RadioBanter - View Single Post - Need help with extra channels in TRC-458 (858PLL)

March 11th 04, 12:27 PM

On 10 Mar 2004 09:40:20 -0800, (2LD751) wrote:

I have a TRC-458 (Has the 858 PLL). I need to replace the switches for
the extra channels. The mod that I found says to use two switches -
one SPST and one SPDT center off. The switches that are currently in
the radio (and are broken) are DPDT switches. The one in the S1
position only has two wires hooked up to it. The S2 has three wires.
The wires are soldered across both rows on each switch.

My question is this - should I replace the switches with what the mod
says or use the same switches as what's in there? I'm assuming that
the person that did the mod may not have had the right switches, so he
just used DPDT switches instead. The previous owner of the radio said
that the buttons on front, for the NB, etc... are also used with the
extra channels, but the mod I found makes no mention of extra channels
with these buttons.

Any ideas?

The thing with extra channel modifications are that each "tech" has
their own "style" WRT how the mod is implemented. I could not even
begin to fathom what the thought process was when the original mod was
made.

The only thing I can tell you is that the upd-858 PLL uses a BCD
(Binary coded decimal) encoder for the /N counter. The pins that are
of the most interest to channel expanders is 22, 21, 20, 19 and 13
(for the gap channels). In order to understand the relationship of how
each pin relates to frequency selection, it becomes helpful to create
a truth chart for the known frequencies. From there it become easy to
extrapolate additional frequencies.

This PLL is capable of synthesizing 399 individual "channels".
However, the radios bandwidth limits practical range to around 200
channels. A stock radio, with the factory crystals will start at
26.065, and end at 30.055 Mhz. The VCO can be tuned to any 2 Mhz
segment within that range.

IMHO, this Uniden 858 chassis has been my all time favorite CB
chassis. There were a lot of interesting modifications that could be
done, and it performed well too.

Dave
"Sandbagger"
http://home.ptd.net/~n3cvj