Rebuilt my 2m vertical today

[kb2vxa]

"Writing fail on my part."
Say two Our Fathers and six Hail Marys and you are forgiven my son. Dominoes, dominoes, Romano cheese, go your way and sin no more.

I can't say what effect a length of coax between the tuner and antenna would have except add its capacitance to the variable thus affecting the minimum capacitance, the tuner was designed to feed the antenna directly and I never saw one used any other way. I wouldn't chance exceeding the breakdown voltage rating of the coax which can easily happen feeding a half wave or multiple thereof, you'll find several kilovolts of RF at the tuner output unless you're running QRP. That reminds me, a variable cap with a decent plate spacing would help. FYI, the advantage of this design over the C-L-C T network is the capacitor rotor is grounded so it may be adjusted hot with no danger of RF burns. The afore mentioned T bites fingers when they contact the knobs set screws. I wish they'd make them L-C-L Ts like AM broadcast tower tuners made that way for a reason not too hard to guess. (;->)

[mw0uzo]

Since half wave length antennas work great with the right matching network, then there can only be one reason my 80m 1/4 wave L is not good on 40m, massive loss in the coax and 1:1 transformer at the feedpoint. I'll try removing the transformer and putting the tuner at the feedpoint, as you suggest. Any reason why a CLC tuning network would not be suitable for this test? If no major reason, I'll use that temporarily and build a matchbox so I don't have to leave my tuner out in the rain :)

My tuner has got an internal transformer inside connected to the balanced output I think. I'll have a peek inside and avoid that path.

[kb2vxa]

Where'd everybody go? Looks like we have the thread all to ourselves. (;->)

OK, first of all I assume your 1:1 transformer is a balun (voltage or current?) when an end fed antenna requires a 9:1 un-un. In any case the ends of a half wave are voltage loops, the current loop is at the center so feeding the end you're looking at about 2,000 ohms. "Massive loss in the coax" says it all, I can't imagine the SWR! That's what a matching network is all about, it's a phase shifter actually, the impedance depends on where in the phase (sine wave) you're looking at. Eh, a C-L-C T network will work just fine when the antenna is connected to the "wire" binding post with the jumper removed, just ground the "gnd" post to the earthing rod with a short length of heavy wire. Don't be dismayed when the heavy wire won't fit through the hole in the post, just solder about an inch of smaller diameter wire to the end. (;->)

On edit; a "tuner" doesn't tune a darn thing, it transforms (matches) impedance which is why E. F. Johnson called theirs the Matchbox. The impedance and SWR on the transmission line connected to the antenna doesn't change, that's why your small voice is telling you there's massive loss in the coax. That's why if any transmission line is used to feed the antenna open wire ladder line is used, it doesn't care about SWR and it has practically no loss even when badly mismatched. Oh there's a trick to end feeding with it but this is getting long, I suggest you get some reading material from the RSGB or a fellow ham.

"My tuner has got an internal transformer inside connected to the balanced output I think."

I think too, today's tuners are all pretty much the same electrically. For balanced output the jumper is in place from the wire/balanced output terminal to an unmarked terminal and you connect the parallel line to it and the other balanced output terminal. They don't have a balanced output per se, the output is single ended unbalanced and for balanced push-pull output it uses an internal balun. Here's a funny depending on POV, I nearly fried a 3KW MFJ tuner with only 100W of AM. I was loading a Johnson Viking Valiant into a 160M sloping V on 80M, mind you the V is half wave on 160 with the current loop in the center where the open wire balanced line was connected but that feed point is high voltage on 80M. I didn't know the line was also a half wave on 80 which means that very same high voltage appears on the other end in the shack where the balanced output of the tuner is connected. No problem with a quick tune up on a dead frequency (careful not to QRM anybody) but the moment I applied modulation I heard a brief bit of voice followed by my silence as I heard an ominous hiss. OMG, THE BALUN IS ARCING!!! I dropped the carrier instantly, thank goodness the bloody thing didn't carbon track and short out or a winding burn open.

Note to control operator K2PG, sell the MFJ and dig up a Johnson Matchbox at a hamfest (rally). Oh, the Matchbox is link coupled and has balanced output by design, for single ended output just use one hot and ground.

[K7SGJ]

<snip>[QUOTE=kb2vxa;548736]Where'd everybody go? Looks like we have the thread all to ourselves. (;->) <snip>

We are all watching you and judging you on content and accuracy.

score card1.jpg

[kb2vxa]

Yeah, I have a feeling I'm being watched, you guys must all be alumni of the University of Texas.
http://www.youtube.com/watch?v=0WCRFxtnydM

[K7SGJ]

Yeah, I have a feeling I'm being watched, you guys must all be alumni of the University of Texas.
http://www.youtube.com/watch?v=0WCRFxtnydM

Now you know the real meaning of UTs are standing by.

