0.3dB is simply an unbelievable figure whether it refers to dissipative loss or mismatch loss! If it were dissipative loss it would mean 100W dissipated when passing 1500W If it were mismatch loss it
Ken, EZNEC predicts that a 100ft dipole used on 80m is only a fraction of a dB less efficient than a full half-wave; the feedpoint current only has to increase by about 19% to "compensate for the mis
Here are some "complete system" numbers drawn from EZNEC, VK1OD's line loss calculator, and W9CF's tuner simulator: Half-wave 80m dipole at 30ft made from #14 wire: Antenna copper losses: 0.19dB 100f
Gene, EZNEC predicts the feedpoint impedance of an 80m half-wave at 30ft over average ground as 51 Ohms at resonance - that was close enough for me to call the RG213 "matched" ;) But you raise a very
Ken, If by "efficiency" we mean the power radiated by the dipole as EM energy compared to the power applied, what you say simply isn't true. If we apply 100W to a 70ft dipole made of #14 copper on 80
And the matched loss per unit length of the resulting 150 Ohm twin will also be exactly the same as the 75 Ohm coax. Steve G3TXQ _______________________________________________ ______________________
We need to remember that the loss figures for 450 Ohm line given in TLW and in the Antenna Book are optimistic by a factor of about 2:1. Use the VK1OD calculator for more accurate results. Steve G3TX
That seemed a bit unlikely to me so I just tried it! I took a 26ft wire and placed it in 3 positions around a 20m Yagi: 4ft behind the Reflector, 4ft in front of the foremost Director, and 4ft off to
The ARRL Antenna Book has a section on "Resonance in Guy Wires" which includes a chart of lengths to avoid for the eight HF amateur bands. From that chart, 26ft would be a **good choice** to avoid pr
Frank, You may not have the resources to raise or lower the antennas, but tools like HFTA are very useful for assessing trade-offs and making cost/benefit choices. Take a look at the chart in Section
Some designs here: http://www.karinya.net/g3txq/chokes/ 8 turns on a FT240-31 core is good for 20m thru 10m - it gives >2k Ohm choking impedance across the range and is predominantly resistive. Steve
Assuming your top-loaded vertical was close to resonance, the UnUn application is not very demanding. I'm not sure what core material Balun Designs use, but a quick calculation for 2x6 turns on a FT2
Jim, I doubt it's material with as low a permeability as #61 or #67. If you look at the photos of the UnUn, you'll see it comprises 6 turns of coax on a core that is significantly smaller diameter th
Mike, I'm not a betting man, but if I were I'd bet heavily that those UnUn losses are significantly less than 0.2dB. Here's my reasoning: The core in the Balun Designs photo looks to be about a size
Here's one commercial balun manufacturer that _does_ publish useful performance data: http://www.balundesigns.com/images/Model%201171%20Choking.jpg Steve G3TXQ _______________________________________
Yes, 8 turns on a single core. I don't agree that RG58 is "junk"; it's rated for 380W continuous average power at 28MHz into a matched load - that's adequate for UK power levels. If you want to go hi
Jim, I see reasonable agreement between measurements I make on my AIM and the results I get using a signal generator/scope method, provided the AIM is calibrated accurately to the measurement plane.
Jim, I just double-checked my results for the 6 off #31 bead choke. I looked carefully at the ratio of the Resistive (loss) component of the choke impedance to the Reactive component, across the rang
Jim, I forgot to mention that Jim Brown's data pretty much confirms my data. Take a look at the chart at the bottom of his page 25 here: http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf You'll see