[Elecraft] high-power tuner

[Don Wilhelm]

Vic,

Be aware that loss in the tuner can reduce the signal pickup - I would 
not be so quick to pass judgement that the Matchbox is less efficient 
than the T-network tuner - I know the link coupled tuner (properly used) 
is more efficient.

You may want to double check your test conditions and instrumentation.

73,
Don W3FPR.

On 3/10/2012 4:38 PM, Vic K2VCO wrote:
> I just did the following experiment: I coupled a grid-dip oscillator to my feed line far
> from the tuners and switching relays.  I put it a few inches from the feedline equidistant
> from the conductors. I found that the T network plus DXE balun reduced the signal pickup
> by about 15 dB over the Matchbox!
>
> That means that both radiation and noise pickup on the feedline are much less with the T
> than with the Matchbox. At the same time I verified that there was no detectable
> difference between the strength of received signals coming from the antenna.
>
> This is amazing! It means that the T network and balun is significantly better than the
> Matchbox in this important respect.  So much for mythology.
>
> On 3/10/2012 1:11 PM, Vic K2VCO wrote:
>> 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.
>>
>> -- 
>> Vic, K2VCO
>> Fresno CA
>> http://www.qsl.net/k2vco/
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