Bandwith AM

[ScanHen]

When I am tuned at 132.35 MHz with my brand new SDS200, I am not only hearing communication at that frequency but also at lower and higher frequencies. These upper and lower freqs don't trigger the squelch but when communications start at 132.35, I hear mutiple comms and even acars signals all mixed together.
I tried different filters and the INVERT filter is best in this case, although I still hear some comms from upper side freqs.
I have read that the my previous Uniden BCD536 has a 20 KHz bandwith at AM and this I thought was already too wide.
In stead of making it narrower in the SDS200 it is even wider. Why?

What is positive at the SDS200 is that it is more sensitive at the Airband. It picks up signals that the 536 doesn't hear. For digital signals (DMR) at VHF/UHF the 536 is better, at least in my case.

 

[Saint]

I had good results using a FM Trap with my sds100 scanner, you can try that and see if it's will help you, I had big problems in the AIR band until I started to use the FM Trap.
Steve

 

[toad99]

Also if you have a local TV station on channel 13 it can trash your airband reception on any of the SDS scanners. 536 too.

 

[Ubbe]

In stead of making it narrower in the SDS200 it is even wider. Why?

The last filter are a software one and are actually more narrow than most scanners. What happens are that there's a lot of internal mixing products in the reciever that makes you receive frequencies some 350Khz and 600KHz away and lot more, from your monitored frequency. It changes with the filter settings and also if you enable IFX.

You can hear how my SDS100, that uses the same receiver chip, receives from a single frequency from a signal generator on several, or most frequencies, nearby to the actual signals frequency.

Signal received on many frequencies

/Ubbe

 

[iMONITOR]

Also if you have a local TV station on channel 13 it can trash your airband reception on any of the SDS scanners. 536 too.

That's odd as I think TV channel 13 is 210-216 MHz.

 

[iMONITOR]

The last filter are a software one and are actually more narrow than most scanners. What happens are that there's a lot of internal mixing products in the reciever that makes you receive frequencies some 350Khz and 600KHz away and lot more, from your monitored frequency. It changes with the filter settings and also if you enable IFX.

You can hear how my SDS100, that uses the same receiver chip, receives from a single frequency from a signal generator on several, or most frequencies, nearby to the actual signals frequency.

Signal received on many frequencies

/Ubbe

Ubbe,

Is the SDS200 being an SDR more susceptible to this than other scanners?

 

[Ubbe]

Is the SDS200 being an SDR more susceptible to this than other scanners?

Very much so. Other scanners have nothing like those interferencies that are evident in SDS100/200. SDS scanners behaves pretty much like a $20 RTL-SDR usb dongle receiver. The chinese sales site AliBaba sells the receiver chip in SDS100/200 for 85 cent or something like that.

/Ubbe

 

[toad99]

That's odd as I think TV channel 13 is 210-216 MHz.

Yes, it's odd, but I use an open coax stub on my feed line to attenuate in the vicinity of 213 mHz. If I remove the stub, airband reception is greatly reduced. Channel 13 television does not seem to affect a 996T or 780XLT. I haven't found anything that will beat the 780 on airband.

 

[Ubbe]

I haven't found anything that will beat the 780 on airband.

It uses narrow tuned filters that follow the frequency in the Hi-VHF band, like most professional 2-way radios and some $100 DMR radios that can be used in analog mode with excellent performance.

When Uniden added their Close Call feature to scanners they had to abandon that filter type as Close Call needs as wide filters as possible, and it's also more expensive to make advanced tracking filters.

/Ubbe