Stridsberg Pre-Amp Setup for 700/800 Simulcast

[JimD56]

OK, guys here we go.
As my subject says; Will a Stridsberg Pre-Amp "Pre-78" help me for 700/800 Simulcast?

Fort Lauderdale/Miami Florida is a HUGE Simulcast hotbed with several different systems and locations.

System 1 - 3 different Simulcast Antenna Sites, on the same system, the closest site 5 miles from my house. (Broward County)
System 2 - 2 different Simulcast Antenna Sites, for another system, the closest site is 8 miles. (Fort Lauderdale, Coral Springs)
System 3 - 2 different Simulcast Antenna Sites, for another system closest site about 25 miles out. (Miami)
Also, some NOT Simulcast 800 systems. (Hialeah and some business commercial radio)

I currently use one (1) Yagi "in the attic" pointing to System 1, the closest site. However, I have been experimenting with a mobile antenna on a mast in the back of the house where the HOA doesn't see it, and I'm getting good results from close systems and mixed from distant sites. Better than the attic Yagi.

Will a Stridsberg Pre-Amp "Pre-78" help me with the outside mobile 700/800mhz antenna, to receive ALL the systems?
The Pre-78 is rated at an 18db gain and an Electrolione EDA-2800 (Cable TV combi RF Amp/Splitter) currently in use is rated at 4db. I will run the PRE-78 into a
Stridsberg MCA780M 700 Mhz/800 MHz Receiver Multicoupler as suggested on the Stridsberg site.

The Pre-78 would be right at the window sill where the cable comes in, and there is a power outlet. There is a 20-foot stretch from the antenna and then a 20-foot stretch to the shack. I welcome all suggestions and ideas.

Thanks
Jim

 

[dave3825]

What is it that you are listening on? Scanner, sdr?

 

[JimD56]

What is it that you are listening on? Scanner, sdr?

Sorry. SDS200 and SDS100.

 

[737mech]

Jim D56 Curious how that works out please post results.

 

[prcguy]

First off the Stridesberg preamps are not very good by todays standards with 3.5dB noise figure and a 1dB compression point or IP1 of 12dBm. What the preamp will do if placed at the antenna is amplify the signal with some extra noise which can make up for feedline loss and some splitter loss. With 18dB of gain feeding a passive 4-way splitter you will still have about 10 to 11dB gain left over which is on the high side but probably ok. You don't want to feed that into another amplified splitter, that will further increase noise, create IMD and make reception worse.

So that Stridesberg amp is a whopping $180 for very mediocre specs, but it does have a bypass relay that passes signals straight through when the power is off. I guess that's ok even though the "straight through" that is not what it appears with a rated 2dB loss! I would recommend a much less expensive amplifier from MiniCircuits, the ZS60-P103LN which has about 14dB gain at 800MHz with only .5dB noise figure and a 1dB compression point or IP1 over 22dBm or 10dB better than that Stridesberg thing. And the cost is about $113 new or I've bought several off eBay in the $50 range used. BTW this amplifier is actually rated 50MHz to 3GHz and it has better specs in the VHF/UHF range.

Or you could go with the MiniCircuits ZX60-0916LN which targets the 840-960Mhz range with similar specs except for a slightly degraded IP1 of 16.5dBm. Cost new on that one is about $75. You also have to understand you can't make up for lack of antenna with an amplifier. If you look at the signal off say a 10dBd gain antenna, you will not get the same thing using a 2dB gain antenna and an 8dB gain amplifier. The signal to noise ratio is determined at the antenna and you can only improve that with a better or higher antenna. An amplifier will degrade the signal to noise ratio even though the signal level will be higher. But the noise level will also be higher.

 

[RFI-EMI-GUY]

Jim;
Some, if not most of those 800 systems in your area are NPSPAC and have adjacent channels in the next county. Coral Gables and Broward County if I recall. Hialeah IS simulcast and NPSPAC and there may be some adjacent channels to the north.

My point is, that if you have a preamp with too much gain, you may get some adjacent channel interference that you may not notice due to trunking and digital, but will miss communications when it happens.

