[TenTec] New Jupiter on its Way _ A Few Questions

Sat Apr 26 16:56:33 EDT 2014

Rick - DJ0IP / NJ0IP wrote:
> 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.

10-30 MHz.
> 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.

Sorry, link is not working here. Do you mean that 1" of insulation and 
shield is removed at the halfway point of the small loop of coax?
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at 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 at 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 at contesting.com] On Behalf Of
>> Stuart Rohre
>> Sent: Friday, April 25, 2014 11:40 PM
>> To: tentec at 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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