c22. Digital modes


Packet radio

Concentrated on using few different VHF/UHF rigs. All rigs had similar connection via a 5pin DIN connector with a 1:1 cable to the TNC
The equipment were Storno CQM612, CQP612, Shinwa MA452, SRA FN205 and Salora SRP24C and SRP25C. In one case
PYE Westminster was used, and AP2000 70cm rigs were wasted very much time with, but they were eventually discarded. See selections below to find notes.

b.90. Salora 2m VHF transceiver mods SRP25C (SRP24C)
b.91. SRA C-400 and C-500 VHF series rig mods, and 10m FM conversion for C-502
b.92. Storno 2m CQM/CQP612 mods and practice
b.95 PYE mods R18FM, R17FM, T30FM, W15FM, Europa
b.97 Shinwa 70cm rig mods MA452
b.99 AP-2000 70cm (Norwegian text article, figures missed)
Sometimes we used 70cm antennas shown on page a2

TNC's were mainly homebrew danish version of TNC2-DL, also one TNC2-DL and MFJ1270B




Tuning indicator for 300Bd AFSK.
My first packet radio TNC was KPC-2, and the only signals were on 20m. The AM2910 demodulator was impossible to tune in the 300bd signals, so a tuning unit was needed.
It is not possible to have the two ellipses to cross exactly 90, but with some experience you learn soon how they should look like.


The tuning unit.The possible shift frequencies were set to 1200/2200Hz and 1270/1070Hz, selected by a dpdt switch.
L1=L2 = 77mH (European standard). C1=C2 = 100nF, C3= 3,9nF, C4=22nF, C5 =2,2nF. C6 =68nF, C7 and C8 not used, C9 =220nF, C10 not used
Signal input is 1Vpp. An amplifier with uA741 with a signal level indicator were used, but they are usually not neccessary. The rig was Yaesu FT-7, also used Drake R-4C receiver.


Tools:

Packet radio test-box.
It is inserted between TNC and transceiver using an extra standardized cable, as mentioned above. It is available testpoints for PTT, TX-AF (modulation) and RX-AF
Have standardized the audio level to the transmitters on all my equipment, it is 100mV RMS into 1k load, so it is possible to adjust the transmitters with a single 1K resistor or connect to a TNC.
It is also mounted an SPST switch for PTT after the picture was taken.


#12.11. It is important to have available an RF pick-up tool as shown for RF level meters and frequency counters, it will work over the frequency range 10-500MHz, and may also be used to inject signal from a generator to RF coils when the receiver seem death.
Above 1000MHz with strip-line this is not effective, the coupler should be plane as shown in the second figure, but it is important to remember insulation for the pick-up wire.




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2004.10.07