Co-Phased Radios

[LouisvilleScanMan]

A friend asked me to put up a post asking if you could connect two cb's in different locations (one in the house and one in the garage) to one antenna without sending the power from one radio into the other.FYI both radios would not be on at the same time.

 

[k9rzz]

If you put a switch in line to cut one out, sure. Otherwise ... nope.

John K9RZZ

 

[ReceiverBeaver]

Yep, Lot's of CB home stations have done this over the years. Beavers say, "The more radios the merrier", and you can quote us on that.

As John mentioned above, all you need is the typical 2 Position Coax Switch. Ordinarily they are used to connect 2 antennas to one radio. For the application of 1 antenna to 2 radios, you simply turn the switch around backwards in the circuit.

Sold everywhere for 20-25 bucks. Get a ham radio rated switch and not some small el~cheapo "CB-only" piece of crap. I've used the MFJ 1702 unit and they've been around forever. Rated for 2,500 watts and only 19.95 Several other brands around as well. Available at any ham radio dealer. The Beavers have braved the peril and gone to the great trouble of chewing up a linky for you:

http://www.mfjenterprises.com/products.php?catid=122&type=price

Also can pick a new/used one up even cheaper on eBoinkybay if you shop there.

Tip: Use identical coax for all 3 runs of coax in this system, preferrably coax purchased all at once and off of the same reel. Mismatching coax pieces for transmitting stations many times sees SWR/impedeance matching problems that must be corrected. Not critical for receive-only systems.

 

[N_Jay]

. . Tip: Use identical coax for all 3 runs of coax in this system, preferrably coax purchased all at once and off of the same reel. Mismatching coax pieces for transmitting stations many times sees SWR/impedeance matching problems that must be corrected. . . ..

TIP:
CBer Mythical problem.

you will have minor (or major is you are cheap) impedance transitions at every connector and at the switch.

There is no inherent advantage to using the same or "matched" cable for the separate pieces.

 

[ReceiverBeaver]

NJ ol boy your two statements above contradict each other. You agree that using mismatched cables may create minor or major impedance transitions (which is a bad thing...and darn those pesky differing velocity factors between different sizes and types of cables), and then you state more or less that it is not a good idea or advantageous in any way to use identical transmission line throughout a properly engineered radio trasmitting station layout. I bet you would probably only utilize same-cables throughout your own antenna systems and recommend/sell same specs to customers.

Well...Beavers are gratified that you only USED to claim to be a "communications professional" on this board.

Yep you can be cheap and and piece things together out of a junkbox and get stuff to work some of the time and that's all good. It's always good though to know what the right or best way may be to build your whatever and become familiar with what typical standard practices are.





Whenever Beavers speak.......Trees Listen !!!

 

[N_Jay]

NJ ol boy your two statements above contradict each other.
. . . . .
Whenever Beavers speak.......Trees Listen !!!

No they don't.

It is best to use GOOD cable, but unimportant to use the same cable.


10 feet of brand 1 cable at 50.1 ohms, followed by the bump of the switch followed by 50 feet of 49.9 ohm brand 2 cable is just as good as;
10 feet of brand 1 cable at 50.1 ohms, followed by the bump of the switch followed by 50 feet more of 50.1 ohm brand 1 cable.

 

[Don_Burke]

A friend asked me to put up a post asking if you could connect two cb's in different locations (one in the house and one in the garage) to one antenna without sending the power from one radio into the other.FYI both radios would not be on at the same time.

The switching would be the easy part. Impedance matching would be relatively painless as well.

I would be concerned about mistakenly transmitting into a disconnected terminal on the switch.

With a remotely controlled switch, an interlock would not be difficult to set up.

I would also consider two seperate antenna systems. Yeah, it would be a pain, but it would be pretty close to idiot-proof.

 

[LouisvilleScanMan]

Well my friend is no idiot and he wants to keep it low profile so he is just going to use one antenna.He would probably put the switch at the primary station in the house in plain view so that he won't make that mistake.

