The AM Forum

Hey all,

I'm in the planning stages of putting up a "real" HF antenna at my QTH...tired of lousy signal reports from an indoor compromise thing, and missing out on the lower bands.

I'm thinking of a 100' sloping wire from the 2nd-floor window of my shack, tied off to the corner of a rose fence in the yard. The counterpoise will be 100+ feet of wire hidden in the rain gutter around the front 3 sides of the house. Going to be running these to a LadderLoc insulator at the window, and about 25' of Wireman ladder line to the tuner. And there's my question.

Where are all the kW-rated balanced line tuners for 160-10? :D I've heard good things about the Johnson kW Matchbox, but it doesn't seem to cover 160 without mods. Palstar also makes one, but I haven't really talked to anyone who uses it. B&W made one that looks like a tank, but I know next to nothing about whether it's worth hunting down. Not really interested in the modern MFJ offering.

Are you guys with high-power balanced line setups all using homebrew ones?

Thanks in advance!

Jim
KG4NEL

Hi Jim
One of the better HB tuners some of us have built is called the K1JJ (Tom) tuner.
I posted a picture of mine and the link will get you to the ones others built several years ago.

Can't beat it and simple. Perfect for open ladder line.
A.M. mode and 160M become very demanding on the entire antenna system.

http://amfone.net/Amforum/index.php?topic=10989.0

Good luck

Probably better to homebrew a custom tuner for your situation.  The commercial ones, including the Johnson Matchbox, are by necessity compromises.

I prefer to use a separate custom-designed tuner for each band and each antenna. Changing bands and/or antennas is a matter of rotating a selector switch.
(http://amfone.net/Amforum/index.php?action=dlattach;topic=23734.0;attach=24346;image)

That's great, lol.

"All ahead full...oh wait, QSY to 40M" ;)

Fred, you must be running QRP, that PVC pipe hasnt melted ;)

I got 2 questions..

Whats a tuner and whats balanced line ::)

..yup..build the 'jj tuner...i did, and no regrets....copper tubing, good cap, and away you go...make ur own ladder line as well..cheaper, and well worth the effort...

..tim..

..sk..

In the process of building one here - at least the layout and parts gathering phase.  There appears to be some variations of the K1JJ tuner - some use a split-stator cap and others not.  Also, I saw a version where the capacitor connects to the coil ends and the feedline taps toward the middle of the coil, others do the opposite and connect the feedline toward the outer ends of the coil and capacitor more toward the middle turns.

What are the pros/cons of these variations?

Steve and Jim,

Here's more info with the schematics for both series and parallel tuning.  What you are probably referring to is the need for a low impedance and a high impedance match. Steve/K4HX  shows (in the first post) schematics on how this is done by tapping nearer the ends or nearer the center of the coil, etc.  You will use parallel config for most work (high impedance matches)  and series config for the remaining needed low impedance matches.

By leaving the whole tuner "tap-able" you will be able to handle most any matching situation on any band using a single open wire fed antenna.

BTW, if possible, try to make your antenna center fed and balanced, for best results.

http://amfone.net/Amforum/index.php?topic=18054.0

Have fun.

Tom, K1JJ

Hi Jim:

I ordered the same cores that are used in todays "balanced" antenna couplers.  Homebrew baluns from these cores were tested in the above coupler design(s).  It became evidednt these couplers were not quite balanced.  

At times, some baluns became hot and there was non-balanced current distribution along the tested antenna systems.  At times some of the rollers inductors would arc.  The above negatives did not happen all the time because I was testing both good and poor antenna system layouts.  My power was about 120-85 watts output, 160 - 10 meters.  

Some times off the shelf coupler designs work good but they are not as forgiving as the link coupler when it comes to challenging antenna system lengths.  The Link Antenna Coupler, Universal Link Antenna Coupler or K1JJ tuner eliminate todays antenna coupler design weaknesses as described below.

If you build the link antenna coupler without an antenna swithch, balun, roller inductors and antenna relay then your balanced coupler has eliminated the greatest threats of arcing, heating and non balanced distribution of current.  That is not to say you can't arc one of your capacitors.  That can happen with most coupler designs attempting to work with an antenna system length that is challenging and with capacitor plate spacing to small to handle this antenna system length.  And, it is possible to have non balanced current distribution if your antenna system is built incorrectly, i.e. antenna system is coupling to other objects.  

On the whole, the link antenna coupler offers more bang for the buck.  It is a proven tool.

