Resonate on one band only?

[koØm]

This is a good starting point, my horizontally (40' above ground) mounted OCF Dipole (balanced feed input) suddenly, only works on one band, 20 meters.

I use a Dentron Super Tuner Plus with a Yaesu YC-60 watt-meter to read reflected watts between transceiver.

I go to the settings I have transcribed for each band and, the reflected watts shows that the Tuners is not transforming the load to the radio; the SWR meter on the radio shows a "bad match".

I hooked my MFJ-259 Analyzer in place of the radio and tried the settings for the different frequencies; tuner doesn't tune balanced load.

One last thing, I have a bad feeling about this, the last time I heard a tuner "singing" it was internal arcing, the internal balun screaming in pain. This was surprising at first, an MFJ "3KW" tuner arcing with only 100W of AM, modulation struck the arc followed by the hiss of carrier arcing inside the balun. It was more the antenna system than the tuner, a 160M sloping open delta fed with open wire ladder line. It turned out the line was a half wave on the 75M AM Gangsta band sending the high RF voltage at the antenna feed point down to the tuner, baluns like current feed, voltage feed kills them. This is where the old Johnson Matchbox shines over today's tuners, it has a balanced output and one leg can be shorted to ground for unbalanced output, it laughs at high voltage.

There is no arcing or singing from my tuner, running digital power levels; nothing over 25 watts so, how would you diagnose a bad balun in a 2 Kw antenna tuner?

.

[kb2vxa]

That involves equipment few if any hams have like a HVDC high scale ohmmeter aka an insulation resistance checker or megger. A shorted turn will only turn up in an Ix (excitation current) test, trouble is I have no idea what frequency to use on an RF inductor. That leaves component substitution, the guts to any old current balun will do as long as it fits properly, no crowbars allowed. A crowbar circuit belongs in a power supply, not a tuner. (;->)

You asked a specific question so I gave you a specific answer, however a previously working balun subject to digital low power, typically QRP level should never break down. I suspect an open circuit somewhere, a cold solder joint opened up, a THOROUGH visual inspection is in order. If that fails to turn up anything a continuity test with an analog ohmmeter and wiggly fingers is in order. Put the meter across every joint and switch contact in turn, wiggle the wires, rockers and knobs, and watch the pointer for any twitching you'll never see with a digital meter, they don't react fast enough and tend to bobble. If push comes to shove re-solder every connection. You can find bad joints in any hippie... uh, even top of the line equipment, once upon a time I found a terminal lug in a Collins transmitter with not a drop of solder on it. That wasn't the problem but I soldered it anyway, (;->) a fried screen resistor and shorted tube in one of the IPA stages killed grid current and subsequently power output.

[AA1LL]

The quote from K2ORS was great.
73 DE AA1LL, ex W2OPB

[koØm]

That involves equipment few if any hams have like a HVDC high scale ohmmeter aka an insulation resistance checker or megger. A shorted turn will only turn up in an Ix (excitation current) test, trouble is I have no idea what frequency to use on an RF inductor. That leaves component substitution, the guts to any old current balun will do as long as it fits properly, no crowbars allowed. A crowbar circuit belongs in a power supply, not a tuner. (;->)

You asked a specific question so I gave you a specific answer, however a previously working balun subject to digital low power, typically QRP level should never break down. I suspect an open circuit somewhere, a cold solder joint opened up, a THOROUGH visual inspection is in order. If that fails to turn up anything a continuity test with an analog ohmmeter and wiggly fingers is in order. Put the meter across every joint and switch contact in turn, wiggle the wires, rockers and knobs, and watch the pointer for any twitching you'll never see with a digital meter, they don't react fast enough and tend to bobble. If push comes to shove re-solder every connection. You can find bad joints in any hippie... uh, even top of the line equipment, once upon a time I found a terminal lug in a Collins transmitter with not a drop of solder on it. That wasn't the problem but I soldered it anyway, (;->) a fried screen resistor and shorted tube in one of the IPA stages killed grid current and subsequently power output.

The antenna, "she" tunes all bands.

After restringing one leg and touching up weathered solder joints, I installed a new ceramic insulator to secure it to support. I replaced the feedline using zipcord separated by dog-bone insulators.

I believe that the "insulator" failed; it was a mica block capacitor like the one pictured (solder tabs removed ).

mica.gif

The lash-up worked for over 4 winters so, it was time for it to be rebuilt.

.

[kb2vxa]

So am IIIIIIIIIIIIIIIiiiiiiiiiiiiiiiiiii............

I don't know how I missed this but I did, better late than never. I'm glad there was a follow up, I don't know why I overlooked a wonky load, the antenna. There's nothing like ceramic dog bone insulators for wire antennas, but these days they're expensive, and the stranded soft drawn 12ga bare wire I used back in the day seems to have disappeared and took ceramic open wire spreaders with it. Well not quite, I found groups of 4 at Surplus Sales of Nebraska, but enough to make a decent run of line would break the bank at Monte Carlo! I hate plastic and copperweld, but there's a chuckle in it, a goof on copper thieves. Oh yeah, I know those block type mica caps well, but I used them to repair the auxiliary loading in Johnson Valiants, Heathkit DX-100Bs and such transmitters.

[koØm]

So am IIIIIIIIIIIIIIIiiiiiiiiiiiiiiiiiii............

The antenna is too efficient now; my "Flying Vee" Dipole (40 feet in elevation, with one leg running up 10 feet directly up the wall and over the operating position to the roof; that leg is about 30 feet in length. The other leg is about 35 feet in length, it is running parallel to and at the same height as the all wiring and CAT-5 in my apartment!) radiates now in such a way that, the RF gets into my computer that I use to run the sound card modes, eQSL and LoTW logs.

Before, I only had this issue on 10 meters (coming thru the USB bus on the computer), the feed to the antenna was sloppy (75 ohm flat line TV antenna wire) and, one leg was, #16 gauge stranded wire with the mica block for an insulator. Now, it's feed is balanced properly with #12 spaced by dog-bones.

All antenna wire is now, #15 formvar coated magnet wire.

Nope, I cannot change the orientation of the legs, all equipment is grounded to the same point which (my third radiator) runs down three stories to a ground rod.

[WØTKX]

Got an extra manual (need wide range) tuner?

Tune the ground leg, and/or check it with the antenna analyzer.