Lower voltages to deal with beneath the coil too.
> From: [email protected]
> To: [email protected]
> Date: Fri, 27 Feb 2009 00:19:07 +0000
> Subject: Re: LF: Re: LF Antennas - back to basics
>
> Jim,
>
> Yes I can confirm this :-
>
> >>>>
> increasing the height of the top loading, even if only in the middle, does
> lead to substantial improvements. One benefit of doing this is that the
> effective height and radiation resistance is increased by increasing the
> average height of the antenna wires
> >>>>
>
> I made a substantial improvement to the original inverted L system, 35
> feet x 40 foot top , by adding a loading coil to the top of the vertical
> section (actually the 40 feet of top wire wound round a coke bottle) and
> providing 2 x 40 ft capacity wires 6 feet apart back to the house.
>
> Earth is everything that conducts in the garden bonded along with a couple
> of 12 ft alloy scaffold poles sunk in, to one point along with a couple
> of 50 foot ground lying wires as well, feed is via a auto transformer and a
> variometer in series , I did use a parallel tuner but this flashes over
> above 50 watts ,
>
> A bonus , is the system now works well on 1.8 and 3.5 Mhz as well . but
> with a very high Q , 20 Khz qsy on 3.8 is enough for the pa to trip on vswr
>
> Notably, Gary, has modelled his array , similar 35 ft vertical section,
> using mmana and he favours the loading coil to be placed mid section, the
> offset capacity section of my array dose produce a slight slew of the
> pattern, but nothing too radical
>
> tnx- G ..
>
> --------------------------------------------------
> From: "James Moritz" <[email protected]>
> Sent: Thursday, February 26, 2009 11:43 PM
> To: <[email protected]>
> Subject: LF: Re: LF Antennas - back to basics
>
> >
> > Dear Andy, Dave, LF Group,
> >
> > My experience is that improvements to the ground system soon reach a point
> > of diminishing returns where the ground connection losses are small
> > compared
> > to other losses - I would expect you have reached that point already. In
> > my
> > case, literally filling the garden with wire made at best about 0.5dB
> > improvement by reducing loss resistance, compared to having about 5 ground
> > rods spaced a few metres around the downlead and loading coil. However
> > increasing the height of the top loading, even if only in the middle, does
> > lead to substantial improvements. One benefit of doing this is that the
> > effective height and radiation resistance is increased by increasing the
> > average height of the antenna wires. If you are in a fairly built-up
> > environment, the improvement is probably more than you would expect from
> > calculating the effective height from the dimensions of the antenna
> > itself,
> > because increasing the physical height of the antenna puts it further
> > above,
> > or nearer the top of, screening buildings and trees etc., that are
> > surrounding it. Also, moving the antenna further above loss-causing
> > objects
> > leads to a modest reduction in the loss resistance. In my case, with an
> > inverted L about 10m high at the ends and sagging to 9m in the middle,
> > propping up the middle of the span with a fibreglass pole to about 14m
> > increases ERP by 3 - 4dB.
> >
> > As to possible advantages and disadvantages of a loop compared to a
> > vertical, in general the loop ought to benefit from lower dielectric
> > losses
> > due to the generally lower voltages. The directional pattern is often
> > helpful on receive. But the figure-of-eight directional pattern could also
> > be a drawback for a transmit antenna where it isn't practical to rotate
> > the
> > antenna to avoid having nulls in awkward directions. Also, one has to
> > think
> > about the scale. AA1A's loop is quite big in overall dimensions compared
> > to
> > G4JNT's vertical. The radiation resistance of a loop is proportional to
> > the
> > square of the area, which is proportional to the square of the linear
> > dimensions of the loop conductor - so when scaling down a loop, one would
> > expect Rrad to reduce much faster than Rloss due to reduction in
> > perimeter,
> > and so efficiency of relatively small loops to be poor.
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> > ----- Original Message -----
> > From: "Andy Talbot" <[email protected]>
> > To: <[email protected]>
> > Sent: Thursday, February 26, 2009 4:16 PM
> > Subject: LF: LF Antennas - back to basics
> >
> >
> >> Firstly, bearing in mind there is no scope whatsoever to raise one end
> >> of the capacity hat which is defined by the apex of the house roof,
> >> and the other end would also need some major sugery to raise its heigh
> >> substantially, that only leaves the middle, ie the height of the
> >> actual radiator. It wouldn't be too difficult to raise this to 10m
> >> or even more with a fibreglass pole, but will I be throwing away all
> >> the advantage by having the top-hat drooping down to 7m?
> >>
> >> Secondly, pictures of other peoples antennas aften show a substantial
> >> grounding plate immediately under and around the antenna base. Just
> >> how far out is is worth going with a really substantial base. I
> >> could cut more conductors into the ground; while the ground is still
> >> is still soggy in March may be a good time to do this.
> >>
> >> Any ideas please ...?
> >>
> >>
> >> Andy G4JNT
> >> www.g4jnt.com
> >>
> >
> >
> >
>
>
>
> >
> > No virus found in this incoming message.
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> > Version: 8.0.237 / Virus Database: 270.11.3/1974 - Release Date: 02/26/09
> > 14:51:00
> >
>
>
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