[amsat-bb] Cheap rotator setup

Thu Dec 20 05:56:04 UTC 2018

Hi Eli,

I am the author of that webpage you're using for a guide for your own 
set up. I humbly appreciate that you have chosen the page for some 
guidance - that page is one of the Top 5 pages at my site so lots of 
folks have successfully used it. Several of them have been pushing me to 
submit this to QST as an article which I may do (my last one was exactly 
30 years ago - so it may be time for the next one.)

::::::::::::::::::::::::
Note that I extensively edited the web page today so I genuinely am 
seeking additional help from all to help make this page even better and 
to give it more clarity or correct any technical errors - especially 
before I submit the page info to QST....
::::::::::::::::::::::::

Eli, as a result of your question, I just added the below info to the 
web page - along with a slider that shows 31 new photos that give more 
details and a detailed diagram of the antenna's beamwidth....check out 
the page for more info since those cannot be shown here...but for those 
who don't want to look, here is a highlight quote from the page to 
hopefully answer Eli's question.

--------------------------------------

“Why Are You Using a 45° Angle for Fixed Elevation Instead of the 
Recommended 15°?”

I thought I had better add a comment as to why I am obviously using a 
45° angle instead of the recommended 15°.

I am personally surrounded by RF eating 65 foot trees and a RF eating 
two-story house. As a consequence, I chose to move the A430S10 50° 
antenna beamwidth (see below) and center them on a fixed 45° instead of 
15°.

Ostensibly, I would lose coverage from 0° to 20° (45° center angle minus 
half of the 50° beamwidth of the antennas, or 25° =  20° ) by doing this 
– but I’m going to lose those angles (and then some) anyway because of 
the tree and house QRM.

Trust me when I tell you that trees and houses do a damnably good job of 
blocking RF at satellite frequencies – in my case below 30° in summer 
and 22° in winter! (This is going to be one of my next videos on my 
YouTube channel at http://Youtube.com/K3RRR.)

Beamwidth is loosely defined as the width of the main lobe of radiation 
for both transmit and receive. This is a whole discussion by itself but 
for my cheapie antenna system, you’re better off  with a wide beamwidth 
versus a more narrow beamwidth for your antennas. The following diagram 
from Diamond Antennas shows the comparison of what that width of the 
main lobe looks like with my orange arrows showing where they cross the 
3 db points.

If you kinda sorta extrapolate, you can see that an imaginary line from 
the 3 db intersection point to the outer circle would translate to about 
25° either side of the zero mark – for a total spread from both sides 
equal to about 50° of beamwidth. (The other chart shows the same info 
for Diamond’s bigger brother the A430S15 – 15 elements instead of 10. 
you can see how much narrower the beamwidth is albeit with not that much 
difference in gain.)

In more technical terms, the A430S10 has an E-Plane 3 dB Beamwidth = 50 
degrees. In layman’s language, this means that you will have a good 
receive AND transmit signal 25° above and 25° below your center angle – 
which in my case is 45° due to the constraints of Home Depot.

Home Depot?

I picked 45° because Home Depot sells PVC connectors for that angle – 
and only that angle since 90° angles really are not that useful for the 
hamsats!

Again, with these antennas having a 50° beamwidth, my setup handled 
passes between 20° and 70°. This same wide beamwidth also makes pointing 
the antenna more forgiving – which is important for cheap rotators which 
are not all that accurate between calibrations.

(The E-Plane 3 dB Beamwidth = a whopping 95 degrees for the A144S5 two 
meter five element Yagi – so it was not the limiting consideration.)

But enough about me and why I chose 45°. Let’s talk about you and your 
need for 15°.

Permanently Bending Schedule 40 PVC With My Wife’s Help

I need to plagiarize myself and steal a couple of paragraphs I have on 
this other webpage on my site:

Attic AMSAT Antenna – Working the Ham Radio Satellites With A Rotatable, 
Computer Controlled, Yagi Attic Antenna

“If you have played with PVC for antennas for a while you will already 
know they don’t make 15° connectors. So, I was faced with trying to bend 
a straight piece PVC – which I thought was going to be difficult.

“As it turns out, it is surprisingly trivial to heat even Schedule 40 
PVC so that it becomes bendable with a standard 1500 watt hair dryer in 
less than 10 minutes of your time! (Thanks to YouTube for this education!)”

Wife Jan’s hair dryer actually had some attachments and gizmos which 
focused the heat better than mine so I swiped hers for this task. She 
was surprisingly unamused and recommended I get a heat gun for future 
applications. I obediently followed her recommendation and got this 
particular heat gun.

Something about briar patches came to mind for some reason – even though 
there was no mention in the Amazon description.

--------------------------------------

Eli, I have just now added the above information to the cheap antenna 
page – I appreciate the heads up on helping make this clearer for other 
folks too.

Hope this helps...and hope to work you on the birds soon!

73,

Robert K3RRR

  -.- ...-- .-. .-. .-.
73 de Robert K3RRR
http://K3RRR.com
@K3TripleR
http://YouTube.com/K3RRR
-.- ...-- .-. .-. .-.

On 12/17/2018 6:37 PM, Eli Caul wrote:
> Hi folks -
>
> In my ongoing effort to figure out how to use the SSB satellites, I duplicated this setup over the weekend:
>
> http://k3rrr.com/cheap-computer-controlled-tv-rotor-for-amsat-satellites-and-includes-free-satellite-tracking-with-pstrotator-and-the-usb-uirt/
>
> I bought a list of materials based on the photograph,  and it didn't occur to me that the PVC parts pictured put the antennas at approximately 45 degrees and not the recommended 15 degrees.
>
> Has anyone done this setup?  If so, how did you assemble it so that the antennas ended up at the recommended angle?
>
> There were a couple of higher angle passes yesterday (one was at 50 degrees) but so far I haven't been able to 'loop' the satellite.  I'm using a Yaesu FT-991A for uplink and an Airspy SDR on the downlink.
>
> Advice appreciated.   So far I've gotten some excellent advice from AMSAT members and I really appreciate the groups level of expertise and patience with my fundamental questions.
>
> 73 de KK6ZHZ,
>
> - Eli Caul
>
> Director of Customer Care
> Sonic
> 707-237-6201 Direct
> 707-521-0131 Faxline
>
>