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SDS200 Front end overload again

BruceMN

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Oct 25, 2004
Messages
16
Location
Duluth, Minnesota
#21
I had signal desense problems with my GRE PSR-600 while using an outside antenna. I could not receive very much of anything with or without the attenuator activated until I tried an old radio shack FM broadcast filter (88-108 MHz). After I installed that filter everything came to life on the scanner including the 800 MHz P25 in MN and VHF P25 system in WI.
 

sparklehorse

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May 15, 2003
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Portland, Oregon
#22
SDR chips do not have the best RF performance needed to let them be used in a high end scanner without problems popping up in a thougher RF enviroment. Upman ones stated that if you do not suffer from simulcast issues you're probably better off with a BCD436 than a SDS100. Probably the same will apply to BCD536/SDS200.

/Ubbe
You know, I absolutely agree. Every SDR radio I’ve tried has had overload issues. Until I got the Anytone 868. That radio is the best analog VHF/UHF receiver I’ve ever owned. It’s not great as a scanner as it will only scan 50 channels at a time, and scans them at a painfully slow pace. But man it can pull things out of the mud my other radios just can’t. And it does so hooked up directly to my rooftop ST2 antenna. Most of my other radios, including the 536, need a whole string of inline Par filters (FM, TV, Pager) to function properly at VHF-Hi, as I’ve got a huge FM broadcast tower with 9 stations a mile away, a pager tower a mile away, and also three cell towers a half mile away. So the 868 has proven to me that a receiver doesn’t have to be superhet to perform well in a challenging RF environment. I’m hoping the SDS200 will prove to be just as good. Will know tomorrow when mine arrives.

.
 

epilab

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Jul 29, 2007
Messages
69
Location
Mass
#23
OK guys... got a question concerning this overload issue. there is offered a ATT-20 Variable Attenuator with BNC connections. any thought on this as a solution. And the specs include the following Or am I just dumbing down the reception and the sensitivity will suffer

useable frequency range: 0,1 - 1000 MHz
attenuation: 0 to 20dB continuously variable
control: 3 turns of the knob for the range 0 to -20dB
insertion loss at 0dB stop: less than 0,2dB
no intermodulation - passive
input connector: BNC/f
output connector: BNC/m
input/output impedance: 75 Ohms
 
Joined
Dec 28, 2003
Messages
453
Location
Laurel Springs, NJ
#28
Well I brought the SDS200 into my lab at work and hooked it up. It is working like a champ on the New Jersey State Police 800 MHz Motorola trunk system that I can't receive at home. The closest Cell tower is about 1 mile away and a cell phone repeater about 1/4 mile away. The remainder of the close services are US Government VHF FM services with the closest repeater about 3/4 miles away. So the problem is the 2 close cell phone tower about 1500' from my location at home.

I guess I'll keep the SDS-200 because it works fine on my county's 700 MHz P.25 Phase II system. I also like all of the info that is in the display.
 

sparklehorse

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#29
Well I brought the SDS200 into my lab at work and hooked it up. It is working like a champ on the New Jersey State Police 800 MHz Motorola trunk system that I can't receive at home. The closest Cell tower is about 1 mile away and a cell phone repeater about 1/4 mile away. The remainder of the close services are US Government VHF FM services with the closest repeater about 3/4 miles away. So the problem is the 2 close cell phone tower about 1500' from my location at home.

I guess I'll keep the SDS-200 because it works fine on my county's 700 MHz P.25 Phase II system. I also like all of the info that is in the display.
Try that Yagi I linked to in post #20. Might be the best $16 you ever spent. I have three of those now and use them in different places for different things. Using one lets me monitor a small 800 MHz Smartzone system 45 miles away I couldn't previously receive even with a rooftop ST-2.

.
 
Joined
Dec 28, 2003
Messages
453
Location
Laurel Springs, NJ
#30
I bought a band pass filter as suggested and it did not help my problem. So today I returned to work after the President's Day holiday and took the filter with me. I through it on my Rhode & Schwartz FSP-38 Spectrum Analyzer I use in my lab. This spectrum analyzer also has a network Analyzer/Tracking Generator built in. I've used this in the past to calibrate my cables I use in RFI resolution and Spectrum Engineering testing of FAA equipment and filters.

The filter is: BPF-800-N and is tuned for 740 - 861 MHz.

Attached is the results of my testing. The insertion loss is between -4.25 dBm to 7.10 dBm. This what I would expect on a non-custom band pass filter. Just for comparison I spect'ed out a dual band pass filter several years ago for several tests I was asked to complete. This filter, costing about $900 each, covered both the L1 and L5 GPS band. The insertion loss across the operating band pass sections was no greater than -1.1 dBm. So you get what you can for the money you spend (BPF-800N Band Pass Filter | Scanner Master), $79.00.

I have found though even the better and more expensive band pass filters exhibit will have anywhere from -2.0 dBm - 5.0 dBm so you can buy the best but you may trade off signal strength for the benefit band pass filtering.

Anyway tkae a look at the attached *.jpg file and enjoy.
 

Attachments

N0UDG

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Aug 1, 2011
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789
#31
One thing you could try is a cheap cell phone Yagi:

https://www.amazon.com/XHTECH-824-9...1549934949&sr=8-46&keywords=cell+yagi+antenna

You might be able to null out your cell tower interference while boosting your p25 system performance. I’ve used these to help deal with simulcast distortion on my local p25 system with my BCD536 and had good luck. It may take some experimenting with direction, etc. It took me a while to find a sweet spot. If it doesn’t help you’re not out much.

.

Good Idea, however, I have always had to use a short Reverse SMA to N-Type jumper cable between the cell phone yagi and my scanner otherwise I get no reception at all.
 

wtp

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Apr 3, 2008
Messages
2,318
Location
Port Charlotte FL
#32
i also like the yagi idea.
there is a cell tower down the road and the only way to hear my county when near it is to "point" the antenna at the tower. that is the lowest reception direction for a ducky.
if that 1800' is real, you might have to move.
 
Joined
Dec 28, 2003
Messages
453
Location
Laurel Springs, NJ
#33
i also like the yagi idea.
there is a cell tower down the road and the only way to hear my county when near it is to "point" the antenna at the tower. that is the lowest reception direction for a ducky.
if that 1800' is real, you might have to move.
Just recheck the distance. One tower is 1402' and the 2nd is 1428' using Google Earth. So I over estimated the distance.
I might have to try the yagi. It will have to be fairly sharp meaning more elements since the cell tower
at 1403' is about 30 degs. off of the bearing to the desired signal tower.

But then I know my bcd536hp with using the internal attenuator is working so I may just use the SDS-200
for my local fire/rescue and leave it at that.
 

sparklehorse

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May 15, 2003
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Portland, Oregon
#34
Scannermaster sells a better Yagi than the one I linked to on Amazon. It's more expensive, but almost certainly has a sharper radiation pattern:

824-960, 13dBi, Terrawave Yagi Base Antenna | Scanner Master

I own that Yagi as well and really like it.

Edit to add: It's probably more important to get the null lined up with your problem cell towers than getting the aim at your target transmitter just right. But these always require a fair bit of experimentation.
.
 
Last edited:

wtp

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Joined
Apr 3, 2008
Messages
2,318
Location
Port Charlotte FL
#35
i also use the google maps thing.
and you might want/need some metal to help shield the antenna.
i have had some success telling people to use a lazy susan and lay the antenna flat and turn it around.
it works great for handhelds.
another thing is to take the antenna out
works great to find tower or close by transmitters or interference.
 
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