I thought it was the .005 suffix which programmed some radios to narrow the transmit deviation slightly?
The transmission bandwidth does not change.
Keep both radios, when you get a 25kHz you transmit on your current radio, and the few time you get a 8.33kHz frequency you switch to transmit on the new one.
You don’t need one radio set to 25khz spacing and one set to 8.33khz. The 8.33khz mode on your new radio should in reality be named dual 25khz/8.33khz mode. If you are given and select a 25khz frequency the radio will work in 25khz bandwidth and if you are given an 8.33khz ‘channel’ it will work in 8.33 mode. This should all be transparent to the pilot. The radio should know what to do from the frequency/channel selected.
Peter wrote:
I thought it was the .005 suffix which programmed some radios to narrow the transmit deviation slightly?
The transmission bandwidth does not change.
neutron wrote:
You don’t need one radio set to 25khz spacing and one set to 8.33khzI realize this. In my case we have an old KN-155 with 25kHz and a GNS430 set to 8.33, and it takes quite a few revs of the knobs to go through all frequencies.
Arne wrote:
it is practical to have 2 radios, when the frequency selection is through knob-turning.
as long as you recognize if given frequency is 25 or 8.33 quickly….
In AM (amplitude modulation) the carrier deviation is simply equal to the maximum audio (modulation) frequency.
So if eg your voice has highest frequency components up to 2kHz (my ex wife could do it easily) then a 125.000 carrier will move between 124.998 and 125.002MHz.
You can’t change this, in the simple variant used in aviation. Slicker variants might go from 125.000 to 125.002 only so 2x more channels can be accommodated.
All one could do is to more severely limit the modulating signal. We have another more technical 8.33 thread where specs are discussed but I don’t recall that an 8.33 radio has a tighter spec on this.
Michal wrote:
I guess by selecting 005 I am telling the radio to transmit on .000 but narrow bandwith…No, you tell the radio to receive on .000 but with narrow bandwidth.
The transmitter bandwith is always quite narrow as it is determined by the modulation (audio) signal.
achimha wrote:
As of January 1st, 2018, all aircraft with VHF are legally required to have 8.33kHz spacing
Actually only aircraft flying in airspace where radio contact is required is legally required to have 8.33 radios — although I realise that in central Europe there may not be much practical difference.
I think the thread agrees with my initial post then?
I will be legal with a Trig 8.33 Khz radio and my old TKM MX170C. As Peter reminded me, the transmit deviation will be modulated by voice which is 300Hz to 3,500Hz (max) so deviation of no more than 3.1 Khz
So if one has a .005Mhz frequency or a .000 MHz frequency you can use either your new or old radio (with no risk of TX interference).
That means if you are flying VFR and most ground stations are still on the “old” frequencies then you might as well keep your new radio on 25 Khz spacing to save some knob twiddling! In the case of the Trig, a quick press on the freq selector knob will kick it into 8.33 mode when needed!
