Author Topic: UHF radios, 40 Channels to 80  (Read 1241 times)

Offline Acco 4x4

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UHF radios, 40 Channels to 80
« on: January 11, 2018, 11:39:51 PM »
Hi All,
Was trying to explain the UHF channel changes to a friend so thought id waste some bandwidth and post it here too for anyone who might be interested.....

Channels are identical from channel 1 (476.425Mhz) to 40 (477.400Mhz) in frequency only, The old 40 channel use the 25kHz but the new 80 use half that at 12.5kHz, in effect channels 41 onwards uses the new space between the old channels. Simply channel 41 is actually old channel 1 plus a half channel then 42 is old 2 plus a half channel etc all the way to channel 80 which is old channel 40 plus a half channel 12.5kHz

channel 40 is 477.4000mHz
channel 80 is 477.4125mHz which is that extra half channel added.

The Bandwidth has been changed allowing to double our channels over effectively the same frequency range. works like this;
The old radios use a channel that is 25kHz wide (bandwidth)
New radios use channels half as wide 12.5kHz 25/2=12.5
Picking a random channel set;
So channel 14 is 476.750Mhz, on an old radio with a wide 25kHz bandwidth, the channel basically used 12.5kHz below and 12.5kHz above 476.750 to carry our 4x4 chatter so the whole channel is from 476.7375 to 476.7625 which is 25kHz . When we half that the channel width to 12.5kHz (half of 25) it is now from 476.74375 to 476.75625 which is a band of 12.5kHz. This leaves a gap between the old channels of 12.5kHz... insert new channel here! Pretend there is a fence between these channels. We have divided our 25kHz blocks in half, put a new fence down the middle and put a new channel on the old fence......

25kHz 12.5kHz

Channel 13-----476.7250----------------------------Channel 13----476.7250---------------
                                           New Fence-----------------------------------------------------
Old fence-------476.7375----------------------New Channel 53----476.7375----------------
                                           New Fence-----------------------------------------------------
Channel 14-----476.7500----------------------------Channel 14----476.7500---------------
                                           New Fence-----------------------------------------------------
Old fence-------476.7625----------------------New Channel 54----476.7625---------------
                                           New Fence-----------------------------------------------------
Channel 15-----476.7750----------------------------Channel 15----476.7750---------------

Old channel 13 with a 25kHz bandwidth will interfere with new channel 53 etc So its time to retire the old 40 channel radios.
« Last Edit: January 12, 2018, 09:41:04 AM by Acco 4x4 »

Offline dugite

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Re: UHF radios, 40 Channels to 80
« Reply #1 on: January 12, 2018, 06:01:25 AM »
G'day Acco, there is no requirement to discontinue the use of 40ch sets.

Channels 1 to 40 are the same on both types of unit. As you post the additional Channels are achieved by tighter bandwidth paramenters and using the intervening freqs.

Many users continue to use 40ch sets each Channel of which can be adequately received on a like-numbered Channel (1-40) on the 80ch sets.

As long as users of 80ch sets use any Channel from 1 to 40 they can communicate with users with 40ch sets on a like numbered Channel.

In fact IMHE there hasn't been much use of the Channels numbered above 40 anyway. Practical uses of accepted Channels eg. 10 (NPWS) , 40 (road) remains as what it was.
It was initially proposed to cease the use of 40ch sets but this proposal has now been rescinded because there is no practical requirement to do so.

As an owner of both types I can assure you that with a good quality 40ch set there are no issues communicating on with an 80ch set on Channels 1 to 40.

Users of the newer 80ch set owners have another bank of channels they can use with another 80ch set user.
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Offline Ravvin

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Re: UHF radios, 40 Channels to 80
« Reply #2 on: January 12, 2018, 08:16:21 AM »
I think part of the problem is people using some of the older or cheaply made 40 channel sets tend to cause some interference to people using the 41 to 80 channels.
As an example, if someone with an older set is transmitting on channel 20, because of some bleed-over they can interfere with people on channels 59 and 60.
Saying that though, they usually have to be pretty close to each other to interfere and the people using 41 to 80 can easily move to a clear channel.
Part of the regulations in the user manual for every radio certified for use in Australia is that it must not cause RFI interference. The next line is usually that the same radio must accept any RFI interference caused by other devices.

I occasionally find that my harvesting crews using the cheap UHF hand-helds even cause interference to people just one channel above or below what they are using.
There are many cheap overseas radios flooding the market through eBay. I doubt most have been certified for use in Australia and many wouldn't meet the requirements anyway.


Offline kman

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Re: UHF radios, 40 Channels to 80
« Reply #3 on: January 12, 2018, 09:01:12 AM »
The chance of someone using a 40 channel radio being close enough to interfere with someone using an 80 channel radio on an adjacent frequency is so remote in the country that it is unlikely to ever be a problem. In the city the problem is idiot users, not co-frequency interference!

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Offline Acco 4x4

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Re: UHF radios, 40 Channels to 80
« Reply #4 on: January 12, 2018, 09:49:54 AM »
You all have a valid point and i do agree. Although the 40 and 80 channel radios are not 100% compatible they do the job fine. For those of us who use repeaters they do cause issues and yes I need to change channels (again....) but they also cause issues for anyone using the data transfer channels. I use UHF to share maps etc between 4x4's when we travel. You can hear talking on data channels occasionally and this affects the data transfer. Anyway since few use the data i guess who cares!