The AM Forum

I'm thinking of buying an MFJ antenna tuner.

Most are rated in terms of the SSB PEP output they can handle.

There are many in the 300 watt range for SSB PEP.

My question is, how many watts of output on AM can one of these handle?

I assume you have to derate it below 300 watts, but how much?

I'd just buy one of their big legal limit jobs and not worry about it, but they are EXPENSIVE.

Dave

the only real QRO tuner is a home brew

Dave,

The two issues you run into are flash-over and heat; the tendency to arc limits the peak power and heat (due to losses) limits your average power.  In most cases, heat is going to be your big issue with AM operation.

Anything beyond the Ranger class of transmitter is going to be too much for a 300 watt unit and even with a Ranger you might get into trouble with a long transmission on 160.  These types of tuners are going to be much more suitable for controlled carrier AM instead of traditional continuous full carrier AM.

If you have access to minimal power tools (i.e. a drill) you could build a rugged reversible L network which will match any reasonable antenna and also provide low pass filtering.  The parts for mine:  2 "tap" switches (1 to reverse the L and another to switch in additional capacitance as needed), a decent sized roller inductor, and a transmitting type cap (I used a vacuum variable)  can be found pretty inexpensively at hamfests or even purchased from internet sources for a reasonable price.  The total cost for mine was under $200 and I built it to easily handle the output of my Ranger/Desk KW on all bands.

Some of the bigger MFJ tuners would be fine for the current legal limit on AM (375 carrier) but the smaller ones are really meant for the typical 100-150 watt output class transceivers.

Rodger WQ9E

After many, many years of Hamming I'd say only a very, very few tuners are really high-power capable, the KW Johnson Matchbox and NYE Viking are two of them.
I have developed a good rule for MFJ tuners (I've never had one, but have tried to salvage a number of them for friends) and that rule is: Take the MFJ rating, divide   by five, you MIGHT be OK. The "300 watt" tuner then becomes 60 watts, works fairly well at that power level. The "KW" tuner might work at 200W, although I wonder about even that. And, finally, their ratings never consider a more or less constant duty cycle, as AM'ers seem to need. Brief, on-off bursts on SSB are one thing, a long winded gas bag on AM might talk for 20 minutes (at least). I had to work on one of the "300 watt" MFJ units a few years ago for an AM friend of mine, he was running a DX-100 at maybe 100 true watts output at the time, he melted the coil. 'Nuff said.
73  Don, W2DL

Dave,

As a suggestion, a home brew will be the way to go. Take a look at Lew McCoy's ultimate transmatch of the 1970's. I've used one for years and it will handle a Junkston "500" all day long. Old buzzard transmissions will warm up the roller inductor on 75 meters, the 4:1 baluns warms up on 40 meters with my antennas. RF currents are going to warm up something with a AM carrier and buzzard transmissions. But even this design with recommended caps, roller inductor, & baluns limits out at 350-375 watts of carrier.

So, as mentioned already, divide the PEP by at least 4, to get an idea as to how much AM carrier a slop bucket tuna will handle. Divide by 5 for room to spare.

And yes, those old Johnson KW matchboxes will take a lick'en and keep on tick'en. 750 watts of carrier......no problem.

73's
wd8kdg
Craig

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

If anyting on your tuner is getting warm, you need a bigger tuner.

ultimate= balun on output = junk. I built one once and quickly wasted it.
KW match box was designed for 1 KW DC input AM. So around 750 watts carrier modulated. I have run that level through mine ...in the good old days.
I did remove the so239 hanging on the output after it flashed over.

Hmmm...Sound advice.

If your antenna tuner doesn't get warm you need more power!!

G

that says it all!!  Amen, brother!!

and it isn't big enough until it is fugly. Power limit of my tuner is the RG393 feeding it.

For my 2 cents worth.    The output baluns on most tuners available are crap.   I have a MFJ-989C.     I bought a very heavy duty balun rated at 5KW continuous duty and use it, not the one in the tuner.    That works good for me with a balanced line fed antenna and all power levels.      If I had to do it over again, I would build it.    I have used a homebrew L tuner in the past, but it had fixed taps, and every time I made a change to the antenna system, I had to rewire the tuner.    You can buy the parts used in the MFJ tuners, I think from MFJ.   You could build the T-tuner and get a high powered balun to add to the output.    Others on this board poo-poo this configuration, there is a mantra that the only way is with real ladder line and a balanced tuner configuration.  My experience has been that there are many ways to get an effective result.

Yep, if all tuner components are well rated for the job, there's nothing wrong with using an over-rated STRAPPING balun after the L/C network when doing "reasonable" feedline transformations.  The balun ratio is fixed (like 4:1)  and the network before it does the adjusting to give the overall transformation.

