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Re: Antennas vs future



Aloha Rees -

I'll offer my thoughts and experiencese...

>1) Is there agreement on which manufacturer makes the best antenna
>with regard to long term durability?  How well it stands up to
>the stresses of being exposed to sun, wind, rain, ice, snow etc?

I can't comment on snow :-) but I've had the venerable Cushcraft AOP system
up on the roof of my school for 4 years or so... no problems, though it is
getting to be time to change the coax. I've been using radio shack RG8, and
this isn't the best solution for 435MHz!!!

Althought the Cushcraft is an older design, and many prefer the Hygain and
M^2 antennas, it has worked for me. There is a rumor that the 435 side on
the Cushcrafts detunes with rain, but then, I've rarely put a meter on it
to monitor SWR in sun/rain, and again, it has worked for me. I've also
taken the antennas to field day, to other remote setups and to Palau
(KC6/T88) and set them up on the ground, hanging from the eaves of houses,
propped up on chairs and so on....

There are other rumors about the other antennas, and HyGain seems to have
the best reports.... but I've had little to no experience with them.



>2) Does anyone have experience with the suggestions presented in
>the June issue of CQ VHF with regard to mounting cross polorized
>antennas in a "x" rather than a "+"?  Any comments with regard
>to lightning protection that this affords by using metal vs
>fiberglass masts?

With a metal cross-boom, it is best to mount them as "x" because that will
minimize interaction with the pattern. On my setup, the 70cm side is out in
front of the boom, and so won't interact, but the 2M side is balanced on
both sides...

(check out http://165.248.121.94/PCHSARC.html   for some views of the shack
and antennas and antenna mounts)


No real lightning here... so I haven't worried about it... or haven't done
anything about it.... :-)  about once a year we get some lightning, but it
tends to be Cloud<->Cloud lightning and only occasionally cloud to ground
up in the hills.



>3) Would investing in an AZ/EL system merely give access to AO-10 now?
>Will you need the amount of gain from a typical AZ/EL configuration to
>use the new Phase 3D?  In other words, will spending money now give
>over kill capability in the future.

Overkill in what sense - I use the Az/El system to talk with MIR crews - it
means I can chat the entire pass. [REM - before the flames, I live in
Hawaii, look at the map, there ARE no other stations wanting to contact
MIR]

I use it to peak the signal on Mode A, B, J as when I'm using a LEO to
communicate, it is typically low on the horizon to work DX, yes, I could
use fixed elevation, but, a 10 degree aiming difference can bring a
noticible signal difference.

Also, if you are going to do Tropo and Aurora (we can't do that here) and
MS and EME, then elevation can yield interesting results.


>4) Is an AZ/EL a high maintenance configuration?  I realize it
>depends on how it was put together in the first place, but would
>putting an AZ/EL system on top of a 50 foot tower be crazy?  The
>purpose of doing so would be to use these antennas for long distance
>tropo as well as satellite use.

As you say, it depends on how they were put together... since my antennas
were basically free, and the rotor system cost me $30, plus some Radio
Shack mast and tripods, I have to check it out once or twice a year.
Tighten bolt and the like. My system is on top of my school building and I
have the key to the roof :-) the antennas are easily worked on by standing
on a chair... of course, if I fall one way it will be 4 storys to the
ground :-(

My problems have been - skewing in the wind... I went up the other day and
tighened some loose bolts, it had been a couple of years since I did that,
and we get 25 mph winds, gusts to 40-50mph.  and an occasionally flakey
rotor controller (probably associated with the unusually gusty winds, but
other mysterious things go on.)

If I remember - I aim the antennas into the wind, or downwind when I turn
everything off... We have pretty consistent winds out of 040 to 060

Putting up good rotors will probably be worthwhile... install it on the
ground for a few days and work it out... get everything tight enough and so
it doesn't slip... with metal booms, consider putting wooden inserts in so
the tubing doesn't crush, for the Fiberglass, consider a small screw to
keep the antenna in one position - so it doesn't twist.

>5) I have read that using a well installed cross polorized satellite
>antenna can and has been used for EME as well.  This depends on working
>the other ham who uses a very large antenna system on their end.  What
>size of antenna (gain) is needed for this for either/both 2 meters and
>70cm?

