It is impossible to cover an entire area of the amateur radio hobby in one article - working via satellites. I will dwell only on the most difficult moments - various methods of working via FM and SSB satellites and correction of the Doppler effect.

About types of transponders

A transponder in a broad sense is a radio transponder, that is, a radio transmitting device that sends an outgoing signal when an incoming signal arrives.
In the amateur satellite service, a transponder is a repeater of signals from ground-based amateur radio stations located on board a satellite.

All satellites use “crossband” repeaters. Transmission to an amateur radio satellite is “bottom-up” in the 432 MHz range, and reception is “top-down” at 144 MHz. Or vice versa: 144 MHz - up, 432 MHz - down.

Satellites have FM, linear and linear inverting transponders.

FM satellites use a single channel - all radio amateurs work on the repeater in turn, just like in a regular repeater. Examples: SO-50, Fox-1D (AO-92). Advantage: simplicity and accessibility. Disadvantage: often the same correspondents with strong signals on each turn occupy the frequency and do not allow weak stations to work.

Linear SSB/CW transponders - a section with a width of about 20-300 kHz is allocated. The entire input band, without changes or processing, is transferred to another range - where the reception takes place.
The advantage is that dozens of radio amateurs can work on the satellite at the same time, there is no crowding. The disadvantage is that Doppler correction requires either expensive transceivers such as the IC-9100 or PC control due to the Doppler effect.
Examples: AO-7 mode A.

Linear inverting - additionally change the type of modulation - if LSB modulation is at the input, then USB is at the output, and when you turn the tuning knob higher in frequency on Uplink, it decreases on Downlink. This is 99% of all SSB/CW satellites. Example: FO-29, XW-2A, AO-7 Mode B.

To operate via satellites, the transceiver uses two VFOs (variable range generators)
*MAIN*- for reception in USB mode (downlink, downward communication channel Space-Earth)
SUB**- for transmission in LSB modulation (uplink, Earth-Space uplink)

In some transceivers, for example, Yaesu FT-817, FT-857 this VFO-A and VFO-B. Split operation is based on the use of two VFOs (SPLIT) - VFO-A is used for reception, VFO-B is used for transmission, frequencies in different ranges. First you need to tune the VFO-A (MAIN) frequency, then go to VFO-B (SUB) and tune the transmit, and press the SPLIT key - both frequencies will be used each in turn (receive and transmit).

Procedure for working via satellites

The antenna must be directed at the satellite in azimuth throughout the entire visibility period (for low orbits up to 60 degrees, you can use fixed elevation 30-45 degrees). You need to rotate the antenna in azimuth manually or using a rotor (possibly with a controller and control from a computer). The work is carried out in the same way as on VHF - the correspondent’s call sign and yours are transmitted, followed by a short greeting 59 and your QTH locator. The transmitted power should be small - usually 2 W (in extreme cases 5 W) - because the transponder receiver will lose sensitivity when the signal is strong. Increasing the elevation angle over 30° needed for highly directional antennas - more than 5 elements, or antenna arrays (“stacks”).

Techniques for working via satellites

1. Historically the first way to work through linear CW/SSB satellites

A second CW/SSB transceiver or control receiver is used for reception. This is duplex mode (I hear and transmit at the same time).

1. Set the frequency on the transmitter to the input frequency of the satellite
2. Set the output frequency on the receiver (downlink or downlink)
3. Rotate the transmitter tuning knob and while in transmission, select the frequency transmission to match its reception frequency. To do this, a series of points are transmitted by telegraph and the tuning knob smoothly changes the transmission frequency until they find where oneself can be heard.
4. Send CQ or answer a call.

The advantage of this method is

• any transceiver can be used for transmission, even without a CAT interface (it’s enough to know input and weekend frequencies of popular satellites).
• full duplex - self-control and ease of control of your signal
• confidence that you can be heard.

Disadvantage of this method:

• it is inconvenient to move from satellite to satellite, because... no frequency memory.

2. Hardware method of working via satellite in modern transceivers

A radio station (such as ICOM IC-820, IC-910, 2000, IC-9100, IC-9700 or Kenwood TS-2000) is responsible for correcting the frequencies of both reception and transmission to compensate for the Doppler effect. The memory of an amateur radio transceiver can store duplex pairs of satellite reception and transmission.

It is possible to set the frequency change law to NORMAL or REVERSE.

