Understanding and Programming your RT85
DISCLAIMER : -
The drawings, proceedures and words are for
information only. No claims are expressed or implied as to the safety,
usefulness, or accuracy of this information. I will not accept any liability
for any damages caused to people or property from the using of this information
or from any associated links. Your actions are your responsibility - VERIFY and
CHECK information out before proceeding, and don't attempt anything without the
required skills, if you cannot agree to this, leave this page now . . . . . . .
Chris.
This exercise started when I was "given" an
RT85 for my 2 metre Amateur station several years ago , I decided to work them
out , hope this helps..
The frequency data is stored in eprom and is divided
into 2 groups which consist of a 3 byte sequence ( 24 bits ) . 17 bits are used
by the PLL and the remaining 7 bits for "aux" information. The first
block starting at 0001H is channel 0 reciever data. The data block finishes at
03EFH. Theoretically there is enough room for 80 channels. The next 16 bytes
are reserved for personality information - 03F0H to 03FFH . ( See the
programming sheet that AWA used to give to the customers, to aid them in
"programming" the radio) . Starting at 0400H is the transmitter data
and it is arranged identically to the recieve data block. Starting at 0000H is
the "scan" channel sequence, and this data fits between the PLL data
and there can be a maximum number of 32 channels scanned. This first drawing
will hopefully assist you in understanding what I just said. (I'm sorry for the
jpg size, but b&w didn't show up the highlighter)
Looking at the personality codes, the first byte holds
the radios programmed channel number , ie 64 ,80 whatever , this is entered in
"decimal", the next 3 bytes are made up of bits that are designated
"options" for the radio, and the chart below will make this clear
.
Operation - The 17 bits are loaded into the PLL IC701,
7 bits to the "a " counter which controls the prescaler divider and
10 bits for the "n" counter. There are 2 PLL systems which are
interconnected. A reference of 5.12Mhz is divided by 4 ( or 8 ) for the Tx side
and by 1024 for the "main" PLL. The Tx reference after division is
1.28 Mhz and applied to the phase detector ( IC103) . The error signal holds
the VCO ( Q108) on frequency to produce Fo. This is amplified by the PA. The
o/p is fed back to a mixer with the main PLL Fl to produce a difference (+/-)
of 20.48 Mhz. ( Tx IF ) This is divided by 16 (IC106) and fed back to the phase
detector ( 1.28Mhz) and lock is found. The "main " PLL after the
reference is divided by 1024 produces 5Khz reference to it's phase detector.
The error from this holds a VCO (Q707/708) on frequency to produce Fl for the
other PLL via the mixer and for the Rx ccts. This Fl is fed back through the
prescaler ( /63 or /64 ) , through the programable dividers and back to the
phase detector to hold the frequency selected. The "a " counter on
the count changes the pre-scaler divisor, the "n" counter being the
"main" counter. See diag below
There are a number of programmers about for RT85's ,
The original AWA , an EAY-06EK ; there has been one somebody did in "Basic"and there is an " exicom MRP70",
which I think is the best, ( If you have the lastest version software ) I don't
recomend hand coding an entire eprom, like I did the first time, as you could
be sitting at a calculator for hours, but if you need to change a channel or
two it is fairly easy . Look at the data of one that is close ( or several ) ,
you will most probably see the second byte is the same and won't require
changing , ( and see note at bottom ) The 3rd byte will need to be changed ;
just work out the offset and add or subtract it off your "close"
frequency . An example might be ; ( radio has no modifiers - ie not narrow band
etc. ) 147.825 Mhz Rx, is 40 C5 85 and we want to go up 25Kc to 147.850 Mhz Rx
, then add 5 to the third byte and the data becomes 85 to 8A. Doing a bit check
we find that the first byte is 40H. So the new frequency is 40,C5,8A . A bit
check you say? , first byte will need to be an 00 or 40H . This can be worked
out by writing out the 2nd and 3rd bytes in bit format and if it is even the
number is 00H , if odd its 40H . ( If the radio beeps at you , you got it
wrong! try the otherway, or possibly the "data" is incorrect. ) . The
Tx is the same , going from 147.225 to 147.250 Mhz . 147.225 data is 00 C6 05,
adding 5 to it gives C6 0A, checking the 1st byte we find it's still even so
the new data is 00 C6 0A. The offset value will be may be different for other
radios with different "modifiers" like narrow band , different
reference freq, etc. By examining the frequencies and the data you should be
able to work out whats happening.
Getting hold of a programmer makes life easy , the
basic program is useful as it can give you a dump of the new data, even the
software of the mrp70 is useful as it will give you that dump too, the hardware
that comes with it makes it easy by not having to unsolder any eproms . (
Incidently - if you want to put a socket on your daughter board, use a low
profile machine socket and re-solder the "inline" connectors with a
strip of veroboard under them to space them off the surface a bit. ) The next
drawing is a table from the MRP70 booklet, which I will include to show you
some of what versions of "RT85" are about. ( Quite apart from the
RT85 A , B, C's which are still basically the same , but have a different micro
and eprom , there is as well the "midlands" which are a copy of the
RT as well, and I have seen an "exicom" version as well . - it seems
they were considered a pretty good radio by the number of copies about! )
I have also modified half a dozen low band (70-85Mhz )
RT's for operation on 6 metres. I have had a complaint that one was deaf, and
needs re-alligning , but the one I have in my shack seems to work fine, (I have
another 2 spares and I haven't heard from the others.. ) The 6 metre
eprom file can be obtained from this link. It has 64
channels and basically covers everything in the 6M band for FM ( which isn't
much ! ). The modifications are below for getting your RT85 on 6. . . . . The
Tait 499 are also modifiable for 6 metres, here are the 2 roms for that. -
Rom 1 / Rom2
Good luck Chris.
