INTRODUCTION:

A half duplex version with 54 MHz tx/rx shift is working yet in about ten nodes at speeds of 38 kb/s to 76 kb/s in Holland.
The described version, here, is fully revised and improved.
My first concern was to find and stock up specifics components.
A pic micro-controller (16F84) replaces the original Atmel controller (not available easily). First IF frequency has been changed for using standards crystals (48 MHz) .
The vco is replaced by a " plug and play " version with printed coils. The vco runs at the first time after soldering.
The pll loop filter is changed for using G3RUH modulation and Manchester modulation.
The original version could only work with Manchester modulation.
All 23 cm band is covered with 100 kHz steps.
Changing frequency is comfortable, using two keys and frequency is displayed on LCD display, 1 line of 16 characters.
And the main modification is the separate boxes for TX and RX with their own pll and vco. Shift rx/tx is tunable with the value you want, and all modes are possible (full duplex, half duplex and simplex) ( see different modes on picture joined)

There are different possibilities :

- RX in one box with its frequency keys tune and the lcd display.
This RX will be built by listeners, swl, for no connect satellites packet at 38 kb/s and more. And for listening to wbfm voice. This RX kit can be built without hams license.
- TRX half duplex kit in one box, like original PE1JPD version.
Using only one pcb, but tx/rx shift is definitively fixed on one value 59 MHz in France, 54 MHz in Holland. You have to cut no standard crystal for 2nd mixer at 48.3 MHz for 59 MHz shift, or 64.7 MHz for 54 MHz shift.
- TRX full duplex in two separates boxes. One box for RX, the other for TX.
Each box has its own pll and vco, frequency tuning is totally independent.
You can choose the shift you want, including no shift for simplex mode.
Only one lcd display and only two tuning keys for controlling both the RX and the TX boxes.
This version can do half duplex and simplex modes, pins diodes are available on the two boxes, the antennas can be switched.
In any case, for every version, the vco are never switched to guaranty minimum TX delays.

TX CHARACTERISTICS:

- Synthesized channels from 1240 MHz to 1300 MHz with 100 kHz steps;
You can reduce step by readjusting reference frequency with the trimmer near the 6.4 MHz crystal;
- TX bandwidth modulation from 40 Hz to 180 kHz;
- Modems modulations possible fsk G3RUH and Manchester;
- Fm deviation from +/-15 kHz to +/-75 kHz;
- Printed coils vco with very reduced phase noise;
- Speed 38 kb/s to 115 kb/s;
- Txdelay (if used in mode half duplex and simplex) = 10 ms;
- Efficient speed =4k characters in 76 kb under tcp/ip protocol, half duplex mode;
- Tx channel width = 250 kHz;
- Tx power 2 Watts;
- Available signals on db9 connector : txdatas, ptt;
- Antenna output on BNC connector (can be changed);
- Metal box, europe format, size 160 mm x 100 mm x 50 mm;
- LCD display and tune keys fixed on the box.

RX CHARACTERISTICS:

- Synthesized channels from 1240 MHz to 1300 MHz with 100 kHz steps.
- Sensitivity around -100 dBm.
- Vco same type than TX vco.
- First IF RX 58.7 MHz, (59 MHz for one-box version) 2nd IF at 10.7 MHz.
- RX band pass width = 280 kHz.
- FM wide band demodulator, 250 kHz max or 500 kb/s.
- Available signals on db9 connector: rxdatas, rssi (s-meter), ptt, dcd
- Antenna input on BNC connector, (can be changed).
- Metal box, europe format, size 160 mm x 100 mm x 30 mm

TX DESCRIPTION: (see bloc diagram joined)

I begin here the TX description and construction.
It has to be mounted before RX kit, because it will be used as a 1.2 GHz generator for HF, IF and demodulation during RX adjustments.
When you look at the electric diagram joined you can see that TX kit can be understood without comments.
It is very simple.
The vco is directly at output frequency, no need multipliers.
The design of this vco is from Laurent F5SOH whose help was useful.
The pcb design is also from F5SOH.

PLL:

The pll is a TSA5511 from Philips, this pll equips tv tuners, very cheap and easy to find. Its input sensitivity is 100 mV, it has a prescaler by 8 and can work from 50 MHz to 1400 MHz. It is controlled by a two wired I2C bus with bi-directional protocol.
In the way in, it receives the division ratio number, given by the pic.
Its address is given by electric value on its pin 10.
For the TX this pin will be at 5v, for the RX at 0v, grounded.
With the two different address, I control both pll (TX and RX) with only one pic and one two wired bus I2C.
In the way out, the pll gives the pll status (locked or not locked).
I use this information and display it on the left of lcd display by the letter L for Locked or N for Not locked.
The reference pll crystal is a cheap 6.4 MHz, not accurate (50 ppm) that gives 300 Hz error to multiply by 1300/6.4, about 60 kHz that explains the trimmer next the crystal.
This trimmer can reduce the error to 1 kHz, it is largely enough for wide band TRX. You can also reduce the steps for 50 kHz or 25 kHz, by readjusting this trimmer (but display will not change).
This trimmer is to be tuned after 5 min, when temperature is stabilized.
The reference crystal does not need thermal regulation, for we are using wide band 250 kHz, a drift within 20 kHz is not important.
 

PLL LOOP FILTER:

It includes transistor BC547 and some RC filters. It has been calculated for low limit at 40 Hz and high limit at 180 kHz.
You can traffic on Manchester from 9.6 kb/s to 115 kb/s and on G3RUH from 38 kb/s to 115 kb/s.