You should use low loss cable for the omni antenna. Start with RG6U as it is cheap, never mind the impedance. If that is not good enough, as PRCGUY says use a preamp at the antenna. But be prepared to install an attenuator to knock off excess gain at the end of the coax. Given the environment where you are at, the preamp will be happiest with a preselector filter or at minimum an FM broadcast trap.

 

[Ubbe]

SDS scanners use a R860 SDR receiver chip that are not high performance and will reduce its sensitivity if it senses a too strong signal within a 10MHz window around the monitored frequency. It has intermodulation like issues when it receives signals at -80dBm or stronger. There are both IFX and different filter settings like Normal and Inverse to try and move the interference problems to other frequencies but they will still be there.

If you get better reception with an antenna that gives a lower signal indicates that you already are overloading the scanner. In your case I would try and use the yagi antenna and add a variable 0-20dB attenuator at the scanner to be able to adjust the signal level to the most optimum for the scanners receiver. Also try all possible filter settings and also in combination with IFX to each frequency to see if it will do any improvement.

SDS100 receiver test

F Connector Coaxial Cable Variable Attenuator 0 20dB Coax RF Digital TV Freeview | eBay

Digital (freeview) and analogue signal signals. If everything seems to be installed correctly and you are still getting problems with reception, buying this attenuator will establish whether your signal is too weak or too strong.

www.ebay.com

/Ubbe

 

[JimD56]

I Attached a PDF so you guys can see what I'm dealing with. Just ordered my 3rd SDS as well because of the TON of simulcast I'm dealing with.
I want to be able to receive, optimally, all these surrounding systems.

 

[Ubbe]

Can you do a quick check when using the yagi, to look at the dBm signal value from the strongest signal you can receive and then engage the attenuator, Fn+4, and see if the signal drops 20dB? You could also look at the D-error and check how that reacts when attenuator are being switched on. This is a yagi with a Electroline combiner?

You will probably need two yagis, one for each scanner as transmitters are in opposite directions. What's the model of that mobile antenna and does it have any gain? Maybe you can use a higher gain and much longer vertical omni antenna and then use a preamp directly at the antenna like the one suggested by prcguy and then a passive splitter at your scanners. It's always a good thing to have a signal to be variable adjusted in level to dial in the exact level where a scanner will perform at its best.

/Ubbe

 

[RFI-EMI-GUY]

SDS scanners use a R860 SDR receiver chip that are not high performance and will reduce its sensitivity if it senses a too strong signal within a 10MHz window around the monitored frequency. It has intermodulation like issues when it receives signals at -80dBm or stronger. There are both IFX and different filter settings like Normal and Inverse to try and move the interference problems to other frequencies but they will still be there.

If you get better reception with an antenna that gives a lower signal indicates that you already are overloading the scanner. In your case I would try and use the yagi antenna and add a variable 0-20dB attenuator at the scanner to be able to adjust the signal level to the most optimum for the scanners receiver. Also try all possible filter settings and also in combination with IFX to each frequency to see if it will do any improvement.

SDS100 receiver test

F Connector Coaxial Cable Variable Attenuator 0 20dB Coax RF Digital TV Freeview | eBay

Digital (freeview) and analogue signal signals. If everything seems to be installed correctly and you are still getting problems with reception, buying this attenuator will establish whether your signal is too weak or too strong.

www.ebay.com

/Ubbe

Wow that test is pretty revealing . I assume the Stabilock itself is free from spurious emissions? If so the SDS receiver is pretty shoddy. I was just thinking I should get an SDS200 as an upgrade from my 536. Now I am back at considering a commercial radio with NAS?

 

[JimD56]

I don't have a second yagi and I don't have any way of measuring signal loss or gain.
The antenna is a Laird 800/900mhz mobile on a Base ground plane kit connected to the mast and the ground plane radials are the correct length for optimal 850mhz> higher reception.

 

[Ubbe]

The antenna is a Laird 800/900mhz mobile

Is it the one that has a fat base and then it's just a 3 inch steel pin sticking up? Then it has no gain and you could probably improve reception a lot with a much bigger gain antenna. Check the frequency where you have the weakest signal that you would like to receive and get an antenna that have the best gain at that frequency. Sometimes Ebay have surplus antennas at a low price.

