OH2FFY - CB Conversions
01/10/07
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When I moved to Finland I brought along with me , a few high quality CB
radios.
In Australia we have 2 types of cb , UHF , and 27mhz HF.
The
HF ones that I brought have 12 watts output on sideband and are very
well designed and made, with performance figures in the ballpark of
some ham
transceivers.
I used to do a lot of DXing on the CB band with many overseas contacts
, and from Australia, that is a long way.
They are however generally classed as unmodifiable.
This
was a deliberate action or agreement between the radio authorities and
the radio manufacturers in an effort to prevent tampering and obtaining
off
frequency usage.
But I brought them here because I was sure that
at least the components inside could be salvaged and used again in a
ham band TRX.
After many months pondering over the schematics I
have worked out a way of making them go down to at least 20 meters ,
perhaps even 40., but it is only practical to have it for one band.,
not switchable between bands.
This is more of a cabinet space limitation that an electronic one.
The PLL system would have to be removed and replaced with a stable VFO.
(perhaps huff and puffed)
I
am preparing to build a VFO now , and have drawn up the board ,
although it will be revised a few times yet depending upon the exact
size of components.(that i don't as yet have on hand)
Additionally 3 IF style transformer cans need to be rewound for the
receiver side and 4 for the transmit side.
Also
the (8) bandpass and low pass filters on the output need to be rewound
but they are very straight forward to do as they are air wound.
Apart
from that ,its just a matter of alignment., and unlike other CB
conversions to 10 meter this will preserve the full sensitivity and
output power of the radio ,and not be limited in any way.
This
radio (Uniden AX-144) has features like a real noise limiter (for
mobile use) , real USB (not
DSB) and a single conversion receiver (not direct conversion which are
not single signal radios.)
Oh yeah , and a real squelch and signal
meter (that might need to go if I put a digital frequency display in)
and a generously powered audio amplifier.
The VFO build is coming probably within this week.
Next week should be disassembly and removal of the now unused sections
of the radio.
The week after would be winding the coils.
Following that is reassembly.
Maybe , in about about a months time I will have a neat high performing
QRP radio for 20 meters. (1 month! , yeah he's optimistic:-)
If
I don't mess it up I will document the mods and put them up on this
website , as there is no one else that has ever done it , ,, that I
know of.
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The radio that I will be modifying is the Uniden AX-144.
The radio has the Uniden PC833 chassis which is common between many
different radios.
PC833, PC965, PB015
Cobra 146GTL:
Midland 6001/7000 (late):
Midland 79-260:
Pearce-Simpson Super Cheetah:
President P300:
President AR-144:
President AX 144:
Realistic TRC451:
Sears 663.3810:
Uniden PC244:
This is a close up of the PLL chip, VCO , clarifier offset and USB AM
and LSB offset circuitry.
Some parts of this will have to be removed, and some left.
This schematic part is from the AR-144 manual as my copy of the AX-144
one is quite fuzzy* -- They
are almost identical.
*I have since
located my original AX-144 schematic and
this is shown in proceeding pages.
