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Jan 20th, 2010 at 9:03am
I agree with you; the CODAN manual is not clear.
If you put exactly 70 MHz IF input, and set the CODAN to 14200 then the actual transmit frequency will be 14200 MHz.
Your modem will have fine tuning steps (e.g. 50 to 90 MHz in 10 kHz steps) which you will need to use if your transmit frequency is, for example, 14201.5 MHz. In this case set the CODAN to 14200 or 14201 MHz and set the modem to 71.5 or 70.5 MHz. I've found it helps to avoid mistakes if you choose a CODAN frequency that is at a convenient integer step 0, 10 or 20 MHz below the actual transmit frequency, so that it avoids subtraction. 14200 and 71.5 =14201.5 is easy to understand, 14203 and 68.5 = 14201.5 is difficult to understand. The exception to this is if you are transmitting multiple carriers spaced over 40 MHz, in which case set the CODAN to some 10 MHz step nearest the middle. All the lower carriers will involve a negative calculations. Get someone else to check your maths before you turn the carrier on, transmit at very low power CW and observe the CW carrier in the downlink to verify the frequency before increasing the power.
Useful commands:
VPS view parameter settings
STA0 to STA25 set attenuator
STF14000 to STF14500 set frequency
SPA1 turn on
HLP help
Serial cable 3 wires RS232
Plug Mil Canon 14-19 MS3116F 19 pin.
D=0volts, H=TX data to CODAN, J=Rx data from CODAN
When setting the CODAN attenuator and modem output level avoid extreme settings such as modem output at minimum and CODAN at zero attenuation or modem output at maximum and CODAN attenuation at 25 dB. I suggest starting with the CODAN at 25 dB, and expect to end up between 5 and 15 dB.
If you have some expensive SSPA take extreme care to not to accidentally overdrive it and thus damage it. Always start with modem output level at minimum and monitor the HPA output if possible.
Best regards, Eric.
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