Question on spacing antennas

redferrariowner · #1 (**permalink**) 10-04-2007, 01:48 PM

Ok, I have a pickup truck with a scanner, and soon a CB. On one side of the truck bed, I have a 3 foot firestik scanner antenna. I plan on mounting a 3 foot Firestik CB antenna on the other side, about 4 feet apart. Now say, "Hypothetically", my CB put out 250 watts, is the antenna spacing adequate? Could that power transfer to my scanner and damage it?

N_Jay · #2 (**permalink**) 10-04-2007, 01:52 PM

Given you are running 250 watts, I would suggest you hook the output of your CB directly to the input of your scanner!

Don_Burke · #3 (**permalink**) 10-04-2007, 01:59 PM

Quote:

Originally Posted by redferrariowner

Ok, I have a pickup truck with a scanner, and soon a CB. On one side of the truck bed, I have a 3 foot firestik scanner antenna. I plan on mounting a 3 foot Firestik CB antenna on the other side, about 4 feet apart. Now say, "Hypothetically", my CB put out 250 watts, is the antenna spacing adequate? Could that power transfer to my scanner and damage it?

That would be a bit much to ask of the scanner, although some would be up to it.

Is there any chance of getting more space? Putting the scanner antenna as far forward as you can with the CB antenna as far back as you can and on the opposite side would get you quite a bit more space.

redferrariowner · #4 (**permalink**) 10-04-2007, 02:01 PM

Huh, Im kind of a newb, but that sounded a little sarcastic. So what exactly are you saying?

redferrariowner · #5 (**permalink**) 10-04-2007, 02:02 PM

Quote:

Originally Posted by Don_Burke

That would be a bit much to ask of the scanner, although some would be up to it.

Is there any chance of getting more space? Putting the scanner antenna as far forward as you can with the CB antenna as far back as you can and on the opposite side would get you quite a bit more space.

So put as much space inbetween them basically? What would hooking up the output to the input of the scanner do?

N_Jay · #6 (**permalink**) 10-04-2007, 02:03 PM

Quote:

Originally Posted by redferrariowner

Huh, Im kind of a newb, but that sounded a little sarcastic. So what exactly are you saying?

250 watts is not a legal CB.

redferrariowner · #7 (**permalink**) 10-04-2007, 02:04 PM

Quote:

Originally Posted by N_Jay

250 watts is not a legal CB.

"hypothetically"

Scott_PHX_APP · #8 (**permalink**) 10-04-2007, 02:06 PM

I think what the guys are trying to say is this. Get as much space between them as you can. I'm guessing here, but I think you will de-sens the scanner a lot when you transmit, ("Hypothetically") with that much powerand might even overload the receiver. As to damage, it would depend on the scanner, it might and it might not. I'm not sure if you put a tuned trap on the scanner input would help, but it could.
Later...

redferrariowner · #9 (**permalink**) 10-04-2007, 02:09 PM

Quote:

Originally Posted by Scott_PHX_APP

I think what the guys are trying to say is this. Get as much space between them as you can. I'm guessing here, but I think you will de-sens the scanner a lot when you transmit, ("Hypothetically") with that much powerand might even overload the receiver. As to damage, it would depend on the scanner, it might and it might not. I'm not sure if you put a tuned trap on the scanner input would help, but it could.
Later...

Its a newer Radioshack scanner, there isnt a seperate input output, so I dont know how that would work. What do you mean by De-sens?

N_Jay · #10 (**permalink**) 10-04-2007, 02:09 PM

Quote:

Originally Posted by redferrariowner

"hypothetically"

Well "a hypothetical" a 250 watt CB puts out 4 watts, because that is what a CB is.

The other radios are officially called "illegal transmitters".

Don_Burke · #11 (**permalink**) 10-04-2007, 02:12 PM

I am lost. Hook the output of what to the input of the scanner?

Quote:

Originally Posted by redferrariowner

What would hooking up the output to the input of the scanner do?

