Testing Session 2
A lot of pre-work was carried out creating Excel spreadsheets with embedded VBA code, which calculate the required bytes for proposed frequency changes to both radios.
These could then be used to programme an Eeprom via the Arduino programmer
To start with, we worked on the “Ian” Radio (with the Plessey NJ8812 PLL chip in it), as this was closest to 2m band, and would require less adjustment to the VCO.
The Eeprom was programmed up, such that the first eight channels contained a selection of the original Eprom settings, ie transmitting around 170Mhz
The remaining channels were set up as follows
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"IAN" |
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Channel |
Frequency (MHz) |
Use |
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9 |
145.500000000000 |
FM Calling Channel |
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10 |
144.000000000000 |
Bottom of Band |
For alignment |
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11 |
145.000000000000 |
Mid Band |
For alignment |
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12 |
146.000000000000 |
Top of Band |
For alignment |
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13 |
145.512500000000 |
Simplex |
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14 |
145.525000000000 |
Simplex |
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15 |
145.537500000000 |
Simplex |
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15 |
145.162500000000 |
COLD ASHBY |
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COLD ASHBY RX |
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145.762500000000 |
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So, the new Eeprom was fitted and the radio powered on.
So firstly, we looked at the TX.
The radio transmitted as before (around 170MHz) with the transmitted frequency being monitored with a DFM and an SDR.
The PLL DC control voltage was monitored with a Voltmeter and seen to be around 4V DC.
With the TX frequency set to 145Mhz the voltage dropped and the PLL shut down.
By adjusting the variable Inductor on the PLL PCB we got the PLL to re-lock with the DC control voltage set to 4Vdc. This was then re-checked at 144MHz ad 146 MHz. The manual suggests doing this to ensure the control voltage does not hit the supply rails.
The transmit was checked out on the other test frequencies.
Then turning to Receive .. ..
The radio was producing no AF. This was traced to the CSCSS add-on board (Communications specialists TS-32). This card has an Audio Mute circuit. The AF signal is routed through the card. We tried disabling on the card, but this had no effect. We then took out the connection to the main Rx board and put in a link. We could now receive.
Finally, we realised there is a problem with the received frequency being off. Several attempts were made at quicky changing the Byte in the Eeprom, but to no avail. We got a link to a 2m Handset, but only by checking through various frequencies until we got a “hit”. This needs further investigation.