SDS100/SDS200: Squelch/Antenna
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Ubbe
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I monitored a frequency in the 400Mhz band with a signal of -100dBm, just a little noise in it so it can be heard if the sensitivity changes. I used the filter set to Off, which is the standard symetrical filter used in any other scanner.
I injected a -50dBm signal and at a frequency 7MHz lower than the monitored one. The RSSI changed from showing -100dBm to -60dBm.
When I got within 3MHz it started to show -50dBm.
You can look at some more of my tests of the SDS100 in the thread: SDS100 radio performance tests
You seem to have too many strong transmitters at your location that confuses the SDS100 and makes it difficult to find a filter setting and IFX that works, or perhaps it is impossible to do. But a general rule would be to try and find the weakest signal, the higher number of negative dBm, when trying out filters and IFX. It's the totally opposite of any other scanner type than the SDS, but are the result of how the signal strengh meter are working in a SDS scanner.
All different filter settings and IFX will always pass your monitored frequency untouched but what changes are how much of interferencies that the filters manage to block. The more it blocks interferencies the higher the negative number of the dBm and the less signal bars you'll have.
But it's best to ignore signal strenght and only use NOISE and D-ERROR as indicators. They should be as low as possible. Noise below 500 for an analog channel and D-Error below 5 for a digital channel.
/Ubbe
Why do you have the hold time at 255?????
Ubbe
Member
Could be that when the antenna are position to receive the interference with the weakest signal, the monitored frequency are less interfered. With SDS scanners the goal are to reduce interferencies as much as possible and the actual monitored frequency will then improve. When you point the antenna at a source it will receive that signal with the weakest signal. It can be used to find a source, either a transmitter or an interference, by pointing the antenna from you horisontally and slowly turn around and try to find the weakest signal. It ideally will be two weak directions, when pointing straigth at it or the totally opposite 180 from it and the body would also attenuate that signal a bit more. RF signals bounce around so it's much easier to pinpoint out in the open.
If you receive a totally dead carrier, it has no modulated audio but a signal strenght, it will show a low noise value, but as soon as that signal are modulated with speech it will go up in numbers and a digital signal will have the most modulated audio and will kick that noise number up even higher. It should be a fairly constant noise number when receiving a digital signal, lets say it varies between 200 and 300, but if it suddenly jumps up 500 it could be an interfering transmitter that keys up and needs to have different filter settings tested against it to see if it helps. D-error are the best indicator to be used with digital signals as it shows how well the actual signal are received.
/Ubbe
From what I read and what I observe, it stays on the system quite well. If I put it to 2, it constantly flickers. Is this wrong to do?
It doesn't happen often or every where but sometimes in my back room or even my office depending on the time, day, and activity the indicators improve when I lay the radio flat. Even in my living room, theres one partiuclar spot where that works, but even the slightest milimeter of movement or the antenna somehow moves it will recycle again. When in usual range NOISE is 200-400's. The only time I ever see it skyrocket is when it does cycle between frequencies randomly or during transmissions as they are talking which might be obvious I don't know. Maybe thats what your saying about the dead carrier.
When I read the manual originally, it mentioned between 2 and 5 is ideal. I honestly never noticed a difference between any of it with Digital until I switched from 2 to 1. 3-15 I noticed nothing and between 0 and 1 nothing. That's why I don't get that this system flickers when there is activity on 2, but receives normally at 1. But, other Digital systems works fine regardless, like my local police never flickered with Squelch on 2.
Then I read something about maybe they are all close in frequencies and the police may over power. I don't know.
I have a 100 and a 200 (and a 436).
I basically never take any of them off of squelch = 2.
Of course it will (stays) - basically, it never scans another system......
EX: I have all my systems (everything) set at 0.
Hold is a timer that is applied to how long the radio stays on a trunk system control channel before moving on to the next system or channel. The intent of the default of HOLD=0 is to have the radio only stay on a control channel long enough to check for activity of interest (to improve the scan rate/performance).
At 255, it basically never moves on (or better said, until 255 passes, which is essentially the same)....
