[amsat-bb] Arrow modification

Wed Jan 2 02:43:17 UTC 2019

Cushcraft, MFJ, Hy-Gain, and Jetstream all make dualband yagis with both
bands having the same polarization.  Cushcraft is a little unique in that
the elements for one band are on the top of the boom, and the elements for
the other band are on the bottom side of the boom.  Both bands have driven
elements that are coax fed and there is a coax harness with a T connector
and short runs of RG-58 which does to the feedpoint for each driven element.

The other brands use elements that go through the boom, and they are
interspaced with each other on the boom.  I know Jetstream only has the
coax attached to the 2 meter driven element, and I think it couples to the
70cm driven element through their harmonic relationship.  I think Hy-Gain
and MFJ do the same thing, but I am not positive on those, as I haven't
looked at their manuals recently.

I have the Cushcraft A270-10s which has 5 elements on each band on a 6 foot
boom.  I have the 2 meter elements on the bottom side of the boom, and the
70cm elements on the top of the boom.  The band which is on the bottom of
the boom seems to have a pretty normal pattern.  The band which is on the
top of the boom seems to have its pattern skewed where the main elevation
lobes are at a pretty high angle.  On Mode J satellites I don't hear the
satellite very well unless it is a rather high pass, and I don't hear it
well during the beginning or end of the pass.  SO50 is rather hard to hear
at all, AO51, AO27, and FO29 are/were easier to hear, but it still shows
the same type of pattern, you don't hear much until you get above 25 to 30
degrees of elevation.  The Mode B satellites exhibit a much more normal
pattern-I can hear the XW2 and CAS-4 satellites throughout most of the
pass, and AO91 and AO92 through most of the pass also, with some fading
here and there when the satellite changes polarization.

I have also owned the Jetstream dualband yagi in the past and it had pretty
impressive performance for an antenna with a 2 1/2 foot boom.  Its
elevation pattern seemed to be more normal than what I get with the
Cushcraft on 70cm.  The biggest problem with the Jetstream right now is
finding one.  R and L electronics is out of them, Jetstream is out of them,
RW antennas on ebay is out of them also.  I bought a used one on ebay and
when it arrived it was the Jetstream dualband vertical instead.  They
luckily refunded my money, but they didn't have the used yagi to send me
instead.  They seem pretty scarce right now, but they did perform pretty
well on the satellites.

I have not used the MFJ or Hy-Gain yagis so I cannot comment on them.  The
MFJ yagi with the 4 elements on 2 meters and 7 elements on 70cm uses a
circuit board for the feedpoint.  That looked a little too fragile to me
for the long term. MFJ has a newer yagi with 3 elements on 2m and 5
elements on 70cm with a different feedpoint arrangement.  I think it is
pretty much a direct copy of the Hy-Gain dualband yagi, since both
companies are owned by MFJ.  I cannot comment on the radiation patterns of
these antennas, but they could be similar to the Jetstream since the
elements go through the boom like they do on the Jetstream.

If we had many more satellites running Mode J I would replace the Cushcraft
with one of these others.  Right now with only 2 satellites using Mode J,
and FO29 still pretty workable, I haven't bothered as I am also into 2
meter SSB and the Cushcraft is twice as long as the others in terms of boom
length so it is probably a better performer on that band.  It also seems a
little more rugged than the others.  The Jetstream is limited to 100 watts
and I blew out one of the driven element arrangements on 2m running 80-90
watts through it.  It was under warranty so Jetstream sent me a new driven
element, but I still had to go up on the roof and replace it, something
that might be hard to do depending on one's setup.

For a portable hand held yagi I think the Jetstream would work very
nicely.  It is light, doesn't need a duplexer, will handle 50 watts from a
FT100/FT857/FT991/FT897/Icom 706MKIIG type of radio, and the elements are
attached with wingnuts which can be broken down very easily for transport.

73 John AF5CC

On Tue, Jan 1, 2019 at 7:53 PM Douglas Quagliana <dquagliana at gmail.com>
wrote:

> I'm not sure if anyone has modified an Arrow to put the elements in the
> same plane.
>
> However, Kent's "cheap LEO" yagi puts the 2m and 70cm elements all in the
> same plane, so it can be done (if you know what you are doing.) See
>
> http://www.wa5vjb.com/references/Cheap%20Antennas-LEOs.pdf
>
> 73,
> Douglas KA2UPW/5
>
> > On Dec 31, 2018, at 9:37 PM, Kenneth P Alexander <ve3hls at gmail.com>
> wrote:
> >
> > Hi Doug,
> >
> > Simply moving them into the same plane will likely cause problems because
> > the bands are harmonically related.  The 2m elements will make a mess of
> > the 70cm radiation pattern if they're in the same plane.  That said, I
> did
> > just stumble across a satellite yagi design where the elements were
> > intentionally in the same plane.  Only the 2m yagi is fed and a passive
> 70
> > cm driven element is placed close to the 2m driven element so the 2m
> > element excites the 70 cm passive element, causing it to radiate on 70
> cm.
> > I believe it's called an open sleeve design.  I think it was 3 elements
> on
> > 2m and 3 or 4 elements on 70 cm.  Sorry I didn't bookmark the page.  I
> > don't remember where I saw it.  Hopefully someone else saw it and
> remembers.
> >
> > Happy New Year,
> >
> > Ken
> > bueng-ken.com
> >
> >
> > On Tue, Jan 1, 2019 at 10:20 AM Douglas B Tabor via AMSAT-BB <
> > amsat-bb at amsat.org> wrote:
> >
> >> I’ve been using my well faded Arrow for 4 years. The boom is a much
> >> appreciated LIDstick so the old man can swing it as well as a 3 year
> old.
> >>
> >> Has anyone modified the Arrow to have 2m and 70cm elements in the same
> >> plane (instead of stock 90 degrees)? I’m just curious what the
> performance
> >> result might be - I know it would be easier to get in and out of the
> >> RoverMobile instead of doing the twist-and-angle it out.
> >>
> >> HNY and 73,
> >>
> >> Doug, N6UA
> >>
> >> Douglas Tabor
> >> dtabor52 at icloud.com
> >>
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