Speaking of balanced lines and tuners, I recently did an experiment that surprised me.
I have a dipole fed with 600-ohm open-wire line (and some window line indoors). I usually tune it with a Johnson Matchbox, a fully balanced link-coupled tuner. I was lucky enough to get my hands on a massive, high-quality edge-wound rotary inductor in a well-made aluminum enclosure. So I built a high-power T-network tuner with it. I purchased a good (and expensive) 1:1 balun designed for use after a tuner from DX Engineering, and compared the T-net + balun to the Matchbox. I didn't notice any difference in the strength of received signals between the tuners. But here is the surprising part: I expected that the Matchbox would provide better balance, which would reduce radiation and pickup from the feedline. To test this, I coupled a grid-dip oscillator to the feedline about 20 feet from the tuner. To my great surprise, the signal from the oscillator was much weaker with the T-network + balun than with the Matchbox! Signals the same, 'noise' weaker. So much for the need for 'truly balanced' tuners! On 4/5/2012 12:28 AM, Adrian wrote: > > I disagree, your coax suggestion has 32% loss against a good wl installation > which would provide 9% loss. > Use of RF ammeter on each leg can be used to balance the loading via antenna > leg adjustments if required. > > A dedicated eg: Johnson matchbox or GQ balanced tuner etc at TX would give > good results. > > The 450 ohm to 72 ohm connection is of no issue centre fed. The ladder line > length will have an impedance transformation effect. > Trying for common multiple of half wavelengths on FL length -vf at the > frequencies used will be a good idea if possible to represent the feedpoint > impedance at the TX end if possible. In any case the tuner will take care of > the transformation. > > Any decent low loss coax on this length will cost lots. > > I assume that the guy can't get the antenna closer, trees in the distance > etc probably, but I have seen many good examples from the USA of successful > long distance 450 ohm wl runs with wire antenna's. > > A ladder line setup here will outperform your RG11 etc by 1.2dB. > > When wet your RG11 setup will have a 1.4dB advantage. I guess it all depends > on the weather, and the guys bank balance. > 213 is ordinary for coax, I much prefer lmr400, which I use with my BD > 4115-ocf. > > vk4tux -- 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
