Manual Tuner Problems

[N6OSB]

Hello,

I've recently built a prototype L-Network tuner. I've been able to have a couple QSOs at 100w with no problem. This morning I tried getting on 40m again, I tuned and got 1.1:1 SWR and as soon as I transmit at 25w+ my SWR goes hay wire. I ended up not being able to transmit any higher than 20 watts.

What's going on?

Hope you guys can help.

TIA,

Gabriel

[WB2WIK]

I'd guess you arced a variable tuning cap. If that happens, it can permanently damage the cap because it will continue to arc at the same location, at lower and lower voltage, until it's repaired or replaced.

Just a guess, but it's a fairly common problem with tuners -- especially those using close-spaced capacitors.

You might look with a strong light and magnifying glass to see if you can find any evidence of damage.

[K9ZMD]

Gabriel, if a cap did arc, but the tuner was working OK previously, then look for why it arced. Same advice, even if a cap didn't arc. I know you're probably focused on the prototype tuner, but don't forget that something could have unexpectedly gone haywire in the rest of the system. Are your antenna elements are still connected to the transmission line? Are all connectors still tight? Anything fall across your antenna or transmission line? Any part on the ground now instead of elevated? Wet instead of dry?

[WB2WIK]

Gabriel, if a cap did arc, but it was working OK previously, then look for why it arced. I know you're probably focused on the prototype tuner, but don't forget that something could have unexpectedly gone haywire in the rest of the system. Are your antenna elements are still connected to the transmission line? Are all connectors still tight? Anything fall across your antenna or transmission line? Any part on the ground now instead of elevated? Wet instead of dry?

Good suggestions.

I'll never forget one day when I lived in NJ at one of my "many" homes I was on 3.818 checking into a VHF weak signal net on 75m to make a moonbounce sked when all of a sudden my tuner flashed and SWR went sky high. I thought the tuner failed.

But before tearing it all apart I went outside to look at my 75m inverted vee. A small part of the side of my house was on fire.

One end of the inverted vee was normally a few feet from the vinyl siding, but it was very windy and there was more play in the wires than I thought, and the end of the vee wire actually touched the side of the house while I was transmitting, setting the end insulator and the end of the wire on fire, as well as that panel of vinyl siding. It was all burning when I went outside.

The siding self-extinguished as it should but the plastic molded insulator didn't, it just kept burning.

I guess STEP 1. troubleshooting any antenna tuning problems should be to walk outside.

[N6OSB]

Wow how much power were you running 1.5k?

I looked at the cap but didn't see any damage.

After that I got on the air on 17m 100w no problems. But 40m I still can't tune up. Could it be my rolling inductor? I tired running up with internal tuner and it worked fine. I know it's not a difficult match.

I have cleaned it but maybe there's something else going on.
http://imageshack.us/photo/my-images/694/imageoswe.jpg/

[K8JD]

[QUOTE=WB2WIK;2482920]Good suggestions.

I'll never forget one day But before tearing it all apart I went outside to look at my 75m inverted vee. A small part of the side of my house was on fire.
setting the end insulator and the end of the wire on fire, as well as that panel of vinyl siding. It was all burning when I went outside.
t the plastic molded insulator didn't, it just kept burning.
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That's why you should use porcelin or glass insulators !!!

[KE3WD]

Try reheating all of your solder joints in the project, adding a wee bit more o' the resin core...

[N6OSB]

I changed out the 4:1 balun to a 1:1 and now I can tune up 40M. I wonder if the 4:1 balun was becoming over saturated?? Is that possible? I think I heard of something like that. The 1:1 balun was the only other balun I had.

[N0SYA]

"The siding self-extinguished as it should but the plastic molded insulator didn't, it just kept burning."
Moral of the story:
use ceramic insulators

I had a transmatch that would zap every now and then, the wire around the ferrocore that added the highest switched inductance had popped insulation. Replaced the vinyl(?) insulated wire with teflon insulated wire and all is good.