Topband: Monopole Radiation Patterns, takeoff angles etc

[ZR]

At the prior QTH the shunt fed tower with a 4 el 10-20M Christmas tree was 
resonant at 1520KHz and worked "gangbusters". While this was only around 
107* vs 90* I see no reason that a bit taller would work as well. The 
question is at what point is too much? I do know the 2:1 BW was very narrow 
but the last year I was there the ARRL 160M CW contest was won and a good 
portion of the band was used. As usual no tuner was used, just a modified 
amp pi net.

With the L including significant high angle it could be an excellent all 
around antenna. If instead of an L a 2 wire top hat replaced it that high 
angle is cancelled.

I need 2 antennas to cover high and low angles however at times even 
somewhat locals tell me I have an aurora sound on the verticals. Under those 
band conditions I do well into the auroral region and possibly by the very 
low angle part of the signal running below the ionized layer and getting 
less attenuation.

Gray line remains mysterious as at that prior QTH I was the first New 
England station to work JA on 160 and worked 3 that morning with that 107* 
vertical.

Now that its rather commonplace Ive done it more with the 180' high inverted 
vee. Maybe its because the 2 elements are broadside to JA and the pattern is 
a figure 8 with less gain than endfire.
Its all guesswork!

Carl
KM1H


----- Original Message ----- 
From: "Herb Schoenbohm" <herbs at vitelcom.net>
To: <topband at contesting.com>
Sent: Sunday, May 06, 2012 5:07 PM
Subject: Re: Topband: Monopole Radiation Patterns, takeoff angles etc


> In 2006 Tom Rauch, W8JI mentioned the disappointment with 3/8 wave
> vertical antennas and Carl mention today abut how "BCB stations migrated
> from 5/8 wave and 1/2 wave antennas."  I added to Tom's rejoinder that
> several AM stations spent considerable amounts of money with the
> Franklyn design which was claimmed to lay more radiation at lower
> angles.  This is possible if the two is insulated and a phasing device
> is place between the upper and lower tower sections.  Presumably it can
> be accomplished even with reduced height or a squashed design of the
> true Franklyn.  Admittedly I have yet to hear of any TB'er to use this.
> However a 3db signal enhancement at low angles in all directions may be
> something to consider.   I would also wonder if putting to much RF below
> the critical angle (since DX-ers) are not particularly interest in
> ground wave coverage and need sky wave instead) would be detrimental.
> There are times when a higher angle take off is the difference between
> being heard or not especially, I think, during SR/SS Grey line
> enhancements, and maybe on some skews and spotlights.  I post the
> Franklyn information just the same for those who may have missed the
> original post.
>
>
> Herb Schoenbohm, KV4FZ
>
> Quoting Tom Rauch<w8ji at contesting.com>:
>
>
>>/  Some of the biggest failure antennas I have used were 5/8th/
>>/  wave verticals at broadcast stations. We loaded one AM tower/
>>/  that happened to be a 5/8th wave on 160, and it was poor/
>>/  compared to a short vertical./
>
> The balloon lengths has increased my curiosity in learning what principles 
> are
> working here. Theoretically, very low angle radiation could be obtained by 
> a
> balloon supported long wire with "controlled current distribution".  (ARRL
> Antenna Compendium Vol. 2 pp. 132-135)
>
> As I mentioned before in my case the 5/8 vertical 308 foot insulated 
> tower,
> totally surrounded by sea water was a big disappointment on 160 meters. I
> tried it for 5 years and the lower antennas were always noticeably better.
>
> I once worked for KUOM which shared a tall tower with KSTP 1500 kHZ in
> Minneapolis. Stan Hubbard, owner of KSTP was convinced to erect a Franklin
> antenna design which was supposed to modify the current distribution on 
> tall
> towers to lay out a stronger ground wave then the 1/4 wave or smaller AM
> radiators.  All the theory, the engineer and construction cost, sort of 
> like a
> Ringo Ranger for the broadcast band were very disappointing. Years of A/B
> testing driving across the Dakotas, WCCO (although lower in frequency) was 
> the
> king of signals from the Twin Cities by a significant margin.  Both were 
> 50KW
> clear channel stations. (KSTP bragged 100KW Effective Radiated Power) 
> Some claimed
> this was due to sky wave and ground wave out of phase arrivals in which 
> case the
> Franklyn actaully redued the sky-wave component, at least in theory.
>
> The Franklin concept can be found in Jasik's First Edition Antenna 
> Engineering
> Handbook pp. 4-35 and 4-36.  A traditional Franklin was two half waves 
> stacked
> end to end and fed in phase.  KNBC (Los Angles)built one in 1949 as a 
> means
> of lowering the angle of radiation, but used a 550 foot tower since at 680 
> Khz
> a true Franklin would have been 1500 feet tall.  They were apparently able 
> to
> design a much shorter structure since their top portion was top loaded 
> with a
> capacity hat and only 150 feet tall.  (Put "KNBC Franklin Antenna" in your
> search engine for some awesome pictures of this antenna.) Did it actually
> improve coverage for KNBC? Are they still using it today?
>
> It would be interesting to learn if any AM stations still use the Franklin 
> design and if
> the shortened Franklin (ala KNBC) has any  merit for consideration on 160
> meters as a shortened gain low angle DX antenna  As far as I have been 
> able
> to find out, collinear verticals below VHF are just not worth the effort, 
> but
> that is not what the books tell us.  Yet in practice a 1/4 to 3/8 wave 
> appear
> to be the best topband performers for all the reasons stated in
> previous posts. (The 3/8 wave if converted to an Inverted L was popular in 
> the 60's
> as it provided a 50 to 60 ohm feed point with just some inductive 
> reactance to tuned out
> to actually resonate the wire as a 1/4 wave.  In an inverted L 
> configuration there is
> radiation in both the horizontal and vertical portion.  I mention this 
> since this would
> be a totally different antenna then a bottom feed 3/8 wave vertical 
> tower.)
>
>
>
>  Herb Schoenbohm, KV4FZ
>
>
>
>
>
>
>
>
>
> On 5/6/2012 12:31 PM, ZR wrote:
>> The BCB stations migrated from 1/2 and 5/8 wave antennas, diamond shaped
>> towers, and mountain tops by the early to mid 30's as they started to
>> understand how things worked...or didnt.
>>
>> Carl
>> KM1H
>>
>>
>>
>>
>
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