OverviewOverview
Rx front end, Tx exciter and VCO
Control Panel
IF and Audio
Base board
Synthesiser
1overview.tif 2Tx-Rx-VCO.tif 3ctrlPanel.tif 4IFandAudio.tif 5baseboard.tif 6synth.tif Plessey_UHF.pdf Plessey_80_160.pdf mrt8143.BIN (c) TONY BARTEL VK3ZOT V2.0 Ch6 = 52.525 with a 38.0MHz Xtal 6MTR8144.BIN Needs 37.9 MHz Xtal, 24 channels, 52.500 to 52.975 repeaters, Ch1 52.050, Ch2 52.525 simplex, Ch3 53.550/52.550 Ch4 53.575/52.575 etc.. And will work with the 100 channel head.
On the Tx-Rx-VCO board there is a TTL /8 chip thus achieving ~5MHz of
frequency span. Also a second xtal for a wider Rx/Tx frequency difference.
IC5 and IC6 is the divide by N, 4 + 8 bit binary MC14526 & MC14569
Max clk typ 5MHz @ 10V, actually, centered around 2.8MHz.
eprom 0x700 hex is 1792 dec. x 12.5KHz = 22.4MHz / 8 = 2.8MHz.
IC1 MC14069 Hex inverter
IC2 MC14013 dual D flip-flop
IC3 MC14568 Phase comparitor/presetable counter, does the 12.5/15KHz or 25/30KHz channel spacing.
IC4 MC14069 hex inverter
IC7 & IC8 74C374 latch, non inverting, stores the channel number.
IC9 2716 eprom, 5V only type, CMOS do not work, outputs don't go above 5V.
So with a max 1st VCO sweep frequency of 1.2MHz, (3MHz +- 0.6MHz) we can have
about 260 channels @ 30KHz or 320 @ 25KHz.The N values, 600 to 1000.
4.8MHz Xtal /64 =75Hz / 3 = 25KHz, / 5 = 15KHz, / 10 = 7.5KHz, / 12 = 6.25 KHz, / 15 = 5KHz
Set with jumpers and an eprom bit that selects 25 / 30 KHz or 12.5 / 15 KHz, then a further / 8
Also on the Rx board is a 53760KHz xtal and an empty xtal socket, on the IF board a crystal filter,
a 44.545 2nd LO xtal and a 455KHz final IF filter CFM455 E.
From the file Plessey_80_160.pdf mine is a Low Band unit, 80 - 84.99 unit.
Circuits above are UHF.
The synth circuit mentions 12.5 and 15KHz channel spacing.
IF, 44545 + 455 = 45000 which is divisable by both 30 and 25 KHz. Thus 1st IF 45.000 MHz.
My unit is Low band VHF.
For 82MHz, on the Rx & exciter board, the Rx VCO will be at 127MHz.
Mixing 127MHz with (53.760 x 2) => 19.48 / 8 => 2.435 MHz the LF PLL.
Tx, (53.760 x 2) - 82.0MHz => 25.52 / 8 => 3.19 MHz, both within the 2.18 to 3.4MHz range.
The 53.760 xtal sets the range the set will cover. A second xtal selectable by the eprom
allows a wider frequency range.
Sweet spot calculation, where PLL N is same for Tx and Rx.
45000 / 2 = 22500
(53760 x 2) - 22500 = 85.020 MHz with the LF PLL on 2.8125 MHz
With a PLL divide N of 750 for 30KHz.
Two remote head Channel boards one has a 10 and a 12 pos switch.
Another has a 12 pos switch and an A/B switch.
========== CTCSS ===============
A MC14569 programmable divider fed with 1.2 MHz an 82S23 prom or 2716 eprom maps
the channel number to a divisor. 1.2MHz / 64 / 155 (0x9b) => 123Hz
0xcd => 91.5 Hz, 0xff => 73.52 Hz
==== 6m centered on 53.25 MHz 25KHz spacing ====
53.25 + (45.0 / 2) = 75.75 / 2 => 37.875 Mhz the ideal Xtal
----------------
My xtals junk box has 13 x 37.900MHz and 27 x 38.100MHz Xtals, HOWZAT
Tx 52.525 with the 37.90MHz xtal, (37900 x 2) - 52525 = 23275 KHz / 12.5 => N of 1862 or 0x746
Rx 52.525 (37900 x 2) - (52525 +45000) = 21725 KHz / 12.5 = N of 1738 or 0x6ca, 2.715625 MHz on TP10
These N values match the eprom in the converted to 6m MTR8143.
Leaving the 53.760MHz xtal in in the unconverted unit, Tx and Rx will be 84.245MHz
My Eprom for a 37.900 MHz Xtal 52.525 in bold.
Rx
0000f0 ff ff ff ff ff ff ff ff 26 24 22 20 1e 1c ca 18
0001f0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 16 17
Tx
0002f0 ff ff ff ff ff ff ff ff 3a 3c 3e 40 42 44 46 48
0003f0 ff ff ff ff ff ff ff ff 17 17 17 17 17 17 17 17
With a CMOS eprom NMC2716Q the +5V is +6.5V, and doesn't work.
Use only "normal" NMOS eproms.
===== This MTR 8143 here has a 38.0MHz Xtal and eprom 36ch =====
With the 120ch head has 30 channels. One row here.
