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Author Topic: High Power Remote Tuner?  (Read 4030 times)
KF6VB
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Posts: 19




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« on: October 16, 2012, 09:04:42 AM »

Hello,

    In my endless search for ham radio perfection, I am thinking about remote tuning.  The station antenna is a 5BTV ground mounted up the hill behind the house.  It has approximately 50 radials ( actually, I lost count Smiley.   I have made many many trips up and down that hill ( oh my aching knees ) setting up and tuning that antenna, and it works pretty well.  I use a Heath SA2040 in the shack to touch it up.  Sure would be nice to have some sort of tuner out there with the antenna, and not separated from it by a hundred fifty feet of coax.

   Such a tuner would have to be either automatic or remote controlled.  It would have to tolerate the full 1.5kW.  Looking at commercial offerings, I see the MFJ998RT - which seems to be a bit of an abortion.  They took their desktop autotuner and stuck it in a weather box.  So there is no remote control available at all.  The only control available in the shack is turning
the power on and off, and piping RF up to it.  Under the hood there is an interface consisting of a couple of buttons and a small LCD display.  So any setup has to be done at the antenna.   I suppose it wouldn't be TOO hard to make something with a little video camera ( to watch the LCD ) and a couple of wires hooked to the pushbuttons.

   Or I guess I could just build something.  I'm reasonably good at electronics and firmware programming.....  Not sure if I want to work quite that hard though Smiley.  Maybe put the SA2040 in a big box with three screwdriver motors? 

                                                   - Jerry, KF6VB
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WX7G
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« Reply #1 on: October 16, 2012, 09:49:54 AM »

Whether a remote tuner will help much depends on the VSWR, the type of coax and how much line loss you can tolerate.

1. What is the VSWR by band?
2. What type of coax?
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G3TXQ
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« Reply #2 on: October 16, 2012, 11:12:04 AM »

http://www.hamware.de/hardware/tuner615U/beschreibung%20at-615U-d.pdf

Steve G3TXQ
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W5WSS
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« Reply #3 on: October 16, 2012, 11:23:12 AM »

The Trap 5btv provides provision within the very nice design to achieve a match and efforts to tune the antenna pay dividends.

Remotely locating the auto tuner for this system is expensive and unless there is some problem tuning it within the 5 design bands spend the money elsewhere.

what would pose such a problem to need an auto tuner for an tuned trap vertical?

Perhaps a different vertical or antenna would be better served by a remote auto tuner

73 Smiley
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AA4PB
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« Reply #4 on: October 16, 2012, 11:36:48 AM »

If you are thinking of trying to use the tuner to force the trapped vertical to operate far from resonance while running high power - DON'T!  You could wind up smoking a trap. When operated near resonance the vertical should be a pretty good match for coax without the use of a tuner.
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K5KNE
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« Reply #5 on: October 16, 2012, 12:38:21 PM »

It sounds like you are going to a lot of trouble to make that antenna work.  I don't care for ground mounted verticals. I used to have one and tried a lot of things to make it perform like I wanted it to. A ham friend once told me "verticals radiate equally pooly in all directions."

I don't know how much room you have or if you can get a pole up to get some height, but I would go with conventional inverted vees, G5RVs or even long wires and see if you like them.

You don't need high power to make a lot of contacts if you have good antennas. 100 watts is plenty.

Good Luck  Walter K5KNE



















I concluded that the radiation angle was so differnet than dipoles and other conventional antennas - I was the weak kid on the block. 

You say you plan to be capable of 1.5 KW!  Why? I use only 100 watts now and got rid of my linear. A good antenna is far more important than high power - you do have to hear them to talk to them. It is good that you are trying to improve the antenna and I encourage you to keep trying different things. Some of the suggestions above are good - escpecially trying to make a poor antenna work good with high power. You might even try a long wire up the hill and see how that works. I use inverted vees for 75 and 40 and a triband beam for 20, 15 and 10.

Good Luck.  Walter K5KNE 
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KC4MOP
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« Reply #6 on: October 17, 2012, 03:23:44 AM »

If you are thinking of trying to use the tuner to force the trapped vertical to operate far from resonance while running high power - DON'T!  You could wind up smoking a trap. When operated near resonance the vertical should be a pretty good match for coax without the use of a tuner.

I never realized that.
I know the feeling being restricted to just little chunks of a band on a trapped or any vertical, for that matter.
Do you have room for a dipole? And how high can you string it up?? Fed by open ladder and a tuner in the shack can give 160-10M....Really 160-40 is a better focus for a dipole. Yagis are good for 20-10M.
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K3VAT
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« Reply #7 on: October 17, 2012, 04:24:27 AM »

If you are thinking of trying to use the tuner to force the trapped vertical to operate far from resonance while running high power - DON'T!  You could wind up smoking a trap. When operated near resonance the vertical should be a pretty good match for coax without the use of a tuner.  

