Ratings on Antenna tuners

[KE6DF]

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

[WA1GFZ]

the only real QRO tuner is a home brew

[WQ9E]

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

[Don, W2DL]

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

[WV Hoopie]

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

[WB2YGF]

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

[Steve - WB3HUZ]

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

[WA1GFZ]

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.

[WB2YGF]

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

Hmmm...Sound advice.

[W2INR]

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

G

[The Slab Bacon]

the only real QRO tuner is a home brew

that says it all!!  Amen, brother!!

[WA1GFZ]

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

[K3ZS]

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.

[K1JJ]

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

[Ed/KB1HYS]

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). ..

[flintstone mop]

I'll agree with HOT  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

[Jim KF2SY]

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

[kc2ifr]

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

[kc2ifr]

Here is my tooner.....

[WB2YGF]

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

[K1JJ]

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

T

[kc2ifr]

Hi Guys........well I still use the dryer....   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

[kc2ifr]

The rest of the story......

[K1JJ]

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

[kc2ifr]

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