POWER STAGE :

It uses an hybrid integrate circuit M67715 that gives 2 Watts.
It has a permanent vcc of 13v for its last stage and the 8v supply is made by a 7808 regulator.
The transistor BD136 will conduct if ptt signal is enabled (0v).
The 8v will supply both power hybrid i.c and the last mar8 preamplier.
The input sensitivity of the power ic is 10 mW.
This 10 mW are given by 2 monolithic amplifiers mar8 (or era3).
First amplifier is used as a buffer after the vco, to avoid the pulling effect.
The pulling effect is the variation of vco frequency when the the load of the power stage is changing.
The junction between the two mar8 is made by strip lines coupling.
It works like a HF transformer. This guaranty a minimum damping and a good impedance adaptation.

OUTPUT CIRCUITS:

It is made with two pin diodes that conduct when ptt signal is enabled (grounded).
Logically, these diodes are useless for full duplex mode, but they do not disturb.

PIC AND LCD DISPLAY :

Pic is a micro-controler which control at once the pll, the display, tuning keys and frequency memory.
I will no give more information about pics, see Microchip® company on its web page.
Keys freq+ and freq- are used to tune up and down frequency with 100 kHz steps.
Frequency memory is effective when keys are released. On the next power on you will find the two last frequency displayed before power off (TX and RX frequency).
The tx/rx switch permit to separate TX and RX frequency tune.
It is used only for setting frequency, don't put ptt signal on this switch.
The letters 'TX' or 'RX' on the right of display recalls us to know which box is now tuning (TX or RX box)

REALIZATION OF TX KIT:

The pcb is on a europe format, size 160 mm by 100 mm, double side in epoxy FR4 16/10 (see layer picture joined)
The RX and TX pcb are strictly the same but partially mounted.
On the implantation picture joined I represent only TX strips layers.
The components side is fully coppered and is used for ground plane.
Most of holes are 0.7 mm drilled with an isolation of 2 mm diameter on the components side.
The ground pass holes don't have to be isolated on the components side.
A drilled hole of 5 mm diameter will serve to put the vco bfr91a.
The long lead of bfr91a is its collector, the middle lead is the emitter.
The varactor diode bb405 and the 2 pins diodes ba479 are not necessarily smd but will be soldered like smd, on the printed side, cut their leads very short.
Don't forget ground for pin 5 of pic, 17 of  TX pll.
Pin 10 of  TX pll is to be isolated with 2 mm diameter on components side and connect this pin to 5v line on the 5v strip just near.
Mar8 amplifiers are fragile, for their ground, first solder a piece of wire (components leads) with U form on the component side. Then solder on the printed side and cut very short. Then you can put the mar8.
Don't let your soldering iron too long.
Pll must be placed directly on the pcb, don't forget its ground on pin 17.
Pic needs support, don't solder it on the pcb, soft updates can modify the program.
The little rectangular ground plane, on the printed side, is surrounded with small ground pass holes. Solder every holes through with a piece of wire and don't forget one. This little ground plane is a screen which protect the vco against troubles from the 2 watts of the power amplifier.
If this ground plane is not totally grounded, the pll could be out of lock.

FIXING THE POWER AMPLIFIER:

To do at least. Fix the power amplifier on the bended corner of the box  not the corner to be soldered.
Beforehand, the ground side, (components side) has to be soldered all around to the  metal box, specially behind the hybrid power amplifier.
If not done, the box will be transformed as an antenna and will trouble the pll that will lock out.
The ground of power amplifier is its heater. For tests before you put the kit in its box, you have to join 2 far points of the heater to ground area on the components side of pcb.
Not too long, the power amplifier get hot very quickly when not fixed on an external heater.

CONTROL VCO:

For test and control the vco, no need to supply the power amplifier.
With 10 mW without PA, you have margin for testing with frequency counter.
You can also do external link, around 2 km with the 10 mW power.
If you don't have frequency counter, you can see the letter L on the left of the display. This letter indicates that pll is locked.
The V tune on the varactor diode bb405 must change between 1v and 10v when you tune with the 2 keys freq+ and freq-.
Pin 7 and 6 of pll give the crystal frequency/512 and the vco divided frequency. Output pin 7 is a 12.5 kHz squared signal.
Output pin 6 is a positive edge impulsion at 12.5 kHz from divided vco. Vco is locked when these two signals are in phase no move between them when you see both signals on an oscilloscope.
These two outputs are open collector. If you want to see the signals, you must put R of 12 KOhms from the pins and the 5v supply.
The decoupling capacities must be a good quality ceramic for value under 470 nF.

ADJUSTMENTS:

Deviation adjustment (FM swing):
It is done with adjust R of 100 Ohms, the method will be seen after building the RX kit, because we have to see its effect on the demodulator output.

COST AND AVAILABILITY OF COMPONENTS:

The cost for the complete TRX kit is estimated at 175 EUROS (1200 FFrancs).
In France, all components are available at :

CHOLET-COMPOSANT
18 rue Richelieu
F-24660 Coulonieix Chamiers
France
Tel    +33 (0)5 53 05 43 94
FAX +33 (0)5 53 35 41 46
Ask for Mr Marcelaud with reference to me.

If you want more information contact me on my e-mail box
Have a good enjoyment building up this kit, and good high speed traffic.

My 73 de Victor F1BIU