[Elecraft] high-power tuner

[Vic K2VCO]

I've recently been experimenting with tuners. I have a "275 watt" Johnson Matchbox (which 
is actually good for more than a kW on CW in most cases) and a huge T network that I just 
built with a massive edge-wound rotary inductor and capacitors with air gaps of about 3/8" 
(near 10mm). The T network has a DX Engineering "5 kW" rated 1:1 balun on the output.

The antenna is an 88-foot dipole fed with 500 ohm open-wire line and some 450-ohm ladder line.

I can switch between these tuners instantly. On 40 meter received signals I can detect 
absolutely no difference in signal strength. The T network is adjusted for the least 
possible inductance that gives a 1:1 SWR, and the output capacitor is at maximum (300 pf 
air plus 300 pf ceramic padder)..

There is also no difference in noise level. If one of the tuners provided better balance, 
one would expect that there would be less noise pickup on the feedline. But I don't see this.

One anomalous result: there is a weak unstable carrier that I can hear on the Matchbox but 
not on the T network. I have verified that this is not a birdie, but an actual signal. It 
could be attributed to feedline pickup -- but wouldn't you expect the matchbox to be 
better in this regard? I'm investigating further.

On 3/10/2012 12:31 PM, Erik Basilier wrote:
> As has been clearly demonstrated in this thread, there are multiple methods
> of measurement. The one that gets my vote for elegance is the one with two
> tuners back-to-back. With respect to the method that measures temperature
> rise, taking into account the mass of the tuner, one also needs to take into
> account the specific heat capacity of the tuner. One kilo of material x
> doesn't heat up at the same rate as one kilo of material y when the same
> heating power is applied. The tuner will of course be a mix of materials, so
> one would have to measure the rate at which the tuner heats up when heat is
> applied through a know heating source rather than TX power. If it is done
> that way, one needs to know neither the mass nor the specific heat capacity,
> since what one is measuring is essentially the mass times the specific heat
> capacity.
>
> 73, Erik K7TV
l

-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/