SDS100/SDS200: Reception Issues / Antenna selection?

[cvk14]

Thanks everyone in advance for constructive feedback!

I'm listening to a 700MHz P25 type II Simulcast system . I have an APX4500 on the same system on different talkgroups. I would assume the APX4500 receives better, but I am surprised in how much better than the SDS100. I'm want to determine if its something I'm doing wrong?

The SDS100 is connected to a NMO mag mount with a larsen quad-band antenna. It was also hooked up to a PCTEL quad band, and a long VHF whip which was tuned way out in the low 100s. Cable is about 12 feet to a BNC plug, converted to SMA at the scanner.

Obviously a properly tuned antenna would received best, but I want to listen to more than just 700MHz. The Larsen is the best performer, but still very poor reception. The Larsen is the best performer, with the PCTEL second. the VHF whip is by far the worst.

I also have tried the remtronix REM-842S, which receives best of all of them, but doesn't perform well because the scanner sits low in my vehicle.

Open to suggestions. The scanner is really under performing...

 

[Whiskey3JMC]

Try experimenting with different filters on the SDS100

 

[nessnet]

Maybe try a REM-820S...?
Different mounting spot?

Any multi-band antenna is always going to be a compromise.

 

[nessnet]

Try experimenting with different filters on the SDS100

Not is a mobile environment.
Remember, filters are location specific.
Not a good idea in a moving vehicle.
I'd recommend filters be set on off, or normal when mobile.

 

[Whiskey3JMC]

Not is a mobile environment.

Worked fine for me while mobile, but individual results do vary...

 

[nessnet]

Worked fine for me while mobile, but individual results do vary...

If I am not mistaken, and from my experience, the filters actually decrease sensitivity - which is the OPs reported problem....

 

[Ubbe]

If I am not mistaken, and from my experience, the filters actually decrease sensitivity - which is the OPs reported problem....

In a totally interference free environment they do. If set to Off it will have the best sensitivity. But any interference will usually reduce sensitivity and then the filter settings can actually increase performance, as well as the IFX function.

/Ubbe

 

[palmerjrusa]

Try experimenting with different filters on the SDS100

Those filters can make a huge difference, i.e. between no signal or clear reception.
Wide Invert seems to work best for me with weak signals from digital systems.

 

[nessnet]

Those filters can make a huge difference, i.e. between no signal or clear reception.
Wide Invert seems to work best for me with weak signals from digital systems.

Those filters can make a huge difference, i.e. between no signal or clear reception.
Wide Invert seems to work best for me with weak signals from digital systems.

But stationary, correct?

 

[nessnet]

In a totally interference free environment they do. If set to Off it will have the best sensitivity. But any interference will usually reduce sensitivity and then the filter settings can actually increase performance, as well as the IFX function.

/Ubbe

Because the OP was asking about what sounded like a sensitivity issue, I stand by my recommendation.
If in a mobile environment, the off setting (or normal), is the best option.

Of course, if there was a source of RFI in the vehicle itself, a filter / IFX would be warranted.
But, I'd think the chances of RFI being generated by the vehicle, or an accessory, is remote.

 

[jtwalker]

.

 

[tvengr]

But, I'd think the chances of RFI being generated by the vehicle, or an accessory, is remote.

You want to keep the antenna cable away from vehicle computer cables. LED headlights are a major source of noise. Also, USB power adapters can create wideband interference. It shouldn't be as critical at 700 MHz, but I've seen reports of interference wiping out 2 meter and 70 centimeter band amateur radios.

 

[palmerjrusa]

But stationary, correct?

Yep!!

 

[Ubbe]

...If in a mobile environment, the off setting (or normal), is the best option....

But keep in mind that the SAW filters used in the scanner do not have a flat curve where it pass a signal and then suddenly drops all signal outside of its bandwidth, it's a sloping curve at the edges. The Off setting use the filter in the middle of its pass band and Normal and Invert are right at the edges where it could drop something like 3dB. I think I measured a 5dB loss in my SDS100 with one of those settings.

It's two filters in the scanner that it can switch between, that you also can do from the IFX function, a 260Mhz and a 380Mhz filter, and those can have different attenuation of the signal, as Uniden use the cheapest components they can find that have lower quality, and if you drop the scanner those filters are fragile and will be among the first components to go bad from vibrations.

/Ubbe[/QUOTE][/QUOTE]