Then that is very easy.
Study the detail pictures of the antenna on that link I sent you.
(http://www.dj0ip.de/my-favorite-antennas/old-folks-antenna/ )
It shows close up details of how to wire the big and small loops.
Then simply replace the capacitor (which consisted of a short stub of RG-213
plus gimmick capacitor) with a variable capacitor.
One thing I did on the foldable antenna shown in the picture at the bottom
was use a small variable capacitor (50pF) and then switch in fixed
capacitors in parallel for changing bands.
I don't think you told us which bands you want it to cover, or if you did, I
missed it.
Actually for receiving we can make it cover all bands but not on TX.
Building one for receive-only is really easy to do; not much you can get
wrong "if" you build it as I show in the detail page. Pay special attention
to how the small loop is prepared. Note that I removed about 1 inch of the
shield half way around the coax. This is important. Everything else is
pretty easy.
73 - Rick, DJ0IP
(Nr. Frankfurt am Main)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Lee
Sent: Saturday, April 26, 2014 12:27 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] New Jupiter on its Way _ A Few Questions
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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