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I can't understand why the claim that the T2FD is relatively immune to local electrical noise is 'disputed'. Any balanced-feed antenna will by definition 'phase-out' local electromagnetic noise - at least from the broadside direction. This antenna works, by the way. The small size (and especially the resistor) make it look like a dummy load on paper, but it isn't, (and I don't know why either! :-). It works even better if you stick a big piece of insulating tape over the 'S' meter and just listen. Chris G4PDJ (Contact via qrz) 08:44, 11 January 2007 (UTC)
"Removed technically naive qualification re. ATU as passband filter"
Dear Chris, I stand my ground. ATUs are not designed as passband filters. Even in a lowpass-type ATU like an unbalanced pi-section with capacitance to ground and inductance on the signal path, you may end up with a great match that adds nothing in term of filtering. If the match is good to start with (not granted, but possible with this antenna, a low C - low L - low C, i.e. an almost-bypass setting would give you good SWR. Another matter: lots of people equate mismatch woth harmonics - yes, there is indeed a relationship on various levels, yet it's a weak one. You can have horrendous SWR but no harmonics, and also plenty of harmonics but not enough mismatch to look worrisome at the SWR bridge. Even worse, I have a very effective 26-30MHz t-section ATU with L to ground and C's in and out - that's a HIGH pass filter. The edit I removed even contained an indication that a broadband antenna is more likely to radiate spurs such as harmonics compared to a resonant one. Apart from being an inefficient way of suppressing harmonics, relying on antenna response to do so would even be illegal in some jurisdictions. Having said that, I occasionally DO use an ATU for transmitting with a T2FD, not for harmonics only but to protect an extremely old and fragile non-self-throttling solid state rig - just as you said. :-)
Regarding the folded dipole picture I just removed (July 14, 2008) - T2DF is broadband, folded dipole is resonant - the depicted folded dipole showed a roughly 300-Ohm BALANCED antenna connected to an UNBALANCED, and generally lower impedance coaxial cable, both very bad ideas (impedance mismatch), and worse (poor antenna-coax insulation) the higher the operating frequency, so even as a folded dipole proper, it's a technically misleading drawing.
To be totally nitpicking, both should be referred to as antenna + feed systems, although it's normal to use the part (antenna) for the whole. In both cases the antenna proper is just the wire portion, and lead, balun, resistor, insulators, wires etc. are just the things you add to keep the wire in the right shape and to properly bring the electric signal to the antenna or away from it.
Sorry! The two names are rather false friends, although the two antennas look much the same.
DOES ANYONE HAVE A T2FD DRAWING WITH AN APPROPRIATE COPYRIGHT SITUATION? Spamhog ( talk) 15:16, 14 July 2008 (UTC)
I've found another use for ye olde T2FD. Where I am living at the moment there is a lot of electrical noise. I am a QRP operator, and when 'digging-out the weak ones' on 80m CW, I have found that using the outdoor inverted 'L' wire for transmit and the (attic/loft) T2FD - with its lower noise floor - for receive really works. The signals are not massive, but the noise is even less. You can compensate by 'upping' the AF gain and even switching-in the preamp with the T2, which would be excruciating when receiving on the inverted 'L'. It means a quick flick of the ATU antenna selector every time you 'over', but you only need to do it for the really weak ones. Also good for no-antennas 'clandestine' operating - i.e. use the loft T2FD on 7MHz-to-28MHz PSK31/Olivia etc during the day, and 'throw-out' a secret 80m transmitting wire after dark :-) Maybe someone can think of a shorter wording and put it on the page. (Chris G4PDJ/G6CSL) — Preceding unsigned comment added by 217.43.2.15 ( talk) 21:08, 20 September 2011 (UTC)
![]() | This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||||||||||||||||||||||
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I can't understand why the claim that the T2FD is relatively immune to local electrical noise is 'disputed'. Any balanced-feed antenna will by definition 'phase-out' local electromagnetic noise - at least from the broadside direction. This antenna works, by the way. The small size (and especially the resistor) make it look like a dummy load on paper, but it isn't, (and I don't know why either! :-). It works even better if you stick a big piece of insulating tape over the 'S' meter and just listen. Chris G4PDJ (Contact via qrz) 08:44, 11 January 2007 (UTC)
"Removed technically naive qualification re. ATU as passband filter"
Dear Chris, I stand my ground. ATUs are not designed as passband filters. Even in a lowpass-type ATU like an unbalanced pi-section with capacitance to ground and inductance on the signal path, you may end up with a great match that adds nothing in term of filtering. If the match is good to start with (not granted, but possible with this antenna, a low C - low L - low C, i.e. an almost-bypass setting would give you good SWR. Another matter: lots of people equate mismatch woth harmonics - yes, there is indeed a relationship on various levels, yet it's a weak one. You can have horrendous SWR but no harmonics, and also plenty of harmonics but not enough mismatch to look worrisome at the SWR bridge. Even worse, I have a very effective 26-30MHz t-section ATU with L to ground and C's in and out - that's a HIGH pass filter. The edit I removed even contained an indication that a broadband antenna is more likely to radiate spurs such as harmonics compared to a resonant one. Apart from being an inefficient way of suppressing harmonics, relying on antenna response to do so would even be illegal in some jurisdictions. Having said that, I occasionally DO use an ATU for transmitting with a T2FD, not for harmonics only but to protect an extremely old and fragile non-self-throttling solid state rig - just as you said. :-)
Regarding the folded dipole picture I just removed (July 14, 2008) - T2DF is broadband, folded dipole is resonant - the depicted folded dipole showed a roughly 300-Ohm BALANCED antenna connected to an UNBALANCED, and generally lower impedance coaxial cable, both very bad ideas (impedance mismatch), and worse (poor antenna-coax insulation) the higher the operating frequency, so even as a folded dipole proper, it's a technically misleading drawing.
To be totally nitpicking, both should be referred to as antenna + feed systems, although it's normal to use the part (antenna) for the whole. In both cases the antenna proper is just the wire portion, and lead, balun, resistor, insulators, wires etc. are just the things you add to keep the wire in the right shape and to properly bring the electric signal to the antenna or away from it.
Sorry! The two names are rather false friends, although the two antennas look much the same.
DOES ANYONE HAVE A T2FD DRAWING WITH AN APPROPRIATE COPYRIGHT SITUATION? Spamhog ( talk) 15:16, 14 July 2008 (UTC)
I've found another use for ye olde T2FD. Where I am living at the moment there is a lot of electrical noise. I am a QRP operator, and when 'digging-out the weak ones' on 80m CW, I have found that using the outdoor inverted 'L' wire for transmit and the (attic/loft) T2FD - with its lower noise floor - for receive really works. The signals are not massive, but the noise is even less. You can compensate by 'upping' the AF gain and even switching-in the preamp with the T2, which would be excruciating when receiving on the inverted 'L'. It means a quick flick of the ATU antenna selector every time you 'over', but you only need to do it for the really weak ones. Also good for no-antennas 'clandestine' operating - i.e. use the loft T2FD on 7MHz-to-28MHz PSK31/Olivia etc during the day, and 'throw-out' a secret 80m transmitting wire after dark :-) Maybe someone can think of a shorter wording and put it on the page. (Chris G4PDJ/G6CSL) — Preceding unsigned comment added by 217.43.2.15 ( talk) 21:08, 20 September 2011 (UTC)