Stan, I was trying to highlight a particular issue - that averaging the dB figures themselves is a pretty meaningless exercise. In my example, the average rearward power ratio would be 12.6dB not 15d
Really? What's to stop CM still flowing along the braid? Or along the boom? Or both? Steve G3TXQ _______________________________________________ _______________________________________________ TowerT
Jim, If you want to use Free Space as the environment for comparison - which I whole heartedly support - simply use dBi; I never came across dBd in the whole of my professional career. What you then
Does this help? http://en.wikipedia.org/wiki/Signed_zero Steve G3TXQ 73, Mike NF4L _______________________________________________ _______________________________________________ TowerTalk mailing li
The proportion of current that flows back down the shield compared to that which flows into the attached dipole leg will depend on the relative impedances of those two paths. In the case of a half-wa
I just tried a SPICE analysis using those two leg impedances and a 4:1 voltage balun. With a moderate braid path impedance - 200 Ohms - there was no significant difference in braid current whichever
However, the OP proposes to use a Balun Designs 4125 at his feedpoint; that's a 4:1 voltage balun, which is why I mentioned it :) "I have chosen Balun Designs 4125 for the 4:1 balun, recommended for
Kelly, Maybe this will help understand what is happening: Take a look at the SPICE schematic here - It models the feedpoint of a low(ish) 80m OCFD fed one third the way from one end through a 4:1 vol
178.57 Watts Steve G3TXQ On 26/01/2015 15:59, TexasRF-- via TowerTalk wrote: Out of curiosity, what power level was used for the simulation? Gerald, K5GW _____________________________________________
Here's the corresponding schematic if a 4:1 unun is used instead of a 4:1 voltage balun. http://www.karinya.net/g3txq/temp/ocfd/80m_ocfd_unun_spice.png There's a small *drop* in the CM driving voltag
Kelly, You are quite right to take me to task! I was addressing more points than you asked - probably because I was anticipating a wider readership. To try to summarise: 1) The OCFD is particularly p
In the PPT you linked, there are slightly fewer effective turns on the binocular than on the tall stack; he's comparing 3 complete turns through a stack of 8 toroids, with 3 turns through part of the
Jim, That is such a revolutionary statement that I felt I must investigate it. So I loosely wound 4 turns of PTFE wire on a Type 43 toroid - the wire was barely touching the toroid. The impedance mea
Yes - that's exactly what happens with the common-mode current in a choke! I could just as easily have wound the toroid with coax, had a differential-mode signal flowing in the coax, and driven commo
The common-mode voltage at the feedpoint of an OCFD can be many times the differential voltage across the feedpoint. Take the common example of a 132ft wire fed 44ft from one end at a height of 35ft.
The 51ft "G5RV" performs well on 40m, 20m and 10m - bands where the SWR(50) at the ladderline/coax junction is moderate. On other bands the SWR(50) is high, and how well it performs will depend on th
If you use a G5RV, the simplest way to get improved signal strength reports is to announce that you are using something else ;) This from W8JI: -- On The Air Testing One of the only ways to reliably
Bob, Even the technical literature wont give you a complete picture because it wont take account of the stray capacitance introduced by the choke winding. The most effective technique I've found is o
Jim, This one may be of interest: http://hamwaves.com/antennas/inductance.html It's the most accurate I've found. To quote the web page: "The inductor calculator presented on this page is unique in t
Rick, That's interesting - I typically see large differences. I just tried an arbitrary example and got 101uH from Wheeler's formula with 130uH from the HamWaves calculator. But we're now heading off