Splitters, Attenuators, Filters, Diplexers, Other Signal Gear

[tvlurker]

Originally Posted by holl_ands

What??????
It can operate as EITHER a splitter, or a combiner when reversed.....

Perhaps the OP was asking if you could terminate the "input" of a splitter, and then use 2 of the "output" ports as outputs to TVs and the other two "output" ports as inputs from two antennas. IOW, use the device as a four-port hybrid.

Frankly, I don't think most consumer 4-way splitters are wired that way. I think they are wired as two cascaded 2-way splitters. And they're designed for isolation between ports.

[firimari]

splitters/combiners work with one input and many outputs or many inputs and one output.

So, no, you can't combine 2 antennas and distribute the signal to 2 TVs with one box. you can use two 2-1 splitter/combiners and a short bit of coax between the two...

Insert lots of caveats about combining antenna signals here.

[holl_ands]

Isolation between ports is "typically" 20-30 dB....
So signals going in on one port are highly attenuated before going out another port.

[blueroomelectro]

To clairify it's two antennas to two TVs. The antennas work fine as the signals are 90d apart and although there is a little loss when combining they do work great. What's inside a splitter / combiner anyway? I thought they were simple passive devices.

=>-<=

= two coax
> combiner
- coax
< splitter
= two coax

[Marbles_00]

Replace the "- coax" with one of these:
http://rocky.digikey.com/WebLib/CUI%...os/BA-2010.jpg

They can found at Sayal Electronics, or from Digikey (or most likely from any surplus store). This way it keeps that section to a minimum. I used one for connecting my antenna combiner to the input of the CM-7777 preamp.

[Marbles_00]

I've often thought about using one of those 3-female F-type Tee adapters for interfacing a coax notch filter inline where the antenna feed on one end, feed to the TV on the other, and the coax notch off the center. But I'm curious, what would happen if this was used as a combiner? Would too much signal bounce back and fourth between the two antenna feeds and wreck havoc on the system? I gather that would be the case, otherwise this would of been the solution for everyone long before I thought of it.

[majortom]

I wish there was a way to cross-calibrate a store bought attenuator with those ones you've got to see how accurate they actually are.

The BNC definitely has to go, for UHF purposes. Just doesn't mate snug enough. Might be OK for some 45 MBS M/W radio or sumthin...
Took one apart, consists of nothing more than a Bourns, Inc
3100T-151-750, mounted on decent looking PCB / ground plane, on a project box, hard wired inside the project box to the BNC connectors.
Took a quick look around, on Bourns site, Digikey, etc. and couldn't find any data on the part

3100T - assuming that's the product series, for the variable attenuator.
151 - assuming => 15dB
750 - assuming that means 75 ohm in/out impedance

It's actually from an ancillary kit of an old Harris Farinon M/W Radio.
Just guessing it was originally intended as an aid in aligning some M/W Radio.
The completed assembly is Farinon p/n 077-103130-005.


Who knows, maybe there's some old Farinon employees around here from Montreal.

[Marbles_00]

Opps, sorry about the retail link...didn't mean that, but here is the "T" adapter from my previous post (image only ).


Question as before, could this work as a combiner?

[roger1818]

Originally Posted by Marbles_00

Question as before, could this work as a combiner?

Since I don't have the technical specs. I don't know for sure, but it looks like it just hard wires the three connectors together. If so, although it would work as a combiner, it wouldn't be a very good one as there wouldn't be any impedance matching.

[BobbyDing]

Hi folks,
I have two antennas facing different directions. Each antenna line is split and sent to two different rooms. One room has a PC with each line running to a dedicated tuner card. The other room has a single TV and I use an A/B switch to select the antennas. It dawned on me tonight that whichever line I'm not using is probably unterminated inside the switch, which I assume may cause signal issues at the tuner card in the other room. Does anybody make an A/B switch that terminates the unused line? I checked Summit Source, but none of their Switch descriptions listed termination of the unused line. If nobody makes one, can I make one myself (are the coax terminators simply resistors)?

Thanks for any help.

Bobby

[Jase88]

I suppose it depends on the A/B switch. However, I suspect most terminate the feed when switched off. Mine, for example, does terminate the switched-off feed. I know this for two reasons: (1) I opened it up, and (2) I don't see ingress on analog cable channels 13 or 6 (where local OTA stations broadcast in my area).

In your case, where both feeds into the A/B switch originate from antennas, I doubt you'll note a performance issue assuming the off feed is not terminated.

However, if you have analog cable on one feed and an antenna on the other--and note ingress or interference on the cable channels where off-air local signals are broadcast--you've likely got a non-terminating A/B switch (or a cable fault somewhere in your setup).

[BobbyDing]

Thank You for that info. I'll have to see if my switch can be opened to check for myself. It's an old radio shack one I think (20+ years old). Might I inquire what brand/model your switch is? I'll go and buy one if I'm sure it terminates.

Bobby

[Jase88]

My A/B switch is a generic one (no brand name or manufacturer indicated), bought from a local electronics store. It has a sticker on the side that indicates "This device is verified to comply with FCC Rules Part 15 for use with cable television service".

Now while I'm not familiar with "part 15 of FCC Rules", one would assume that since the FCC regulates signal leakage from cable TV systems, the rules must stipulate termination of all live connections.

So I'd look for an FCC approval on any A/B switch equipment.

[majortom]

Finally disassembled that 75 ohm variable attenuator, and replaced it's BNC connectors with F-female connectors. I use three feeds total off my pre-amp,
so I split once, Splitter A's output 1 gets split again via Splitter B, to provide two drops. Spitter A's output 2 goes to this variable attenuator, set to 3dB, and drops to the third drop.

Also disassembled a 75 ohm directional coupler i had in the junk bin, and replaced it's BNC's with F-Female also. It's basically a 75 ohm Mini-Circuits Directional Coupler inside a Pomona project box. The coupled port is 10.5 dB down from the thru Port. Kinda cool, cause now I can throw that in line and use the 10.5 dB down coupled port to eyeball signals on the spectrum analyzer, without the Spectrum analyzer loading things down significantly.

[goforit]

John, in addition to the 4228 hacks, have you tried multiple UVSJ splitters? I think I remember you tried one that didn't make a diff. I used 3 UVSJs and it really calmed down 11 and bumped up the other signals.