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/ >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> -- Vic, K2VCO Fresno CA http://www.qsl.net/k2vco/ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