{ Note: - The programmed values correspond to a bit
pattern that is applied to the counters. Some bit patterns are not valid which
means that the second byte must be incremented and the third byte is reset to
it's lowest valid bit pattern. It may be possible to get 2 valid solutions to a
frequency. ( Also the first byte maybe 01 or 41 combinations or others ,
depending on if the channel has tone or other options { Eg, the above example
147.225 Mhz , a 91.5Hz tone on Tx would be 42 C6 05 )} Unfortunately I never
was able to get any spec. sheets on the counters as they were priviledged
information. If anybody has the specs , email it to me please and I will write
the procedure to program it , without any "maybes" . If you have a
lot to do it is really best to get hold of some programmer software.}
ALLIGNMENT ( briefly)
Synthesizer - Ensure 13.8 volts is being
supplied. With Test Point 701 monitor the voltage. Less than 1.7 or greater
than 6 volts indiates the PLL is unlocked. A tone and "95" may be
displayed as well. Pick a channel that is mid-point frequency from your list,
and adjust L702 for a TP701 voltage of around 3.5. This is done to symetrically
centre ALL the channels PLL voltages. The Tx side , remove the exciter coax
(J366) and operate PTT. Adjust L107 monitoring TP101 for around 3.5 volts for
theTx, using a Tx mid frequency. Re-check the Rx and Tx test points again for
symetry around a centre frequency for all channels. Connect a freq. counter to
J365 and adjust CV701 for
f = (RX freq - 21.4Mhz) +- 200Hz . . . . for VHF (HB)
and UHF
f = (RX freq + 21.4 Mhz) +- 200Hz . . .for VHF
(LB)
(Usually by selectng a "mid" frequency
channel all the other channels fit into the PLL capture bandwidth, it is only
when trying to fit for example, CB and police bands (UHF), that are relatively
wide apart, that special attention may be needed to shoe horn them all
in)
Reciever allignment - all coax's re-connected,
Ensure 13.8 volts is being supplied.
Connect a voltmeter to CM202 pin 4 ( pin 2 is a
missing "key" pin), select the centre frequency channel. Connect a
freq. generator to the antenna input with the same Rx frequency. Use a minimum
signal strength to obtain results. Adjust L209 and L210 (VHF) or CV202 and
VC203 (UHF) for a maximum reading. Connect a voltmeter to pin 3 and adjust
L201,202,204,205 (VHF-low) or L201,202,204,205,206 (VHF-high), or
L201,202,203,204,205,206 (UHF). Adjust for a maximum reading, the voltage may
be negative until sufficently tuned. Gradually lower the injected RF signal
voltage into the Rx, re-adjusting all for a max voltage (and good tone if your
freq gen modulates audio as well). A reciever sensitivity of 0.2uV should be
possible, lower is better.
Transmitter allignment
Connect a 50w power meter to the antenna with a 50 ohm
load. Select the mid frequecy channel. Set RV502 fully clockwise. Ensure 13.8
volts is being supplied. Operate the PTT and adjust CV501, 502,503 for maximum
power output. ( UHF also do CV504). Re-adjust until they are all peaked. Adjust
RV502 for an output of 25 watts. - power high . {A lousy PA strip may only give
you 15 watts but I have seen better than 45 watts}. If de-power is used ( p302
and p303 on back of remote shorted), adjust RV501 for required output. CV102 on
the synth board may need re-peaking if insufficent output is obtained, or you
may be able to sneak a little bit more.
Deviation and mic gain.
With a dummy load on the antenna output, use a
deviation meter to set a deviation of a MAX of 5Khz with your normal voice and
mic distance. A good start is to have both the mic gain RV102 and deviation
RV101 set midway to start with. It is good to have another Rx , scanner etc
monitoring your transmitted voice quality so you can lift the loudness, cut out
background noise etc. Mic gain will affect the deviation level, adjust the two
inconjunction. RV103 sets the aux Tx audio level (CTCSS tone). Too much
deviation will result in reciever distortion. Too
TONE
A number of tone boards were used with the RT85 , the
simplist was an un-programmable "fixed tone" version that injected
into P358 , pin 6. The programmable version allowed the selected channel to
apply a different tone. It had another connection to the eprom board as well.
Further variations to connections were required if "selcall" was used
as well. Selcall was a coded data stream to alert another radio that you wish
to make contact.
Below is the pin-outs of J398 and 391 .
Some Links . . . . . .
Phil's RT85 page - If you got a low band 85 and want
to get on to 6 there's some good info here, as well as a programmer.
NSW Emergency services - Col has some info and
pictures of 85's, as well as work related pictures.
VK3BIZ's RT85 page - Information , source code and links
etc.
VK3BYY's RT85 page - Some more info, etc
VK3TAE's RT85 page - Some hints and tips, schematics,
bin files etc.
Mr Skinnys RT85 page - More info and pictures
etc.
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