A different way of making QSO's on amateur radio frequency's is by using a satellite. A satellite is like a repeater, but not stationary as the ones on land. It passes overhead about every hour. A pass is also calles orbit. There are different satellites with different frequency use and modes. For example the FO29 satellite has a 145 MHz uplink (send) and a 435 MHz downlink (you have to receive). The AO7 has the opposite, a 435 MHz uplink and a 145 MHz downlink. If you want to know more about all the different satellites then klick on this link AMSAT and Amsat will give you the information you need.

It is not as easy as it seems to work a satellite. The best way is to use a seperate transmitter to send with and a receiver to monitor the downlink.
I have used my FT-100 to work the SO-50 FM satellite. This was possible because the downlink and uplink are on one frequency with a FM broad modulation and therefore in 95% of the time it will work. I could not hear myself on the downlink while transmitting, but it worked.
With the other satellites this way of work is not possible. The mode used is LSB on the uplink and USB on the downlink with a band spectrum of about 1 Mhz which you can use. For example with the AO7 the uplink is between 145.900 and 146.000 MHz.

Another difficulty is the dopplershift. This is a time delay which changes all the time and could even get to 30 KHz on 435 MHz. The trick is to keep your downlink signal steady because others listen to it. You therefore need to adjust your uplink frequency all the time to eliminate the doppler shift and keep the downlink steady.

Personally I had some interferance of my 145 MHz signal on my 435 MHz receiver. The 3rd harmonic came through a bit to strong. I tried to use all kinds of band filters, but the best solution was the use of a diplexer. A diplexer is normally used to connect 2 antenna's to one transmitter. In my case I use the 70cm part and shutoff the 2 meter section with a 50 Ohm resistor. I measured more than 60 dB reduction of the 2 meter signal and all my problems were solved. Here is the information of my diplexer:





L1 = 1 winding 6mm diameter (internal), 1mm CuAl wire
L2 = same as L1 but 90 degrees turned from L1
L3 = 3 windings 6mm diameter (internal)
L4 = 4 windings 6mm diameter (internal)
L5 = same as L3
C1 = foil trimmer condensator 15pf (3-15pf)
C2 = same as C1
C3 = same as C1
C4 = foil trimmer condensator 40 pf (4 to 40 pf)
C5 = same as C4
3 chassis connectors (BNC or N)
Coils L3, L4 and L5 need to be mounted 90 degrees from each other as shown on the photograph.

A tip: use ceramic trimmers if you want to apply more than 40 Watts of RF power. The coils can be wound on the end of a drill. A 6mm drill is standardly used.

Last updated 9.6.2004