Actually, isn't it the other way around?!  The trap's maximize loss occurs at the resonant frequency of the trap, not at some frequency above or below.  Given two traps: one at, say, 7.100 and one at 6.500, which trap has the greater loss at 7.075; which could go up in smoke at 7.125?  I believe that most trap failures, other than physical-related issues (such as incorrect form-factor size/material, wire type/spacing, and the like) occur with the extended transmission at power levels more than the trap was designed for and/or at frequencies close to the resonant frequency of the trap.

For a more cogent explanation please see: http://w8ji.com/traps.htm.  

73, Rich, K3VAT
« Last Edit: October 17, 2012, 04:43:34 AM by K3VAT » Logged
K5USF
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Posts: 83




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« Reply #8 on: October 17, 2012, 07:18:54 AM »

I have 3 fiberglass verticals: 43, 33 and 18.  Depending on the wind and bands. I built a high power remote ATU.  It is a T-Network with two 4.4KV air variable caps and one 28uH roller inductor.  I control it remotely from the shack.  The antenna connects to the ATU, then goes to a 1:1 current balun and from there I have 70 feet of 1/2 inch hardline.  I don't have options for a beam or tree strung dipoles.  I use this setup from 160m (with a based loaded coil and shunt coil) up to 10m.  Rarely use 160m because the antenna just doesn't cut it on that band.  Bottom-line, I have been using this ATU for 2 years: -5F up to 110F, rain, snow, dust storms.  It has NEVER failed me.  Now, the solid state tuners have all broke (with the amp off!).  So, I dumped them and built my own electro-mechanical ATU.  Best thing I ever did!  Good luck in your endeavors.   73s, Jim

PS.  I know the R and X values for all of my antennas, so I know where to run power and where not too.  Just because one has a high power tuner, does not necessarily mean you can run high power across all the bands.
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WX7G
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« Reply #9 on: October 17, 2012, 07:27:21 AM »

I wouldn't worry about smoking a 5BTV by running it on a WARC band at high power. It's an inexpensive antenna.
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W8JI
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« Reply #10 on: October 17, 2012, 07:38:11 AM »

I never realized that.
I know the feeling being restricted to just little chunks of a band on a trapped or any vertical, for that matter.
Do you have room for a dipole? And how high can you string it up?? Fed by open ladder and a tuner in the shack can give 160-10M....Really 160-40 is a better focus for a dipole. Yagis are good for 20-10M.

Interesting comments.

I think that is a myth for most traps, which commonly are parallel tuned.

The series-tuned traps in a Butternut vertical are an exception. A series-tuned trap is subject to damage because a capacitor is in series with the element and an inductor. Forcing current would result in I*X voltage drop across the capacitor. Make no mistake about it, the series circuit in a Butternut is a form of trap, and despite marketing claims has loss.  The trap is just series resonant instead of parallel resonant.


With parallel tuned trap, like most standard traps, the idea forcing current out of band can cause trap failure strongly appears to be false. Peak voltage and peak circulating current occurs when the trap is "trapping". If the trap can handle 1500 watts near resonance, it can certainly handle well over that power out-of-resonance.

Let me give an example that I think might turn the light on. When running a standard trap triband Yagi on 20 meters, like a TA33 SR, the antenna will handle 3-4 kW easily. This is because the traps are not "trapping". There is very low voltage and almost no circulating currents in the traps. They only carry normal common mode antenna currents.  Take that same Yagi on 15 meters, especially exactly at trap resonance, and trap loss peaks. The trap has highest voltage and highest current at the SAME time, because it is a tank circuit! As a matter of fact if we increase resonant Q, we also increase voltage and current! That same Yagi will arc and fail at 1000-1200 watts at exact trap resonance (fortunately the traps are slightly out-of-band).

I disagree with a claim using a tuner is a recipe for trap failure, unless there are special cases. A Butternut trap would be a special case, because it is an abnormal series-tuned trap. It could have a great deal of capacitor voltage if common mode current is high.

73 Tom  
 
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N3OX
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« Reply #11 on: October 17, 2012, 07:53:44 AM »

Actually, isn't it the other way around?!  The trap's maximize loss occurs at the resonant frequency of the trap, not at some frequency above or below.  Given two traps: one at, say, 7.100 and one at 6.500, which trap has the greater loss at 7.075; which could go up in smoke at 7.125?  I believe that most trap failures, other than physical-related issues (such as incorrect form-factor size/material, wire type/spacing, and the like) occur with the extended transmission at power levels more than the trap was designed for and/or at frequencies close to the resonant frequency of the trap.

