Radio Shack splitter working good

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eorange

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I have the Diamond D-130J Discone with a SO-239 connector, running about 90 feet of RG-8X mini cable ending in a PL-259. From there I use adapters to plug my antenna into either my BC780 or Icom R-7000.

I recently bought a cheap Radio Shack CATV splitter:

http://www.radioshack.com/product/index.jsp?productId=2062050&cp=&origkw=splitter&kw=splitter&parentPage=search

...to feed my antenna signal into both scanners.

I am happy to report that the splitter works well. For the time being, I have a non-optimal mishmash of F, BNC, and PL-259 adapters, and F and BNC cables that now hook everything together. It's just what I had on hand after buying the splitter. There's a hamfest coming up this weekend where I plan to get the right connectors and minimize my adapter-fest.

I listen to the AM airband, VHF high band (public safety, marine), mil air (225-400), and 400 MHz public safety. Receive performance on these bands is still the same when using the splitter. In particular, the mil air band seems unaffected...I can hear the same mil air transmissions that I have been listening to for a long time.

The only negative: there is one 800 MHz analog trunked system that I could pick up with no problem. With the splitter, I can barely lock onto the control channel. That's not too surprising, but fortunately I just listen to that system occasionally (and it's not a big deal to bypass the splitter!)

Just food for thought since there's a ton of questions here on using splitters. Try it first - for $8.00 you can't go wrong.
 

STiMULi

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eorange said:
The only negative: there is one 800 MHz analog trunked system that I could pick up with no problem. With the splitter, I can barely lock onto the control channel. That's not too surprising, but fortunately I just listen to that system occasionally (and it's not a big deal to bypass the splitter!)
Most of your loss will be in the higher MHz area.
 

gcgrotz

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They make splitters for satellite that are optimized for 900-1500 MHz. Seems like that would be ok on 860 if that's your main interest. Probably won't be good at lower freqs though.
 

Grog

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I would assume that if it keeps the 900-1500 signals "inside", they should do just as well on the lower freq stuff.

In other words, it'd be like trying to pass a softball through a hole sized for a baseball.
 

kb2vxa

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Hi Grotz and all,

"They make splitters for satellite that are optimized for 900-1500 MHz."

They're not splitters, they're diplexers. The crossover frequency is all wrong for anything but a SAT/CATV combo. That's the one bit of info I left out of my "Diplexer Trek" adventure as it's irrelevent for that reason.

Eric, UHF TV used to go up to 900MHz and I see no reason why "they" would have redesigned the splitters since 800MHz was reallocated, if it ain't broke don't fix it. Remember that a splitter literally splits the signal in half (3 or 4 ways too depending on the number of outputs) giving you a 3dB loss right off the bat. In any device loss increases with frequency so you can add a bit at the upper frequency limit and if the signal is marginal to begin with you may notice severe degradation by introducing any device and more coax into the transmission line(s).

If this is a problem using a UHF coaxial switch available at ham retail outlets and the scanners one at a time will improve reception significantly. BTW, you can easily simplify that arrangement by using RG-6U quad shield coax and F connectors between the splitter and the scanners. Of course use the appropriate adapters but the point is you'll eliminate some adapters and end up with a neater installation. Never mind those who insist that adapters introduce loss (HORSE HOCKEY!) when the point is cleaning up a messy cabling job.

Last but not least always use the best coax you can afford for long runs, Belden 9913 air dielectric or Times Microwave LMR series. Short runs aren't quite as important but above all avoid RG-58 and RG-59 at frequencies above 30MHz. There's no point in losing in the cable what you gained in the antenna and ending up with less than you started out with.
 

prcguy

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Well, a splitter is a power divider but a diplexer is a completely different item. Lower frequency, broad band TV splitters resemble a transformer inside with tiny wire wrapped around a ferrite bead. Narrower band splitters such as the 900-1500MHz types are usually a Wilkinson divider with specific length stripline traces and balancing resistors. A transformer or Wilkinson divider will degrade below their advertised operating frequency, don’t try to use a satellite version on a scanner antenna. I was testing some broad band 75ohm 40-2150MHz splitters last week and found they had about 3.5dB loss at the low end and almost 8dB loss at the high end, even though they were advertised as a 3dB loss device. They weren’t broken, it’s just the way cheap consumer TV/satellite crap is made. I suspect one reason the 800 signals degraded on eorange’s system is because the splitter loss increased noticeably at the high end. If I get a chance I’ll sweep test a typical 5-860MHz TV splitter and report the results. I’ll bet a paycheck it will not be 3dB loss across the whole range!
prcguy
 

kb2vxa

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Hi PRC again,

"Well, a splitter is a power divider but a diplexer is a completely different item."

