Problem to select radio frequencies

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bravodeltafr
Airman
Posts: 25
Joined: 22 Nov 2018, 09:46

Problem to select radio frequencies

Post by bravodeltafr »

Hello,
I use the C172.
I notice that it is impossible for me to settle the Comm with certain frequencies.
I'm not talking about scrolling by plot of 5 units
I get by example the following frequencies by turning the button: 122.80 and then 122.82 then 122.85 and then 122.87 and 122.90. Or 122.80 then 122.83, then 122.85 then 122.88 and 122.90, then 122.93, etc ...
How to display for example 122.81?
What is this problem?
Thanks for your help !

flapman
Staff Sergeant
Posts: 457
Joined: 10 Oct 2013, 21:35

Re: Problem to select radio frequencies

Post by flapman »

bravodeltafr wrote: 19 Apr 2021, 11:56How to display for example 122.81?
The unit does not let you tune this frequency because it is not a valid one for communication.

EDIT: Oh, it is a valid frequency. Just not for this equipment. It's also not a valid one for FSX, don't know about P3D.

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Nick - A2A
A2A Captain
Posts: 13734
Joined: 06 Jun 2014, 13:06
Location: UK

Re: Problem to select radio frequencies

Post by Nick - A2A »

Yes, to provide a bit more info, the venerable KX 155A radios installed in the 172 support 50 kHz and 25 KHz channel spacing (depending on whether the inner tuning knob on the COMM radio is pushed in or pulled out) which is why the units 'jump over' some frequencies.

In the real world, 8.33 kHz channel spacing (i.e. 3 digits after the decimal) is now used for crowded European airspace so you'll see some real comm frequencies which the radios can't tune. FSX and P3Dv4 don't support 8.33 kHz channel spacing, but 8.33 kHz spacing support was one of the features added with P3Dv5.

Providing proper support for this in the 172 would mean installing new NAV/COMM radios such as KX 165A units. However, if you're using P3Dv5, you should be able to tune these frequencies using the 'autotune' feature in the ATC menu. Certain third-party GPS units like the Garmin GTN series will also allow you to select 8.33 KHz channel spacing to directly tune comm frequencies such as 122.810 kHz.

Thanks,
Nick
A2A Simulations Inc.

bravodeltafr
Airman
Posts: 25
Joined: 22 Nov 2018, 09:46

Re: Problem to select radio frequencies

Post by bravodeltafr »

Thank You Flapman and Nick for your explanations !

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