Hi Graham yes another good, well tested approach and good if you cant get
the feed pont away from buildings.....it reduces the voltage on the vertical
portion. I was rabbitting on so much I had to draw a line somewhere. :-))
But I did get a report from N Germany with 1mW ERP. so dont dispair Rob.
Alan
----- Original Message -----
From: "Graham" <[email protected]>
To: <[email protected]>
Sent: Saturday, January 28, 2012 12:33 AM
Subject: Re: LF: Conds
> Good guide lines Alan
>
> I would add , try a top loading coil at the end of the vertical
> section , that seems to increase the amps in the vertical ,
> I found using a U shaped top wire, one end of the U connected , the
> other open, gave better gain than a parallel set up.
>
> 73 -G..
>
> --------------------------------------------------
> From: "Alan Melia" <[email protected]>
> Sent: Saturday, January 28, 2012 12:05 AM
> To: <[email protected]>
> Subject: Re: LF: Conds
>
> > Hi Rob it sounds like you must have a loss resistance in excess of
> > 100ohms,
> > it you can only get an amp with 90W. Unlike Top Band, putting ground
rods
> > under the vertical doesnt help much at LF. Most (55%)of the return
current
> > is collected from under the remote ends of the to wire.
> >
> > Think about it....this is where the maximum voltage is, and the current
> > passes through the top capaxity to ground. The bigger the area of the
> > top-wire/ground acapaitor the less loss in the ground "plate". If you
have
> > poor conductivity ground try running a wire back from the remote
> > groundstake
> > to the TX ground. If it doesnt make any difference you can remove it
> > easily. The next step is to incease the top load capacitance. More wire
in
> > the air. The paralell wires should ideally be around 70cm apart minimum.
> > They can be connected anyhow series, parallel, or meander. Dont worry
> > about
> > current cancelling, these wires dont radiate anyway. Dont run the top
wire
> > into or close to or over bushes or foliage. I you terminate the top wire
> > on
> > a tree make the end insulator as far from the tree and it is above the
> > ground. Even if this shortens the antenna it will reduce the
> > "environmental
> > loss" Dont run the top wire over roofs and keep the vertcal as far as
> > possible away from walls. If necessary slope it out to the top wire. The
> > top
> > wire only needs to be thick enough to support its own weight. Resistance
> > up
> > there doesnt matter, this part of the aerial is above the effective Rrad
> > (in
> > the vertical section) so doesnt add to "loss" (even though that sounds
> > counter-intuitive).
> >
> > The best way to improve the aerial is to build a simple bridge, not a
> > noise
> > bridge that wont work at LF, the aerial has to be a measured at the
> > frequency of use, because the loss is frequency dependent. You require
to
> > use several volts of bridge source drive (to overcome the received
signal
> > pick up) and a tuned detector like a receiver. A good bridge null will
be
> > of
> > the order of 50dB deep or your bridge is not working properly. It will
> > tell
> > you whether simple quick alterations are improving things before you
spend
> > a
> > lot of time and money "engineering them" properly. You measure the
> > untuned,
> > (unloaded) wire so it saves risking you PA and keeps the qrm down too.
It
> > looks like a capacitance and resistance in series and the resistance is
> > "ALL
> > LOSS" the radiation resistance is minimal. So try mods to increase the
> > capacitance and reduce the resistance emasured.
> >
> > This is distilled from 15 years of experiments on the band by many of
the
> > pioneers (G3XDV G3LDO, G3AQC, EI0CF, MOBMU, Bill Ashwell US Lowfer, and
> > many
> > other too) using normal domestic enviroments . Dont be diverted by what
> > the
> > "professionals do" they dont operate from a domestic premises and use
> > verticals or umbrellas.......they use earth mats because you need those
> > under a vertical but they are not really any advantage under an "L" or
"T"
> > unless they are at least 1/8th wavelength in dimensions (300 m
square!!).
> > Bill built an aerial over virgin rock, but he needed a lot of elevated
> > isolated radials (counterpoise) to get it to work properly. On the very
> > poor
> > ground, the radials couple to the lossy ground, increasing the loss over
> > the
> > use of elevated wires.
> >
> > Some may disagree but what works will depend on your particular location
> > and
> > ground conditions, and what works for someone else may not work for you.
I
> > sit on top of heathland, very sandy with the water table about 60 feet
> > down....not exactly ideal. But I got an aerial loss down to around 40
> > ohms,
> > in approximatly the same size as you have there (60m top "L")
> >
> > Good Luck with it
> > Alan G3NYK
> >
> > ----- Original Message -----
> > From: "Rob, M0DTS" <[email protected]>
> > To: <[email protected]>
> > Sent: Friday, January 27, 2012 7:52 PM
> > Subject: Re: LF: Conds
> >
> >
> > My TX is now working all be it fairly QRP 90W ;-)
> >
> > Antenna is 53m horizontal at ~9m high.. a droopy 'T' single strand
> > copper all the way.
> > I'm also receiving on this antenna too with much better results than the
> > loop i have.
> >
> > Problem is going to be getting enough routes to earth, my last attempts
> > were getting ~1A antenna current with the same power but it looks much
> > worse on G4WGT's grabber than last time so i guess it's less than 1A.
> > Will do some more improvements over the weekend.
> >
> > Rob
> > M0DTS
> >
> > On 27/01/2012 18:56, Stefan Schäfer wrote:
> >> Hi Rob,
> >>
> >> Thanks for the report.
> >> Oh yes, looking forward to see you on the band (or hear?).
> >> What will you use as the TX antenna?
> >>
> >> 73, Stefan/DK7FC
> >> PS: Conds (local) are excellent again this evening! Worth to come to
> >> QSO mode ;-)
> >>
> >>
> >> Am 26.01.2012 19:29, schrieb Rob, M0DTS:
> >>> On 25/01/2012 23:28, Stefan Schäfer wrote:
> >>>> LF,
> >>>>
> >>>> Excellent conds on 137 in a range of 2500km! Signals show up in RN,
> >>>> 4X, TF, YO at good strength. Worth to try!
> >>>>
> >>>> 73, Stefan/DK7FC
> >>>>
> >>>>
> >>>>
> >>>>
> >>> Stefan.. vy good tonight again too, you're 579 here.. best I've heard
> >>> you!
> >>>
> >>> Still trying to get time to re-assemble the tx and make some
> >>> transmissions.......
> >>>
> >>> Rob
> >>> M0DTS
> >>>
> >>
> >>
> >
> >
> >
>
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