[AMRadio] Antennas for AM (was Legal limit AM amplifier, homebrew)

Sun Nov 13 18:16:02 EST 2011

Have you run the dx 100 on that antenna?
Anytime I ran AM into anything with traps or baluns, even 100 watts, smoke 
came out.

My last experiment was an alpha delta dx lb plus, 160 to 10 meter dipole 
using a fan setup for 40, 20, 15 and 10, and loading coils for 80 and 160, 
about 130 feet long.

Running a couple of hundred watts, the coils melted...

Smoke came out of the B+W all band antenna, smoke came out of any antenna 
with traps, but the butternut vertical held up.
It did not work worth a crap on 80 or 40, more of a dummy load, but it did 
not zorch.

I really do not like amplifiers for AM.
Lots of heat for little power output.
I built a 4x 813 amp for my flex radio, and running 200 watts had things 
getting very hot, even with forced air cooling.
My pair of 813's plate modulated runs 600 watts out and stays cool.
Same pair of tubes for the last 25 years....

One of my favorite rigs was a pair of 812a's in push pull link output, 
modulated by a pair of 811a's.
I ran everything at 1500 volts and got 340 watts out.
It was a very smooth operating rig.

My rule of thumb is to have as much audio power as carrier power, but I 
cheat, and drive all the modulator grids from an 8 ohm audio power amp as I 
have had a lot of different rigs in the shack at one time and it makes it 
easy.

Brett
N2DTS

----- Original Message ----- 
From: "Rick Poole" <wa1rkt at arrl.net>
To: <amradio at mailman.qth.net>
Sent: Sunday, November 13, 2011 11:50 AM
Subject: [AMRadio] Antennas for AM (was Legal limit AM amplifier, homebrew)

> At 11:17 AM 11/13/2011, Rob Atkinson wrote:
>
> >>>>>
>>Is it one of those carolina windom jobs?
> <<<<<
>
> Good morning, Rob.
>
> Not exactly.  It doesn't have the vertical radiator or the choke 1/4
> wavelength down the coax.  It is fed at about the 1/3-2/3 point with
> a 4:1 current balun and 50-ohm coax to the shack.  Works pretty well
> on the fundamental and even harmonics.  Currently it is mainly used
> for 80 and 40 but I plan to put up another one for 160 and 80 and use
> that with the AM station.  I suspect most or all of my AM activity
> will end up on those two bands anyway.
>
> >>>>>
>>If you can ever get a
>>center fed ladder line 1/2 w. dipole up to around 50 feet and fed with
>>a KW Matchbox, things will work out a little better I think.
> <<<<<
>
> I had a KW Matchbox and sold it several years ago.  Probably
> shouldn't have done that!  I still have two NyeViking KW tuners I
> could use, but both of those are what Bernie characterized as a "POS
> that place a balun on the output" :-).
>
> Of course open wire balanced feeder antenna couplers are simple
> enough to build so I suppose I could build one.
>
> I have a 160-meter inverted V fed with ladder line and a tuner, but I
> think I'm going to try to avoid open wire feeders this time
> around.  The position of the AM station and the general layout of the
> shack would require perhaps 15-20 feet of open wire feeder to be
> strung around the shack to where the matchbox would have to go, and I
> don't have much confidence in being able to avoid RF-in-the-shack
> problems, especially since I have three computers running here, two
> of which are used for mission-critical business purposes (I'm a
> medical device software engineering consultant in my other
> life).  I've seen what can happen to computers if you try to run them
> in a high RF environment, and it was not pretty.  So I think I'm
> going to stick with coax and a resonant antenna for this one... an
> OCF antenna carefully tuned for 1.9 MHz will also resonate on 3.8 MHz
> and that should put me about where I need to be on both bands.
>
> I plan to rent an 85-foot cherry picker next spring and use it for
> some projects around the property, including putting up some new
> antennas.  I did that once before with a 45-foot cherry picker and it
> worked quite well.
>
> The 35-foot OCF is mainly used for NVIS stuff and I'll still need that.
>
> Rick WA1RKT
>
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