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Simple Antennas for Schools

PostPosted: Sun Dec 08, 2013 8:41 pm
by g3wgm
We are interested to determine suitable, simple antennas for use at schools, so if you are using one of the antennas listed below (or something similar), we would be interested to know the results you are obtaining from the FUNcube tlm beacon, AT HIGH POWER, ie during daylight. We would be interested to know:

A. What percenatge of the packets do you receive on an average pass
B. How low down can you copy the TLM beacon?
C. What receiver you are using, eg FUNcube donlge, or stand alone radio (if radio, what type/model).
D. Any other comments eg a link to a picture or deccription of the antenna

We think suitable antennas might be
- Simple dipole
- small Yagi (eg 3 elements, hand held)
- Elk see http://shop.amsat.org.uk/shop/article_4/Elk-2m_70cms-Log-Periodic-Antenna.html
- Turnstile http://winklerantennenbau.de/kreuz137.htm
- Ground Plane
- Quadrafelix
- Eggbeater.http://on6wg.pagesperso-orange.fr/Doc/Antenne%20Eggbeater-Engl-Part1-Full.pdf
- Halo
- Anything Else!

Thank you
Jim G3WGM (FUNcube Project Team)

Re: Simple Antennas for Schools

PostPosted: Tue Dec 10, 2013 11:49 am
by G3VDB
As no-one else has yet volunteered anything, my experience may start the ball rolling. This is almost my first experience above 30MHz and is my first experiment with Sats so I also am interested in answering the very questions you ask. I don't yet have a permanent installation but last week I used the following:

RX: FC Dongle Pro Plus
Ant: Homemade Turnstile at 20 feet with 30feet of RG213 and 10 feet of RG58, no masthead preamp (!)
Software: Dashboard

Two passes examined. The log files reveal:

Date Time 04/12/2013 10:31
Duration 720 Secs
Avail Frames 145
First to Last Decode Time 274 Secs
High Elevation Frames 55
Actual Decodes 34
PerCent Decode Total / High Angle 23/63
Elv/Az of First Decode 32.7/70.9
Elv/Az of Last Decode 10.7/163.4

Date Time 04/12/2013 12:07.
Duration 730 Secs
Avail Frames 147
First to Last Decode Time 250 Secs
High Elevation Frames 50
Actual Decodes 17
PerCent Decode Total / High Angle 12/34
Elv/Az of First Decode 25.8/328.6
Elv/Az of Last Decode 14.4/240.7

A simulation of the Turnstile suggests the polar plot is not ideal, but, knowing its location, the above suggests that a more important fact is it is not in the clear on the roof. It is screened by my house and the neighbour's from about 20 degrees round through north to 200.

I dismantled the TS for political reasons.

I then used my 80m dipole on the FC with ~100Foot of RG213. [!!!???!!!] With this unlikely combination I can see the TLM sync on the waterfall of HDSDR when the sat is between 2 and 10 degrees on almost any bearing. HDSDR allows me to record the whole "band", to watch and measure the Doppler, see the cyclical fading of the Telemetry and observe and demodulate the transponder in the evening. And I can decode a few frames from high angle passes.

By measuring the TLM frequency at the predicted zero velocity time, I believe the TLM frequency is high, perhaps by 1.4 to 1.8kHz.

For the future I hope to make an eggbeater, probably the K5OE version, as described by WB5RMG and ZR6AIC. I shall acquire an Elk dual band log periodic, though that is not the simple / low cost solution you are probably considering for schools.

Hope that is encouraging to someone

Jim
G3VDB (IO83ug)

My FC oscillator is checked against GB3BUX which is GPS locked on 50000. and 70000.0 kHz so I believe any frequency measurements may be accurate.

Re: Simple Antennas for Schools

PostPosted: Wed Dec 11, 2013 10:38 am
by SGAARC
Hi Jim

Where did you get

G3VDB wrote:Date Time 04/12/2013 10:31
Duration 720 Secs
Avail Frames 145
First to Last Decode Time 274 Secs
High Elevation Frames 55
Actual Decodes 34
PerCent Decode Total / High Angle 23/63
Elv/Az of First Decode 32.7/70.9
Elv/Az of Last Decode 10.7/163.4


from?

Paul
2E0CUP

Re: Simple Antennas for Schools

PostPosted: Wed Dec 11, 2013 12:23 pm
by G3VDB
My starting point was the .log CSV text file that the dash board saves in the folder specified under the Dashboard Settings | Files Tab.

Mine (on Windows XP) is C:\Documents and Settings\MY_USER_NAME\Local Settings\Application Data\FUNcube-1\

[That "Local Settings" folder is hidden by default, but so many programs store stuff there that I unhid it many years ago ].

In there, you will find a file for each time Dashboard was started and stopped. Anything that is 1k is likely to be the headers only and can probably be ignored. Each successfully decoded frame is listed in the log file, The overall file format is not ideal but the info is there.

