The Nine Things They May Forget To Tell You About When You Are Getting Started on AO-13 and AO-10

by Timothy Hickman, N3JON.

When I got started on Oscar 13 and Oscar 10 several years ago there were several things I had to figure out or be told. The following is a list of mistakes I or others have made getting started on AO-13 and AO-10.

Lower Side Band up / Upper Side Band down

Since AO-13 and AO-10 are inverting transponders you can't be received in USB unless you transmit on LSB.

Offpoint Angle

When OSCAR 13 switches in B mode (435 MHz up 144 MHz down) from the Omni antenna to the directional antenna how strongly you can get into and hear the bird is determined by the off point angle. The offpoint angle or how far off the satellites directional antenna is pointing away from you is displayed in degrees on your tracking program. Less then 20 degrees is good - more than 20 starts getting not so good.

This information is computed by your tracking program from information on the satellite's attitude called Blon/Blat. This information is not part of the element set you download or copy into your tracking program. The information must be entered by hand to your tracking program from the AO-13 schedule available on BBSs, Packet and newsletters. InstantTrack lists the information as Attitude: +xx, +xxx. This is Blat/Blon the reverse of the schedule's Blon/Blat just to confuse things. An attitude of 180/0 is good with a lot of good offpoint angles and an attitude of 240/0 is not so good.

OSCAR 10 does not have a published attitude and is always in mode B therefore you do not compute its offpoint. I have observed that it is stronger on the way to apogee than at other times.

Transponder Schedule

When AO-13 changes from Mode B's omni to directional antenna or to mode S or off is contained in the same schedule as the Blon/Blat and is also part of the element set. This is written in a 0 to 256 phase noted as MA xxx.

If you are using InstantTrack the phase can be displayed on your screen by entering in the schedule line the phase a mode starts and the letter for the phase i.e. 000o030b120s150b230o.

Epoch Time

When you get a printed element set the Epoch Time is in a 4 or 5 digit period than 7 digit format. However when you type it into InstantTrack it must be in the 2 digit (for Year) type a space then the 2 or 3 digits then the period then the 7 digits.


If your tracking program asks for the R.A.A.N. its the RA of Node in the tracking program.


You must use headphones. Without headphones you add another echo and drive others trying to listen to you crazy.

Speech Processor

Don't use it! It does not improve the intelligibility of your signal and makes you sound like a CBer trying to talk over the sound of the semi's motor.

Finding Your Downlink

Do not set your transmit frequency and then tune your receive frequency to find yourself. Your likely to be tapping your key on top of someone's QSO. Find a clear frequency and move your transmit frequency to find yourself.

Beacon's Level

Listen to the loudness of the beacon and don't crank up your signal any louder than the beacon's. Oscar 13 has only 35 watts for everyone to share, if you hit it too hard you will steal power from everyone else or have the satellite shut back to a safe level.

Original text by Timothy Hickman, N3JON ( HTML conversion by KB5MU.