Am reception bandwidth?

[ea3grn]

Hello,

it seems, according to some web comments, that the AM reception in this firmware is set to a bandwidth of 8.33 Khz. Is it possible to try to set for the aeronautical band that the AM bandwidth is 25 Khz? I have not been able to find the chipset command guide, but maybe it is possible to make the change in the firmware to see if this improves the AM reception quality (right now pretty bad).

If it is possible for you, would you be so kind to see if it is possible to implement this change?

[Tunas1337]

It's on the list of stuff to look at. Someone sent something promising, I'll check it out.

[ea3grn]

If I can be of any help, I am at your disposal.

[pawol]

I do not think so. It is possible to change channel width on AM between 6.25 and 12.5 kHz and the difference is easy to hear. 8.33kHz is only used in context of frequency raster and nothing more.

[Tunas1337]

So, wide/narrow works for AM?

[pawol]

sure. Do not mix bandwidth 6.25/12,5 kHz (depends on band plan) with frequency raster 2.5, 5,0, 6,25, 12,5, 25 and 8.33 kHz
I have noticed that AM on 6.25 channel bandwidth is less sensitive and less hissing then 12,5 channel bandwidth. Same settings are for FM and then ones are called NFM or FM (6.25 or 12.5 kHz)

[pawol]

Just set some AM air band frequency, disable squelch (menu 0 --> 0) and change band width (menu 10 --> wide or narrow).
You will hear big difference in reception of noise and aero chats.
Frequency raster 8,33 kHz is not equal with 25, 12.5 and 6.25 kHz raster but starts on the same air band frequency 108 MHz.
8.33 is quite new issue introduced after year 2012 to get more channels in the aero band and this is not still widely used by the aero planes. Of course there is no common sense to use bandwidth 12,5 kHz when we use the raster of 8,33kHz. Generally we can say that bandwidth divided by 2 give us max audio frequency. For Instance 8,33 gives us 4,12kHz of audio band, 12,5kHz gives us 6.25 kHz of audio band and 25kHz gives us the best quality of 12,5kHz audio band. But everything depend on radio band plan and changes very often even in the same band.

[ea3grn]

I can confirm there is no improvement between NARROW and WIDE mode in AM. In both modes the audio is distorted.

[pawol]

Sure, because it makes an influnce on audio band pass only. IMHO there is problem with gain control or DSP signal processing. It seems to be possible to control one by DSP. DSP cuts hight AM peaks of amplitude like guitar fuzz effect.

[SteefW]

Sure, because it makes an influnce on audio band pass only. IMHO there is problem with gain control or DSP signal processing. It seems to be possible to control one by DSP. DSP cuts hight AM peaks of amplitude like guitar fuzz effect.

That's just it i guess. Sounds like distorted AGC as well. It seems that especially with strong signals it looks like the problem is bigger.
Thanks for the attencion about this prob. Did not try UHF AM though yet.

[Sthrenor]

According to SDR airband reception bandwidth is only 2khz for air band. Maybe lowering it is the solution. Just give it a try if posible.

[pawol]

Nonsense. 2kHz of channel width results with 1kHz voice band pass only. AM with voice frequency up to 3kHz (normal for telecommunication purposes) have to have at least channel band width 6kHz

[Sthrenor]

If you listen to aircraft emisions with an SDR you will see that the bandwidth is 2khz. I will make a video about it and will link it here. I suspect that quansheng airband bandwidth is 12,50 or 25khz as is FM transmissions and that is why we get all that background noise on airband. If is testable....

Wikipedia says:
Audio properties
... However, most airband voice transmissions never actually reach these limits. Usually, the whole transmission is contained within a 6 kHz to 8 kHz.

Even if is 6khz I think quansheng is using 12,5 or 25khz as I said upper.

[pawol]

Understand one thing. 2 kHz of channel band width is against the AM modulation theory. max voice frequency * 2 gaves us channel band width. So 3 * 2=6. Have you ever heard voice chat when 1KHz is max frequency of voice? Has to be terrible to understand.

[pawol]

AM channel band width can be wider then expected without any problem but the channel selectivity will be smaller and the signal sensitivity will be higher. Wrong way...

[Sthrenor]

I listen to airband with my HRD-747 set at AM 2khz bandwidth perfectly and with SDR. With the quansheng I can't. It enters tons of background noise and I thought that could be this. But if you say it goes against AM modulation theory, don't try it... It was a suggestion. Sorry for the inconvenience.

[Sthrenor]

Is at least posible to set the AM bandwidth with the theorical minimun bandwidth for voice of 6khz?

[marusc1]

8.33 channel spacing guilts for America. In Europe the channel frequencies end with 5 kHz, eg 128.805 but most radios still transmit in the old raster of 25. In shown case at 128.800

[gg33fr]

Hello, I found this video.
Replacing a CMS component
audio Hi-Cut (1nF capacitor)
If anyone has the material to try.
THANKS

https://www.youtube.com/watch?v=j4ccuYOg2NU
https://drive.google.com/file/d/1d8XvcFDsEhNsPAyp1co9DTeig5Db1OO3/view

[pawol]

Nothing common with AM reception. Just changed audio amplifier characteristic

[ericek111]

@marusc1
Even though the frequencies seemingly end with a 0 or 5, in reality, they're transmitting on different frequencies. European Union has implemented the requirement for 8.33 kHz-capable radios above FL195 in 2018. Refer to this image:

One advantage of the 25 kHz frequencies is that they allow to extend the range using CLIMAX (+/- 2.5 kHz carrier offset).