Why Feedline Matters

Mike-VA3MW

Dudley WA5QPZ

John - AI4FR

Erika - KØDD

Mike-VA3MW

I have a google document that I just paste them into.  

The fun one to watch is the 160M inverted L move it's resonance around as the ground freezes.  It will swing about 80Khz at times resulting in having to actually cut and lengthen the vertical part.

Erika, nice comments and very real numbers.

M

Paul - K6HR

Ned K1NJ

    Wonder what you would find if you hung a watt meter and dummy load on
the end of that old RG8x.  2 to 3 S-Units on rcv is downright scary when you
think about similar loss on transmit.  Try it on 6m.  ( OMG! )

     Ned,  K1NJ

KI4P

Mike-VA3MW

Hi Ned

Yes, that would be a great idea and a great way to do that exact test.  Good for you.

I am fortunate enough to have some good test equipment, and I think I did do a path loss on it.  I'll go pull the SD card off it see if I captured it earlier this year.  If I can find it, I'll post it.

73

John KB4DU

Mike-VA3MW

Yes, that is what you would think.  For me, it was a 2-3 db decrease in noise floor and less RF pickup in the receiving department.  

When I swept the feedline about a year ago for path loss, it was about 1db at 3Mhz, so the RF exiting was not as attenuated as much. I use a Rhode and Schwarz FSH4. 

 I thought I had a screen shot of the path loss, but I guess I didn't take it.

Short story is the feedline does have a shelf live.

73

Stan VA7NF

Mike-VA3MW

Hi Stan

I think there are 2 parts to this.  

Receiving, yes leakage from local switching power supplies (2 in particular that I know of that I used to see and now I don't see at all).   

About a year ago, I swept the RG8X with an FSH 4 from end to end.  I know the loss was more than I expected but not surprising given its age.  I pulled the SD card to see if I saved an image, but it I guess I didn't.  I did have hand written notes that showed it was about 1.5db at 3Mhz, which is a full db more than spec which should be about 0.6db  at 3Mhz.  The feedline is 31M long. 

The LMR400 was amazingly better of course when I swept it from end to end with the FSH 4 at 0.11db.  See the attached image.

I do have Mix 31 chokes at each end of every feedline which I highly recommend of course.

I have yet to measure any difference at HF frequencies using N connectors and I am not convinced I would hear the difference if I made the change to N on anything less than 30Mhz when actually operating.  However, it is an option.  We did this as a college project a long time ago (our Prof was a Ham, so he wanted to know). 

Mike