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Re: Easy mode A RX



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On Sat, 31 Jul 1999 22:28:29 -7, ka7hbb@janel.navicom.com wrote:

>Please note that the uPD858 usuallu only get up into the low 28 mhz 
>without a crystal change.

Absolutely not true.  There are one or two pins at the high end of the
BCD code that are not used and tied to common.  It's been a while since
I've done this, but the programming range of the uPD858 is capable of
covering 26 to 30.  Of course, the radio is not broad enough to cover
that entire range at once, but the PLL chip is capable.  I have
modified several of these rigs over the years for 10/11 meter coverage,
so I know of which I speak.  I had my mobile rig setup to cover 26.5 to
29.0 with no dropoff in performance except at the very edges, no gaps
in coverage, and no crystal change was required.  There is even a mod
for the TX circuits to make it more broadband.  The coolest mod is to
replace the CB channel selector with a set of BCD thumbwheel switches
so you can dial in your freq directly.  Of course, you can get more
elaborate than that, but it was simple and easy, and there was a direct
correlation between what the switches read and your operating
frequency.

 
>  Also, I'll agree that some of the SSB CB's are more sensetive. I've 
>got an old SBE that picks up 11 meters alot better than my TS440. 
>Kinda like the old single band ham rigs. 

I'm not talking sensitivity, I'm talking selectivity and overall audio
quality of the RX.  Sensitivity is moot, anything below about .25 uV
only brings up the noise floor.


>   Back to the CB conversions. in 73 Magazine theres usually a 
>company that advertises CB to 10 meter conversions and don't forget.
>  IT DOESN"T HAVE TO TRANSMIT!  That means you can sometimes
>find the 11 meter SSB that doesn't XMIT for free!


There have been a lot of CB-to-10 conversions published in 73 over the
years, but I generally ignored them because they used crystal changes. 
I cut my teeth modifying CB rigs for CBers years ago, and that's when I
learned just how far you can take them up the band.  Before anyone
flames me for this, I will point out two things: 1) I haven't done this
sort of work for CBers in over 15 years, and 2) I *always* aligned the
rigs so that the PLL dropped out before they reached 28.0, unless the
person had a valid ham licence.

- -- 
Jim Shorney                   -->.<--Put complaints in this box
jshorney@inebraska.com
nu0c@amsat.org
NU0C
Lincoln, NE, USA
EN10KA
http://incolor.inetnebr.com/jshorney/
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