The efficiency of the T-network can be less than the Matchbox-type tuner or an L-network because it is possible to find a suboptimal combination of component values that will give you a 1:1 match. I believe that the most efficient match is achieved when the T inductance is set to the minimum value that will give you 1:1.
This can require large values of capacitance in the T network for the lower bands. In my case both input and output capacitors have maximum values of 600 pf. That is probably not enough for a wide range on 160 meters. The impedance range within which the T is efficient depends on the minimum and maximum values of inductance and capacity that you can achieve. Using a pair of vacuum caps would be best, but would be VERY hard to tune if you didn't know where to set them first! I think the Tentec 229 tuner is an L network. It is as efficient as it can be when it is adjusted for a 1:1 match. I don't know why you got better results with your balun than Tentec's -- maybe yours was better! On 4/5/2012 12:52 PM, Matt Murphy wrote: > One related question, when speaking of the efficiency of a balanced feedline > + balun and > tuner, what would be a best/worst case scenario for the loss introduced by the > balun+tuner? Would loss vary significantly by frequency for a nonresonant > antenna? I'm > trying to develop an intuition about the lossiness of the tuner+balun > compared to, say, > 50' of RG213. > > I've opted to use a 1:1 balun at the end of 450 ohm ladder line, then a short > length of > coax into a TenTec 229 tuner. In the informal test that I performed, the > homebrew 1:1 > balun + coax jumper improved the performance of the antenna compared with > connecting it > directly to the balanced line connectors on the back of the tuner. > > 73, > Matt NQ6N > > > > On Thu, Apr 5, 2012 at 12:23 PM, Don Wilhelm <[email protected] > <mailto:[email protected]>> wrote: > > Vic, > > Where was the frequency of the GDO with respect to the band the tuner > was set to? If it was below the band of interest, I would expect > something like that - the T-Network is a high pass filter. > > 73, > Don W3FPR > > > On 4/5/2012 12:28 PM, Vic K2VCO wrote: > > 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! -- 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
