On Sun, 05 Oct 2003 13:50:43 +0100, Paul Burridge
wrote:

snip

I'm getting very little output. After tuning the transmitter, per the
specs, and measuring the output using the method suggested by the
author of the web page, I figure I'm getting 1 watt or less.

How is this figure arrived at? How are you measuring it? 1W doesn't
sound much, but it can go a long way on 40M., given an efficient
antenna system with short, low-loss feeder and matched radiation
resistance.

Voltage is measured across my 50 ohm dummy load and rectified using a
..05 mfd ceramic disc cap and a 1N34A diode. Then I'm calculating
thusly:

Power = (Voltage x Voltage) / 50

I'm taking the author's word that this works for a ballpark estimate.
I'm measuring 7 volts across the load, maximum, which works out to 1
watt or less. I've verified that my meter is accurate.


I am
running this into a dipole cut for 40 meters, which is 7 feet off the
ground.

That's *way* too low! As you must know for any ariel, you gotta get
that thing up as high off the ground as you can and that's even more
important at low frequencies like 7Mhz.

We have a mess of power lines around the house, so it's hard to find a
spot to even get it 7 feet high in a straight line. I'm thinking
about trying it on the roof, which is about 20 feet high at the
highest point, and mabye angling it in the center.


One of the transistors (Q2) is supposed to be heat sinked. I have put
a large homemeade heat sink on this, using plenty of heat sink grease,
and it gets so hot I can barely touch it.

Something's wrong, then. The heat dissipated in your final transistor
should equate to the output power at the antenna if the system is
matched properly. Sounds like your tranny's trying to dissipate rather
more than a Watt. Are you sure you don't have a feeder/matching
problem somewhere? Have you cut the ariel to the right length? Are you
using a balun? Have you tried a substitute balun?

The length of each element is 32' 11", which I calculated for use at
7110 kHz. There's no balun; I'm using coax, the shield is connected
to one element and the center conductor is connected to the other.
The coax might be 75 ohm. Pretty soon I'll have RG-58 for the entire
run, but right now it's a mix of RG-6/U and RG-59/U.


Get another ham a couple of miles away from you to give you a signal
report. It might show up something useful.

I will do that. Thanks.
--


-John Sandin KC0QWE

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