Splitting an antenna - coax impedance mismatch?

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Fizz306

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Sorry in advance if this is super elementary, or if a mod decides there is a better subforum to discuss this topic.

I just installed an ST2 antenna, including the 50 feet of 75 ohm RG6 coax. Ran into the home, and plugged directly into a scanner, it sounds great.

Bought a TV coax splitter (I know, I need a multicoupler, but I don't have $200 right now for one...it's on my short list). When I run the RG6 into the splitter, and use 3 feet of RG59U 50 ohm patch cables on the other 4 ends, the signal degrades significantly. Much more so that I would have expected. Previous systems, including an 800 mhz TRS that needed attenuation in the scanner to prevent the CC from overloading, have had their signal cut by a factor of 4-6 times.

Is this a coax impedance mismatch thing going on here, or the splitter? I've split cheaply like this before using a BNC T adapter with little noticeable difference in gain. If it were up to me, and money was no concern, the whole system would be fed with LMR400, a quality multicoupler, and a quality LNA. Unfortunately, I don't really have the $500 bucks to realize that reality right now. I just want to get a few scanners running off this antenna for personal listening and an RR (Broadcastify) feed.

Splitter - Amazon.com: 2 GHz 90dB 4-Way F-Pin Splitter DC Passing: Computers & Accessories
Antenna - Amazon.com: SCANNER ANT-BASE 30-1300MHZ 50'RG6 15ELM: Electronics
Patch Cables - BNC M/M RG59U - 3ft - Monoprice.com
 

KevinC

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That splitter will have a least 7dB of loss (possibly more if it's made badly). 7dB is a lot (you're losing at least 80% of your signal) and will definitely be noticeable.
 
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rbm

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It sounds like you're using a 4-way splitter.
That can be problematic if your signals are weak or you don't use a preamp.

'Ball park' losses for splitters:
A 2-way splitter has around 4 dB loss
A 3-way splitter has around 7-8 dB loss
A 4-way splitter has around 9-11 dB loss
Those numbers vary widely depending on manufacturer so you have to check the specs.

If you ARE using a 4-way splitter, any signals that aren't very strong to begin with will be lost forever.

You can try adding a preamp before the splitter to make up for some of the loss.
Here's one way to do it. It's cheap, and worth a try unless you have some very strong signals nearby.
http://forums.radioreference.com/scanner-receiver-antennas/228728-so-i-bought-antennacraft-st2-scantenna-5.html#post2015393

While the ebay link for the inline amplifier is old, you can search for 'Holland LA-520'
They run around $5 each.

You'll need a wall wart power supply ($?), a DC Power Inserter ($5), and a DC Block (another $5).
So, for around $15 and the price of a wall wart if you don't already have one, you can create your own 'multi-coupler'.

Rich

Edit: By the way, if you can, get rid of the RG59 and replace it with at least RG-6. I don't particularly like RG59 even for very short runs.
 
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737mech

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SPLITTER

Yes it's the splitter killing your signal. Many of us are on the same path as you a little further down the road so don't worry. Step one remain calm. Step two you could do like I did and add one of these Electroline Eda 2800 8 Port CATV Low Noise Amplifier | eBay they are cheap but they work great! Especially for many scanners and one antenna. The subject has been debated alot here in the forums, some have money for a Stridsberg, others (like me) try cheap first. If it works don't fight it right? OBTW there's 4db gain from this model, Electroline also has the 2802 with 0 gain, I have both and really like a small amount of gain it improves my airband and milair alot. This drop amp also has nice port to port isolation so one scanner won't mess with the others.
 
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chief21

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And it's not just about the loss of signal strength. If you're using a common splitter, it's also likely that you'll get some interaction between the connected devices themselves. A multicoupler provides isolation to prevent such interaction... a signal splitter doesn't.
 

rbm

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Here's something to consider. ;)

The ST-2 is NOT the best antenna, but ..............
I normally feed 32 scanners with one of them using two of the assemblies you can see in the photo below.