What coax are you using now? For a simple RG6 it's something like 2-2,5dB attenuation for a 40ft length at 800MHz. You will get rid of any coax and connector attenuation when using a preamplifier directly at the antenna.

/Ubbe

 

[JimD56]

Thanks, Ubbe. A bigger antenna is no go with HOA. I'm using LMR-400 15 feet to the window and then 15 feet to the shack.

 

[Ubbe]

Then you have to experiment more with that yagi in the attic. I think the best yagi to be used with a scanner where only $25 from Amazon but there are others more expensive ones that performed much worse, so avoid those. Search the RR forum for the one that performed well. And I guess the yagi are also using LMR400.

As you don't get a good signal from the yagi, can you take your BC125AT and listen to the control channel data up there in the attic in different locations and listen if the there could be some isolation materials that blocks radio signals that makes it almost impossible to use an antenna indoors? Or you actually are receiving too much signal for a SDS200? The BC125 have a pretty good receiver to tell if it is a RF problem, connect it to the yagi and compare with the SDS200 when listening to a weak control channel in analog mode.

/Ubbe

 

[Ubbe]

I assume the Stabilock itself is free from spurious emissions?

I think it is spurious free. I haven't noticed anything out of the ordinary. I did some reference tests with a UBCD3600XLT (BCD436EU) and TRX-1 and both didn't show any spurious at a -60dBm level that I used for the SDS100 test so I had to go to -40dBm. The SDS100 have the exact same sensitivity as the TRX-1 at 0,35uV.

UBCD3600.mp4

drive.google.com

TRX1 test.mp4

drive.google.com

/Ubbe

 

[JimD56]

Wow that test is pretty revealing . I assume the Stabilock itself is free from spurious emissions? If so the SDS receiver is pretty shoddy. I was just thinking I should get an SDS200 as an upgrade from my 536. Now I am back at considering a commercial radio with NAS?

I would love commercial radio as well. I would need 5 Moto APXs $$$$$ to listen to the 5 different systems near me. I have XTLs for my UHF Agency analog stuff.

 

[prcguy]

I would love commercial radio as well. I would need 5 Moto APXs $$$$$ to listen to the 5 different systems near me. I have XTLs for my UHF Agency analog stuff.

Harris XG-100Ms are much cheaper than APXs and most people I know who recently got some are preferring it to the Motorola. Myself included.

 

[Ubbe]

Harris XG-100Ms are much cheaper than APXs and most people I know who recently got some are preferring it to the Motorola. Myself included.

Seems to be extreme value for money when looking at Ebay. VHF-Lo and Hi and 700/800 trunking Edacs and P25 and analog +GPS and Bluetooth and remote head and a mic and speaker for $1,100.

/Ubbe

 

[prcguy]

Seems to be extreme value for money when looking at Ebay. VHF-Lo and Hi and 700/800 trunking Edacs and P25 and analog +GPS and Bluetooth and remote head and a mic and speaker for $1,100.

/Ubbe

Just a few months ago the prices were much cheaper, radio bricks were $249 to $400, new control heads for $34, new mics for $22 and the brick to control head CANbus cables were $25 new. I bought four complete radios and lots of accys. Compare that to a cheap bargain eBay APX8500 for $6k. Even at $1,100 the Harris is a bargain for what it can do.

 

[devicelab]

First off the Stridesberg preamps are not very good by todays standards with 3.5dB noise figure and a 1dB compression point or IP1 of 12dBm. What the preamp will do if placed at the antenna is amplify the signal with some extra noise which can make up for feedline loss and some splitter loss. With 18dB of gain feeding a passive 4-way splitter you will still have about 10 to 11dB gain left over which is on the high side but probably ok. You don't want to feed that into another amplified splitter, that will further increase noise, create IMD and make reception worse.

I've had very bad luck with their preamp versions. The passive versions seem to work fine but I had way too much noise in the other version. I'd recommend a quality band pass filter instead of the preamp.