With link coupling you have a half a dozen or more circuits to choose from.  Off the shelf couplers are usally limited to one or two circuits.  And, Walt, W2DU, found that the differential output capacitor type cirucit, Johnson Matchbox, did not work as addvertised.

Search W2DU within AMFone.com and you can read more about this.

Jim, if you build the link coupler with "traditional" circuits you will have the very best in terms of a balanced antenna coupler.
73,
Chuck

A KW Matchbox is FB for a center ladderline fed dipole 80 - 10 m.   the honest truth is that any ham who tries to get one single dipole to perform well 160 to 10 m. is kidding himself.  You simply cannot cover all of HF and 160 well with one antenna.  The laws of physics are against you.   you need two 1/2 wave dipoles at a minimum, one for 80 and 40 and one for 20 to 10.   The KW Matchbox will get you on the WARC bands with these.   What about 160?  Unless you can get a dipole up at a minimum 100 feet on that band, and 140 is better, you are better off working against ground with an inverted L or 1/4 wave hot tower, or something shut fed and use coax and an unbalanced L network tuner and lots of radials.   OTOH if you are one of around 5 AMers in the US with the support(s) for 160, then homebrew a big copper pipe coil K1JJ link tuner and bury everyone's meter.

BTW, those non-link coupled balanced tuners can exhibit problems depending on your location, with out of band RF coming in on them because of the direct continuity between the balanced feed and the coax.

These are the simple honest truths or, you can join the ranks of thousands on 160 who have dipoles at 30 feet and who are both piss weak and in denial.

Rob

Roller inductors are for kids.

Along the line of this topic, I have a question regarding link coupled balanced line tuners.   I have a bunch of the TVL transmitter type output plug in coil assemblies.   Are these suitable for use in a link coupled tuner for their respective bands?

Stevef:

When there is a high current loop near the antenna coupler ladder line connection, this is a low impeadance point i.e 200 ohms or much less.

For the above, set your link coupler for series tuning such as:

1. connect your output tank capacitor (one capacitor) in the middle of the output tank coil.  By doing this you mechanically now have two smaller tank coils with the output tank capacitor in series with the left and right sides of this coil.  One half of the ladder line is tapped on the left coil and the other half of the ladder line is tapped on the right coil.  Depending on the band in use determinds the placement of the taps.

2. or, (when using two capacitors and one tank coil) connect one capacitor rotors to the the left side of the tank coil and another capacitor rotors to the right side of the tank coil.  One half of the ladder line is connected to the stator of the first capacitor and the remaining half of the ladder line is connectied to the remaining capcitors stator.

The rotors are tapped to the coil at different locations depending on the band in use. 

These are two means of series tuning a low impedance point on the line with the link coupler.
Some one jump in hear is I got my rotors and stators mixed up.

Parallel tuning is prefered if there is a high impedance point at the coupler ladder line connection point, i.e. 200 ohms or much greater.

73,
Chuck  

It should work--I would connect the swing link to your unbalanced input with it across the center to ground and then the far ends of the TVL to the balanced feeder path (with your cap(s) parallel across the feeders).  I'd connect the inner TVL ends together.  That is the arrangement I'd start to experiment with and have the swing link half meshed.  Once you get close to a match you could move the link in and out to see what that does for you.  

The only problem I see is that I don't think the TVL will handle much power as they were used in < 200 w. rigs if I am not mistaken but maybe you are not running a big maul so it is okay.

rob

Another advantage to the TVL and HVL coils is that you can use those inner connections for series tuning, without the need for two separate tuning capacitors.  Just use a split stator as you would for parallel tuning, and connect the OWL between the inner terminals, which are normally strapped together.  I once modified a set so they would be self switching between series and parallel tuning when I switched coils to change bands.

I did find that sometimes the commercial coils have too many turns to get high enough Q to allow the transmitter to load fully. I removed a few turns at each outer end of the coil and it worked perfectly.  You could also short them out if you didn't want to permanently alter the coil.

Not wanting to steal the thread but I got to ask. I have 126 ft center fed dipole I'm running one of the true ladder line things. If I build a tuner that will handle it will I be able to talk on 160. My dipole is about 30 feet off the ground. I have no room for a vertical this reads no room for ground radials. I hate when all the fun is on 160 and I’m not.

John N8QPC ;D

N8QPC:
For testing I have a short (height) 75 meter center fed inverted V using open wire feeders.  It works well on 160 with the link antnna coupler.  The appex is 40 feet up.  For 160 this particular antenna is effectivly (almost) on the ground.  This antenna system cannot compete with the big antenna farms regarding DX.

