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Old 06-14-2018, 3:56 AM
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Default SDS100 analog VHF and AIR AM mode performance

We all know now that the SDS100 does digtital simulcast decoding as well as the best in class.
And that's probably what people gonna use it for, a dedicated digital simulcast scanner, but can it be used as a multipurpose conventional scanner?

How does it perform in analog 30MHz, 155MHz and AM mode airband?

Reports like "I can receive a tower 30 miles away" "I can hear lots of aircrafts" is useless. You'll need to COMPARE with another receiver using similar antennas and in a similar situation. The best would be to have another scanner next to a SDS100 and perhaps have a 118-136MHz search going and nothing else or scan a single group of VHF analog frequencies.

How does it perform with CTCSS tones? Search finds it quickly? Open and closes SQ quietly without any noticeable delay?

I often find air AM mode to have a too open SQ level in scanners. It is much more noise when SQ opens compared to FM as AM mode use the same filter as FM mode and sometimes even use FM 25KHz instead of the NFM 12,5KHz filters when the optimum should be something like 6KHz for AM. I guess that SDS100 are no different and use old way of thinking and do not use super narrow SFM 6KHz filter for AM and NXDN narrow channels? Uniden have volume offset per channel/TG in some scanners but offset SQ would also be useful.

/Ubbe
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Last edited by Ubbe; 06-14-2018 at 5:41 AM..
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Old 06-14-2018, 7:37 AM
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Quote:
Originally Posted by Ubbe View Post
How does it perform in analog 30MHz, 155MHz and AM mode airband?
Performance is very similar to the 436 when both are connected to the same antenna. I've been listening to airband with both scanners side by side and reception is pretty much identical, except for sometimes catching different simultaneous transmissions on different frequencies.

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How does it perform with CTCSS tones? Search finds it quickly? Open and closes SQ quietly without any noticeable delay?
The SDS100 has no issues with CTCSS tones. If anything, it has less squelch tail and other similar issues than the 436.

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I often find air AM mode to have a too open SQ level in scanners. It is much more noise when SQ opens compared to FM as AM mode use the same filter as FM mode and sometimes even use FM 25KHz instead of the NFM 12,5KHz filters when the optimum should be something like 6KHz for AM. I guess that SDS100 are no different and use old way of thinking and do not use super narrow SFM 6KHz filter for AM and NXDN narrow channels?
AM is inherently noisier than FM because it has a linear relationship between the RF S/N ratio and the audio S/N ratio, not because of IF filter width or squelch settings. AM has no capture effect like FM.
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Old 06-14-2018, 9:06 AM
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Thats exactly what i want to know!

Thanks for asking before me


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Old 06-14-2018, 1:58 PM
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If you played with a SDR dongle and SDR#, and I'm sure you have, you know that reducing the filter in AM mode to 5-6KHz will not affect the audio but cut out most of the noise.

All scanners use the SQ connected to the FM discriminator in AM mode. That makes the AM level too low when the SQ opens as the signal/noise ratio are so much worse than compared to FM with that signal level. That SQ setting are not optimal for AM monitoring, and in the same way that NFM have worse signal/noise than FM and are compensated for by changing the SQ circuits values, AM mode should change the SQ levels even more. But that have not happened in earlier scanners.

If the SDS100 are fully software designed even in the discriminator and squelch functions it should be easy to finally make a correctly functioning FM/AM scanner with the proper filter and SQ settings.

/Ubbe
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Old 06-14-2018, 2:36 PM
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Quote:
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All scanners use the SQ connected to the FM discriminator in AM mode. That makes the AM level too low when the SQ opens as the signal/noise ratio are so much worse than compared to FM with that signal level. That SQ setting are not optimal for AM monitoring, and in the same way that NFM have worse signal/noise than FM and are compensated for by changing the SQ circuits values, AM mode should change the SQ levels even more. But that have not happened in earlier scanners.
None of that applies to a SDR receiver.

And when you narrow the AM filter width, that cuts off the high frequency audio response. Max audio frequency is half the channel width. Standard for CB is 10KHz channel and 5000Hz audio cutoff. Narrow aircraft is 8.333KHz channel and audio cutoff just over 4KHz.
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Old 06-14-2018, 7:02 PM
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I would think we all know that the norm for radio and telecommunication speech audio response lies between something like 300Hz and 3000Hz. So a 6KHz filter for AM mode would be perfect then, and not the 25KHz filter that UPMan once stated was used in pre SDS100 scanners, and never responded to why Uniden didn't use the 12,5KHz filter that also where available?

Now is the chance to set everything straight, if all are done in software.

/Ubbe
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Old 06-14-2018, 7:19 PM
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I would think we all know that the norm for radio and telecommunication speech audio response lies between something like 300Hz and 3000Hz.
We don't "all know that" because that isn't accurate. CB goes above 3000Hz as I already pointed out. So does aircraft AM. Also, digital audio goes down to about 100Hz--that's why some people complain that it sounds "muffled" or "bassy".
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