Are PL259 patch lead lengths important ?

[cb4ever104]

That's the question . I have 4 of them handmade between the radio and the antenna . Should they be cut to any particular lengths , or doesn't it matter ?

Sammy

[JM62]

Never really had a problem myself, though generally I make em about 30cm long.
I have no doubt somebody will have a theory on em mind.

[northern35s]

As long as they need to be in order to connect your equipment together, any more and it's a waste of cable and energy

[bigpimp347]

oh lets see..
50ohm antenna/aerial..
50ohm radio..and 50ohm coax..
now if i'm right 100ft of 50ohm coax is 50 ohm yet 10inch of 50ohm coax is 50 ohm..

so no it's makes no odds what so ever, if it does then you have a big problem.!!

[Monsta]

That's the question . I have 4 of them handmade between the radio and the antenna . Should they be cut to any particular lengths , or doesn't it matter ?
Sammy

Well technically not ...although smaller than 4 inchs are bloody useless
so build them longer than that

[Ian1800]

That's the question . I have 4 of them handmade between the radio and the antenna . Should they be cut to any particular lengths , or doesn't it matter ?

Sammy

Length shouldn't be a problem at HF (as no frequency was mentioned)
When you get to VHF and above the connectors can have a big loss to consider.

[cb4ever104]

Length shouldn't be a problem at HF (as no frequency was mentioned)

CB section m8 . Thanks for the replies .

Sammy

[sureshot]

I have had high SWR with short patch to amp leads, i use the suggested 90 cm is it i think a fraction under 3' not coiled up though, if its shorter and SWR is ok then its cool.

[Oggy]

oh lets see..
50ohm antenna/aerial..
50ohm radio..and 50ohm coax..
now if i'm right 100ft of 50ohm coax is 50 ohm yet 10inch of 50ohm coax is 50 ohm..

so no it's makes no odds what so ever, if it does then you have a big problem.!!

How very true, who came up with this importance of cable length crock anyway.
I just make all my feeders and patch leads as long as I need them to do the job.
Like Mark says 50 OHMs is 50 OHMs........unless you run a dipole and the old hands will drum the 75 OHMs is the only way of feeding it card.
But ladder line is better anyway for losses.
So length is unimportant for patch leads , I use top quality grey mini 8 these days for mine.

[Ian1800]

Length shouldn't be a problem at HF (as no frequency was mentioned)

CB section m8 . Thanks for the replies .

Sammy

Hi Sammy,
Not sure of the CB frequencies you use in Espana

Ian

[cb4ever104]

CEPT here m8 . All the best !

Sammy

[Coppernob]

Np not really...How many people swr their ariel by cutting lumps of the coax...
One of my friends did this and hes a m3...
Just shows you what way the ham licence is going.
Whatever you do to the coax will have no effect has to how the ariel is radiating/matched...do they get their licence in a box of cereal now days?
Regards Coppernob Roger.

[bigpimp347]

do they get their licence in a box of cereal now days?
Regards Coppernob Roger.

yup...


the only time coax length alters SWR is if it's a bazooka/saturn aerial where you need the coax as the ground/earth astroplanes, same reason.
and if you have a silver rod type aerial screwed to a fascia board or wall with no pole on it, then it uses the coax as the earth/ground but as a rule should make no odds, unless you have a dodgy aerial.!

[RadioPixie]

I agree. Having to cut the coax is a sign of a dodgy mis-matched antenna system. It's a myth that keeps going around like an ever perpetrating echo mic....

[northern35s]

Just to put the record straight, where some people have maybe misunderstood a fundamental aspect of the relationship between coax and wavelength. If your antenna is a genuine 1:1 match then the length of coax, other than it's resistive loss, won't make any difference, however anything that isn't 1:1 match will show a slightly different figure dependent on where you measure the antenna input VSWR, that is except at electrical half wavelengths or their multiple, this is where the coax will show the same resistive input as you would see if you attached the meter to the base of the antenna.

What is an electrical half wavelength? This is a half wavelength long of coax multiplied by the it's velocity factor, so for RG58, which has a velocity factor of 0.66, if our half wavelength was 9', we would multiply 9 by 0.66, therefore our electrical half wavelength of coax would be 5.94' long.

What is velocity factor? Velocity factor is the speed of light along the coax conductor, this changes dependent on coax construction and materials, as previously mention RG58 is around 0.66.

Note: it's only when we have a problem with the antenna system that we normally turn to electrical half wavelengths, if your feedline is carrying high common mode current, then the electrical half wavelength will help with tuning your antenna, however it doesn't tune the antenna

HTH

Caveat: If you change the frequency, then you change the half wavelength



Here's an extract from the ARRL antenna handbook:

The Half-Wavelength Line

When the line length is a multiple of 180° (that is, a multiple of λ/2), the input resistance is equal to the load resistance, regardless of the line Z0. As a matter of fact, a line an exact multiple of λ/2 in length (disregarding line losses) simply repeats, at its input or sending end, whatever impedance exists at its output or receiving end. It does not matter whether the impedance at the receiving end is resistive, reactive, or a combination of both. Sections of line having such length can be added or removed without changing any of the operating conditions, at least when the losses in the line itself are negligible.