Topband: Bowtie Flags

[Don Kirk]

Hi Mark,

I had no idea a terminated bowtie previously existed, but does not surprise
me.

Thanks for posting.
Don

On Tue, Dec 13, 2016 at 2:00 PM, Mark Connelly via Topband <
topband at contesting.com> wrote:

> As Nick undoubtedly knows, Bowtie antennas have been in use by medium wave
> broadcast band DXers for some time now.
>
> One I tested here in 2010 is shown in this sketch:
> http://www.qsl.net/wa1ion/pictures1/bowtie_s_yarmouth.gif
>
> Some use a dual feedline scheme so the pattern can be reversed.  This
> would be implemented by 16:1 transformers at each end if 50-75 ohm coaxial
> cable is used or 9:1 transformers if using 90-150 ohm balanced feed (CAT-5,
> speaker wire, two conductor zip / lamp cord, twisted pair etc.) as
> recommended by Dallas Lankford and others.  In the balanced feedline case,
> a 1.8:1 or 2:1 transformer (e.g. #73 binocular core with 4 turns : 3 turns
> or 7 turns : 5 turns) is used in-shack to get to unbalanced coaxial en
> route to the receiver / transceiver, RPA-1 or similar amp, or phasing unit.
>
> Dual feedline split flag is another variant:
> http://www.qsl.net/wa1ion/pictures1/dual_feed_split_flag.gif
>
> Dual feedline antennas have a 4-pole 2-throw switch at the shack end so
> either end can be switched to the receiver path and the opposite end to a
> 250 or 500 ohm pot that facilitates in-shack null termination adjustment.
>
> Some people go with a single orientation antenna and put a preamp such as
> the Wellbrook FLG100LN ( http://www.wellbrook.uk.com/FLG100LN-1 ) right
> at the forward side.  This tends to overwhelm any feedline pick-up
> (common-mode or otherwise) although common-mode choking is still advisable
> near the antenna when longer runs (over 60m / 200 ft.) of feedline are
> involved.
>
> In the case of a single orientation set-up, you then get to figure out
> what termination end scheme is best.  These basically boil down to the
> following options:
> (1) Fixed resistor in the 680-1200 ohm range either modelled / guessed-at
> or determined by use of a potentiometer if it can somehow be adjusted
> midway up the side of the antenna while monitoring a target station to null.
> (2) "Vactrol" termination: a photoresistor adjusted by a DC voltage
> applied on a control line from the shack: see page 9 of
> http://www.durenberger.com/documents/PRESBT2016.pdf
> (3) Potentiometer adjusted by a motor drive: see http://www.bamlog.com/
> remotepotbox.htm
>
> My experience with the Bowtie I installed in 2010 was that it was about
> 10-12 dB less sensitive than a Flag or Kaz Delta occupying the same
> rectangular "box" of air space.
>
> Nulling off the back could be wider than that of a Flag but the bandwidth
> at which the null stayed optimum at a particular terminating resistance was
> not as wide as with the Flag (or its SuperLoop base-fed variation:
> http://www.bamlog.com/superloop.htm ).
>
> Seeing that the MW broadcast band 530-1710 kHz has a greater max/min
> frequency range ratio than the 1800-2000 kHz of 160m, issues that might be
> problematic for broadcast DXers could matter a lot less on 160.
>
> Some of the perceived problems of low gain and null bandwidth could easily
> have been cured by a combination of rigorous common-mode choking as done on
> the Waller Flag ( http://www.kkn.net/dayton2011/N4ISWallerFlag.pdf ) and
> high gain at-antenna amplification.
>
> Mark Connelly, WA1ION
> South Yarmouth, MA
>
> <<
> Nick,?
>
> ?
> Although I did not measure it, the front to back, and front to side is
> better, overall more quiet.
> ?
> It is receiving toward the Caribbean.?
> Europe, and USA stations, are lower in signal strength.
> ?
> Can often work?Caribbean and South American stations through a small
> pile up when they are not working split.
> ?
> In my case it was a worth while change.
> ?
> The original plan was to be able to drive my car under it.
> ?
> 73
> Bruce-K1FZ
> ?
>
> On Mon, 12 Dec 2016 16:35:14 +0000, Nick Hall-Patch wrote:
>
> What specific improvements did you note when the Delta was raised Bruce?
>
> Thanks,
>
> Nick
> VE7DXR
> >>
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