Chuck

Hey Carl
I run legal limit A.M. and there was more at one time and no problems with any heating whatsoever with the PVC. The coils barley get warm after an ole buzzard

I'm pondering the two questions. They may be traps....oh boy another antenna term.
Fred

Tnx Don and Rob on your comments about TVL coils.   I actually have the KW versions along with a huge bread slicer variable that was used with them.   I'll try them out.

   The versions of the B&W jack bar mounted variable link, center taped
    coil line were, as I recall, BVL = 75 Watts (5 pin tube style base), TVL =
    150 Watts, DVL = 500 Watts and HDVL = KW...

    These were a group of 5 coils; 160 through 10 meters ( before we were
    given 15 meters). I assume B&W produced a 15 meter unit in their later
    production runs...

     I still have my 80 to 10 meter HDVL's and am using the 80 in a clip lead
     series tuned setup on my CF Zepp on 80 meters.
     
     For some reason the plastic on my set is still in good condition, perhaps
     because I purchased mine in the late 40's when plastics were much
     improved over pre-WW2  stocks
   

a single antenna will cover all bands with the right tuner BTDT
KB3AHE runs 160M with his folded antenna 66 feet long.

For anyone interested, here is a sketch of it.

It works reasonable on 160, but it straps on 75 and 40

A 120' center fed dipole used on 160 will have a low radiation resistance and some reactance which will need to be matched.

Coupler, feedline and dipole conductor sizes should be made large to keep resistive losses low.

Certain feedline lengths can help transform to easier values for the coupler but it can still be a bit of work to keep the R.F. from turning to heat.

If you land up with 8 ohms -j2000 at the coupler expect feedline current to be at least six times what it is at the 50 ohm port of the coupler.

At  800 watts that figures out to be 24 amperes.

To put it into perspective 14 amperes is what one would expext in a 50 ohm system at 10,000 watts.

Thanks, guys. Just put an order in for 130ish feet of 18awg CCS...I'll try the center-fed approach with the feedpoint at the house. Lowest point of the antenna would be 25', highest would be 60'.

Just a random question - I know the WA1FFL "Ladder Lock" insulator is the "commercial" version, but what else have you guys tried for a ladder line center insulator? Seems harder to find than the SO239 version. Thanks!

 

Hi KG4NEL:
Here is a YouTube link on home brew center insulators for home brew ladder line.  Hope this helps.
Chuck
http://www.youtube.com/watch?v=qzFKGB6qkXs

The "ladder-loc" works fine for window line.   It acts as a good strain point also.   You can get #14 window line.   Its Z is slightly lower but that doesn't matter for most applications.

I guess I don't understand the question.  It implies that some kind of special center insulator is needed for ladder line.

I just use a plain old dogbone porcelain insulator.   I have never used the plastic versions because when I'm soldering the ladderline to the dipole, I'm afraid the heat will melt the plastic.   I use a lot of silver bearing solder, get the wire pretty hot with a big 150 watt iron, and really saturate the connections with solder and they seem to hold up real well outside.

If I had it to do over again, I would use two dogbones tied together end to end or one of those big glass buzzardly dogbones that are around 6 inches long for the center insulator, just to get more space between the two halves of the dipole for when the center is at a voltage maximum.   No problems with one though, so two might be overkill. 

I saw one of the big glass dogbones at hamfest last winter but the guy selling it wanted a ridiculous price for it, around $40 as I recall, so I skipped it.   I think it was made with Pyrex.  If I were putting up a dipole made with no. 8 stranded and running shortwave broadcast level power, I would have bought it  :D

http://www.radiobooks.com/llock.htm

Look at this web site, the ladder lock is mainly used as a strain device for window line and also provides a tie point if you want to use a center support rope.   It is just convenient to use, you can solder the wires first before clamping it down.

Okay Thanks Bob, I think I have seen that before but it has been awhile and I forgot about it.

Rob

Thanks for the advice so far. My situation changed a little bit - looks like I can run ladder line over the driveway, so a center-fed doublet all in the trees is what I'll be doing, with a Palstar balanced line tuner. If it works on 160, so be it, but not too worried about that.

Just one more question - how do you guys support ladder line going into the house, from a mechanical standpoint? I'm thinking some kind of a pulley system, but I could use photos of how other people have done it for inspiration :) Thanks!

The video just shows the spreaders, not the center insulator.

