problem with new length of co-ax...

[Red Rider]

Right...
i was in the garage using a 4-5ish meter length of co-ax (the rg-213 stuff, not the shitty cheap gear!) and everything was working perfect... A swr of 1, perfect mod and signal... Cracking out well but since i've put in a longer length (about 10-15m...ish) from the aerial into the house the swr has gone up to 1.7 and has knocked several miles off my range where i could get people before with no problem i'm having to get people to 10-5 to people i normally chat to as clear as a bell to let them know i'm there!
I used to run a piece of cable into the house before and never had this poor performance...
At first i thought interferance from electrical stuff since the cable runs past the computer and electrical sockets but it only makes interferance when the computer is on, and i knew that already and always dx with the computer off so i really don't know what's killing it as it's a brand new piece of co-ax and i soldered the plugs up myself and they're perfect...

i wouldn't have thought making a longer length of co-ax would have this much impact! I know people that run co-ax for a good 20-30 meters down to the bottom of their gardens and don't have this trouble!

[killer cam]

i got 20m with no probs make sure the bradle is in contact with the pl259 make sure the cable is not pinched and it could be other interference have u got a bt vision box or somthing similair they cause interference

[Red Rider]

Nah, just got normal cordless phones (which we had when i had my previous setup in the house with no probs) and my netgear router...


I did have to cable tie the cable up from the garage roof over to the gutter on the house to bring it down the wall into my room so it didnt sag...
Would it being pinched there cause this?

[stampman]

is it new cable or old stuff reused check for water or damp in the cable

[Red Rider]

brand new straight off a new reel i ordered last week

[killer cam]

i know when co-ax cable is pinched it causes loads of problems

[Red Rider]

WIEEERRDDDDDDDDD!

had another butchers at this today and poked around at the coax and aerial and whilst checking the aerial on the back of the garage i moved all the ladders off the garage and its back to my usual low SWR and operational range...

Dodgy connection or was it the ladders?

[porky.69]

i like the mini 8 grey coax

[stampman]

only way to tell is to put the ladders back up realy but interesting never the less we learn something everyday

[killer cam]

weird

[ForzaCFC]

for 11m operation run your coax in 11ft multiples, I read this in the 'Screwdrivers guide to CB Radio' section on radio theory, swr etc or something like that.
Anyway tried out there suggestions regarding coax and was running around 77ft of coax up a full length scaffold pole and into a sirio copy of a sigma 4. So got up the double ladder with trusty swr metre and basically tuned over 120ch a swr of 1.1 to 1.4
I ran 100watts out of a zetagi amp and a president george and dx'ed into Cleveland, Ohio, USA, at over 8lb and radio5 no problem at all.
I also regulary dx'ed to a staion in the french alps near Chamonix at over 6lb radio 4/5
it definetly works.


quote="Red Rider"]WIEEERRDDDDDDDDD!

had another butchers at this today and poked around at the coax and aerial and whilst checking the aerial on the back of the garage i moved all the ladders off the garage and its back to my usual low SWR and operational range...

Dodgy connection or was it the ladders?[/quote]

[The Wizard]

for 11m operation run your coax in 11ft multiples,

Absolute rubish
11m has no correlation to 11ft !!!!!!!!!!!

[stampman]

AND ANOTHER MYTH BITES THE DUST

[FISH]

lol.. =D> =D>

[ForzaCFC]

for 11m operation run your coax in 11ft multiples,

Absolute rubish
11m has no correlation to 11ft !!!!!!!!!!!

Well thanks for the scientific replies, always easy to dispel without proof to back up the argument so here's mine.
I knew somwhere I had read about this previously, and admit I had read as explained about this subject in the best selling 'screw drivers guide to CB'
I found this post on another forum after some homework. The words pipe, in,stick that and smoke come to mind

This was taken from
http://tinyurl.com/CoaxLength

Just wondering if what the guy say's is correct???

Any person who says that, "coax length has nothing to do with SWR's" has no knowledge or understanding of broadcasting. I have been in commercial and private radio broadcasting for 25 years, and it's time to dispel the myths about SWR and coax.