I used one of the outputs to create this video on YouTube of SatCom reception.
It was feeding 31 other scanners at the same time.
Milsat Satcom Satellite SDRSharp with Eztv668 SDR dongle e4000 chip - YouTube

My Broadcastify feed is on one of those 32 ports so you can judge for yourself.
Some of the signals on that feed are 38 miles from me.
(I have private feeds and other things running on different antennas.)

Rich

 

ridgescan

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You could also get a low loss coax switch like mine. The one on the left runs three HF receivers to my shortwave antenna, the one on the right runs two scanners to one d130j antenna. I suspect though, you want to listen to multiple scanners simultaneously, which these switches won't accomodate. It's hard for me personally to listen to more than one scanner but that's me:)


HTH
 

737mech

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Neat setup RBM what are the specifics? Sorry the pic is a little blurry on my computer can't see the actual specs of the holland splitters etc. And what brand are those 8 way splitters?
 
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Fizz306

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You could also get a low loss coax switch like mine. The one on the left runs three HF receivers to my shortwave antenna, the one on the right runs two scanners to one d130j antenna. I suspect though, you want to listen to multiple scanners simultaneously, which these switches won't accomodate. It's hard for me personally to listen to more than one scanner but that's me:)


HTH
nice idea, although i am looking to feed multiple devices at once (rtl and a few 996t's).
 

rbm

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Neat setup RBM what are the specifics? Sorry the pic is a little blurry on my computer can't see the actual specs of the holland splitters etc. And what brand are those 8 way splitters?
You should be able to keep clicking on the magnifier at the bottom right corner of the image until you get a hi-resolution image.

The Holland amp goes from 50-2050 MHz.
20 dB Gain
12 - 18VDC @ 50 mA
Full specs are here: http://www.hollandelectronics.com/catalog/upload_file/LA-Series-Amplifier.pdf


The splitters are SWM8 (2-2150 MHz splitters) available on ebay (or Amazon) for around $10
Here are two examples.
Amazon.com: Directv 8-Way Wide Band Splitter for SWM LNB: Electronics
or here:
New DirecTV SWM 8 Way Splitter Green 8 Way DTV HDTV Swim Satellite High 8WAY HD | eBay

Rich
 

Fizz306

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And it's not just about the loss of signal strength. If you're using a common splitter, it's also likely that you'll get some interaction between the connected devices themselves. A multicoupler provides isolation to prevent such interaction... a signal splitter doesn't.
this splitter advertises 90db of isolation between devices. i figured this was enough, but correct me if i'm wrong. i'm leaning more and more towards a device like 737mech is recommending.

however, rbm...have any further details or a link to your setup? i'm intrigued.
 

Fizz306

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Yes it's the splitter killing your signal. Many of us are on the same path as you a little further down the road so don't worry. Step one remain calm. Step two you could do like I did and add one of these Electroline Eda 2800 8 Port CATV Low Noise Amplifier | eBay they are cheap but they work great! Especially for many scanners and one antenna. The subject has been debated alot here in the forums, some have money for a Stridsberg, others (like me) try cheap first. If it works don't fight it right? OBTW there's 4db gain from this model, Electroline also has the 2802 with 0 gain, I have both and really like a small amount of gain it improves my airband and milair alot. This drop amp also has nice port to port isolation so one scanner won't mess with the others.
so... i had some points left of my amazon card, so i'm going to give this a shot and see if it works any better for my needs right now. will report back on what this can do for me for ~$30.

http://www.amazon.com/gp/product/B001EKCGT8/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1
 

737mech

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Specs

this splitter advertises 90db of isolation between devices. i figured this was enough, but correct me if i'm wrong. i'm leaning more and more towards a device like 737mech is recommending.