 

[jhooten]

First item on the page.

http://www.durhamradio.com/s/home.php?printable=Y&cat=1667

AS100 automatic switch. Should solve your problem.

Beaver,
You do know that the so called UHF connector (PL-259) commonly used on CB radio equipment is not a constant impedance device,don't you? This means that you will have a mismatch every where you have a UHF connector. Don't matter what cable you use there will be mis-match.

 

[Don_Burke]

Well my friend is no idiot

_Everyone_ has idiot moments.

and he wants to keep it low profile so he is just going to use one antenna.

I can understand that.

He would probably put the switch at the primary station in the house in plain view so that he won't make that mistake.

It is not a question of if. It is a question of when.

I like the automatic switch jhooten found for this job. It looks like it addresses all the concerns.

 

[LouisvilleScanMan]

There's a place here in KY that has it a little cheaper but I'll tell him.Does anyone else make anything like that or is it the first of it's kind?

 

[ReceiverBeaver]

Yo JH,

Now you're doing it. Perhaps you and NJ should get together and party some. Ya'll seem to think alike in that you offer preposterous arguments against industry standard practices and everyday items which are proven technologies....as well as ignoring common sense. Now you are saying that any use of the common PL259 UHF connectors is going to cause impedance mismatch problems.

Wish ya'll would stop trying to mislead and confuse the poor folk who inhabit this site and seek assistance with their stuff. You're not helping and apparently just enjoy arguing and seeing your names up in lights. Perhaps you guys should become hams and gain some practical real-world transceiving experience.

NJ would have everyone cobble their antenna feedline systems together using whatever 13 differing pieces of scrap coax ya got laying around and everything will be fine. And JHooten is suggesting everyone throw away all of their UHF connectors......and do what instead? Solder feedline conductors directly to circuit boards and antennas?

 

[N_Jay]

. . . Perhaps you and NJ should get together and party some. Ya'll seem to think alike in that you offer preposterous arguments against industry standard practices and everyday items which are proven technologies....as well as ignoring common sense. Now you are saying that any use of the common PL259 UHF connectors is going to cause impedance mismatch problems.

Wish ya'll would stop trying to mislead and confuse the poor folk who inhabit this site and seek assistance with their stuff. You're not helping and apparently just enjoy arguing and seeing your names up in lights. Perhaps you guys should become hams and gain some practical real-world transceiving experience.

Please tell me the EXACT "preposterous arguments" of mine in this thread?

All I pointed out is that your preposterous tip is nothing but a stupid myth.

Your "tip" was the first confusing thing in this thread.

Maybe you just don't read well enough to understand the conversation.

EVERY comment that you consider confusing, is clearer and MORE TRUE than your "tip"!

 

[ReceiverBeaver]

NJ, You're talking crap.

Nobody in the world.....besides you....would recommend mixing different type pieces of coaxes together to construct a good and proper system.

Any institution or commercial entity WOULD recommend that such systems be physically and electrically matched to construct an antenna system that would be reliable and expected to work.

Now you can come back and argue with that all you want but you're just continuing to be argumentative and make yourself look stupid. So go right ahead and keep discrediting yourself.

The tip I offered was proper and accurate.

Many of your over 5,600 posts on this board only seek to pick on folks and argue.

 

[N_Jay]

NJ, You're talking crap.

LOL, The only problem here is you don't know crap when you spew it!

Nobody in the world.....besides you....would recommend mixing different type pieces of coaxes together to construct a good and proper system.

I guess all the major sites that have different cables for the antenna end jumper, the main line, the in building cabling and the jumper to the equipment are all F--ed up and not designed by people as smart as you!

Oh wait, I forgot the various pieces of transmission lin within the antenna itself, and within the combining, multicoupler, and/or duplexer systems.

Oh, what about the pieces inside the station itself?

Any institution or commercial entity WOULD recommend that such systems be physically and electrically matched to construct an antenna system that would be reliable and expected to work.

Again, you have absolutely no idea what the hell you are talking about.

