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:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
