Bonkventures‎ > ‎

Scanner conversion

So I have a Uniden Bearcat UBC60XLT-2, which I bought used few years back.
It works perfectly, but I don't really have any proper use for it.
it covers the following bands:
  • 66-88MHz
  • 137-174MHz
  • 406-512MHz

I find 4m (70MHz) interesting so I promptly decided to modify the scanner in to a 4m band HT.
As the IF is 21.4MHz, it should be possible to filter out and amplify the 70MHz component.
So we need to tap the LO used on VHF-LOW, mute the audio some how, add in a 21.4MHz TX shift oscillator, add in some DBM or other mixer for upconversion (I'm planing using SA612 with 21.4MHz as the TX shift osc), some bandpass filtering to recover only the 70MHz product, amplify it (MAR-6 driving a MAV-11l), low pass filter it and last add in some T/R switch. Microphone amplifier can be a simple op-amp thing based on SM0VPO design and feeding the output of the PLL loopfilter via some suitably high inductor and cap. 

1st Order of business is to find the LO used on LOW-VHF and tap it with a buffer.
I'll likely use some small jfet like J310 to do it. The high input impedance should not load it too badly. It should be available both on at the PLL prescaler input pin. and LA1186 mixer LO input pin.
There is more space around the LA1186N pin, so I'll likely stuff the buffer underneath the pcb and bring the LO up via some thin coax.

The LO on LOW-VHF and HIGH-VHF is lowside with 21.4MHz IF. On UHF the LO is Frx - 21.4MHz / 3.


J310 based high impedance VHF buffer amplifier.
Panoramic Adaptor Tap, uses J310 as 1st stage

TX/RX switch and the logic for it, likely SW-239 from M/A-Com and some hexinverter or quadnand in SMD to drive it and other stuff.
GaAs SPDT Switch

Driving GaAs stuff without negative voltages

TX lowpass filter.

TX PA chain, likely MAR-6 + MAV-11l, or just MAR-6.

TX mixer, likely SA612 in smd.

NE602 primer

NXP AN1986 "Applying the oscillator of the SA602 in low-power mixer applications"

NXP AN1993 "High sensitivity applications of low-power RF/IF integrated circuits"

TX 21.4MHz shift oscillator. A simple source for 21.4MHz crystals is a scrap 21.4MHz filter.
The SA612 built-in oscillator is good enough for this.

Post TX mixer low pass filter.

Hole for microphone, microphone preamp with possibly some filtering. So mic capsule from some old cellphone and some op and as the filter and amplifier. Microphone preamp can be lifted from this Likely based on LM358 as those are cheap and I have a bunch in soic8. Some BSS138 or other fets in the VCC line for this to disconnect it on RX.

LM358 dual op- amp

PTT! There needs to be a PTT button somewhere and it needs to be small but sturdy, all while managing to fit everything inside the case. Along with a soic14 logic chip to do the T/R switching and enabling.

74HC00 quad nand
74HC04 hexinverter
BSS138 N-Channel Logic Level Enhancement Mode Field Effect Transistor

Some tech specs of the thing:
The 5V regulator seems to be a shunt regulator with 28ohm power resistor and 2SD1803.

TLC271C as likely PLL loopfilter part.

LA1186N Car FM receiver frontend as mixer:

NJM2070 as AF PA

MC3361 as FM demod and as IF mixer and IF amp

NPC SM5158A as PLL "up to 200MHz".