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40/15M dipole question
Let's say I build a horizontal dipole, trimmed for minimum SWR @
7.200 mhz. I'll probably use 14-16 gauge insulated house wiring for this antenna. It'd be a "nominal' quarter wavelength per leg. This dipole will be fed with 50 ohm coax, and it will be erected horizontally, 30 feet high over "average" ground. What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? Thanks, folks...... FjLee KA0FPJ |
40/15M dipole question
On Apr 6, 5:56*am, " wrote:
What SWR *reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com |
40/15M dipole question
On Wed, 6 Apr 2011 03:56:21 -0700 (PDT), "
wrote: What SWR reading could I expect to see...? 15:1 73's Richard Clark, KB7QHC |
40/15M dipole question
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40/15M dipole question
On 4/6/2011 6:28 AM, Cecil Moore wrote:
On Apr 6, 5:56 am, wrote: What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John |
40/15M dipole question
On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote: On Apr 6, 5:56 am, wrote: What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John Oops! I just noticed that I had zero wire resistance. Changed it to copper but only got a slight change: Impedance = 87.47 - J 184 ohms SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042 |
40/15M dipole question
John - KD5YI wrote:
On 4/6/2011 2:51 PM, John - KD5YI wrote: On 4/6/2011 6:28 AM, Cecil Moore wrote: On Apr 6, 5:56 am, wrote: What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John Oops! I just noticed that I had zero wire resistance. Changed it to copper but only got a slight change: Impedance = 87.47 - J 184 ohms SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042 If you tune it down a bit so you resonate at perhaps 7.15, then the third harmonic will be closer to 21.3. It's a dipole, so not real high Q, particularly on the fundamental, so maybe what you do is go for a compromise tuning.. A bit low on 40 and a bit high on 15. |
40/15M dipole question
On 4/6/2011 7:57 PM, Jim Lux wrote:
John - KD5YI wrote: On 4/6/2011 2:51 PM, John - KD5YI wrote: On 4/6/2011 6:28 AM, Cecil Moore wrote: On Apr 6, 5:56 am, wrote: What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John Oops! I just noticed that I had zero wire resistance. Changed it to copper but only got a slight change: Impedance = 87.47 - J 184 ohms SWR (50 ohm system) = 9.960 (75 ohm system) = 7.042 If you tune it down a bit so you resonate at perhaps 7.15, then the third harmonic will be closer to 21.3. It's a dipole, so not real high Q, particularly on the fundamental, so maybe what you do is go for a compromise tuning.. A bit low on 40 and a bit high on 15. Well, yeah, I know. But, I'm trying to simulate based on the OP's info and Cecil's results. John |
40/15M dipole question
On 4/6/2011 2:51 PM, John - KD5YI wrote:
On 4/6/2011 6:28 AM, Cecil Moore wrote: On Apr 6, 5:56 am, wrote: What SWR reading could I expect to see from this antenna if I tried to use it at 21.300 mhz........in the same environment as stated above? EZNEC sez 11:1 with a feedpoint impedance of 100-j200 ohms. -- 73, Cecil, w5dxp.com Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John Are you using 9 segments? John |
40/15M dipole question
On 4/6/2011 8:16 PM, John - KD5YI wrote:
On 4/6/2011 2:51 PM, John - KD5YI wrote: Hey Cecil - I got: Impedance = 85.26 - J 186.3 ohms SWR (50 ohm system) = 10.337 (75 ohm system) = 7.308 Let's see if we can determine why they don't match. I adjusted the wire length for no reactance at 7.2 MHz. I used 99 segments of #14 wire. I did not include insulation effects. How about yours? John Are you using 9 segments? John I think may have missed something on how segmentation works. I thought you needed an even number of segments to split a dipole evenly. So while 99 is close to centered by my logic, if 9 was used it might skew things a bit. If I'm off base please tell me so I can adjust my model of how NEC works. Thanks. tom K0TAR |
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