[MRCA] Fw: FW: [Milsurplus] AS-2259 Conundrum
ersmar at comcast.net
ersmar at comcast.net
Thu Sep 29 23:40:12 EDT 2005
Al (N3FRQ) et al:
FYI. Here's a thread of e-mails regarding the AS-2259 NVIS antenna we
used last weekend at Gilbert. Apparently the model you had at the exercise
was indeed FUBAR. (This is the second e-mail I received telling me that
both dipoles on other -2259s are center-fed as we all thought they should
be.)
Maybe you could confirm whether the short legs really are both on the
center conductor and the long legs both on the shield on your -2259. If so,
maybe you ought to relocate a long and a short leg as we tried to do.
More interesting, though, was Dave's observation that in bypassing the
base transformer (as you are set up to do), and using the appropriate
lengths on the dipoles, they were able to generate more-readable signals via
NVIS paths. Your intention of not using the base transformenr is the right
way to go.
I've been reading Jerry Sevick W2FMI's book on balun and transformer
design. I think I found a couple of designs that would work with the low
impedance feedpoint of the crossed dipoles of the AS-2259 or similar arrays.
I still want to try my (stolen) design of three independent dipoles for 80,
60 and 40 (kind of like my early Ham system of 80/40/20 dipoles on one
coax.). I think I can model this config in EZNEC to check on the impedance,
then build a transformer to match to 50 Ohm coax.
Stay tuned.
73 de
Gene Smar AD3F
----- Original Message -----
From: "David McGinnis" <n7mjw at yahoo.com>
To: <ersmar at comcast.net>
Sent: Thursday, September 29, 2005 9:01 PM
Subject: Re: FW: [Milsurplus] AS-2259 Conundrum
> Gene
>
> The antenna the way you describe is unlike any I have
> seen. I have worked with several AS-2259, original
> types, unmodified. They all are set up with both
> dipoles center fed. That is, the way you described at
> first with each dipole having a half going to the
> center, the other half going to the shield of the
> hardline mast.
>
> The dipole you describe is a Off Center Fed dipole of
> sorts. Perhaps not a bad idea, but both dipole would
> be identical and there would be little reason for it.
>
> We have built 3-band AS-2259 (M)odified. A full sized
> 80 meter dipole crossed with a 60 meter dipole trapped
> for 40 meters. You could make a smaller package if
> you like by using a 60 meter trap in the 80 meter
> dipole (the trap will shorten the overall lenght of
> the 80 meter), but we opted not to do this to save the
> almost 1db loss in the trap on the antenna's weakest
> band.
>
> The antenna is set up to work with a base, and the
> base comes with the small 12.5 Ohm to 50 Ohm
> unballanced transformer. I can only assume this is
> because antennas very close to the earth tend to have
> very low impediance, as well as an attempt to make it
> easier on the antenna coupler for low impediance
> matches.
>
> When you cut your dipoles, figure if you are using the
> base with the transformer intact, and how many
> sections of mast you intend on using. We use two
> extra for a little more height. You will find these
> variables make a big difference, as our low SWR
> lenghts are nothing like we would have expected.
>
> I've found the base is problematic however. They are
> not rated for any more than about 20 watts, and may
> of the surplus bases have the transfomer burned out.
> Whatever the plastic goop they filled it with, is very
> hard to remove and my guys have made several (albiet
> it half hearted) attempts. I believe removal of the
> transformer is key to performance. I'll explain:
>
> Last week we ran a confidence test. Several identical
> PRC-104 and AS-2259 sets, within about 50 miles and
> amongst heavy mountains. Signals were weak but
> readable, as expected. We were able to communicate
> with fixed stations with ideal antennas much better
> than each other. We had very readable signals at
> those stations.
>
> The 3 band AS-2259(M)antenna was hooked to the hub-cap
> base with a (working) 12.5 Ohm to 50 Ohm transformer.
> This setup had an acceptable SWR on our frequency, and
> there was very little difference in both transmitted
> or recieved readability with the PRC-104B antenna
> coupler in line or bypassed.
>
> I moved the AS-2259 off the "hubcap" base on-to a
> AT-1011 base with the AS-2259 adaptor mounted on a
> M151A2 truck. A GRC-193B set was attached to this,
> and the antenna coupler on the GRC-193B had to be used
> to match the antenna because of the absence of the
> 12.5 Ohm to 50 Ohm transformer. The GRC-193B uses the
> exact same Reciever/Exciter as the PRC-104B, a RT1209.
