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VK2AAF
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la7no
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 Posted: Sun Oct 12, 2014 5:18 pm    Post subject: Hi Brian, Power reflected from a mismatched load and being returned to the source, will in most cases be re-reflected towards the load. I guess the only exception to this will be when the output of the transmitter or tuner matches the feeder impedance perfectly - something that rarely will be the case. 73es, Per-Tore DL/LA7NO
VK2AAF
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 Posted: Sun Oct 12, 2014 6:46 pm    Post subject: Hi Per-Tore, Thanks very much for your response. If power reflected from a mismatched antenna travels back down the feedline and then is again reflected off the xmtr output circuit or matching network, it stands to reason that the energy will eventually be dissipated as heat in the resistance/impedance of the feedline. As such, I wonder how non-resonant antenna systems radiate any signal at all. I wish I had the mathematical ability to delve into the theory a bit more, but I'm afraid I'm 'maths impaired!' 73 de Brian VK2AAF
la7no
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Joined: 05 Jul 2014
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Location: Bergen, Norway

 Posted: Sun Oct 12, 2014 7:13 pm    Post subject: Hi again, The re-reflected energy will be partly radiated from the antenna (according to the impedance matchind between antenna and feeder). The rest will again be reflected towards the source. For each 'trip' up/down the feeder, energy will be dissipated. For a reasonable good coax (f.ex. RG-213), with reasonable length (say, below 50m) and at relatively low frequencies (say, below 30 MHz), the coax loss will not be significant. Most of the energy will finally be radiated from the antenna. P-T / LA7NO
la7no
Antenna Theory Regular

Joined: 05 Jul 2014
Posts: 22
Location: Bergen, Norway

 Posted: Mon Oct 13, 2014 7:34 am    Post subject: Some thoughts about resonant vs non-resonant antennas: To put it short, a non-resonant antenna will radiate as much power as a resonant antenna provided there is an impedance match to the feeder. However, a non-resonant antenna will have a different radiation pattern than a resonant one. But for practical reasons we will in most cases not be able to put a resonant antenna up high enough to get its theoretical radiation pattern. A longer wire antenna will capture more of the wave front of the incoming signal. This will help on the receive side. But the challenge is to get a non-resonat antenna properly matched. Many matching devices introduce significant losses P-T / LA7NO
EA1DDO
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 Posted: Thu Nov 06, 2014 10:51 am    Post subject: Hi, I think the term "non-resonant" is not properlly used. For example,a 5/8 vertical antena is non-resonant, but matches perfectly to a 50 OHm coax (because there is an impedance adapter at antenna base). One more example, a simple 1/2 dipole is resonant but shows around 75 OHms so it is not matching 50 OHm coax well. Finally, the key is not to be resonant or not, the key point is to adapt his impedance to the transmission line properlly or not. 73, Maximo
VK2AAF
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 Posted: Thu Nov 06, 2014 10:55 am    Post subject: Very good points about the impedance match from Maximo & Per-Tore! Thanks much. 73 de Brian VK2AAF
la7no
Antenna Theory Regular

Joined: 05 Jul 2014
Posts: 22
Location: Bergen, Norway

Posted: Thu Nov 06, 2014 11:34 am    Post subject:

 EA1DDO wrote: Hi, I think the term "non-resonant" is not properlly used. ... Finally, the key is not to be resonant or not, the key point is to adapt his impedance to the transmission line properlly or not. 73, Maximo

Hi Maximo,

Isn't this what I just said?
In what way is the term being improperly used?

Per-Tore
LA7NO
EA1DDO
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 Posted: Thu Nov 06, 2014 3:34 pm    Post subject: Hi Per-Tore, Sorry, I did not talk about you. When I said "not properlly used" was generic, not thinking in you. Sorry 73, Maximo
la7no
Antenna Theory Regular

Joined: 05 Jul 2014
Posts: 22
Location: Bergen, Norway

 Posted: Thu Nov 06, 2014 3:46 pm    Post subject: OK, no problem. P-T
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