[ARC5] ARC5 Digest, Vol 105, Issue 154

[Darryl Sage]

Hi men i have never used a torid  i want to put the unun in the ant. relay
box what kind of torid should i use?  73  Darryl     ve3cpo

On Wed, Oct 24, 2012 at 10:31 PM, <arc5-request at mailman.qth.net> wrote:

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> Today's Topics:
>
>    1. Re: Why an UNUN? (mac)
>    2. Re: Why an UNUN? (mac)
>    3. Why an UNUN - and a drift into TCS territory (Laura and Jim)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 24 Oct 2012 19:10:33 -0700
> From: mac <w7qho at aol.com>
> Subject: Re: [ARC5] Why an UNUN?
> To: jfor at quikus.com
> Cc: ARC-5 List <arc5 at mailman.qth.net>, Mike Hanz
>         <aaf-radio-1 at aafradio.org>
> Message-ID: <4D5839AA-59D4-451C-BE92-2BCBD9E770E8 at aol.com>
> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
>
>
> On Oct 24, 2012, at 6:24 PM, J. Forster wrote:
>
> >> OK, I remember hearing a figure in that range before. Now, the
> >> command
> >> xmtrs were designed to operate into antennas that presented highly
> >> reactive loads, a relatively low resistance and a large capacitive
> >> component
> >
> > Yes
> >
> >> and the function of the roller inductor was to cancel out
> >> the latter.
> >
> > Sort of. The roller inductor was designed to series resonate the
> > antenna's
> > capacitance.
>
>
> Same thing...
>
>
> >
> >> Reasonable to assume, then, (but not necessarily for
> >> certain) that the variable link alone would allow proper loading of
> >> the transmitter into a purely resistive 13 ohm load or something
> >> close
> >> to it and a 2:1 step-up (4:1 impedance ratio)  transformer (or UNUN
> >> if
> >> you prefer) would then provide a very good match to 50 and 75 ohm
> >> resistive loads with the inductor completely removed from the
> >> circuit.
> >
> > If you short out the inductor, rather than resonating it with a
> > capacitor,
> > you remove a hugh-Q filter from the antenna line. This increases
> > harmonics
>
> Separate issue and may or may not be a problem depending on the type
> of antenna  used, if feeding into a tuner, etc.
>
> > to the antenna.
> >
> >> Not clear from the many comments  whether or not anyone has
> >> actually verified this?  Also, seems to be some confusion as to
> >> whether or not a series capacitor would still be required which
> >> should
> >> NOT be the case.
> >
> > If you short the coil, you don't need the cap. See above. IMO, this
> > is a
>
> > bad idea.
>
> Still haven't received an answer  my question...
>
> DD
>
> >
> >> I've never tried the UNUN approach, BTW,  series caps and the roller
> >> always worked FB here as I've mentioned before.
> >>
> >> Dennis D.  W7QHO
> >> Glendale, CA
> >
> > Best,
> >
> > -John
> >
> > =========
> >
> >
> >
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>
> ------------------------------
>
> Message: 2
> Date: Wed, 24 Oct 2012 19:11:44 -0700
> From: mac <w7qho at aol.com>
> Subject: Re: [ARC5] Why an UNUN?
> To: jfor at quikus.com
> Cc: ARC-5 List <arc5 at mailman.qth.net>, Mike Hanz
>         <aaf-radio-1 at aafradio.org>
> Message-ID: <28F078B1-AD80-40DB-92B8-4A98C70BD972 at aol.com>
> Content-Type: text/plain;       charset=US-ASCII;       format=flowed;
>  delsp=yes
>
>
>
>
>
>
> On Oct 24, 2012, at 6:45 PM, J. Forster wrote:
>
> >
> > Not really.
>
>
> Yes really
>
>
> >
> > A transmitter, like a battery or other power supply, can be modelled
> > as a
> > Thevinin Equivalenrt, an ideal Voltage Source in series with an Output
> > Impedance.
>
>
> The equivalent circuit of a class C amplifier would look like an AC
> (RF) voltage source with a very low internal resistance.
>
>
>
> >
> > There is a circuit theory theorem that, for maximum real power
> > tranfer,
> > the load impedance should be equal to Complex Conjugate of the source
> > impedance.
>
> We're not talking about maximum power transfer here.  A Class C amp is
> designed to provide a particular power output at a high efficiency,
> not maximum power transfer which results in an efficiency of 50% .
> You''re thinking of class A.
>
>
> >
> > This means equal to, if the source and load are purely resistive.
>
> >
> > This means if one is inductive, the other must be capacitive, and the
>
>
> We keep the load resistance seen by the PA tube purely resistive here
> with our resonant tank circuit.   In practice we strive to present the
> amplifier with a purely resistive load if possible. Small values of
> reactance reflected into the tank circuit can be accommodated by
> tuning adjustments.  In those cases where the reactive components are
> too large external antenna 'tuners" are employed.
>
>
> > inductive reactance equals the capacitive reactance.
> >
> > This means if the source is complex (resistive + inductive), the
> > load must
> > have a load where the resistive componants are equal and the
> > capacitive
> > reactance is equal, and opposite, to the source inductive reactance.
> >
> > ie:  The L & C are resonant at the operating frequency.
>
> See above
>
> Dennis D.  W7QHO
> Glendale, CA
>
>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 24 Oct 2012 19:29:44 -0700
> From: "Laura and Jim" <mcenfalz at humboldt1.com>
> Subject: [ARC5] Why an UNUN - and a drift into TCS territory
> To: <arc5 at mailman.qth.net>
> Message-ID: <318236059720468387192B89C1BFD64E at HomePC>
> Content-Type: text/plain;       charset="iso-8859-1"
>
> I successfully run my TCS into a dipole in this manner:
>
> Crank the loading inductor to near zero turns, add a 365 PF series cap
> outboard, then add 1:4 autotransformer to feed the coax.
> Hot and ground go to separate posts on the autotransformer box, coax out
> the other side, T-network "tuna" to an NVIS dipole. I get good reports and
> the full 20W out.
>
> Now my ARC question: I have a 20 foot portable whip and 16 radials out on
> the lawn 30 ft away from the shack. What's the best way to feed the whip?
> a) Beefy cable from the TX antenna post to the whip feedpoint, separate
> ground wire out to the radials?
> b) Above mentioned UNUN (1:4) set-up and co-ax to the whip? Of so, what do
> I do at the end of the coax? Install another UNUN (4:1) to take the 50 ohms
> back to 12?
> d) None of the above (most likely............hihi)
>
> 73 DE JIM K6FWT
>
>
>
> ------------------------------
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> End of ARC5 Digest, Vol 105, Issue 154
> **************************************
>