Today's Message Index:
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1. 02:25 AM - Re: Frequencies and 8.33 Channel numbers (Kelvin Weston)
2. 09:02 AM - Re: Frequencies and 8.33 Channel numbers (JonathanMilbank)
Message 1
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| Subject: | Re: Frequencies and 8.33 Channel numbers |
Hi Jonathan
Most low-end GA radios require you to select either 8.33 or 25Khz mode in the setup
and will only display the associated channels or frequencies for that bandwidth.
If you have a radio that allows you to select both channels and frequencies directly
using the frequency select knob, then it may well adjust the bandwidth automatically.
Whichever mode you are in, selecting a frequency of 134.1 in 25 Khz mode or channel
134.105 in 8.33 mode will use the same carrier frequency of 134.1 Mhz for
transmit and receive.
However due to the differing bandwidths, a 25 Khz station should be able to receive
your transmission ok but an 8.33 station (your aircraft) may not receive
a 25 Khz transmission as clearly.
This can be due to a number of factors concerning radio wave propagation, transmission,
etc. and is a known issue. See the 2nd to last paragraph of this article
issued by Eurocontrol:
https://833radio.com/news/show/7
There are lots of similar articles on the web.
Unless you wish to change radio, your current method is probably the best way to
achieve satisfactory comms with regularly used 25 Khz stations.
--------
Regards
Kelv Weston
Kit 497
kelv@kdweston.biz
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=490549#490549
Message 2
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| Subject: | Re: Frequencies and 8.33 Channel numbers |
Thanks Kelvin. An interesting article.
Another factor re Aberdeen Offshore Radar 134.1 MHz occurs to me, viz some years
before the introduction of 8.33 KHz channel spacings, Aberdeen had already introduced
rebro for offshore helicopter communication purposes and thus three
additional remote transmitters were placed on offshore platforms over 100 miles
apart. This also involved telephone links to the remote transmitters and synchronisation
problems were challenging.
>From what I think I was told, the 25 KHz band segment assigned to 134.1 MHz was
subdivided into 4 of about 6 KHz each (I guess) and so the transmissions had
very narrow bandwidth but the receivers remained capable of the full 25 KHz.
At least this is what I vaguely recall from my days of flying helicopters to North
Sea destinations. There were "black holes" in the coverage offshore.
I wonder if the difference between 8.33 KHz bandwidth of my aircraft radio and
the presumed 6.25 KHz of the rebro system causes some "mismatching" effects, when
my radio is erroneously selected to channel 134.105? Any polite suggestions
welcome!
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=490553#490553
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