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#61
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Standing Waves (and Impedance)
Owen Duffy wrote:
Is the sound subcarrier supposed to be at 65.75MHz for your Ch3? I think that's a valid assumption. It's possibly a cockpit error of some kind. I will have to try again. -- 73, Cecil http://www.qsl.net/w5dxp |
#62
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Standing Waves (and Impedance)
Dave Platt wrote:
It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? or perhaps it needs to be switched manually to a "wide FM" mode to do so in this frequency range? It's also possible that I am senile and need to try again. -- TNX & 73, Cecil http://www.qsl.net/w5dxp |
#63
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Standing Waves (and Impedance)
Dave Platt wrote:
It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? I just drug out the IC-706 manual. It receives channel 2 on the HF antenna and channel 3 on the VHF antenna. :-) -- 73, Cecil http://www.qsl.net/w5dxp |
#64
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Standing Waves (and Impedance)
"John Ferrell" wrote
Crazy George wrote: The audio is not mixed with the main carrier? It can be either way. TV aural uses a separate transmitter from TV visual, because the visual amplifier in a TV tx is not linear enough to amplify both the aural and visual waveforms while maintaining r-f intermods sufficiently low (to FCC spec). The aural and visual signals are combined with mutual isolation of the txs, and radiated by a single antenna, typically. In an emergency, TV stations sometimes combine A&V at exciter level and pipe them through the visual PA, which is operated at reduced power to minimize r-f intermods. Typically the TV station is not meeting spec then, however. If you choose to use separate transmitters the demands on antenna bandwidth are greatly reduced. Reducing antenna bandwidth needed also would require separate antenna systems for the aural and visual transmitters. That is done, occasionally - but not often. This doesn't reduce the bandwidth needed by the visual tx by very much, however. Generally it's more cost-effective to use a single antenna to radiate both A&V. RF (RCA Broadcast systems field engineer, 1965-1980) |
#65
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Standing Waves (and Impedance)
US TV aural is frequency modulated, with +/-25 kHz deviation defined as 100%
modulation. Pre-emphasis of 75 microseconds is applied to program audio. It is transmitted as a discrete r-f waveform about 250 kHz below the upper edge of the TV channel. TV receivers typically demodulate it using an FM detector tuned to the 4.5 MHz intercarrier product present in the output signal of its video detector. Therefore if the TV visual carrier (only) goes off the air, no audio will be heard at the TV set, either. Any communications-type receiver capable of tuning to, and demodulating the TV aural carrier will enable listening to it. Even some little "pocket" AM/FM radio receivers have that ability. RF |
#66
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Standing Waves (and Impedance)
"Reg Edwards" wrote
Who cares what is the SWR on the transmission line provided the transmitter is loaded with its correct load resistance? ____________ Probably most people who don't want to destroy their transmission line. Apparently this does not include your esteemed self. RF |
#67
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Standing Waves (and Impedance)
In article ,
Cecil Moore wrote: It's possible that your IC-706 isn't willing/able to lock onto a carrier with such a high deviation, perhaps? I just drug out the IC-706 manual. It receives channel 2 on the HF antenna and channel 3 on the VHF antenna. :-) #splorf# Well, I suppose it does make sense in a way, but it sorta seems to violate the Law of Least Astonishment! -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#69
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Standing Waves (and Impedance)
65.75 is the magic frequency. It does appear the WFM mode can not be used on
this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. Now I have to get in the circuitry and see why the WFM is not operable on this band. "Cecil Moore" wrote in message et... Fred W4JLE wrote: You can if you tune to the audio offset. I have run the IC-706 all up and down the channel 3 60-66 MHz frequencies while in College Station, TX and cannot hear the audio anywhere. -- 73, Cecil http://www.qsl.net/w5dxp |
#70
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Standing Waves (and Impedance)
Fred W4JLE wrote:
65.75 is the magic frequency. It does appear the WFM mode can not be used on this frequency on the 706 MKIIG I have. In the FM position, while distorted it is copyable. The radio shows WFM mode, but it certainly isn't in the wide mode. My original problem was with an original IC-706 which I sold. I'm now mobile with an IC-706MKII with DSP. But my mode switch switches from FM to AM to FM ... and never shows WFM at all, not even when tuned to 88-108 MHz so commercial FM or TV is not worth listening to. I have a Sony Walkman that does receive VHF TV audio and my CCRadio+ does also. -- 73, Cecil http://www.qsl.net/w5dxp |
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