.

I had a problem not unlike yours. I have a THP HL450B (400W max) amp going to a high quality (Palstar) tuner, then to a 4:1 balun (Array Solutions) through about 14 ft. of coax, then to a 100 ft. dipole fed by about 60 ft. of window line. Tunes up fine on 80 through 10. Seems to work pretty well.

When I first started using the amp, it would shut down on several bands even though the tuner was producing a low SWR. RF was getting to the amp. I had been using a 1:1 balun (DX Engineering) with about 25 ft. of coax running to it from the tuner. I had had no problems using my transceiver (an Elecraft K2) at 100W on all bands with the same setup. The THC amps are sensitive to random RF quite evidently.

To reduce/eliminate the RF problem in the amp, I shortened the coax by about 10 ft., adding about 10 ft. to the window line. I also put some snap-on ferrites on the coax at the tuner output.

Regarding which balun to use, both the 1:1 and the 4:1 seem to work well on most bands. There are varying opinions as to which is the better and, of course, other aspects of their design than their impedance ratios are relevant. In my experience the 4:1 produces a lower SWR on the bands I use than the 1:1 so I am using it.
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W8JI
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« Reply #14 on: September 14, 2012, 02:48:36 AM »

I think your problem may be the length of coax between balun and tuner. I recall some (authoritative) advice to the effect that the coax length should be no more than about 15 ft.

I had a problem not unlike yours. I have a THP HL450B (400W max) amp going to a high quality (Palstar) tuner, then to a 4:1 balun (Array Solutions) through about 14 ft. of coax, then to a 100 ft. dipole fed by about 60 ft. of window line. Tunes up fine on 80 through 10. Seems to work pretty well.

When I first started using the amp, it would shut down on several bands even though the tuner was producing a low SWR. RF was getting to the amp. I had been using a 1:1 balun (DX Engineering) with about 25 ft. of coax running to it from the tuner. I had had no problems using my transceiver (an Elecraft K2) at 100W on all bands with the same setup. The THC amps are sensitive to random RF quite evidently.

If that is the case, they need to fix the amplifiers! One of the most RF-immune pieces of gear in the world should be the amplifier. If an amplifier is sensitive to common mode RF problems, it very likely also outputs unwanted emissions.

Quote
To reduce/eliminate the RF problem in the amp, I shortened the coax by about 10 ft., adding about 10 ft. to the window line. I also put some snap-on ferrites on the coax at the tuner output.


Externally remoting a balun can cause issues. Baluns and tuners really belong right next to each other. I understand some people cannot run the ladder line in, and in that case, there should be a legally wired entrance ground panel for the coax.

Beads are a band-aid for other problems.

http://www.w8ji.com/ground_systems.htm
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