Yea, that's what I had in mind, Rick, an antenna that is quiet, so that I
can hear more than just the strongest signals.
On Apr 25, 2014 2:53 PM, "Rick - DJ0IP / NJ0IP" <Rick@dj0ip.de> wrote:
> Stuart pretty much nailed it.
> The only thing I wish to point out is, all he has said has to do with
> building loops which are suitable for transmitting and receiving.
>
> If you only wish to receive, this is really simple Simon.
> No worries about resistive losses in connections.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Stuart
> Rohre
> Sent: Friday, April 25, 2014 11:40 PM
> To: tentec@contesting.com
> Subject: Re: [TenTec] New Jupiter on its Way _ A Few Questions
>
> Rick,
> Thanks for augmenting my post with some important caveats.
>
> YES!, you have to have a room sized to not have the indoor loop too close
> to
> the walls and possible conductors.
>
> I was testing a loop made at our research lab in San Antonio one time,
> indoors. It was just a quick test, not at full voltage, to see what the
> wave form would be from a pulse source dumping into the one turn copper
> tubing loop from a charged capacitor bank.
>
> We were simulating lightning to do near field testing of some sensitive
> amplifiers to be used outdoors.
>
> Although my loop set up was horizontal on some insulating stands and one
> foot from a metal shelf, and that seemed a safe distance for the planned
> "one shot"; when I fired the charged capacitor bank into the loop, I got
> "lightning". A one foot arc to the painted, and insulated metal cabinet,
> (or at least we thought it was insulated up to that point.) (The things you
> do as a junior scientist).
>
> We took the loop and instruments outdoors for waveform testing after that.
> It simulated the magnetic field of a lightning pulse quite well for our
> purposes. It fired at any charging voltage without doing anything unusual,
> except the expected jump, against its supports, from the transient high
> field being discharged.
>
> Oh, the reason it arced? The machine shop who rolled the tubing into a
> loop
> for us, had one spot with a non smooth curve, and it formed a high voltage
> peak at that discontinuity. It was such a minor imperfection it had gone
> un-noticed until it called attention to itself.
>
> As Rick points out, outdoors, even just outside at roof line, you get
> dramatically better results from a loop. And, the loop can be made larger
> (and more efficient) over an indoor model limited by room size and
> contents.
> Don't overlook estimating the field before you stay close to a loop.
>
> The highest quality low resistance joints dictate silver soldering, or
> brazing anything that connects to the tubing, if you can't weld it.
> Other mechanical methods that might work, are to polish the flattened
> surfaces to be joined, then introduce conductive grease to protect the bolt
> joint from oxidation and maintain the connection. Tubing to be bolted
> should use highly conductive washers on the bolt, to distribute a high
> loading to the joint, and dissipate any heat build up. Use of capacitors
> where the current does not have to flow thru a rotor shaft is preferred.
> You can get two big variables twice the capacitance needed, and put them in
> series so that the current only travels via the field thru both rotors, and
> no mechanical rotating connection is a current path.
>
> WB5AOH used a U shaped tubing "rotor" in his trombone capacitor, so that
> the
> field was between the air gap between the U and the two tubes that formed
> the stator. Teflon rings provided a lubricated sliding joint, and spacers
> between the tubes. He had a group of paralled capacitors that could be
> switched into use for 80m.
>
> Coupling to the loop can be by the use of a small loop at one side of the
> transmit/ receive loop.
>
> As Rick said, for low bands 80 and 40, a two turn or more loop allows the
> band to be driven more efficiently. (Smaller loop diamter).
>
> I have been doing research on WW2 NVIS early use, and loops were sometimes
> used horizontally one meter above the roof of a Scout car.
>
> There was also a meander line dipole used one meter off a car roof, as well
> as other designs that seemed to emulate an isotropic source, as that
> radiator was a random structure, not resonant, and single wire fed from a
> larger transmitter, truck mounted.
>
> W5IFQ, another researcher here, uses the early MFJ multi band loop to
> maintain ham radio links when he is on research in distant oceans. He is
> able to maintain email schedules with home by the use of a loop placed
> above
> the superstructure of the ships, which typically are 200 feet long or less.
>
> -Stuart Rohre
> K5KVH
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