[AMRadio] Antenna tuner info

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Wed Jan 10 12:12:04 EST 2007

> Make everything capable of handling your maximum output, x2.
> ie: if the B+ on a capacitor in a modulated stage should be 
> 2500v, use 
> one rated for 5kV.

I don't think it works that way for antenna tuners!
I run 2000 volts on the plates of my 813's, so you say
a 4000 volt cap would be fine in the antenna tuner, yet the
ARRL handbook says 4500 volt caps are good for 250 watts....

> > The pair of 813's can run up to 700 watts
> > of carrier output, but I usually turn it down
> > to about 500 watts out, around 1500 watts pep.
> >   
> You do realize that this is less than 100% of audio, correct?  
> 100w of carrier, modulated to 100% = 400w PEP

Yes, I sometimes run the audio light and do a lot of carrier,
and sometimes run the modulation up to 100% and reduce carrier.

> > the antenna will likely be about 100 feet
> > in a flat top setup, up about 30 feet, fed with 
> > about 30 feet of open wire line, made with #12
> > wire spaced an inch or two apart.
> >   
> John/WA5BXO built an antenna for 'portable' use, which is 
> about as you 
> are describing.  Except, his feedline is a pair of 12ga 
> stranded lines, 
> spaced around 4 or 5 inches apart.  Being in the Computer Repair and 
> service business, he had access to 'boxes' full of drive-bay covers.  
> So, whatever that distance is, is about where his feedline is spaced. 
> 5.25"?  Those drive-bay covers also make it easier to roll up 
> the feed 
> line, but experience has proven over time that they are just 
> as subject 
> to the rigors of UV light.

I have plastic standoffs in huge quantities, they were used
to support cables to racks in the Telco world, they have
slots to fit wire ties through, and I have lots of wire ties.
Had some up for a year with no noticeable degradation.
Cutting the standoffs I can make them 1 inch to about 5 inch
spacing...in one inch jumps...

> > Cardwell is selling new caps, model 153-11-1 100pf 7000 volt
> > for about $100.00 (for a shiny new cap).
> >   
> Man... couldn't you take some older oil-filled caps, and 
> series/parallel 
> 'em to get the same value at about $5.oo (or less) per at a Hamfest?

I never saw a design calling for oil filled caps in antenna tuners,
and these need to be adjustable...

> > Would 7000 volts be enough for most situations?
> > What size copper wire to make the coil with?
> > Bigger is likely better, but what is the minimum
> > size that would work, #12, #10?
> >   
> If it's available, Brett, I'd be tempted to use 8ga solid 
> copper wire. 

I have #8, #10, #12, and #14.
For 600 watts carrier I would think #12 would be ok?

> > Does anyone know what sort of parts were used in the
> > Johnson KW matchbox?
> >
> > The ARRL handbook says for 250 watts of AM, 4500 volt
> > caps and #14 wire are good.
> >   
> You know, lots of tuners were made by simply tapping an 
> air-dux coil.  
> Whatever the size of most of those, then, should be sufficient.
> > Or, what do you guys use for GOOD wire and rope?
> > The rope is in tree's, and the wind rubs it some,
> > the best stuff from home depot holds up 4 or 5 years
> > before it looks bad enough to change out.
> > Anything better out there?
> >   
> How about a pulley, tied to a tree, and the end of the rope pulled 
> through the pulley, with a weight on the end of it?  Let the 
> tree sway - 
> the rope will roll back and forth through the pulley and not become 
> frayed by rubbing on the tree.

I cant get up in the trees to attach a pulley.

> As far as antenna wire, any conductor will work.  I've had 
> fairly good 
> luck with simple 10 or 12ga copper wire.  Of course, the 
> price of copper 
> has gone sky-high.  A 500' roll of 12ga insulated copper wire at the 
> hardware store used to cost $25.oo.  If you want something a little 
> larger in size (for a larger surface area - think 'skin effect') guy 
> line is a conductor, but it's hard to work with.  You would probably 
> have to use cable clamps and some conductive grease would 
> help stave off 
> corrosion over the years.  Guy wire is galvanized and holds up towers 
> for years and years and years.
I used what home depot sells, poly and nylon blend I think.

> --
> 73, etc
> -Geoff/W5OMR


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