It's probably done this way by manufacturers cuz it's a cheaper method. Homebrewers usually use bigger L/C components (and somewhat more complex) to do the job without the balun.  The advantage is that most fully L/C tuners are bullet-proof, whereas the balun is prone to heating or arcing when pushed past it's cozy limits.


From what I understand, many of the MFJ tuners used for openwire use the same simple circuit I posted here for coax to coax:
http://amfone.net/Amforum/index.php?topic=18380.0

PLUS, after this T network, they add a 4:1 balun to handle the openwire.



As far as building a tuner... everyone should have SOMETHING in their shack that is homebrew. A tuner is probably the best item of all to homebrew. It's simple and it is a show-boat item to see - for you and your guests' enjoyment. 

It's a well known and proven scientific fact that no homebrew antenna tuner has EVER blown up ... :-)


T

I used to have an MFJ-989 or what ever. switched coil at 300watts.  it did ok with the TS-520, but when I tried to use twin lead and the valiant it died. The Toroid got HOT and went out to lunch.  So i went direct to the "Long Wire" output and ground and that "worked"  The SWR meter cooked off, and I found the coil had melted (styrene supports?) and the band switch had sizzled.   After that I scapped it for the variable caps and the hardware...  ::)  I put the built in Dummy load (big Tubular resistor) to work as the test load.  That will probably work ok-fine in a paint can full of oil for higher power loads (2-300 watts). 

The schematic is the same as the one posted by K1JJ on the other thread, so it's the right Idea for a coax fed dipole,  but the Components are NOT really rated for 300 watts.

I build the standard balanced line tuna with 1/4 inch tubing and the biggest breadslicer I had. NO problems since, and things don't even get warm.  A small chart makes band changing a snap after the initial setup is done. I use an old Heathkit AM-1 swr/fwd pwr meter when I care about the VSWR. (mostly because I like the designation). ;)..

I'll agree with HOT  :o is bad!! There may be some useful reviews on tuners for losses especially at 160M. QST had an issue with valid tests for HF tuners. There were tuners with as much as 10dB loss on 160M
Losses may equate to heat but there may be other factors that do not show up as heated components. Baluns are usually not a good thing.

The HB tunas are!!

Fred

I too have a MFJ989C "3000 watt"tuner. There were at least 3 versions of the tuner made by MFJ over the years with different roller inductors, metering, changes etc.  But they kept the same 989C model number , very strange.
I also built a link coupled tuna a little over a year ago.  The HB tuna works terrific.  It was a fun and inexspensive project.  Well below 100 bux.  Even cheaper if you have the input or ouput variable tuning caps on hand. 
I would not use more than DX100 power thru a MFJ especially if you are using the internal balun (ugh).
I used to use mine by bypassing the balun.  I am not a big fan of loss.uns  ooops I mean baluns.
My ugly but wonderfully efficient  HB tuna now sits happily on top of the MFJ, and the MFJ is now just an antenna switch (on tuner bypass) and serves as the station SWR/Wattmeter. 
If you have to buy a tuner I would look into the PALSTAR tuners.  But as others have said a HB tuna with balanced line is a great way to go, for many many reasons. 

G/L  my 2 sense
Jim

MFJ tooners = junk. I agree with the others.....a home brew LINK COUPLED TOONER is the only way to go. Avoid baluns at ALL COST although a 1 to1 balun on the INPUT of a tooner is much better than a 4 to 1 balun on the output of the tooner.
JMO.........
Bill

Here is my tooner.....

WOW.  That's an RF burn waiting to happen.  ;D

It's good to see it's the dryer that's never used vs: the other machine... :-)

T

Hi Guys........well I still use the dryer.... ;D  but I use this tooner to tune my 75 meter diperpole on 75 and 160. Driving it with a 4x1 by 833's puts a strain on it on 160 but no heat........it works well. It handles 1000 watts of carrier with no problems.

Bill

The rest of the story......

Oh yeah.... there's a front loading door, so you're all set... :-)

That coil looks like it shud take some serious RF, Bill.  Are you worried about the cap flashing over when you mention, "strain?"

T

Tom.....its very strange the way the tooner works. It a parallel tooner that toons my 75 meter dipole on 160. It should be configured as a series tooner for that band BUT it works as is. It is very sharp on 160 and my feedline which is number 10 wire  gets warm on 160 but the freeken thinks works ???

Bill

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.

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

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

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

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...

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.

dang!  Keep hitting the quote button instead of the modify button. >:(

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.
   

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

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.

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

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

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.

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.

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

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

 ;D

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