I tried his method but could not find suitable ink pens (black, and large enough inside diameter for a ziptie).  I tried some 1/4" black irrigation tubing but it will not allow two passes of a zip tie.   I then tried a piece of Pex 1/4" tubing which passes the zip tie, but unsure of its UV stability.

Palstar's a very nice tuner for storebought, $$ too. You can build one that will work as well or better and the beauty of it is that of you run out of C or L, you can add more to a home made unit but not always easily to a storebought.

By your post, you may not have a center support. That makes it hard to hang the feed without a lot of tension on the legs to keep the center up, inviting breakage.

Is it possible to use any sort of support? The means of support does not have to be so serious as to keep the dipole from sagging, just enough to keep it out of the way.

How long a run from the center of the dipole to the building? There is nothing wrong with some slack, it will give you wind protection. If the feed is short, maybe the weight won't be an issue.

That should be less of a problem with open wire line than with co-ax, if the feeders are made from the same wire as the dipole legs (preferably using one continuous run, with no splice where the feedline attaches to the dipole), and  the spreaders, made of a lightweight material, are kept to the minimum number to maintain good spacing even under windy conditions. The biggest problem I ever had with an unsupported feed point was when my dipole was strung between two trees and it would get whipped around in the wind. Sometimes the 6" ceramic EF Johnson spreaders I was using would break in two, usually every other insulator. I have never had home-made spreaders fabricated from plexiglass rod to break under any circumstance.

At the mid-point of the dipole, use an ordinary antenna insulator, identical to the ones you use for end insulators (unless you use something like those nice 12" long ones EFJ used to make; in that case use a shorter insulator at the mid-point where the feed line is attached). Preferably, the insulator at the midpoint of a dipole should be the same length as the spreaders. If feed-point insulator is longer, use a heavy duty spreader for the first one at the top of the feed-line, so that the wire tension doesn't tend to pull it apart.

For a real classic look, use a set of three 6" Pyrex glass antenna insulators at the end- and mid-points. :)

Nah, I'll have a center support - I'm planning on getting one of those WA1FFL insulators and tie off a rope to a tree, it just won't have a pulley on it like the ends.

Try these folks for spreaders used in ladder line................if 600 ohms is your goal. I haven't had any failures for the last two severe winters. High winds,snow,ice

http://www.trueladderline.com/
They sold me the wire they use for their wire antennas.

Fred

My next antenna will be the one at the above website, that is a continuous wire from feedline and antenna.     I am presently using window line for feeders, but the tuning changes quite a bit on 40M and above when it is raining.    Almost impossible to tune on 10M when wet.

I use a Technical Material Corporation tuner.  Model TAC-1.  Easily tunes down to 160.  Uses dual edge wound inductors. Vacuum cap for 160.  Very heavy duty.  Very heavy.  Very rare.  Works great.

WC1X I wonder if you could post some information on your TMC tuner?
How about a picture or two and a schematic. That must be a very well built unit.

Here's a copy of the manual I found in a Google search. Terrible quality, but better than nothing.

http://www.kevinchant.com/uploads/7/1/0/8/7108231/tmc_tac-1_antenna_tuning_unit.pdf

Hi Frank,

Please see the attached link for the original technical manual for the TMC TAC:

Like nearly all things TMC, it is an extremely well built unit. It's design and production go back to the very early days of the company. I believe it was introduced around 1953 or thereabouts.

The top of the TMC GPT-750 Transmitter cabinet was pre-drilled at the factory for field installation and mounting of the TAC, or the more popular TMC ATS-2 Automatic Tuning System remote control unit.

73,

Bruce

http://www.virhistory.com/tmc/tmc_pages/tmc_manuals/manuals_db/tac/tm_tac_10-4-63.pdf

Very nice. I saw Teflon parts in the parts list so might be an updated manual.
I thought Teflon was a '60s thing.
I think John JN posted this tuner a while ago.

I guess the only thing I'm puzzled about is the use of 18 gauge wire used on some peoples antenna systems. That size looks as if it were intended for stealth or SSB operation. If your using it that's fine with me, I just think it's a bit undersized.

So did I. But PTFE was invented in 1938, and first marketed under the DuPont Teflon ® trademark in 1945 or 1946.

In the early 60's it seemed to be everywhere in mil spec gear so Im guessing it was around well before that such as the Amphenol Teflon SO-239 in that tuner indicates.

I wonder how many of those TAC-1s were made.  Something tells me not many.

I think that tuner was the best 1 KW balanced tuner made.
I see TMC made many single ended tuners.