Rich,

A trap might have troublesome higher resonances on other high frequencies because of coil self-resonances or the whole antenna might have problems because the interacting set of traps and elements has some additional collective resonances where a lot of current can flow through one or more traps.  It's possible to put those outside the design bands of a trap vertical but still have them close to some ham band.  So maybe 40m,20m,15m is perfectly fine but forcing high power on 17m smokes a trap.

I also doubt that a simple LC trap theoretical maximum  loss across the entire HF spectrum is at its resonant frequency when a constant power is applied at the antenna feedpoint.  I think the resonant frequency of the trap is a local maximum for power loss in the trap in a working trap antenna, so that it's useful to shift the trap resonance down a little bit.  But that doesn't necessarily apply very very far from the resonant frequency when the trap will easily pass current and there's a matching network feeding a lot of power to the antenna despite a huge mismatch.

Quote from: W8JI
I disagree with a claim using a tuner is a recipe for trap failure, unless there are special cases. A Butternut trap would be a special case, because it is an abnormal series-tuned trap. It could have a great deal of capacitor voltage if common mode current is high.


It actually turns out I have a concrete example in a model (though not one that hits another ham band).  I have a wire trap vertical design (that I actually built too) for 30/40m.  The trap is a parallel tuned simple trap 4.22uH (with 0.7 ohms loss resistance, Q=340 at 9.1MHz) in parallel with 60pF.

On 10.1MHz the trap has 5% loss.  On 7.2MHz the trap has 2.4% loss.  The trap is resonant on 10MHz exactly and there it has 6.3% loss.   At 9.5MHz the trap has 26% loss, and at 9MHz it's 88% (-9dB)!!    At 8.5MHz the trap has 17% loss.  Looks like the loss peak is at 9.1MHz with   a staggering 98%/16dB loss.  The loss seems to increase continuously as frequency is decreased from the 30m band.  The trap in this antenna example is just sucking up all of the applied power at 9.1MHz even though it is 1MHz below its own resonance and the antenna is very low loss on the design bands.  

Now, this may not be typical.  But the loss in this simple two band trap vertical has a strong peak in between the two bands and far away from the trap's resonant frequency.

Here's the model if anyone wants to inspect it:

http://n3ox.net/files/eznec/30_40_trap_as_built.EZ

Fortunately it's illegal for me to try to burn the trap experimentally since I have this antenna coiled up in my shed Grin
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W8JI
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« Reply #12 on: October 17, 2012, 01:17:19 PM »

It actually turns out I have a concrete example in a model (though not one that hits another ham band).  I have a wire trap vertical design (that I actually built too) for 30/40m.  The trap is a parallel tuned simple trap 4.22uH (with 0.7 ohms loss resistance, Q=340 at 9.1MHz) in parallel with 60pF.

On 10.1MHz the trap has 5% loss.  On 7.2MHz the trap has 2.4% loss.  The trap is resonant on 10MHz exactly and there it has 6.3% loss.   At 9.5MHz the trap has 26% loss, and at 9MHz it's 88% (-9dB)!!    At 8.5MHz the trap has 17% loss.  Looks like the loss peak is at 9.1MHz with   a staggering 98%/16dB loss.  The loss seems to increase continuously as frequency is decreased from the 30m band.  The trap in this antenna example is just sucking up all of the applied power at 9.1MHz even though it is 1MHz below its own resonance and the antenna is very low loss on the design bands.

Interesting. This case has given me something to think about. 

The net reactance of the parallel L-C combination in the trap at 9 MHz (about +j1300) is driven by the top of the lower antenna section to a fairly high voltage and current. I'm trying to understand what the mechanism is.

If I place the top section over a GP and drive it through an inductor of 20 j1300, the inductor has 10 dB loss. 
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G3TXQ
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« Reply #13 on: October 17, 2012, 01:48:15 PM »

Dan's model has me intrigued also!

I make the trap series equivalent 23.6+j1400 at 9.1MHz. I thought that might be resonating with the top section of the vertical, but that section on its own looks to have a capacitive reactance more in the -j800 region than -j1400.

I'm mostly puzzled by the strange current distribution in the bottom section.

Steve G3TXQ
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G3TXQ
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« Reply #14 on: October 17, 2012, 02:26:15 PM »

I don't know if this adds anything to the discussion, and it's probably obvious, but .....

With constant feedpoint power, if you watch the current distribution as you change frequency slightly above and below 9.1MHz you see that the trap current increases with decreasing frequency; however the equivalent series resistance falls with decreasing frequency at a faster "equivalent rate", resulting in less power being dissipated.

The opposite happens with increasing frequency: the trap equivalent series resistance rises, but is offset by the falling current.

At 9.1MHz the I^2R product peaks .......  but then we already knew that !!!

Steve G3TXQ
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