> So in this case, We were using the same antenna, in
> the same location, with in a couple feet of the same
> height. The same Reciever / Exciter was used and an
> antenna coupler was put in line because we induced a
> high SWR by removing the transformer. What happend
> startled me: Revceived signal strenght was greatly
> improved. I could instantly copy with good AGC action
> creating quiet signals for nosiy ones. I went from
> weak but readable to moderately strong signals
> received. How they copied me doesnt matter, as the
> GRC-193B is a 400 Watt set.
>
> I am directing now we attack the rubberized goop in
> one of the hub cap bases agressevly to remove the
> transformer, re-cut the antennas for 80-60-40 SWR
> nulls, and repeat the test. Should it work as
> expected, we will do them all.
>
> I have long heard the mil com guys complain the AS2259
> is a piece of junk, as they perfered a simple dipole
> or fan-lite. I can only see one thing that would
> cause them to make that assesment, the transformer in
> the base. All other things being equal, and given
> clean connections in the hardline, the antenna should
> work as well as any low dipole. (get the ends up, get
> the ends up and put it on top of a car, truck, shed,
> etc if you can!)
>
> I'm glad to see guys are experementing. Keep me in
> the loop of what you all learn.
>
> Thanks
>
> dmcginni at co.missoula.mt.us <<-- my real email, I only
> check the yahoo about once a month.
>
> Dave
>
>
>
>
>
> --- ersmar at comcast.net wrote:
>
> > David:
> >
> > As I've nearly memorized your web page on NVIS
> > antenna modeling, I thought I'd forward this e-mail
> > to you for your thoughts and comments as an
> > experienced antenna experimenter. I'd especially be
> > interested to know how you modelled the AS-2259.
> > That is, did you connect one short and one long leg
> > to the center and shield of the coax as usual? Or
> > did you connect them as I saw them in the real thing
> > - short wires BOTH on the center and long wires BOTH
> > on the shield? And what wire lengths did you
> > incorporate into the model?
> >
> > I'm curious to know if the -2259 we played with
> > this weekend (at MRCA Hamfest, www.mrca.ar88.net )
> > was simply a badly assembled version and a fluke, or
> > whether ALL -2259s are assembled that way.
> >
> > Thanks. I'm in the process of building and
> > testing a three-band version (80/60/40) and could
> > use any help from experienced folks such as
> > yourself.
> >
> > 73 de
> > Gene Smar AD3F
> > Rockville, MD
> >
> >
> > ---------------------- Forwarded Message:
> > ---------------------
> > From: ersmar at comcast.net
> > To: milsurplus at mailman.qth.net
> > Subject: [Milsurplus] AS-2259 Conundrum
> > Date: Sun, 25 Sep 2005 22:46:24 +0000
> >
> > Gents:
> >
> > This weekend I helped assemble and operate an
> > AS-2259 NVIS antenna system.
> > It is puzzlement. Can someone explain it to me?
> > Here's my problem with it.
> >
> > Before seeing this unit, I had always thought
> > that the two dipole wire sets
> > were connected one short leg and one long leg to the
> > center of the coax support
> > pipe and one short leg and one long leg to the
> > shield. You know- just the way
> > we Hams would connect two crossed dipole inverted
> > V's for 40 and 80 to a single
> > coax feed line/balun.
> >
> > But Nooooooo. On the unit we had, the two
> > short wires were BOTH connected
> > to the center conductor and the two long wires were
> > BOTH connected to the
> > shield. I concluded that we could correct this
> > obvious error by relocating one
> > short and one long wire to opposite connectors.
> > However, all four wire ends had
> > small brass collars crimped to them where the tips
> > emerged from the opposite
> > side of the connector. (See
> >
> http://www.co.missoula.mt.us/acs/radios/AS-2259%20antenna.htm
> > , third photo
> > down.) We couldn't remove the wires from their
> > connectors at the top of the
> > mast.
> >
> > Did we erect a -2259 that was hosed up by the
> > last Ham who owned it, or did
> > it come that way from the Government surplus source?
> > I can't help but think
> > that the reports of poor operation on the Ham bands
> > are due in some part to this
> > counter-intuitive configuration.
> >
> > Thanks for any insight or inuendo.
> >
> > 73 de
> > Gene Smar AD3F
> > P.S. We made zero Q's on either 80 AM or 40 CW with
> > our GRC-9 and this beast.
> >
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