The AM Forum

Here's the scoop,  I have a full sized 80 meter loop, feed with twinlead.  It has survived the last storm with lots of ICE on it.  But rather than push my luck, I was thinking of putting some current through it to help keep the ice weight down.  Putting it up in the summer was a bear, and if it goes down now, I'm off the air for the duration.

SO what is a SAFE way to pump a few amps throught it?  I was thinking of a fuze, lightbulb and switch in series with on side of the feed line.  I hesitate though to just plug it in, although that should work fine.

Any better ways?

Photons.  Lots and Lots of Photons!!!

low voltage step down transformer with a variac on the line side.
you want something that will do at least 20 amps.
feed current in until the feedline gets good and warm.

I did this with some #8 when the feeders were glued and the temp dropped suddenly outside. I was worried the epoxy wouldn't set up.

There was about 300-400 feet of #8 all in one electrical loop. I used a variac fed DC supply. The supply was cranked up to where it was providing 500 watts through the #8. I don't remember the voltage. That was just enough to make the wire's temp slightly warmer than without the power. It was disturbing to know all that power was being used without any real noticable heat.

Move to Arizona.

12V 10 amp battery charger worked gooder on my Qubex Quad! Just keep an eye on it while power is applied!

Did you get a QSL card from anyone???

Hmm, I like the battery charger.  I can run it a while and watch to make sure nothing gets too hot...  I have one that just might fit the bill too.

I was contemplating a battery charger feeding a loop for awhile.  I have about 285 feet total in an inv v and ladder line setup now.

I just couldn't see how that 150 watts from the charger would heat 10 ga wire up enough in the winter storms I have here to actually work.  I was thinking of feeding it through a filament choke, should be able to leave it on all winter that way :)

Scrapped the idea and took Toms advice and went with an inv v.  Like it so far, although i might try a loop later.  I wanna see how noisy the V is in the next ice storm.  I left my insulation on, supposedly quiets it down.

--Shane
KD6VXI

It would be really simple to de-ice the antenna. If you know the wire size you'll be able to look up how many amps it can handle. If you have an amp probe and a variac that can handle 15-20 amps, crank it up to about 3/4 the wire rating and watch the ice melt.

Have Shane drive over cross country with his mobile rig :o

Or build a bigger amp.

Fire up a 150 watt light bulb for a minute and then hold it in your hand.
It quickly becomes obvious what 150 watts can do!!
It's all about btu/hr!

I actually tried that, once.  Fed the driver amp (4x5) into the gamma fed groundplane.  The gamma lasted about a minute, reflected shot up, and that was that.

I'm interested in making the bigger amp push pull :)  It's a two tuber, how hard could it be?  Direct ladderline out the back :) lol


--Shane
KD6VXI

No but IXT accused me of jamming him with magnetism.

I like the idea of defrosting your antenna with a little current. So I thought I'd run some numbers.  The results were interesting.

Using a battery charger:
  Assuming for discussion you have a 250 foot loop of #14 copper wire fed with 100' of OWL also of #14, that's 450' of wire.  #14 wire has a resistance of 2.5 ohms/1000'.  So, 450' would be about 1.125 ohms.  Put 13.8 volts across that and it will pull about 12.26 amps.  Sounds like a good match, right? Well that's 169 watts or, .37 watts per foot.

Watts --> heat:
1 btu = .29 watt/hour = power required to raise 1 lb of water (insulated) 1 degree in 1 hour.  
So, how many pounds of ice are there per foot? Probably, not much, an ounce or so?
How much heat is lost to the atmosphere? watts (lost)/hour? Probably quite a bit I'd think. Too much, who knows.
Hold cold is the ice to start with? OR  How many degree rise is required?  

Offhand, I'd say .37 watts/per foot is certainly enough power for the amount of ice you'll likely have. The only remaining question would be overcoming the heat loss and initial temperature.  I think it's close enough to give it a try with a battery charger and the current levels should be safe, for a GOOD size charger.  I wouldn't use a K-mart 10 Amp battery charger. :)


If more power is required I like the variac/step-down transformer method for some higher current.  I usually keep a transformer from a crapped out 1000-1200 watt UPS's around for just such occassions. They typically will deliver 20-40 amps stepped down from 120 and make fairly good power supply transformers for linear regulated 13.8 V supplies.  

If you would, let us know what you have in your antenna system and how you make out if you get that ice.

Mark

Good point about using a battery charger. The 12 volts will cause more amps to flow in the wire. Yea!!! Amps is heat.I think it is good thinking here!!
Fred

I know it works. I've done it!!

With a full sized 80 meter loop ?

Full size 160 Meter loop....... full size 40 meter loop and a Qubex 3 band quad where all 3 driven element were common fed.

You don't need to melt all the ice. Ya just need to give the wire the capability to melt its way out of the ice it's in.

Well, if a battery charger wont do it, my stick welder ought to!

Yup!