Using the UTC of a decoded frame, I used Orbitron, in simulation mode for that UTC, to work out the parameters of the whole pass, and the duration above the horizon in seconds and hence the absolute max number of frames available . I then looked at the time of the first and last successful decodes and used Orbitron to work out the Az and El at those frames. I subtracted the time of those frames to give a duration, in seconds, between first and last decode, divided by 5, and rounded up to get the total frames I should / could definitely have decoded (if elevation was the only issue and there was no fading, which there is of course).

So in detail

Date Time 04/12/2013 10:31 - Approximate start of pass from log file and Orbitron
Duration 720 Secs - Pass Duration - 0deg to 0deg from Orbitron
Avail Frames 145 - Duration / 5 rounded up
First to Last Decode Time 274 Secs - From Log File Times of decoded frames on this pass
High Elevation Frames 55 - First to last decode seconds divided by 5 and rounded up - "High Elevation" is not the best term, but it applies my case!
Actual Decodes 34 - Simple manual count of decodes in log file
PerCent Decode Total / High Angle 23/63 - Percent of (Actual Decodes / Avail) and (Actual Decodes / High Elevation)
Elv/Az of First Decode 32.7/70.9 - From Orbitron using time of first decode
Elv/Az of Last Decode 10.7/163.4 - From Orbitron using time of last decode

Hope that helps, Paul. It was largely a manual process with a little spreadsheet help. I feel a programming project coming on. (So many possibilities, so little time).

Jim
G3VDB

Re: Simple Antennas for Schools

PostPosted: Wed Dec 11, 2013 1:40 pm
by SGAARC
That explains why I couldn't find it all in the dashboard log file!

I will install Obitron and give it a go and report back.

Paul
2E0CUP

Re: Simple Antennas for Schools

PostPosted: Wed Dec 11, 2013 8:37 pm
by Ted
Jim,

I use a PC, FUNcubePro+ dongle and a Turnstile antenna (from Moonraker), which is designed for reception of NOAA weather satellites. The latter is mounted on a tripod and the top of the antenna is about four and one half metres high. It is connected to the dongle with a 10 metre length of RG213 coax. My QTH is located fairly low down in the Lea valley with rising ground to east and west. As you can see from the results below, I receive just a handful of frames at an elevation of 15 degrees.

These are some bin recordings.
Elevation Decoded Frames
80 48
73 67
70 60
69 32
63 33
58 41
48 52
48 43
46 41
39 18
38 54
22 21
15 5
15 4
Kind regards,
Ted G3YWA

Re: Simple Antennas for Schools

PostPosted: Thu Dec 12, 2013 7:54 am
by G3VDB
I receive just a handful of frames at an elevation of 15 degrees.

Interesting figures, Ted.

When I built my Turnstile it was initially for terrestrial use. Simulation suggests at 2m above ground it has a polar plot like a Mexican Hat with a single overhead peak and good omnidirectional low angle at about 15 degrees. As you raise it, the single peak becomes multiple, according to the number of wavelengths above ground. Your figures may illustrate that.

The eggbeater with an artificial ground plane would seem to have a better polar plot. I am interested to try that in comparison.

Jim

Re: Simple Antennas for Schools

PostPosted: Thu Dec 12, 2013 3:46 pm
by SGAARC
Here is my cut down version from a single pass today. I am going to look at all of our data as time permits.

Start 11:57:21
End 12:09:44

First Frame 11:58:36
Azimuth = 3.9
Elevation = 4.4

Last Frame 12:03:50
Azimuth = 288.0
Elevation = 30.9

Frames Received = 17

We are using a turnstile antenna from Moonraker too with a FUNcube Dongle Pro+. The antenna is mounted on a single storey building so particularly high :(

It will be interesting to see what is blocking the signals. From the above something blocked the signal at a fairly high point in the pass. Not too sure what we can do about it though :(

Paul
2E0CUP

Re: Simple Antennas for Schools

PostPosted: Thu Dec 12, 2013 4:29 pm
by G3VDB
More interesting figures, Paul.

I have some suggestions but they are a bit off topic, so I'll try to contact you by email.

Jim

Re: Simple Antennas for Schools

PostPosted: Fri Dec 13, 2013 10:57 am
by Ted
Jim,
I was interested to read your message to me, explaining that the polar diagram for a Turnstile antenna is like a Mexican hat. I look forward to hearing about your proposed experiments with a VHF eggbeater antenna. I searched the Internet for such an antenna, but could find no UK supplier. I did find a supplier in the USA. However, the antenna concerned, the EB-144/RK2M costs $221, which might prove rather costly for UK schools, when other costs are added. You will be well aware that there are several designs published on the Internet and some secondary schools with workshops might be able to construct the antenna. Unfortunately few primary schools have such facilities. Could a UK manufacturer be persuaded to produce an eggbeater?
Ted G3YWA