[ARC5] ARC-5 transmitters and antennas
Mike Everette
radiocompass at yahoo.com
Fri Oct 26 22:24:39 EDT 2012
The only conversion article that ever got the antenna part right about the Command Set was the one in the ARRL Handbooks from about 1959 through 1967. I think it was probably written by Lew McCoy, W1ICP (later W1FB). The conversion was for Novice use of the Command Set rigs.
In this article we are advised that a series variable capacitor -- without looking at the article, I seem to recall it calls for either 200 pf or 365 pf (I used a 365, that's what I had) -- should be inserted into the antenna lead; and that while almost any length of antenna will work, the minimum length for an antenna is about 1/8 wavelength -- i.e. 33 feet for 80 meters and 16 feet for 40 meters. We are also advised to use a pilot lamp bulb, loosely coupled to the antenna, as a tuning indicator. The series cap, along with the frequency (the rig was modified with a plug-in crystal oscillator adapter), coupling and inductance controls are adjusted for max bulb brightness.
I can testify that this does indeed work. And well. The KISS Method at its finest.
Back in my Novice days, it's what I used at first... except my 30-odd feet of antenna wire, strung under the eave of the house (my parents were scared of lightning) was fed with a single wire, connected approximately 20 feet from one end at the point where the wire passed by my window; and it was all of 10 feet off the ground, maybe. Must have been some magic in that, or maybe the Lord looks after fools... My T-19 loved it!
But when I became "enlightened" and put up a full size 80 meter inverted vee (with a 50 foot metal push-up mast -- grounded! -- as the center support) fed with RG-59, I noted that my transmitter would not load it well and I suddenly didn't make very many contacts... until I borrowed a DX-40, which would load well into the IV.
By the way, in that Handbook conversion, the final plate voltage on the ARC-5 transmitter runs between 425-450 volts. The power input was therefore something like 35 to 40 watts in my case.
73
Mike
W4DSE
--- On Fri, 10/26/12, Darryl Sage <trifid284 at gmail.com> wrote:
> From: Darryl Sage <trifid284 at gmail.com>
> Subject: Re: [ARC5] ARC5 Digest, Vol 105, Issue 154
> To: arc5 at mailman.qth.net
> Date: Friday, October 26, 2012, 7:19 PM
> 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:
>
> > Send ARC5 mailing list submissions to
> > arc5 at mailman.qth.net
> >
> > To subscribe or unsubscribe via the World Wide Web,
> visit
> > http://mailman.qth.net/mailman/listinfo/arc5
> > or, via email, send a message with subject or body
> 'help' to
> > arc5-request at mailman.qth.net
> >
> > You can reach the person managing the list at
> > arc5-owner at mailman.qth.net
> >
> > When replying, please edit your Subject line so it is
> more specific
> > than "Re: Contents of ARC5 digest..."
> >
> >
> > 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
> > >
> > > =========
> > >
> > >
> > >
> > >
> ______________________________________________________________
> > > ARC5 mailing list
> > > Home: http://mailman.qth.net/mailman/listinfo/arc5
> > > Help: http://mailman.qth.net/mmfaq.htm
> > > Post: mailto:ARC5 at mailman.qth.net
> > >
> > > This list hosted by: http://www.qsl.net
> > > Please help support this email list: http://www.qsl.net/donate.html
> >
> >
> >
> > ------------------------------
> >
> > 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
> >
> >
> >
> > ------------------------------
> >
> > _______________________________________________
> > ARC5 mailing list
> > ARC5 at mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/arc5
> >
> >
> > End of ARC5 Digest, Vol 105, Issue 154
> > **************************************
> >
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
More information about the ARC5
mailing list