Scanner Antennas: Height and Coax

[N4DES]

The amount of current that flows in an antenna is one of the most important factors affecting the performance of transmitter equipment. As much of the rf energy generated as possible must be efficiently transferred to the antennas to secure the maximum radiated power from a transmitter. Also, for best reception, maximum transfer of energy from the antenna to the receiver must occur. Efficient transmission and reception conditions prevail whenever the transmitter (or receiver) is properly matched to the transmission line and the transmission line is properly matched to the antenna.

http://www.infodotinc.com/neets/book21/88b.htm

 

[K2KOH]

Considering that your cable run would be approximately 45 to 50 feet, 9913 is just fine.

 

[gr8amp]

RG6 is 75 ohm coax and not the correct type. You want to use 50 ohm coax which is RG8.

Yes, the scanner may be 50 ohms, but the actual impedance of the antenna system is going to vary greatly over the frequency range that the scanner covers. If you were to cut the antenna for one frequency, and just leave the receiver on that frequency all the time , sure....use the 50 ohm coax.

Huh? The cable impedance changes? No, try the VSWR and Return Loss changes across the frequency bands at the termination to the antenna. The cable impedance remains constant no matter what frequency you put thru it.

HUH???????I never said the characteristic impedance of the cable changes. Where are you reading that :? I am talking about the overall antenna system, and the impedance that will be seen at the antenna feedpoint. Although antenna design is a major factor here, this impedance is most always frequency dependant.

Also, the articles that you are quoting are true, but cannot be applied directly to a system with great variations in frequency(like a scanning receiver) for the reason stated above. Like I said before, if the receiver is going to remain within a small band of frequencies, or you are sure the antenna respose is nearly flat across the desired frequency range, make sure everything is matched, otherwise using 75 ohm coax is perfectly fine.

High performance 75 ohm coax is often easier to find, less expensive, and sometimes more flexible and easier to install...why not use it?

Also, my problem with 9913 is with its physical construction, not its electrical characteristics.

 

[Voyager]

Considering that your cable run would be approximately 45 to 50 feet, 9913 is just fine.

Yea - if it's a straight line from the antenna connector to the scanner connector. 9913 goes to **** REAL quick when you have to bend it.

(as was said multiple times above)

Joe M.

 

[opus]

Hey. I use 75 Ohm cable with TV Amps. I have a diamond X50 running into a broad band TV amp and then I have that fed into another TV amp that combines VHF/UHF feed with a UHF Band 5 feed. What? Yes thats right. My 800MHz antenna goes into the Band 5 input. Neat Then I have one RG6 cable running down into my multicoupler. I hear stuff I have never heard before with this system.

I needed to do it this way as I live in a Villa type situation with what we aussies called a body corporate (akin to your condo boards?). The only way they were going to let me have antennas were that they were nice and slim so discones and grove beams etc. were out of contention. And only have one line to keep down the questions. They all think I am just an amateur who does not transmit Don't want too many questions from people who don't understand the hobby.

Opus

 

[sking128]

Hey. I use 75 Ohm cable with TV Amps. I have a diamond X50 running into a broad band TV amp and then I have that fed into another TV amp that combines VHF/UHF feed with a UHF Band 5 feed. What? Yes thats right. My 800MHz antenna goes into the Band 5 input. Neat Then I have one RG6 cable running down into my multicoupler. I hear stuff I have never heard before with this system.

I needed to do it this way as I live in a Villa type situation with what we aussies called a body corporate (akin to your condo boards?). The only way they were going to let me have antennas were that they were nice and slim so discones and grove beams etc. were out of contention. And only have one line to keep down the questions. They all think I am just an amateur who does not transmit Don't want too many questions from people who don't understand the hobby.

Opus

Can you give the technical info on your antenna rig??

 

[brwkem]

LMR400 bend radius

How much of a bend can LMR400 handle without creating any major problems?
Ready to pull my line through drywall then up into a large walkup attic.
Only problem is the bend when it goes up to the attic.
Can't handle 80-90 degree bend read that.
Guess I dont follow what a 1" bend radius means?

Thx for the help.

brwkem

 

[loumaag]

Re: LMR400 bend radius

Guess I dont follow what a 1" bend radius means?

I can't help with the rest of your question, but a 1" bend radius means the measurement from the inside of the arc to an imaginary center point of the arc, 1" away. Imagine a circle; the radius would be 1", the diameter would be 2". I guess what they mean is you can't bend it more sharply than the arc described by a 1" radius.