Ratings on Antenna tuners

[Opcom]

I bought a MFJ-993B Dual 300 / 150 Watt IntelliTuner Automatic Antenna Tuner. I am pleased with it for use with a 100W radio like the TS0430S or the Sunair GSB-900DX.

Its rating for 300W is only for the impedance range of 6-1600 ohms. The range is 6-3200 Ohms at 150W. The selection of this range does not do anything other than limit the available impedance range to protect the parts from cooking. I have never had any problem using it with the 25W carrier those radios will produce. And of course I get no QSOs with those power levels and my crappy antennas either. I have used it successfully for SSB tests. Its purpose is emergency communication work and it will do much better once the tower and dipole is up this year. (The tree-cutters are coming next week to haul away the cut-down branches and cash.)

I chose that model because the antennas I have stink and are hard to tune and I change frequency alot. It really improves SWLing to have the antenna matched and works on any frequency because of the wider impedance range. That is without the balun, which I do not use and have no intention of using. I use the long wire connection for the 45FT horizontal end fed  and the coax connection for the vertical.

One interesting feature of this model is that if it does not tune a difficult load the first time, you can push the tune button again and it will try and get closer till it does actually match well. It makes the devil's racket with the speed and length of time at which it tries combinations. I thought it was broken at first. The power supply is a cheezy 12V jack. Could have been 120V but no..

Because I want it to last a long time, I would not consider it for anything other than 100 watt PEP work. The plan is to build a balanced-balanced tuner with 50 ohm 5KW balun at the input once the good antenna is up. Got most the parts, could use a few more. hate it when I have one of something that I need two of. A person ends up with alot of "ones" of things that way.

I have a beef with MFJ roller inductors and I won't have a tuner with them. The one top of the line tuner I bought, the Ameritron ATR-30, like the MFJ-989D I believe, had one of themmuch hyped roller inductors, and the radial position of each of the two roller axle supports are secured on a round shaft by cheap little screws. Repeated use (like running the inductor back and forth 20 times in one day. severe duty!!) makes this assembly loose and then the inductor gets hard to turn due to binding as the roller axle is no longer parallel to the shaft, degrees-wise. Once it is loose, no amount of tightening will fix it. They should have machined flats onto the main shaft for the supports so they would stay put. I returned it.

[kc2ifr]

One more point..........
If the feedline gets warm and NOT the tooner than the tooner is doing its job. The Z of the dipole is very low on 160 and it seems that the tooner is coupling the power to the feedline/antenna. The signal reports I get on 160 seem to confirm this ...........
Bill

[K1JJ]

It looks OK to me, Bill. You're tapped in towards the middle of the coil vs: at the ends, which is normal for the set up you have.  The distance you tap in will be much dependant on your feedline length. If you happen to feed it at a lower impedance point, you would have had to go inwards even more. But the way it looks, you most likely don't need to go to the series config - especially cause your coil is not heating up at 1KW.

For years I lived with parallel feed and never even tried series. At times I was tapped into the last few turns at the center. The coil got warm for sure.  My guess is if you can stay out at least + - five turns per side from the center, (on 160M)  there's not much to be gained going to series tuning. Though, ideally, if one wants to get anal about it, the very best place to be is tapped is at the ends of the coil  - and series tuning would give that opportunity. 


T

[Steve - WB3HUZ]

Sure does. You had a good signal on 160 the other night!

One more point..........
If the feedline gets warm and NOT the tooner than the tooner is doing its job. The Z of the dipole is very low on 160 and it seems that the tooner is coupling the power to the feedline/antenna. The signal reports I get on 160 seem to confirm this ...........
Bill

[KL7OF]

I have the big ass homebrew tuner using a gates roller coil from a 5 kw rig and a 40 KV split air variable mounted on a piece of 3/4 inch plywood for my  900 ft end fed wire....It is totally exposed and mounted on the wall at the 7 ft level to prevent RF burnage......Works with all max scrote AM transmitters in my shack.... Dentron super tuners are OK ..however,I have heated mine up to the point where the coil sagged running 500watts AM....MFJ turners melt at AM duty cycles.....MY EXPERIENCE...

[WB2YGF]

Dentron super tuners are OK ..however,I have heated mine up to the point where the coil sagged running 500watts AM

Thanks for that report.  Exactly what I needed to know.  I won't be running more than 200W AM except possibly with controlled carrier AM.

[WB2YGF]

dang!  Keep hitting the quote button instead of the modify button.

[W2VW]

Some thoughts from a small patch of land owner:

Dentron Stupid Tooner isn't half bad unless you use it into a shortie antenna. It is an average quality semi gloss blaq box. Very wide range compared to a Johnson matchbox. Same idea as any other high pass T network with a voltage BalUn at the output. No inherent defects like almost every one of Denny's amplifiers.

