G4DDK Nacton Transverter on 71MHz

The place to discuss reduced bandwidth fast scan amateur television on 70cms and below
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G4FRE
Posts: 52
Joined: Fri May 26, 2017 6:57 am

G4DDK Nacton Transverter on 71MHz

Post by G4FRE » Wed Sep 12, 2018 6:57 pm

After previously experiencing the consequences of insufficient filtering on my 4m RB-TV down converter, I started to look in the"previous projects box for alternatives. I came across my old Nacton 70/28MHz Transverter and wondered if I could modify it for 71/437 MHz up and down converter operation. I removed the 42MHz xtal and disabled the onboard oscillator. The needed L.O. was provided by an AD4351 oscillator board, programmed to 366 MHz. The onboard 42 MHz BPF was changed to a 366MHz BPF. Transmit down conversion needed no further modification and produced the expected 50mW output. 71 to 437 upconversion needed the post mixer 28MHz BPF changing to a 437Mhz BPF, the converter gave 2.2dB NF with 18dB gain.

I took the Transverter and a dipole on my trip to the Rugby Rally last month. Using the adalm pluto, with predriver (mine produces -10dBm only) and a 30w Module Amplifier into an HB9CV beaming East from home, signals were easily seen over the 69km path.

Next I want to make the LO switchable 366/362Mhz so I can also listen to the 4m beacons to check system performance

Dave
G4FRE
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G4FRE
Posts: 52
Joined: Fri May 26, 2017 6:57 am

Nacton Transverter on 71MHz, Portsdown tweaks

Post by G4FRE » Thu Nov 08, 2018 1:32 pm

Note that each of the 4 quadrants on the minitione display seem to have 4 quadrants. Discussing this with G8GKQ at the BATC convention suggested that an early range of BATC built modulator boards did not have the optimum component values for low rates, as used on 71MHz. My board was identified as being in that range. The needed Resistor changes are in the lower part of https://wiki.batc.org.uk/Filter_Modulator_ver2.

replace R24A with 86.6K
replace R24B with 43.2K
replace R24C with 32.4K
replace R24D with 21.5K

I replaced the resistors with 0603 sized resistors (as i got the part numbers wrong) rather than 0805 size

The issue has now been resolved, now I only see 4 quadrants

Dave
G4FRE

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