Towertalk
[Top] [All Lists]

## [TowerTalk] wire antennas

 To: [TowerTalk] wire antennas jreid@aloha.net (Jim Reid) Thu, 03 Jul 1997 08:53:25 -1000
 ```At 01:41 PM 7/3/97 +0200, Jurgen Geldhof wrote: >Hi, >Here's my question : > >Is there a formula to calculate the necessary thickness (or diameter) of an >antenna wire to support a certain amount of power at a certain frequency ? > >I know, the thicker the better, but I prefer it as light as possible. Hi Jurgen, Seems to me it will depend upon the effective radiation resistance of your antenna. A rhombic wire antenna has a pretty high value, so the voltage on the line would be high, but the current will be low, for a given power level, compared to say, a simple half wave dipole wire up a half wave or so where the effective resistance would be around 75 ohms or so. Consider some imaginary situations: transmission lines in which it has been attempted to match to the rhombic antenna, but we still have a 3:1 VSWR in the antenna-feed system. Using the following feed lines, we would measure (I think): 50 ohm coax will have a voltage of 474 rms, and carry a max current of 9.5 amps. 72 ohm transmitting twin lead, voltage, 570 volts rms, current, max, 8 amps. 450 ohm twin line, rms voltage, 1423; max current, 3.16 amps. The losses which I assume concern you, would be related to the current losses of a particular wire size. So the answer you seek depends upon a lot of factors of the situation, and it is going to be impacted by the height of your wires, there length at a particular frequency, etc. I just measure the forward voltage on my 50 ohm coax going to my tribander. Find a vswr of around 1.2 or 1.3:1 (tough to measure exactly when so low). With 1500 watts or so peak showing on SSB voice peaks, read a max voltage forward of about 300. Forward current, max, then is the voltage divided by the line impedance, or 300, by 50, or about 6 amps max. Did this on 20 at 14154, no one else around there right now, so didn't QRM anybody that I could here from out here anyway. Anyway, just some thoughts about your question; am sure someone else will be able to give you better, and perhaps even a correct answer. My answer may be way too simple minded!! 73, Jim, KH7M -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com Search: http://www.contesting.com/km9p/search.htm ```
 Current Thread [TowerTalk] wire antennas, Jurgen Geldhof [TowerTalk] wire antennas, Jim Reid <= [TowerTalk] wire antennas, k4sb@worldnet.att.net [TowerTalk] wire antennas, Darrel Van Buer [TowerTalk] Wire antennas, stu