Well, the toroid in my R5 was anything but "large" (I don't even
think it was 1.5 inch diameter) and there was no way that network
was efficient.
I happen to have an R5 network board (need to drill a new case since
the old one failed). I haven't dragged it out to measure the toroids
but from memory they appeared to be 2 inch. One can see pictures of
the network here: http://www.iol.ie/~bravo/r7_vertical.htm, here:
http://pa0fri.home.xs4all.nl/Ant/R5/onhr5eng.htm and here:
http://www.mrs.bt.co.uk/mrs/r5/
The R5/R6000/R7/R7000/R8, etc. are all off center fed vertical dipoles -
one toroid is an auto-transformer (~4.5:1) and the other a common
mode choke (balun). Both re quire efficient when operated within their
design limits.
I might also point out that, generally speaking, it is often extreme
overheating (usually voltage overstress) that causes a toroid to
fracture into several pieces.
With the OCF verticals it is typically using a tuner to load the
antenna on a band for which it is not designed (e.g. 30 meters with an
R5/R6000) or using to use an R7/R7000/R8 at high power on the "other
end of the band" - beyond the 2:1 SWR limits - that causes failure of
the ~4.5:1 transformer and common mode choke. The common mode choke
does not have sufficient choking impedance where the feedline is an
odd multiple of 1/4 wavelength and the stress on the core can be very
significant with high power on those bands.
73,
... Joe, W4TV
On 2014-09-12 10:27 AM, David Gilbert wrote:
Well, the toroid in my R5 was anything but "large" (I don't even think
it was 1.5 inch diameter) and there was no way that network was
efficient. I might also point out that, generally speaking, it is often
extreme overheating (usually voltage overstress) that causes a toroid to
fracture into several pieces.
As I say, the reality is that simple vertical elements (I made one for
20m and a separate one for 15m, later replaced with a 40m vertical for
40m/15m) fed against a haywire collection of ground plane wires
stretched across the roof significantly outperformed the R5 in the exact
same location.
73,
Dave AB7E
On 9/11/2014 9:22 PM, Dave Heil wrote:
There was nothing really wrong with the R-5. I used one for almost
all of my 12 and 17m operating as 9L1US in the 1990-91 time frame.
Maybe all you needed to do would have been to mount it on a steel
railing atop a three story building on a 400 ft. hill overlooking the
Atlantic. :-)
The large toroid in the matching network in the plastic box fractured
into several pieces by the time I was 5H3US. Cushcraft wanted to sell
me the entire box full of components only at a very high price and I
got rid of the rest of the thing.
I keep a Hustler 6BTV with 25 radials here in case I lose a wire
antenna or have a rotator problem.
73,
Dave K8MN
On 9/11/2014 21 51, David Gilbert wrote:
Not to heap coals on the fire, but I also owned an early R5 and it was a
terrible performer. I had it over a year and when I finally got rid of
it and put up a simple 20m vertical in the exact same spot on the roof
and fed it against random length wires as a "ground plane", the
improvement was astounding. I don't think the basic concept was so bad,
but the implementation was horrible. I realized what I had as soon as I
opened up that little box at the base and saw what some clueless person
thought could act like a matching network.
In general, though, I think it is a mistake to characterize all
verticals a poor performers. It's all a function of efficiency
(avoiding losses) and location. Check out the ground conductivity
charts across the U.S. and you'll see huge differences, with some areas
essentially acting as terrestrial dummy loads. Nearby structures that
can absorb energy or distort patterns represent other possible culprits
for bad results with verticals. I used nothing but verticals for most
of three decades, but mine were always on a flat roof and well in the
clear of anything nearby.
73,
Dave AB7E
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