My TAC-1 tuner is serial number 417.  I've used it in 36 hour RTTY contests running 1.2 kw and little or no heating was evident.  I guess you could probably run 4 kw SSB (1 KW AM) all day without issues.  To call it a 1KW tuner IMNSHO is a misnomer.

Right--it was made in the heyday of TMC and AM and the "1 KW" probably referred to 1 KW input AM just like the KW Matchbox is by modern standards a ~ 2.5 KW tuner but the TAC-1 is probably still conservatively rated even by those standards.  Some of that may depend on the Z of the load at the TAC-1's balanced feed terminals.  IOW it might have been built to handle a lot of current at QRO.

I suppose it depends on your knowledge, experience and attitude as an amateur operator.  To me, the biggest Johnson Matchbox is a KW tuner.

Maybe "You think a Johnson Kilowatt Matchbox is a 2.4 KW Tuner" should be added to the following list:

You refer to one's name as the "first personal" or just "personal".

You end a QSO with "Seventy-Thirds" or "Threes".

You try to enter an ongoing QSO by yelling "Contact".

You finish an AM transmission in a QSO that is NOT operating fast break-in, and just drop the carrier with no prior warning like uttering a callsign or saying "over", "back to you", "go ahead", etc., leaving the other operator(s) wondering if you lost power or your rig crapped out.

You pronounce QRZ.com as "CUE ARE ZEE dot com".

You tell someone with a strapping signal he is "wall to wall, treetop tall".

You call operating AM "Going to the AM side".

You insert "there" between every two or three words in your conversation.

You call the phone bands the "SSB bands".

You think a "cold 807" is a type of tube (or you never heard of an 807).

You give everyone in a contest and every DX station you work a five-nine or 599 whether you can hear him or not.

You think the ideal horizontal antenna is the G5RV, and the ideal 160m vertical is 43 ft. tall.


What others can you think of?

Here are some pics of my TMC TAC-1 tuner alongside my Johnson KW flashbox.
Notice the larger plate spacing of the TAC-1 air variable. 
I like both tuners but I'll never give up the TAC-1.   

I in no way said or implied that there was any equivalence between the KW Matchbox and the TAC-1.

Below is my post (emphasis added):

<<Right--it was made in the heyday of TMC and AM and the "1 KW" probably referred to 1 KW input AM just like the KW Matchbox is by modern standards a ~ 2.5 KW tuner but the TAC-1 is probably still conservatively rated even by those standards.>>

The TAC-1 is clearly a better constructed product, but in fairness to Johnson, the KW Matchbox was not built for military service, but rather for hams, and by modern standards is a vastly superior tuner compared to what is available new today.   I am pleased and content to run mine but of course I would not turn down an opportunity to purchase a TAC-1 if I could afford it.

Don, I saw your post on the AMradio reflector and wondered if my comment precipitated it.  Kindly notice the qualifier "modern standards" in my post.   I freely admit to being an appliance operator by the standards of most AMers and absolutely make no pretense of being anything else.  I am working hard to learn and improve my ability as an amateur radio operator, however I fully realize that at this point in my life I may never live long enough to attain the level of ability and knowledge some of you have, who have been building and learning from an early age.   I find your comment surprisingly excessive and out of character.   Perhaps it was in humor and I misinterpreted it.

73

Rob

I've been thinking about this all evening. I've come to the conclusion that Don said what he did from an AM perspective.

Can it really handle 2.5 kW on AM? I can't say, but my guess is that the answer is no.

I've read dozens of different posts that claimed that the KW matchbox is good for far more than 1 KW. But I think that they were referring to CW and slopbucket operation. :-)

I have a lot of respect for Don and his technical expertise, but even the best of us get moody sometimes. How about if we all forgive and forget, and move past this as mature men?

Dealing with big BC rigs for years shows one that in any L/C net (which an antenna tuner is), the contact surface comes into play for the I carried, the insulation for the E.

Figure a bit under 4.5 A @ 220 V @ 50 Ohms = about 1kW RF wise.  That ought to be where your highest I is, on the 50-Ohm input circuit.

On the balanced wire line output, say 600Z for instance, the E is over 750 with the I down to just over 1.25, and that is without modulation.  It gets pretty tingly approaching 100% mod....

Insulators and caps need good insulation, rollers & switch contacts need low resistance in terms of square mm to handle being adjusted while in operation and not burning up or arcing over. 

Seldom does a small diameter wire crap out, even with lots of RF on it.  Where it connects to something, on purpose or by accident, is where the grief comes from.

