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 < [email protected]> 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 > >> > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