:)->)

"Lower frequency, broad band TV splitters resemble a transformer inside with tiny wire wrapped around a ferrite bead."

Yeah, I have had them apart and guess what? It's a 4:1 balun transformer with each leg connected to an output port working against a common ground giving constant unbalanced impedance throughout rather than balanced transformation but still has each leg 180 degrees out of phase. That's one of the bugaboos that drive people nuts when they try to use them as combiners, unexpected phase cancellation effects.

"Narrower band splitters such as the 900-1500MHz types are usually a Wilkinson divider with specific length stripline traces and balancing resistors."

That's what makes it a diplexer. Each stripline has a specific bandpass and a diplexer is simply two bandpass filters (stripline or standard L-C) back to back.

Now if you look up the specs instead of taking them apart and trying to figure them out yourself you'll see why they're diplexers and not couplers. The LNB output is typically in the 900MHz range well above CATV and each must be kept separate and routed to thier respective receivers. Often times a common transmission line is used with one at each end so the bands are combined, then separated again.

"They weren’t broken, it’s just the way cheap consumer TV/satellite crap is made. I suspect one reason the 800 signals degraded on eorange’s system is because the splitter loss increased noticeably at the high end."

I believe I already said that in different words but it amounts to the same thing.

"If I get a chance I’ll sweep test a typical 5-860MHz TV splitter and report the results."

I already have and confirmed our suspicions.

"I’ll bet a paycheck it will not be 3dB loss across the whole range!"

You'll find my mailing address in the FCC database, cashier's check or postal money orders only please. I'll mail you the printout upon receipt. On the other hand I really don't like sucker bets so you can take my word it's more than 3dB in some places and less in others and I never took the time to average the figures nor analyze the core permeability. (;->)

Oh, just to set the record straight, a "splitter" is a voltage divider. A power divider is known also by another name, a coaxial phasing harness. Oh don't go into microwaves and get everybody confused, they probably think a waveguide is a surfing instructor. (;->)

Anyway we agree on something, a CATV/SAT device is completely unsuitable for the job at hand and in any case loss rises with frequency. Let's see if we can agree on this, do you think we have confused the casual hobbyists enough or should we continue the tech talk or maybe get into Boolean Algebra? (;->)
 

eorange

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All good discussion. I am not too surprised at the degraded 800 MHz signal; remember I have a LONG coax run and perhaps the splitter was also just enough to degrade the signal.

Again, the splitter and mess of adapters experiment is proof that you don't always have to spend $$ for a dB amplifier/multicoupler and still get decent results.
 

prcguy

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An RF splitter and divider as discussed here are the same device and a 2-way version will have at least a 3dB power loss and 6dB voltage loss through each output port unless it’s a “resistive divider” which is usually 6dB or more power loss per port. A “Satellite Diplexer” is a specific filter with a low pass port for frequencies below around 800MHz and a high pass for frequencies above around 900MHz. There used to combine off air TV signals with “L-band” satellite TV signals from consumer dishes so the customer can have just one coax going to a specific room with both signals present. The narrower band splitters and dividers that are being discussed (both transformer and Wilkinson types) have the same frequency response at each port and are usually specified at 950-1450MHz, 950-1750MHz or 950-2150MHz for the various outputs of satellite LNBs. There not diplexers unless they say “Diplexer” on the lid. Maybe Warren has some in his junk box and the labels fell off. I have stockrooms full of them and every other conceivable consumer satellite and TV RF accessory and a lab with new HP Agilent 75ohm Vector Network Analyzers and 50ohm Scaler Network Analyzers to characterize them. It’s not just my hobby, its part of my job.
prcguy

kb2vxa said:
Hi PRC again,

Snip...
"Narrower band splitters such as the 900-1500MHz types are usually a Wilkinson divider with specific length stripline traces and balancing resistors."

That's what makes it a diplexer. Each stripline has a specific bandpass and a diplexer is simply two bandpass filters (stripline or standard L-C) back to back.

Now if you look up the specs instead of taking them apart and trying to figure them out yourself you'll see why they're diplexers and not couplers. The LNB output is typically in the 900MHz range well above CATV and each must be kept separate and routed to thier respective receivers. Often times a common transmission line is used with one at each end so the bands are combined, then separated again.
 
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