If the feedline gets warm there is work to be done. The amount of power wasted in "warm" feedline can be much more than one might fathom. I have constructed balanced feedline using plexiglass spreaders and epoxy glue more than once when the WX went below freezing. Using 2 part epoxy on the spreader to wire joints, I decided to try heating the whole deal so the epoxy would cure in cold WX. One time the feedline was a pair of #8 THHN  shorted at one end stretched around the lot. Total length was about 110' or 220' single conductor. Hauled out the junkbox low voltage strapping variac supply and hooked it across the 220 feet of #8. Dialed it to 30 volts. It pulled about 35 amperes at that voltage setting. Feedline was JUST a little warm outside in the 30 degree air. All that power was just enough to make the wire slightly warm to the touch. The epoxy didn't cure anywhere near the time it would have taken in 55 degree WX.

Point is: A whole lot of power can go up in heat with warm feeders/doublet found in short antenna situations. Same can be said for tooners but that can be easily confirmed by modeling and then measuring R.F. current.
   

[kc2ifr]

Thanks guys for the info.......I hope this will help the original poster.
And Steve......the last 2 times I ran into u on 160, I was just leaving.......gotta get my beauty sleep!
I hope to stick around the next time.

See ya all later,
Bill

[KE6DF]

Thanks guys for the info.......I hope this will help the original poster.

Thanks everyone. It did indeed help.

Dave

BTW, if any of you are looking to build a REALLY BIGGGG am rig, there is a mondo
broadcast driver transformer that just came up on ebay.

http://cgi.ebay.com/CTC-Audio-Driver-Transformer-for-810-845-833-Tube_W0QQitemZ290291569468QQcmdZViewItemQQptZBI_Electronic_Components?hash=item290291569468&_trksid=p3286.c0.m14&_trkparms=66%3A2|65%3A10|39%3A1|240%3A1318

I post this under the ebay section as well.

[K4TAX]

Keep in mind that a tuner rated at X watts PEP should have the power figure divided by 4 to get the AM rated carrier value.  This of course presumes everything is good and some very low antenna R is not trying to be matched.  Tuners don't typically like very low Z antennas. 

Also, if you desire to run more than 100% positive modulation the "divide by 4" should be something like divide by 6.  That says a tuner rated at 300 watts PEP is really good for about 50 to 75 watts of carrier.

As to baluns, the basic coaxial balun frequently described as "the ugly balun" is about the best way to go.  Otherwish the better way is a truly balanced tuner like the Johnson Matchbox series.

I am also a proponent of the "L network" as opposed to the more common "T network" tuner design.  The L network will have 1 point or combination of L and C  that matches and the same point provides most efficient transfer of energy.  The  T network can have more than 1 combination of settings that appear to provide a good match.  However, there may be 2 or 3 points that appear to "match" but don't produce conditions where maximum transfer of power exisits.  Under these conditions it will however produce maximum smoke.

73
Bob, K4TAX

[W3SLK]

John asked:

Anyone know anything about Dentron?  I have a 160-10AT-1KW ("Super Tuner").  Seems pretty sturdy compared to Mighty-Fine-Junk

Duane, KK4AM has used one with a BC-610 for about the last 15 years. He never had a problem with it.

[Steve - WB3HUZ]

Dentron made the Super Tuner and the Super-Super Tuner. As one might guess, the Super-Super Tuner was about 2x as strapping as the Super Tuner. I used a Super Tuner for a while back in the 80s. One-hundred watts from a 32V-3 would make it warm when it was tuning a 120 foot long flat top  on 80 meters with about 80 feet of ladder line.

[WA1GFZ]

a T tuner is a high pass while an L is low pass. You can make a T a low pass by using 2 inductors and 1 cap.

[Opcom]

was unable to see the dryer tuner picture before. That is a fine setup there.

[flintstone mop]

Hey Bill
Pics of your station look FB OM.
And warm transmission lines, coax or ladder, is just from a low-to-the-Earth antenna.
During my JN days on A.M. in the middle 90's, I had a T-368 and RF ammeters on the feedline and there was about 10amps of currrent out there and burnt tree limbs here and there from a bunch of wire going everywhere about 30 feet high. # 8 solid wire.

Fred

[KX5JT]

 

Okay.. my station currently runs about 180 Watts carrier AM.  I am using the MFJ-962 roller inductor tuner and (i know i know) a 102' G5RV.  (it's all temporary, I will get it upgraded to something more appropriate at some point)

Well tonight I was having a nice qso with k5ayd Lum in Oklahoma when it was time for my final as he signed and was listening in.  Zzzt.... the crosshair needles on my external meter (I never used the meter in the 962) just shot up like a Pentacostal praising the Lord!   Crap!   

I suspected the weakest link... the tuner. So I took it apart and lo' and behold the antenna selector wafer had signs of burning.  Wait a minute... I only have ONE antenna!  I don't use the internal meter on this thing....
... out with the snips and the soldering gun.   

The air caps and roller inductor look hefty enough for my 180 watts.  It is obviously the darn selector switch that keeps the ratings down on these things.  So I proceeded to yank out the unwanted/needed switches and meters and soldered the SO-239s hot leads directly to each of the air caps....

Tadda!  A basic T-matching tuner now without failure prone components to get in the way and I am presently calling CQ on 3885 FB.

KX5JT