Run the numbers and take a look at the guts of whatever unit you want to use, see if you think it will hold up.

73DG

I think you did. I also posted a similar one on QRZ.com too, and a few people got bent out of shape, but most thought it was funny. Think of it as in the combined spirit of W2OY and George Carlin. Or maybe Burt.

BTW, here is another one to add to the list:

   You refer to output transistors as "Pills"  ;D

The answer to that depends on the load. But more than 2.5 kW has been run through a Matchbox.

Was that 2.5 KW of AM?

I doubt an EFJ matchbox would withstand a fully modulated 2.5 KW carrier for very long before things started heating up.  And it would probably flash over on modulation peaks before you got anywhere near 100%.

Maybe, if the load were just exactly right.  But IMO you would have at best a very narrow range between excessive heating, and tuning capacitor (and maybe switch) flash-overs.

"Pills."  Yeah, I forgot about that one.  I should go look at QRZ and see what was posted. 

Let's see....As I recall the KW MB caps are pretty widely spaced.  Not sure where the flashing takes place.     The bandswitch and link/inductor and taps all seem to be capable of handling a fairly decent amount of current.  I think all of the leads to the inductor are silver plated strap.  Unless I am mistaken it was built to handle the Desk KW.  Around 600 watts. 

speaking of power, I finally have a 3 A thermocouple meter in line with a decent 50 ohm load.  I am looking forward to seeing how 2 or 3 A of RF squares with these watt meters I have.

Have you ever tried it?

2.5 KW PEP no problem, 2.5 KW carrier rots of ruck.
The SO239 connected to the output will be your first failure

With AM carrier power levels between 1 & 5kW and if your tuner is in a box, time to go to type LC, 7/8" EIA, or better yet 1-5/8" EIA.  Even 7/16 DIN is OK.

If an open breadboard job, think at least of using 7/8" heliax for the 50-Ohm TX-to-tuner link. 

Also, stand clear.

I once walked past an open & operating 50kW ATU on a wall and my hair stood up (what was left of it and by itself!) when I neared the output end, as it was a short daytime stick with really high -J.

73DG

Have you tried it?

into a dummy load of course but I flashed over the SO239 on the output side.

I love this website.   ;D

Try it into open-wire line and get back to me.

I once tried a homebrew link coupled balanced tuner feeding my 80m dipole on 160 as a quarter-wave dipole.  The tuning cap was a BC-610 plate tuning cap, 150/150 pf @ 7 KV.  I think the EFJ KW Matchbox tuning cap has the same spacing or slightly smaller. The the tuner end of the OWL was exactly midway between a high current point and a high voltage point, so it presented a highly reactive load to the tuner. I was able to tap down on the coil with the OWL and get a good match to the coax line from the transmitter.  But running 100 watts, I could not modulate 100% without flashing over the tuning cap.  I added another 60 ft. of OWL, bringing the tuner end of the OWL to a high voltage point, and I  parallel fed it directly off the tuner without tapping down. I could then 100% modulate as much carrier as I had the capability of generating without flashing anything over.  As expected, the tuning is very sharp, and I cannot QSY more than about 5 kc/s with that set-up without re-adjusting the tuner, but I worked all over N. America with that antenna before I got my ground radials laid to allow me to use the tower as a quarter-wave vertical..

Maybe. But I've seen 5 and 10 kW run through RG-8 and multiple UHF connectors on continuous-duty medium-wave transmitters.

It got warm, but it was not hot by any means.

I'm not recommending that anyone do that, but I know what I saw.

Frank is definately right!!

As you all know, I run a short antenna, so this definately raises some tuner / feedline issues. Especially at high power.

I dont have any problems on 80 and up, but I do on 160. I have a short run of coass between the tuna and the balun. (yea, yea, I had to do it that way but it works)
At 700w or so of carrier on 160, I have to keep the modulation down to around 90% or a little less. If I crank on the audio, I will burn the PL-259s off of the coass and/or the SO-239s off of the tuna chassis!! Done it several times!!  ;D  ;D

The little skinny center pin of a type "N" connector wouldn even think of holding that much feedline current. (Remember that the coass isn't running at anywhere near 50 ohms)

If you have to sin with extreemly high swr on coass, it is always better to run the coass at a lower impedance where I-R losses are your only issue vs a high impedance where the capacitive reactance of the coass ends up absorbing all of your outpoot power.

I removed the output UHF jack on mine.   After reading something Frank posted about it sometime last year I got rid of the stock UHF jacks with the phenolic and put in a new one with teflon on the input.