Are PL259 patch lead lengths important ?

[Arcone]

I know this is a very old post, but I was doing some research, stumbled on this and felt the need to point something out.
Many of you are quick to dismiss the patch lead and coaxial length thing, often making jokes about it and ridiculing people. What you don't understand is in some scenarios it absolutely has an effect. Unlike this instance where we have an SWR of 1:1, which implies a 50 ohm antenna with a 50 ohm radio, if you have different impedances the coax behaves as a transformer. That is if the antenna is not 50 ohms, the impedance shown at the other end of the coax will change even though it is 50 ohm coax. Except if the feedline is a half wavelength or multiples thereof when taking in the velocity factor.

Now if the operator is not measuring the SWR right at the antenna feedpoint, they could have a mismatch and not be aware of it. They think it's 1:1 or a little over, however the length of feedline is attenuating the reflected power and absorbing their reading. The longer the feedline the lower the indicated SWR and you are going to have some transformation going on.

Second instance is when you're running an amplifier, and I believe this is the origin of most of this patch lead talk. Many of you don't think to measure the SWR between the radio and the box when keyed. It could easily be 2:1 or more, especially with homemade and crudely made linears out there. Then the patch lead length is most certainly going to change things. In fact by altering this length can effectively tune the system. If you don't believe this, it can be proven by noting the output power. When you have a better match between the radio and the amp, it will excite the the amp more, you will have improved the efficiency of the system. It is a handy and effective way of correcting an impedance mismatch. One of the other advantages of this is when in receive mode, the coaxial line bypasses the linear and the system is happy. What I mean by this is if you were say to attempt to correct the mismatch with a quarter wave matching stub, this would affect the receive a little.

I intend on using this technique for a problematic box. I will trim a patch lead by trial and error until I get it down to an acceptable level thus making the radio happier and the box do its job better.