[Elecraft] high-power tuner

[Vic K2VCO]

This is why I checked that real signals received through the antenna were not attenuated 
to a detectable degree. I could not tell the difference between the tuners with weak 
signals from distant stations.

Reasons that the T network may be as efficient as the Matchbox for this test:

1) In this case the T output capacitor is maximum, which makes it an L network.
2) No switches in the path.
3) Very high-Q inductor in the T network.

On 3/10/2012 4:06 PM, Don Wilhelm wrote:
> 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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-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/