QRP Club

QRP Station => Antennas => Topic started by: G0BVZ on February 02, 2014, 19:19:40 UTC

Title: More about feeder than antennas, really.
Post by: G0BVZ on February 02, 2014, 19:19:40 UTC
My inverted V ZS6BKW was OK.  It was what it was.  So I lengthened each half, cut out the coax and extended the 300Ohm window feeder to the house wall.  A plumber had changed the shack wash hand basin for another. He had to bore another, lower hole for the new waste water pipe and he sealed the old hole with a dab of nice soft mortar on the outside.

My setup was 300ohm ---> wall ---> balun ---> coax through the previously drilled hole.  All I had to do was drill into the mortar for a 10cm and the rest of the old hole was clear. Nice.  The end result was better than the ZS6BKW and my MFJ versa Tuner did a good job.

I woke up late today with a plan in mind that had hatched while I was sleeping. Does that ever happen to you? I had been putting off a fancy plan (nasty weather, don'cha know?) completely clearing the old hole and inserting a new length of plastic pipe containing two parallel lengths of brass studding (in stock) that would hold end caps in place with a pair of brass locknuts. Then I could simply use wingnuts to secure open feeder to the protruding studding. A great plan but I just wanted a quick and dirty way to see if 300ohm window feeder all the way to the atu would be worth the significant effort.

So I drilled another hole in the mortar plug just big enough for the 300Ohm and shortly after that I had 300Ohm windowed feed all the way from the antenna centre, down 10m of glassfibre mast, then travelling 3m above ground to the house  wall, down it & through it to the atu.  No coax, no balun, just a single run from antenna to atu.

The difference was startling: sigs seemed significantly louder and I began to hear stuff I hadn't previously. On this showing it's a success but what's one day in eternity?  Maybe I'll come to a different conclusion in a month's time so I'll have to keep testing.  ;)

Every ointment has its fly; there's still a balun in my system!  It's in the Versa Tuner, there specifically to couple a balanced feed into the tuner.  So, if this a success after testing then it might be worth looking at an MFJ 974HB.  That has a balun too but there's a difference: the Versa Tuner is basically an unbalanced tuner made to handle a balanced feed via a balun.  The 974 is a balanced tuner tricked out with a balun for handling coax feed; the balun don't feature if the feed is balanced.

I know there's much better balanced tuners out there but I'm QRP and I don't need a high power job that costs the same as an FT817 in UK. -And truth to tell, I quite like MFJ kit's gets-the-job-done, designed-and-built-in-Joe's-Garage sort of honesty.

So... time will tell. It is beginning to look like the old timers may have known a thing or two though.  Talk about returning to roots: doublet antenna, window feeder, balanced atu.  Where have I heard that before? ;D

Vic /learning all the time...