however, rbm...have any further details or a link to your setup? i'm intrigued.
The specs sometimes mis-lead, 90db isolation at what freq? The design is for tv signals not scanner signals like VHF airband and such. I have also tried similiar tv splitters but unfortunately for me bad results. The rbm setup has me concerned only about one thing that may not work for some people. The inline amp tends to amp all the signals and rfi along the coax. 20db is quite loud for my GRE scanners. The front end is too sensitive for that. Also I should disclose my setup. It's a DPD LP antenna, 9913coax to a Par Electronics VHF SYM162 then into a Par Electronics FM then into the Electroline 8 way drop amp. I live in Las Vegas and there's too much FM radio and RFI in this area so the par filters are required for scanners in my setup. The cool thing about the rbm setup is the range he has clear to 2050 mhz!! It's all a try and see with this stuff, like I said before try cheap, spend more if you have to. The Electroline with 4db gain on my setup rocks!! I can hear milair up to 100 miles away,(yes area 51) as well as all the trunked stuff here in town.
 

DisasterGuy

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The specs sometimes mis-lead, 90db isolation at what freq? The design is for tv signals not scanner signals like VHF airband and such.
Cable TV frequencies span from low-band (Channel 1 being 44MHz) to air band (Channel 14 being 121.25/125.75), to 800 (Channel 126 being 805.25/809.75).

Ironically there is a spot that I drive past regularly that has a poor coax connection on the pole that I can hear Cable channel 19 over VCALL10 since VCALL10 is 155.7525 and Channel 19 has an audio frequency of 155.75MHz.
 

rbm

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however, rbm...have any further details or a link to your setup? i'm intrigued.
There's not too much more I can add.

I have five ST-2 antennas with preamps mounted at the base of each.
I also have Several commercial antennas for specific bands.

I have a mix of more than 40 Uniden scanners. (BCT15's, BDC396's, and BCD996's both generations.)
And a number of older GRE scanners. Pro-2006's etc.

And just for fun, here's a video of more than 20 Uniden scanners getting a Close Call hit at the same time. ;)
Uniden Close Call - CC DND - YouTube

Rich

By the way, I do have one antenna with no preamp installed just for comparison purposes.
It's also for use during power outages so I don't have to run the emergency power constantly.
 

Fizz306

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so... i had some points left of my amazon card, so i'm going to give this a shot and see if it works any better for my needs right now. will report back on what this can do for me for ~$30.

Amazon.com: 4 Port Cable TV/HDTV/Digital Amplifier Internet Modem Signal Booster Internet AMP: Electronics
so i got it today, installed in the shack with good results. picking up a lot more than i was before. needed to attenuate several channels/systems in the scanner because of overloading, but that's a good problem to have. still doesn't like the 9600 bd LSM system a county over (signal level constantly fluctuates, will probably need a yagi to do that decently).

all in all, a nice investment for only $30 bucks or so. would recommend.
 

737mech

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Overloading

That's why I was kinda steering you toward the 8 port, the gain is only 4db on each port. Not so bad for the front ends and you would have a reason to get more scanners. :) Glad to hear it's working better.
 

Fizz306

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That's why I was kinda steering you toward the 8 port, the gain is only 4db on each port. Not so bad for the front ends and you would have a reason to get more scanners. :) Glad to hear it's working better.
I just ordered the 8 port version, and I'm returning the 4 port. After listening for a while more last night, far too much is being over driven. Thanks again for the advise 737mech, will let you know about the next round of this (mis)adventure!
 

prcguy

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CATV amps are designed to work within a predictable environment with a finite number of carriers and known levels. Connect the same amp to an antenna and all bets are off and the amp can easily be driven to the point of creating Intermodulation products. Some signs of this are a raised noise floor and duplicate signals received where they don't belong.

Just be aware it may not be your scanner overloading, it could be the amplified divider.
prcguy


I just ordered the 8 port version, and I'm returning the 4 port. After listening for a while more last night, far too much is being over driven. Thanks again for the advise 737mech, will let you know about the next round of this (mis)adventure!
 
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