1. Changing the transmitting and receiving frequencies simultaneously (NORMAL) in one direction.
2. Changing the transmit frequency up leads to the same decrease in the receive frequency (REVERSE).

Disadvantages: Only duplex pairs of satellite frequencies are stored in the radio station’s memory. The law of change is set manually by pressing the NORMAL/REVERSE button. If pressed incorrectly, the station will not stand still, but will run in the opposite direction, enhancing the Doppler effect.

Procedure:

1. when the transmission is turned on to the MAIN VFO, they find a free space on the transponder and “get on a general call.”
2. switch to SUB and change the transmission frequency to hear their signal through the MAIN receiver.
3. During a QSO, you need to use the tuning knob to change the SUB transmit frequency, monitoring your signal through MAIN, so that the voice or CW is on the same frequency all the time.

   This is the so-called "loop test", i.e. end-to-end test of the entire transmission - satellite - reception path.

4. If the correspondent’s signal “floats” a little at reception, we increase intelligibility by turning on the third local oscillator detuning (RIT). A separate RIT knob allows you to adjust the signal deviation up to +-10 kHz during reception (If there is no RIT knob, simply adjust the frequency on MAIN). In this case, the transmission frequency on SUB should not be touched.

3. Modern method - adjusting the transmission frequency with control of reception using a broadband USB receiver with a panorama function

It is a variant of the very first method. But here, instead of a control receiver, a USB “whistle” like FunCube Dongle Pro (FCDP) or a cheaper RTL-SDR 2832u (R820t tuner) with programs like SDR is used#or GQRX. To answer a call (CQ) of another station, you also need to "adjust" your signal using the transmitter to the receiving frequency (at which the calling station operates), observing on the spectrum or by ear. Next, the QSO is carried out on one frequency.
The disadvantage of this method is that the receiver is overloaded during transmission (you need a high-quality bandpass filter at the receiver input).

4. Improved method No. 3 - drift due to the Doppler effect at the receiving frequency is additionally corrected

ДовA very “abstruse” method, but you can’t do without it when you need to completely suppress the Doppler effect, for example, when receiving weather pictures or when receiving PSK or AFSK9600 signals. Once I managed to set up this method according to someone else's instructions. The method is used in automatic receiving stations SATNOGS - set it up once and never touch it again. :-)

Under Windows:
Requires WXtrack program, WISPdde plugin for SDR Sharp.
https://www.qth.spb.ru/forum/viewtopic.php?f=30&t=8264&p=136943#p136943
A similar method is using SDR#with the WISPDDE plugin, but the program is Orbitron.
https://r4uab.ru/sdrsharp-orbitron-dde-tracker-sdrsharp-satellite-tracking/

5. Modern method - calculation of the Doppler shift and frequency correction using a computer

Foreign radio amateurs prefer the SATPC32 program for Windows - it simultaneously controls the rotor and corrects the Doppler shift. The SATPC32 program contains tools for controlling Icom transceivers.

6. The satellite operation method described in the Yaesu FT-857 user manual

Since Yaesu FT-817 and FT-857 do not have duplex, FM satellites use pre-programmed frequency pairs for reception and transmission, taking into account the previously calculated Doppler effect. Frequency values ​​are used for the beginning of the satellite's passage, the middle and the end of visibility, with two intermediate options, a total of 5 pairs of frequencies. It uses VFO-A and VFO-V pairs, split operation. Split provides very fast transmission and reception switching. But you can use storing two separate receive and transmit frequencies in one memory cell, as can be done, for example, in the Yaesu VX-6r. The disadvantage of Yaesu FT-817/857/897 is that there is no self-monitoring (feedback) due to the fact that the radio station is intended primarily for operation on a hike, and not on satellites.

7. Option of working through FM repeaters using two radio stations

It is a more convenient, improved option No. 6 - there is feedback and self-control, but is only suitable for FM satellites.

First radio station - for transmission

Second radio station - for reception

Sources:

https://www.amsat.org/two-way-satellites/so-50-satellite-information/
https://www.amsat.org/ao-92-commissioned-open-for-amateur-use/
https://www.amsat.org/ao-92-commissioned-open-for-amateur-use/
https://www.amsat.org/wordpress/wp-content/uploads/2014/01/LilacSat2_info-20151007.pdf

Last change: 04/21/2025.

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