for all vhf and above discussions


Postby v51pj » Sun Apr 03, 2011 10:01 am

the big question by all is how and what do I need to work satelites

first of all - a satellite is just a repeater in space
now this might make it more interesting as most of us have laked via a repeater already

what do we need
first a basic yagi that can do vhf and uhf build using the same boom

i have used the dk7zb design for a 5el vhf and 9el uhf yagi -using a 1.7m long boom - the reason for 1.7m is that i have a handle at the back of the antenna to hold it.
i mounted this combined antenna on not used camera tripod

now a diplexer might be the optional needed but at this stage we will leave it out.

i took 2 commercial radios one vhf and the other uhf and i programmed the frequencies into the radios.

now to understand satelites we must be aware of the effect called Dopler.
the FM uplink frequency will always be a fixed frequency.

for AO51 it is 145.920MHz and tone 67.0Hz
and for UHF downlink we must add for doppler.
you program the following frequencys on the UHF radio -
now as the AO51 satelite is approaching you by getting vissible on the horizon you call on the fixed vhf uplink frequency and listen on 435.310. as the satelite gets higher you change to uhf frequency 435.305 and as it gets on top of you you change to 435.300 and as it goes down 435.295 and closer to the horizon 435.290
because the radio system on the satelite is 25kHz your radio will still receive over a 5khz frequency variation.
now with your antenna pointing in the average direction of the satelite you will be able to work stations vissible to the same satelite
you will hear yourself on the uhf downlink and that will give you an indication of your signal quality

yes do not use more than 5w for the uplink as you may damage the equipmentbon the satelite

i have worked in one day Marrion island, gouch island and madagascar on one run. so yes many opertunities are available for us.

now when we work ssb satelites, doppler has a major effect on tx and rx. you can manually tune the uplink and downlink but believe me no easy job -difficult

what you do is make sure your radio that you are going to use for ssb satelite work have a way of being controlled by a pc.
you download the following package SatPC32 - freedownload
if the rotator / elevator is also pc controlled you can operate from the inside of the shack
setting up the software is not difficult.
now you have a complete setup ready to communicate via any satelite to the rest of the world

i have tested HRD on satelite but it was not successfull with my radio - 706mk2g. it send the wrong data to the radio and you end up on the wrong frequency when tx'ing

now a diplexer will come in very handy.
i will try and upload the circuit diagram of a diplexer for homebuild.

the diplexer allow you to use the same radio - full duplex of course - to monitor yourself.

when you don't have a pc available for controlling the radio frequency don't run away.
the method then is to set your ssb tx frequency to fixed frequency in the center of the uplink band. now all you have to do is to change the downlink portion.
by listening to the downlink and adjusting accordingly you would be able to do a ssb contact via the satellites.

using HRD or SatPC32 you can also see the footprint and arrange skeds accordingly if needed.

o yes if you have an Iphone 4 you can download a free app - satellite tracker - it shows you where the satelite is - direction
elevation as well as frequencys

de v51pj and hope to see you on the satelites shortly
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Re: Satelites

Postby v51pj » Sat Apr 23, 2011 10:54 am

the diplexer consists of the following parameters
first there are 2 filetrs invlved
one passing through the vhf and teh other passing through the uhf

this diplexer is rated apparently at 10w maximum

as we only use 5w max into the antenna it is more than addequate to handle normal usage

the uhf part consist of the following
a 4.7pF cap in series and after that a 15nH coil in parallel and then again a 3pF cap in series and a 15nH coil in parallel and then again a 4.7pF cap in series to the input from the radio

the vhf part consists of a 68nH coil in series with a 18pF cap in parallel and then again a 100nH coil in series and a 18pF cap in parallel and again a 68nH coil in series to the input from teh radio

of course you use this when you have a full duplex radio connected to the antenna
otherwise again if you use 2 separate radios the diplexer is not needed

the freq range is 146/437 MHz and 10W input

i am busy building my own one with spares available from the shelf and the caps are not the specific value and therefore i will play with the coils values and the sweep generator

i will put my results as i get on with the project here as well
just waiting for the inductance / capacitance meter to arrive via transport and the rest of the spares such as coil wire.
eish had to buy a 1/5kg roll and onkly need a short piece hi!!
at least extra for some faults and other projects

de v51pj
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Re: Satelites

Postby v51pj » Sat Apr 23, 2011 12:17 pm

the following is diameters and sizes for a satelite yagi covering the vhf and uhf spectrum

the size i selected is for a 1.5m boom
i cut my boom to 1.7m allowing me a handle to hold the antenna.

the elements i used is from old tv antennas or FM reception antennas
the elements clip into these plastic clips and is very robust

the clips are positioned at the correct spacing for the element and then i used a poprivet holding it to the boom
a bolt and nut would work better but i had nothing available

the UHF portion was installed on the one side of the square boom and the vhf portion was installed 90 degrees

now this antenna look like a X if seen from the back

the matching is used was the dk7zb match. here you use 2 lengths of 75ohm cable - the sat RG6 type cable has the best velocity factor but i found that it is difficult to solder - alluminium screen so i used RG59 cable

these lengths are cut to a 1/4 wave of frequency used
because of the 10mm diameter of the driven element enough bandwidth is available with a low swr across the spectrum used for SAT communication

vhf parameters 8.3dBd

Diameter Ref Rad (10mm) Dir 1 Dir 2 Dir 3
10mm 1020mm 978mm 935mm 923mm 893mm
8mm 1022mm 980mm 942mm 930mm 900mm
6mm 1024mm 980mm 948mm 937mm 907mm
4mm 1026mm 980mm 956mm 945mm 917mm
Position 0mm 315mm 545mm 1020mm 1480mm

uhf parameters - 11.95dBd

Element Elementposition 10mm 8mm

Ref 0mm 330mm 334mm

Rad 125mm 318mm (10mm)

D1 220mm 302mm 305mm

D2 400mm 290mm 294mm

D3 625mm 280mm 284mm

D4 875mm 276mm 281mm

D5 1095mm 273mm 278mm

D6 1300mm 275mm 280mm

D7 1480mm 266mm 272mm

now with only 5w input you have more than enough gain to even work a repeater over a long distance or doing a SSB contact on simplex
it is portable and easy to disassemble

now go to the AMSAT web page and get the frequencys etc and yes you are now able to do a contact on a satelite giving somebody the opportunity to work a rare grid from you

de v51pj
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Re: Satelites

Postby V51JP » Sat Apr 23, 2011 2:19 pm

very interesting, thanks Pieter!!
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Re: Satelites

Postby v51pj » Mon May 02, 2011 5:21 pm


Amsat Oscar 51 has recently experienced a few shutdowns due to a low battery voltage trip. This is because of increasing eclipses now at 20 minuets per orbit and increasing, poor sun angles and a weak battery.

The transmitter power is down to about 550 milliwatts and AO-51 is now using the 67 Hz P-L tone required mode in order to turn the transmitters off when not in use.

The AO-51Command Team will continue adjusting various parameters, including transmitter power, trigger voltages, and the like in order to keep the battery temperatures reasonable. Keep in mind that the power management feature keeps the transmitters off during eclipses, so you can't bring it up even with a PL tone during those periods. (ANS)

de v51pj
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