ACMA reverses decision ruling millions of uhf radios illegal.

[VK2FMIA]

The reason they want to get rid of the 40 channel units is that when they created the 80 channel units they had to split the current bands as they could not increase the overall spectrum assigned for uhf. They could not add the extra 20 channels to the ends of the existing spectrum.

The 40's run on 25 hertz and the 80's on 12.5 hertz. If you have two units of each type talking to each other on channel 22 for instance then the fourty transmits and receives at 25 hertz while the 80 operates at 12.5 and has been tuned to be in the centre of that range. It actually misses out on 6.25 hertz of transmission on either side of the 40's transmission. That's why the newer units don't pick up the older ones very clearly as they can't catch the full transmission and the older units don't pick up the 80 as loudly as the 40. That's why in a mixed convoy you have people not hearing conversations properly.

the 40's also cause splatter on the higher channels as when they transmit on ch 22 they also transmit 6.25 hertz of their messag to ch 61 and 62 which sit either side of ch 22 on the eighty ch units. A diagram would explain it better.

FM transmitters on the 477 Mhz band (and most other FM bands) can only use a signal 8 Khz wide for voice. On the old 40 channel CB`s the frequencies were spaced 25 Khz apart but only use 4 Khz either side of the channel frequency. The new 40 channels were squeezed in between & a few added to the end of the band at a spacing of 12.5 Khz. Both still only transmit & receive an 8 Khz wide signal so there should be no bleed over, if they do then they are not within legal transmitting bandwidth.