(My proof of this statement was your attempt to bring Velocity factor in to the discussion when it has no impact on cable choice in this application.)

Now you can come back and argue with that all you want but you're just continuing to be argumentative and make yourself look stupid. So go right ahead and keep discrediting yourself.

Why don't you just look at all your posts arguing with me over my correction of your INCORRECT information.

The only reason I look stupid is because I am taking the time to answer a moron like you at all!

 

[kf4pep]

I have rarely seen a professional installation that did not use varying types of coax. I have never seen a repeater installation that used 7/8 Heliax for the jumpers, yet they use it for the major run. Many also use a short more flexible jumper at the antenna.

All very well engineered professional installations. There is no difference between running an coax jumper before a duplexer and heliax after (often with another jumper) and using an RG-8 jumper before a switch and LMR-400 after for a CB.

 

[N_Jay]

I have rarely seen a professional installation that did not use varying types of coax. I have never seen a repeater installation that used 7/8 Heliax for the jumpers, yet they use it for the major run. Many also use a short more flexible jumper at the antenna.

All very well engineered professional installations. There is no difference between running an coax jumper before a duplexer and heliax after (often with another jumper) and using an RG-8 jumper before a switch and LMR-400 after for a CB.

Shhhhhhhh!

You'll wake the Beaver.

You think I was too hard on the Beaver, June?

 

[zz0468]

NJ would have everyone cobble their antenna feedline systems together using whatever 13 differing pieces of scrap coax ya got laying around and everything will be fine. And JHooten is suggesting everyone throw away all of their UHF connectors......and do what instead? Solder feedline conductors directly to circuit boards and antennas?

You're being ridiculous, as well as wrong. N_Jay is not advocating using 13 different pieces of coax. He's saying that using different types of the same characteristic impedance is ok. It's true. It's also considered good engineering practice to use a larger feedline for the bulk of the run, and smaller, more flexible jumpers at the ends. Your tip to use identical cable for all three runs is nice and neat, but electrically unnecessary. I know of professional installations that use as many as 5 different types of coax between the transmitter and the antenna. Let's see... tx to combiner RG-142; intercombiner cabling - 1/4" superflex; top of combiner to entry port - 1/2" superflex; Main feedline run - 7/8" Heliax; Feedline to antenna - RG-214 jumper. Swept time-domain measurements with an Agilent 8722 network analyzer can show all those transitions from one size to another, but really... do we really care about .01 db increases in return loss? I don't. You shouldn't either.

As to the impedance bump using PL-259's, well, I would suggest that at 27 MHz, it doesn't matter. If you sweep those connectors with a network analyzer, you'll see the impedance bump become more significant as the frequency increases. When it takes a $120,000 instrument to see it at 27 MHz, I think it's fair to say it doesn't matter. I wouldn't use a PL-259 above 150 MHz, myself. But that's for another thread.

 

[jhooten]

Yo Bev,

Look at the very bottom of my sig. See the 1X2 call sign listed? In case you are having reading problems here you go N5SY.

In addition I hold a GROL. Radio experience includes 11 years in the Army as a Microwave and Satellite communications systems operator/supervisor and another 17 years as a government civilian Electronics Tech/Telecommunications Specialist.

Care to regal us with your vast experience in the radio field?

UHF family connectors are crap. They are used in low end applications because they are CHEAP. As soon as the warranty is up on my equipment (except CB) the UHF jacks get changed to either an N, BNC, or TNC depending on the use. Of course it does take a bit more skill to properly install those connectors but I'm sure you could learn if you tried.

And on you hammy antenna trunk mounts made by Comet what do you see? Connected to the mount is a short section of RG-174 then a transition to RG-58. I guess according to your standards that must be a defective device and we should boycott Comet for foisting such junk on the ham community.

 

[N_Jay]

Now, come on ZZ and Jerry. Lighten up on Beaver.

It's not Beaver's fault he is so screwed up.

That Eddy Haskel boy has been filling his head with all sorts of wrong information.

He'll grow out of it.

:twisted: :lol: :twisted: :lol: :twisted: