swr mismatch

Steve G1XOW

An odd one....Flex 6400 that shows good SWR on all bands, and near enough matches the readings from my in-line Daiwa DN-801, except on 30m!

On 30m the Flex reads 1.3:1 (hard to be exact due to poor scale, it needs numbers). However, the external DN-801 reads just over 2.1:1.

Without having to buy yet another meter, any ideas?

Jim Gilliam

Pat N6PAT

Changing the coax length worked for me. I added a homebrew 160 mod to my Hustler 6BTV and the SWR was higher than I wanted - about 2:1.

After reading what others did to reduce SWR with different lengths of coax for various antennas  I decided to experiment by adding different lengths of coax and eventually dropped the SWR to 1:1

It does work

James Charlton

This is a problem with having too many test instruments.  The Flex is always right because it is sensitive to a high reflected power, the Daiwa isn't.  The real SWR doesn't matter as long as your Flex will drive the antenna to full power.

For the record, Jim, K6QE, is correct.  SWR is caused by a mismatch between the drive point impedance of the antenna and the characteristic impedance of the feedline.  Therefore, it has to be fixed at the antenna end of the feedline.

Jim AD0AB 

HCampbell WB4IVF

Craig Williams

Agree

Stu 2E0XXO

James Charlton

Johan _ SE3X

Luis del MOlino

James Charlton

Stan VA7NF

Steve G1XOW

James Charlton

I agree with all of above and can only think of one thing to add to reduce a pesky SWR and that is hydroventillated coaxial cable.  The length of the cable determines the amount of SWR reduction you get and is largely wavelength independent.

This cable reduces SWR by absorbing the reflected power along its length.  Therefore, the longer the cable, the greater the SWR reduction.  
Many hams with older and well weathered antenna installations may already be enjoying the benefits without being aware of it.  Until recently, that included me.

If you can't find hydroventillated coax for sale, you can make it yourself.  Start with about 25 feet of the lowest cost coax (off-brands are ideal) you can find.  The length is not critical.  With a sewing needle, poke holes in the covering ever inch or so along its length.  Be sure the holes go all the way through to the braid.

Now, install this coax as part of your feedline, but BE SURE it is outside and not inside your house.  Leaving it coiled on the ground or strung in trees is good.  Running it in a rain gutter is ideal.  That's it.

Settle back and watch as over time, your hydroventillated cable gradually reduces your SWR.
No doubt about it, lossy coax reduces SWR every time it's tried.

Jim  AD0AB

Stan VA7NF