Delay BTW, is the time the radio stays on a channel or talkgroup following a transmission (awaiting a potential response).
Again, my friend - you have something obviously wrong with your radio.
My suggestion is to stop beating a dead (badly wounded) horse and get it fixed.
Send it to Jon to have him take a look.
Either that, or as Jon stated earlier, you have something putting out a hell of a lot of RF in your close proximity.
I'd bet this is not the case....
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I noticed when I had Delay on like 10 seconds, it kept breaking. It would hold, conversation would pause, by time it cycled through it was gone. When I increased to 30 seconds, it slowed down the rate to the next channel. So I lowered Delay to 2 seconds, increased Hold to 255 and Avoided all channels that aren't suitable for me. ID Search and the other Avoids has really helped me pin point
Ubbe
Member
In normal scanners, non-SDS, the squelch works by detecting the amount of signal in the 5KHz part of the audio. Speech are limited to more or less a 300Hz-3KHz range and any audio levels above that frequency band can be considered to be noise that the squelch circuit can use as a noise indicator. The higher the level of noise the weaker the signal are. That signal are converted to a DC voltage that then controls the squelch.
The SDS type of scanner indicate Noise even on speech and more so on digital data if you study the NOISE indicator. If a SDS scanner are monitoring a digital signal the noise level will be much higher and the squelch function will think that it is a weak signal and will have a much harder time to open up the squelch. If the squelch doesn't open it will not try to decode any data signals. Squelch settings only work on weak signals and as soon as the signal are more or less noise free you can have the squelch set to max and it will not close.
The other thread had a much more detailed and better info but got closed, but showed that the problematic system are received at a -100dBm level or worse and a better Remtronics antenna helped. But depending of filter settings an interfering signal sometimes blocks reception and sends the signal level way up to -45dBm, but that level are probably a result of the logic in the SDS and not the actual signal strenght.
Other thread
/Ubbe
The SDS type of scanner indicate Noise even on speech and more so on digital data if you study the NOISE indicator. If a SDS scanner are monitoring a digital signal the noise level will be much higher and the squelch function will think that it is a weak signal and will have a much harder time to open up the squelch. If the squelch doesn't open it will not try to decode any data signals. Squelch settings only work on weak signals and as soon as the signal are more or less noise free you can have the squelch set to max and it will not close.
The other thread had a much more detailed and better info but got closed, but showed that the problematic system are received at a -100dBm level or worse and a better Remtronics antenna helped. But depending of filter settings an interfering signal sometimes blocks reception and sends the signal level way up to -45dBm, but that level are probably a result of the logic in the SDS and not the actual signal strenght.
Other thread
/Ubbe
I believe so last year, that's where you observe the three bars on whatever system you selected right?
What if on Filters, indicators go blank and NOISE skyrockets?
Ubbe
Member
Then you have no signal at all. Without any signal to receive the Nose shows something like 25.000-50.000 and when receiving a clean strong signal it shows 0, if it is an analog signal and someone transmits but no one talks, and indicators show signal bars. If the squelch doesn't open it will be blank indicators, but the Noise value are taken before the squelch circuit and will always show a number.
Remember that there's an automatic gain control in the SDS scanner that will reduce the sensitivity in the receiver, to stop it from going into overload, if it detects a strong signal within several MHz from your received frequency. A result from the receiver chip used that are designed for satellite and tv signals that are 5-10MHz wide but scanner signals are only 12,5KHz or 25KHz wide, 500-1000 times more narrow. If you then have a strong local signal perhaps 1Mhz away from the signal you are trying to receive, it will kill the reception of weak signals in the SDS scanner, like the -100dBm signals you are trying to receive.
/Ubbe
Hi there - its been awhile. Today is the first time the radio works with Squelch on 2, I have Wide Auto as a filter. What I found interesting, it works fine as is, but if I hold on to a Talk Group that's when it doesn't stay on the transmission and keeps blinking like before.
You do know that any auto filter setting will SLOW your scanning down tremendously?
Auto is not a recommended setting....
Auto is not a recommended setting....
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