Well, one with a reasonable amount of gain, good coax, the addition of
ground gain on Moonrise, pre-amp and DSP and an amp....

Using my Cushcraft antenna on 2M, I've copied K5GW calling CQ off the moon.
And detected 3 other EME QSOs but not copied callsigns. I tried responding
with about 125W, and didn't make it. Likewise I tried a sked with W5UN, and
we didn't make it. (I didn't even hear him that evening)

So, possible, yes... I haven't done it - Yet - but I know I am on the
threshold (3 to 6dB) of a contact... The summer plan... 4 Cushcraft 2M
yagis, good coax, and if I can get this amp refurbished... 200-300W and
that should do it.... (all I need is the time :-) )

The big gun stations say that at the proper time, and during moonrise where
ground gain helps, an "OSCAR class" station can make a contact.

This will also be great for the CA-HI tropo duct that occasionally shows up
here.


>6) I have heard that certain antenna manufacturers antennas are harder
>to put together than others.  Hard on the hands and fingers etc.
>Any experiences?  Suggestions?

CushCraft - OK - I'd see if they are using stainless steel bolts, as the
rust factor can be a problem... use the penetrox :-)
KLM with the push through connectors... what I don't like about them is
that it is hard to transport/break down... and I run around with antennas
doing demos and the like. Still, I've used them on 149/136MHz on ATS3 and
they worked OK.

>7) Knowing that Phase 3D will eventually fly, would a lower tech
>omni antenna system be a more sane answer to the question of what
>antennas to use for satellite usage?  Do you really need the gain?

Sane? What is sane about playing with satellites :-) :-) :-)

My feeling is that even with P3D, having gain antennas is a good thing. All
you have to do is turn off the amp!!!! and RX will be great!!! Also, P3D
will have the higher bands... this means more antennas (but smaller ones)
and they will need to be aimed... you probably won't need a tall tower for
those  (unless you want to do tropo at 1.2GHz and up :-)   [KH6HME has
worked tropo Hawaii to California all the way up to 5GHz.. they are still
working on 10GHz]

>8) If gain is required, how much is needed as a minimum to work
>AO-10/Phase 3D when it is at the furthest distance from the earth?

Depends on your system and the satellite... sometimes the satellite
attitude is poor and no amount of power will work. I was on the other day,
100W SSB through 50 ft of RG8 (so probably a 3dB loss or more?) and was in
solid at the peaks and lost at the bottom of the fades... upgrading to 9913
or heliax will help.

So, I'll round it off to 10-13dB antenna, 100W and good coax will give you
great signals when the bird is doing good. Sometimes you'll need to reduce
the power.

>9) Do the antenna manufacturers who supply cross polorized antennas
>for satellite use provide the "switcher box" or just the relay
>configuration on the antenna for switching between left hand and
>right hand polorization?  It is very unclear that one would have
>to build a switcher box to control the relays on the antenna.  It
>would be nice to know who makes them and are they all the same?  Are
>there any software solutions which monitor radio signal polorization
>and provide control options?

Cushcraft doesn't provide the box. You just set it up for what you
desire... I go RHCP.

Other companies provide the switching systems, though you may need to get
the wire to put up the connections.

I've never heard of software control fo polarization... most people switch
manually for best signals...

BTW, on EME, Linear polarization is preferred, most big gun stations are
horizontally polarized. A few can change polarity (Vertical/Horizontal) but
signals between CP stations are tough...as the sense of the polarization
shifts on reflection.. if you are RHCP, the other station better be
LHCP.... But, if they are linear and you are CP, then you pay the 3dB
price... (more noise or less signal depending on which side you are on...)


>----
>
>These questions are the result of a couple of months of "looking into"
>the whole satellite antenna issue.  I guess I am in need of
>experienced input.  I have recently joined AMSAT and have explored
>the AMSAT web site.  I also recently purchased a Yaesu FT-847 and
>want to make an informed decision on the issues of antennas for
>satellite usage.  I want to take advantage of the FT-847's multi
>mode capability on the vhf and uhf bands as well as its satellite
>capability.

Go for it!!!! More importantly, an antenna in the air NOW is better than no
antenna at all :-) I've worked stations on fixed 4 el yagis, barefoot
(10-30W) on AO10 when the satellite is "down" at 20,000 km.


Aloha - ted - nh6yk  BL11aj





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