[NLRS] K1FO Yagi and UT-141 Balun ?

[Gerald]

On Tue, 2005-05-24 at 18:48 -0500, christenson at charter.net wrote:
> 
> I need a little help finding and identifying (UT-141). It is used as 
> the balun in the K1FO antenna for 432. Also, would like any input on 
> this antenna. Is it worth it to build? Looks like for a 33 element 
> it would cost about $100 in parts or so. This antenna is in the Jan.
> 1988 QST. Also in the VHF/UHF antenna classics paperback.
> 
> Thank You,
> Kris
> KC0REO
> If it don't propagate, I don't operate

The K1FO designs are GOOD. Its important you duplicate them fairly
precisely. Element lengths and positions to better than 1/32", half that
preferred, and element mountings precisely the same. Directional Systems
and C3I sell them in kits, which are hardly more pricey than finding the
hardware (stainless retaining rings are the hardest parts to find, next
to the insulating shoulder washers). Both DS and C3I do drill the holes
in the booms so the elements line up. The stand offs with the bifurcated
tops are becoming uncommon these days too.

Way back before the need for precision was understood, few 2m yagis
reproduced well and virtually ALL 432 yagi copies were failures. Some
published designs proved resonant at 420 instead of 432 with only a MHz
or two of bandwidth. K2RIW published a 19 element design demanding 1/64"
tolerance on the construction. That yagi has proven to reproduce so well
(keeping that tight tolerance) that it is the accepted standard of gain
(15.1 dBd) at VHF conferences all over the USA at 432 MHz. Few
commercial antennas from CC or HyGain ever did as well as they should
have and all measured far poorer than they claimed (partly due to
exaggerated claimes, partly due to sloppy copying).

K1FO designs have been optimized for wide bandwidth to tolerate rain and
the resonant frequency shifts of large arrays. They don't tolerate ice
really well though. That is the don't work well while coated with ice.

UT-141 is sometimes mistakenly sold as UG-141 or RG-141, though RG-141
has a braided shield over the teflon center insulator and a fiberglass
braid over the wrapped teflon shield cover. It does have silver plated
center conductor and shield and works great on my 75 meter inverted V.

UT-141 has a solid copperweld center conductor that is silver plated.
Then solid teflon insulation and a silver plated solid copper tube for
the shield. Its decent stuff at UHF and down though the small size leads
to a fair amount of loss at microwave, though the SMA connector was made
for and from it.

There should be multiple sources besides buying lengths new, such as
DEMI and ordinary electronics surplus stores.

The designs from DL6WU are also quite good and a bit more tolerant of
measurements of dimensions. They still need the balun, though they don't
have the adjustable T-match because his designs have a higher feed point
impedance.

-- 
73, Jerry, K0CQ
Dr. Gerald N. Johnson, electrical engineer
All content copyright, Dr. Gerald N. Johnson