Hi Tom, You've surely built and evaluated more BSEF and 8-circle receiving arrays than any of the rest of us. I'm very new to them and after just a few days of evaluation I'm delighted with the results of my new BSEF receiving array consisting of four 25 foot W8JI umbrella verticals spaced 300 feet x 130 feet. I still have my 900 foot Beverages, but so far the performance of my new BSEF receiving array is consistently superior.
I used a pair of 270 foot spaced broadside 580 foot Beverages for several years but the improvement was insignificant compared to a single 580 foot Beverage. I replaced them with single 900 foot Beverages which perform slightly better than the 580 foot Beverages. I have inadequate space for more widely spaced broadside Beverages. If you were to install a new BSEF receiving array using four W8JI inductive/resistive loaded 25 foot umbrella verticals (not an 8-circle array) what spacings and fixed phasing would you use based on your experience and evaluations? tks 73 Frank W3LPL ---- Original message ---- >Date: Sat, 2 Feb 2013 23:58:15 -0500 >From: "Tom W8JI" <[email protected]> >Subject: Re: Topband: New 160M high performance receiving antenna at W3LPL >To: <[email protected]>, <[email protected]> >Cc: Don Johnson <[email protected]> > >> In W8JI's very rural area minimum main lobe beamwidth is more valuable to >> him than minimum sidelobes. Tom's choice of 330 foot broadside spacing in >> a very rural area with little or no local RFI makes lots of sense. >> > >I actually use a little more than 330 ft now in that array, and considerably >more spacing in broadside Beverage arrays. > >Half-wave spacing forms two nulls at ground level, directly of the sides of >the array. You have ONE null on each side at ground level. Most people fail >to realize the side nulls at half wave spacing are at ground level only. It >is a less than perfectly deep null at wave angles above earth level. > >Wider spacing, compared to 1/2 wave spacing, forms a null cone. This >provides **two nulls** at ground level off each of the sides (now you double >the chances of groundwave noise being in a null). Even more important, the >side null forms a cone that reaches maximum elevation off the side. > >This means directly off the side of an array, WIDER spacing gives a deeper >null. This is contarary to what most people assume, because they look at the >null as a ground wave side problem. People tend to overlook the fact that >distant signals and noise come from angles higher than zero degrees >elevation. > >They also overlook the fact that a wider spacing provides four groundwave >nulls (two on each side), instead of just two nulls (one on each side) of >1/2 wave spacing. > >I can't think of a single case, besides a single groundwave noise source >directly off the side, where 1/2 wave spacing would be an advantage. > ><<< >If you look at end-fire cell patterns, you will find closer spacing gives >more directivity. It is easier to have a wider null area with somewhat >closer spacing.>>> > >Right. > > > >> End fire spacing has essentially no effect on beamwidth and sidelobe >> levels, so Tom's choice of 70 foot end-fire spacing makes little if any >> measurable difference compared to 130 foot end-fire spacing. Larger >> end-fire spacing (up to 1/4 wavelength) is somewhat more forgiving of >> phasing errors and mismatched signal levels and slightly more >> efficient.>>> > >Actually there is another very common myth or mistaken assumption about >phasing. We assume phase difference between elements should be 180-s where s >is electrical degrees spacing. We assume with quarter wave (90 degree) >spacing we want 180-90 = 90 degree phase difference, or with 45 degree >spacing we want 180-45 = 135 degree phasing. Once again, despite being in >countless articles and books, this is almost always NOT optimum. The only >case where it is optimum is where we want a single zero wave angle null >directly off the back. > >This is almost never the case, because as with 1/2 wave broadside spacing, >this forms only ONE null at zero elevation. By increasing phase delay we >split the back null into TWO nulls at zero angle, and have a null cone that >is elevated directly off the back about the same as the zero elevation nulls >are angled off the side. > >It's really pretty silly, when we think about it for a while, to design >skywave systems or noise rejection systems that have a single groundwave >null peak. What almost any case demands is a null covering the widest >possible area, and to absolutely be above zero elevation. This not only does >a better job of notching unwanted signals and noise from skywave, it also >doubles the null area on the ground for local noise. > >If I had multiple groundwave noise sources, I would not use 1/2 wave >broadside spacing. I would use wider spacing. >If I had skywave side signals to reject, I would not use 1/2 wave broadside >spacing. > >The only case I would use 1/2 wave spacing would be ground wave noise >exactly off the sides, and nowhere else. > >If I had multiple groundwave noise sources, I would not use 180-s phasing or >1/4 wave endfire spacing. I would use narrower spacing and use a phase delay >of some number greater than 180 - s. >If I had skywave signals or noise to reject, I would not use 180-s phasing >or 1/4 wave endfire spacing. I would use narrower spacing and use a phase >delay of some number greater than 180 - s. > >The only case I would use 180-s phasing would be a ground wave signal >exactly in line with the element's endfire spacing. That would be a single >signal condition. > >This about the problem in three dimensions, and it is easy to see why 1/2 >wave broadside and a 90 deg space 90 deg lag system is almost never the best >choice. Even my 45 degree spaced elements are not delayed 135 degrees, but >rather some larger delay amount. This actually increases null depth and the >statistical likelihood something unwanted is in a deep null. > >73 Tom > >_________________ >Topband Reflector _________________ Topband Reflector