N_Jay · #12 (**permalink**) 10-04-2007, 02:13 PM

Quote:

Originally Posted by Don_Burke

I am lost. Hook the output of what to the input of the scanner?

He was trying to interpret my sarcastic remark that he hook up his illegal 250 Watt CB right to his scanner!

redferrariowner · #13 (**permalink**) 10-04-2007, 02:16 PM

Quote:

Originally Posted by Don_Burke

I am lost. Hook the output of what to the input of the scanner?

Im kinda at a loss too. The second post talked about hooking the output of the cb to the input of the scanner. I have no idea what it would do, but I see the basic idea is seperate the antennas as much as possible. On question left, is a newer radioshack mobile base scanner sturdy enough to catch significant power?

Scott_PHX_APP · #14 (**permalink**) 10-04-2007, 02:24 PM

I think N_Jay was pulling your chain, hooking up the CB directly to the scanner would most likelly screw up the scanner and not do a lot more for the CB. That said, he was also making the statement that 250W from a type approved CB is illegal, etc. All that said, the trap I was refering to would be a Tee in the antenna line to the scanner and a cut length of coax attached to the Tee that reduces the level of the signal at a certain frequency, in this case, the 11 meter band. What I'm not sure of, is if you can reduce it enough for the whole band. Many years ago I did the same thing you are doing, (less the 250W output) and had no trouble other that sometimes locking up the scanner on a frequency when transmitting. It never hurt the scanner, but then as I said, I wasn't pushing any high power.
Good luck.

pogbobo · #15 (**permalink**) 10-04-2007, 02:28 PM

what kind of cb do you have that is putting out 250 watts??

redferrariowner · #16 (**permalink**) 10-04-2007, 02:35 PM

ok, so Ill just try to put as much space inbetween antennas as possible. Would turning off the scanner when transmiting help, or will it still take in the radio waves from the cb either way.

Don_Burke · #17 (**permalink**) 10-04-2007, 02:35 PM

The individual who posted that has been on my ignore list for about eight months now, so I do not see those posts.

You now see why I put that individual on my ignore list. The procedure you describe would stand a good chance of taking out both units. There are apparently priorities other than helping you.

xxxxxxxxxxxxxxx

Each unit goes on its own antenna. Get the antennas as far apart as you reasonably can.

The scanner may need a filter to knock the CB signal down some more. It will be _much_ easier if you do not need the scanner to pick up VHF low as then you can use a really brutal filter.

The CB may need a low pass filter, but only do that if you need to. My guess is that running medium to high power at HF will probably require it.

Desensing is where an undesired signal gets in, normally through the antenna input, and uses up some of the gain of some of the amplifier stages in the radio, leaving less for the desired signals. The symptom is a radio that seems to be having sensitivity problems.

I have not used a newer Radio Shack unit in a strong signal environment, so I will have to defer to someone who has.

On a related issue, I expect extra power on CB will disappoint you.

Quote:

Originally Posted by redferrariowner

Im kinda at a loss too. The second post talked about hooking the output of the cb to the input of the scanner. I have no idea what it would do, but I see the basic idea is seperate the antennas as much as possible. On question left, is a newer radioshack mobile base scanner sturdy enough to catch significant power?

redferrariowner · #18 (**permalink**) 10-04-2007, 02:37 PM

Quote:

Originally Posted by pogbobo

what kind of cb do you have that is putting out 250 watts??

Actually not sure, Im getting it from a relative that had it sitting around for a while.

Scott_PHX_APP · #19 (**permalink**) 10-04-2007, 02:38 PM

What Don Said

Don_Burke · #20 (**permalink**) 10-04-2007, 02:38 PM

There are two issues:

- affecting the scanner without damaging it

- damaging the scanner

If the first one is your only problem, turning the scanner off will just make you unaware of the problem, which may be enough for your purposes. That would be your call.

If the second one is a problem, turning off the scanner is unlikely to help.

Quote:

Originally Posted by redferrariowner

ok, so Ill just try to put as much space inbetween antennas as possible. Would turning off the scanner when transmiting help, or will it still take in the radio waves from the cb either way.