Rx
0000f0 ff ff ff ff 08 ec ea e8 e2 14 ba 2e 2c 2a 28 26
0001f0 ff ff ff ff 17 16 16 16 16 17 16 17 17 17 17 17
Tx
0002f0 ff ff ff ff 08 24 26 28 2e 4c 56 32 34 36 38 3a
0003f0 ff ff ff ff 17 17 17 17 17 17 17 17 17 17 17 17
At 0000ff and 0001ff we have 0x73a = 1850
(2 x 38000) - (1850 x 12.5) => 52.875 MHz (Lawson NSW) but needs tone
52.525MHz, Tx N = 1878 or 0x756 at Ch6 (bold above)
52.525MHz, Rx N = 1722 or 0x6ba
0x714 = 1812 x 12.5 = 22650 => 53.650 MHz (Maddens VK2RMP)
========== 2m calcs, formulae ============
Tx HEX N = ( (Xtal x 4) - F ) / Ref, 25 or 30KHz
Rx HEX N = ( (Xtal x 4) - (F + 45MHz) ) / Ref, 25 or 30KHz
147.0MHz center
147000 + 22500 = 169500 / 4 => 42.375MHz, N = 900
Junk box has 4 x 42.500MHz, fine, Tx N = 920
=========== eprom layout 2716 =============
A0 - A7 pins 8 down to 1, from channel switch
A8 p23 Mode bits and 2nd divider top 3 bits
A9 p22 Tx (lo)
A10 p19 (lo)
/OE p20 (lo)
/CE p18 (lo)
Data D0 p9, D1 p10, D2 p11, D3 p13, D4 p14, D5 p15, D6, p16, D7 p17
The UHF circuit shows:
pins 12 GND, 18, 19 and 20 wired lo
pins 22 and 24 +5 wired hi
A11 p21 not TX -- question re. 2716 or 2732
Here, I need to check the PCB and not believe the circuit where
there is no pin number for this Tx signal at the eprom.
From the eprom file, A9 p22 hi selects Tx.
The second half 1Kb of the eprom is not used, perhaps CTCSS or a Fuse-link 1k x 8 prom, gee that's old.
======== mode bits =======
0 to p5 2nd divider IC5
1 to p11 MC14526
2 to p14
3 hi= 25KHz, lo=30KHz or 12.5KHz jumpers??
4 no channel, sets UNLOCK led??
5 Alt Rx Xtal select
6 to pin 2 IC5
7 not used
MC14526: P0, P1, P2, P3 (Pins 5, 11, 14, 2) — These are the preset
data inputs. P0 is the LSB.
================== from the eprom generator code 120PROM.EXE table ========
Modified by Peter Nieuwendyk C/- Metro Communication Sydney 7/10/1988
From, To, RxN, TxN, Xtal 1
LowBand Tx hex = ( F - (Xtal x 2) in KHz) /Ref [15 KHz, LF VCO 27510 KHz]
LowBand Rx hex = ( F +45000 - (Xtal x 2) in KHz) /Ref [15 KHz, LF VCO 17490 KHz]
70.01,77.99,1166,1834,48.76
78.01,79.99,1534,1466,50.00 or 52.76 on PDF
80.01,84.99,1504,1496,51.255 or 53.76 on PDF
157.45,167.47,1166,1834,46.24
160.0,169.99,1166,1834,46.8775
170.01,174.0,1568,1432,47.8725
UHF Tx hex = ( F - (Xtal x 8) in KHz) /Ref [25 KHz]
UHF Rx hex = ( F - (Xtal x 8) -45000 in KHz) /Ref [25 KHz]
403.0,412.975,1100,700,48.1875, LF VCO on 17.5MHz, IF 45.0MHz [25KHz]
410.0,419.975,1100,700,49.0625
450.0,459.975,1100,700,54.0625
460.0,469.975,1100,700,55.3125
470.0,479.975,1100,700,56.5625
Rx 476.425 - 45 -(8x56.5625) =21.075, /25 =843 or 0x34b as found in the eprom CBPOLRX.BIN at Ch1
Tx 476.425 -(8x56.5625) =23.925, /25 =957 or 0x3bd Ch1 as 0xbd and 0x1b & 0x07 = 0x03
at locations 0x0ff and 0x1ff for Rx and 0x2ff and 0x3ff for Tx.
480.0,489.975,1100,700,57.8125
490.0,499.975,1100,700,59.0675
500.0,509.975,1100,700,60.3125
510.0,519.975,1100,700,61.5625
=========== From 80EPROM.EXE for the MTR-6/7000
70.01,84.99
148.0,174.0
403.0,419.975
450.000,519.975
Files here: CBPOLRX.BIN and cbpolrx.hex
DOSBOX seems to run the programs but there's a problem, within
120PROM.EXE 24CHN.EXE 24EPROM.EXE 24PROM.EXE 80EPROM.EXE
one can't save as entering "3" it acts like "2" in the menu.
But they can load a .BIN file and display the contents.
Programs 120CHNQL.EXE and 120ROMQL.EXE etc. overwrite a .BIN file, be careful.
Low Band complete unit
Control heads 120 channel and 12 & A/B
Xtal osc. and Harmonic filter mods, I didn't do it this way, 3-30p trimmers topside.
56p cap in the Xtal osc brings the frequency down to 38MHz with enough harmonics.
Power amp mods, 22p on T1 red and coils, only L4 3t on 5mm did it for me.
CTCSS board
Alan VK2ZIW