[mw0uzo]

Ok I tried the tuner at the base of the antenna and it matched up great and also transmitted well. With QRO the ATU arced. I tried to bring atu back into the shack with ladderline, but performance was reduced. So, I will build that tuner box exactly as you suggest with wide air spaced inductor and high voltage air capacitor. Got to find a high voltage capacitor - how much pF would you suggest? 150pF, 300pF? Weather proof case with controls on underside should keep out the damp. Thanks for the info and help :)

I also find in my city location that a transformer and gnd really helps reduce the noise. Is there a way I can get the noise reducing effect of gnd and transformer without bringing any lossy ferrite into the equation?

[kb2vxa]

Oh crap, there are so many places where the typical ATU can arc it's not funny especially with high RF voltage on the output. Well, the experiment proved just what I was telling you and that's the important part. Like I said in so many words I built these things 30 odd years ago and only guessed at component values, frankly numbers never entered my mind. I just thought to myself this looks about right and slapped them together.

The inductor is nothing special, if they still made B&W air inductors I could give you a number but in any case it was something like 3" diameter 16AWG (What's that in BWG?) spaced the diameter of the wire about 5" long. I used a flea clip, sort of like an alligator clip with flat jaws to tap it down and bent adjacent turns in to clip to the right spot without shorting the next turn. Sorry, no picture, all Google Images finds is fleas... seriously. Of course it was mounted on ceramic pillars. A roller inductor makes life easy if you have one lying around.

The variable cap is the one that should be fairly wide spaced, it must withstand a few thousand volts and my best guess is about 30-150 puffs (pF you head) should do it, not all that critical. The Frankenstein monster in the basement as I said was breadboard because of the high power broadcast sized components but the outside unit was entirely enclosed in a weather-tight metal box. It's hard to describe but the important things are the coax input was a flange mount SO-239/PL259 tightly wrapped with vinyl tape and the antenna connection through a ceramic tit. On top mounted on ceramic pillars was a lightning surge loop (one wide turn of 1/4" copper tubing and arc gap to discharge static buildup that zapped me once fiddling with the thing and a thunderstorm on the horizon but I digress. Since the operator mostly sat on 3885Khz AM and had infrequent reason to QSY no controls were on the outside. You may consider a box that opens easily because water can enter around shafts by capillary action.

BTW the best and most elaborate solid state controlled ATU I've seen fed a tower that doubled as a grounded vertical folded unipole, fixed capacitors and a motor driven rotary inductor. Each roller position was preset to frequency with a Trimpot and the power supply and control switch was located in the shack. Short story, mostly the system was used by a 1KW AM broadcast transmitter re-tuned for 160M and one day the transmitter tripped out and wouldn't reset. Must be an improper load so let's look inside the ATU. There were bits and pieces of "doorknob" ceramic caps laying in the bottom, all that was left were some mounting posts in the mounting plate. Alright, a junk box mining expedition fixed that BUT the transmitter tripped out again, same problem. Mr. Broadcast Engineer didn't think of basic circuit math, I did and replaced each cap with several smaller values in parallel thus dividing current between them while keeping the same value, problem solved. Bottom line here is the age old engineer vs. technician thing, engineers go by the book and wonder why after all the calculations the bloody thing won't work while the technician throws the book away and uses intuition mostly following in the footsteps of his mother. Mothers are smarter than given credit for, if it doesn't work give it a good bash.

Oh, what's a grounded vertical folded unipole? Electrically, picture half of a folded dipole fed against ground and the far end grounded. Physically it's a regular everyday grounded tower with three skirt wires spaced about 15" off the legs with the top commoned by a heavy gauge copper wire connected to the tower and fed at the bottom with an ATU, all three wires also commoned the same way. For Amateur use the top ring is at the 60 foot level and it operates on 160, 80/75 and 40M but below that (wavelength, not frequency) tuning gets too critical and the vertical pattern lobes unpredictable. Having a low vertical radiation angle it's great for nighttime DX and daytime coverage ain't too shabby either. The beauty of the beast is RF ignores everything above the top ring so the tower can be higher than 60' and support antennas, just bring the coax all the way to the ground and connect the shield(s) to the tower. Any side mounted antennas become part of the antenna (the unipole) and with the coax also connected and brought out the same way they're also ignored. It's an interesting design, it acts like a half wave radiator with the current loop at the top so it effectively packs a half wave vertical into less than a quarter wave of height.

OK UTs, how's my accuracy so far? (;->)

[K7SGJ]

I'm sorry, we weren't listening and missed it.

[kb2vxa]

Want me to repeat?