Your coax is a vital part of the antenna system and must be tuned for proper operation. Installing an SWR meter at the antenna will measure the SWR's (AT) the antenna, but not the SWR's (OF) the antenna. Even with the meter connected at the antenna, any change in coax type or length, will change the SWR reading on the meter. But it doesn't make sense to check SWR's at the
antenna, because the most important component -THE RADIO- does not see the antenna alone. Your radio is reacting to the entire antenna system, including the coax. Even if you were to set the SWR's at the antenna and make them perfect, the SWR will be different at your radio's end of the coax.

Coax not only has resistance, but it also has capacitance which changes with different lengths. Resistance (Impedance), determines how the transmission line and antenna match the radio's requirement to send the greatest amount of signal to the antenna. But capacitance controls which frequency the antenna is best tuned at. Changing the capacitance of the antenna system, will alter the frequency at which your radio sees the best SWR. Any component you add to the coax line, such as a meter, linear, or
even a coax switch box, changes both the resistance and capacitance. My own radio, a Kenwood TS-570DG, has an SWR meter built in to it.

I also use an external set of meters to keep tabs on my radio's performance. When I check the SWR's on the meter in my radio, It shows a perfect SWR at one frequency. When I check the SWR's with the external meters, they show my best SWR at a
frequency almost one full MHz lower. So which meter is correct? They are both correct. My external meter is reading a perfect SWR at Frequency (X). That is because the resistance and capacitance of the coax and antenna is resonant at frequency (X). But
the meter in my radio is seeing the addition of a meter and a 6 foot coax jumper. This changes the resistance and capacitance of the antenna system that my radio is seeing. It also changes the frequency that the antenna system is now resonant at, so the meter in my radio sees a perfect SWR at frequency (Y) 1 MHz higher. Both meters are telling the truth, but the meter in your radio is the most important one to use for SWR. The meter in your radio is reading the SWR closest to your radio's Final output transistors, and that is more important than the SWR at the coax connector on the back of your external meters.

The following is for use ONLY on 11 meters.

For 11 meter operation, use these figures to set up your antenna and coax.

SORRY! I only know the measurements in FEET. Convert them to meters if you need to for better understanding.

For base stations. Cut your RG-8/U coax in multiples of 11 feet. For example.. if you need 50 feet of coax to reach your antenna, use 55 feet instead. 11 X 5 = 55. Or 11 feet multiplied by 5 multiples equals 55 feet total. If you need 37 feet, use 44 feet instead.
11 X 4 = 44. What ever length you need, go to the next highest length that can be divided evenly by 11. Include all jumper cables in that length. Jumper cables should be cut to 6, 9, or 12 feet. Never less than 6 feet, or more than 12 feet. Example. . . If you need 55 feet of coax to reach your antenna, and you want to add a meter in the line. Use 49 feet of coax from the antenna to your meter, and 6 feet from your meter to your radio. 49 + 6 = 55. If you find that 49 feet is too short from the antenna, then add 11 feet to the coax from the antenna to the meters, making your total length, with jumper cable, 66 feet. 11 X 6 = 66. If later on you decide you want to add another device like a linear in the line, do it this way. Do not just add a jumper for the new device. Where your main coax line from the antenna ends inside your home, cut off 6 feet of the coax, and put antenna connectors on each side that was cut, and add your new equipment at that point. The total length of coax stays the same, and the jumper is also the proper length.
For set up on 11 meters in your automobile, use RG-8X or RG MINI coax. Do the same as I instructed for base station installations, except this time cut your RG-8X to 20 feet minimum. Do not use less than 20 feet. Even if you only need 1/2 of that length, still use 20 feet. The extra coax can be coiled up and put in the trunk or under the seat. If it is possible, try to coil the extra coax as close to the antenna as you can get it. If not, the trunk or under the seat is good. It will not cause any problems. A length shorter than 20 feet can cause RF feedback, because of the antenna being so close to the radio. Also, mobile antennas are usually 1/4 wave or less.
This causes more RF to travel down the coax to your radio. A coax length of 20 feet, and coiling the extra coax under the seat helps to stop some of that RF from feeding back into your radio.

I hope I have helped you better understand SWR and antenna systems.

Take care. Dave in U.S.A.