RX description :

It is  relatively simple (see synopsis diagram joined)
For more details see the electric plan joined.
Its characteristics has been provided in the previous TX item.

INPUT CIRCUITS

The antenna input can be strapped by the two pin diodes if ptt signal is used
on the rx box.
If the pins diodes are not conducting  (when inactive ptt signal, high level) the hf signal
enter in mar8 RF amplifier. The mar8 gives 20db gain with 3.5db figure noise and 25db ip3.
 

FIRST MIXER

88It is done with a double gate fet transistor CF300.
This transistor can be replaced by 3SK183 or BF966S.
If C300 or BF966S used, you must place them in a 5mm diameter hole
In case of  3SK183 hole is smaller, 3mm diameter.
 

FIRST LOCAL OSCILLATOR

We find the same vco design than TX vco, printed coil and low phase noise.
The pll is controlled by pic from TX box through the two wired I2C bus.
Pll pin 10 must be grounded to have a different address than tx pll.
The oscillator is in supradyne  mode (local oscillator greater than rf input)
The first IF is 58.7MHz, the rx vco will cover 1240+58.7MHz to 1300+58.7MHz
But rx frequency display will be the rf input frequency.
Local oscillator vco has 100kHz step, like tx vco.
 

PROBLEM WITH 2 VCO

There are not only advantage to work with 2 vco for tx and rx.
Rx kit can receive interference from tx vco, the tx vco is always working.
For instance, if I transmit at 1299MHz, and I receive 59Mhz lower at 1240MHz
the tx vco will be 1299MHz, the rx vco in supradyne will be 1240+58.7Mhz =1298.7MHz.
The tx vco is very near rx local oscillator, only 300kHz, it will interfere and will
substitute to rx vco.
Therefore, in full duplex mode the duplexer will isolate the rx enter from tx carrier
and the kits have to be shielded with good precaution. Use by- pass components
for the 2 wires I2C and for 13v power.
I did tests and had no problem when the kits were shielded.
 

FIRST IF STAGES

It is built with 3 Neosid IF inductances, 0.33µH model 5049.
It is not a « plug and play » design, not a zero tune s.a.w
I  did not find cheap saw, or saw within the frequency I want.
The advantage of tunable IF inductance is the possibility of
choose the frequency, I chose 58.7Mhz to use cheap and standard crystals.
For 2nd mixer the crystal is 48MHz , the difference with 58.7MHz gives 10.7MHz
for the 2nd IF frequency.
The IF amplifier is a double gate fet transistor BF980 (or BF960)
 

DEMODULATOR

It is a large band demodulator MC3356 used for many functions.
Data sheet gives 250khz bandpass that can give maximum 500kb/s speed.
First, we find  an internal mixer. The local oscillator is external , made with
the transistor BFY90 ands its 48MHz crystal.
The output of mixer gives 10.7MHz.
This output goes through a 10.7MHz large band ceramic filter 10.7MA5.
This filter has a 280kHz bandwidth.
The FM demodulation is a quadrature type. The inductance 5056, value 2µH
get the 90° dephasing for demodulation.
This coil is centred to 10.7MHz. It can be replaced by a 10.7MHz inductance
with capacity inside. In this case remove the external 120pF in parallel with this inductance.
The 10k resistance in parallel with the 5056 inductance make a light damping and decrease
the bandwidth. If you want traffic up to 115kb/s it will be better to lower its value, (4.7k).
A 4.7k will reduce the output level but increase the bandwidth.
The demodulator gives different outputs: rssi (S-meter), squelch indicator for dcd
used only if you don’t work on open squelch.
Thera are two outputs for rxdatas, one output named rx-mod is analog signal, this
output will be used for packet and for wbfm voice.
The other output rxd is digital signal, square shaped signal. It has passed through
an internal data-slicer. Not usefull for packet because all hams packet modem
have their own data-slicer.
The rxd output is muted if received level is too low.
 

POWER SUPPLY

To avoid interference between tx and rx, regulators and supply switch
provide each kit.
The 5v via 7805 is permanent. The 8v via 7808 is switched by the transistor BD136 if
ptt signal is active (grounded). The switched 8v will make conduct the two pin diodes.
When these diodes conduct, the rf input is cut against tx carrier interference.
The 13v switched  (by a BD262 or BD680) provide supply for all rx stages
except the demodulator.
This 13v is switched if 8v is not switched.
For full duplex the ptt signal is not required on the rx kit. Then you can omit
the BD136, the bd262 (or BD680) will be replaced by a strap, and you can remove
the two pin diodes BA479.

RX ASSEMBLY (See the PCB design plan joined)
We find again the same type of tx pcb.
See also the implantation plan joined
The tx parts on the implantation plan is not draw
Parts for pic, PA and last mar8 must be free, except
if kit is used for  one-box tx/rx .

The pcb is a FR4 double side, 16/10mm
The components side is totally coppered and used as a ground area.
Most of holes are 0.7mm diameter and isolated on the copper side
with à 2mm diameter. Don’t isolate ground pass holes.
Drill 3 bigs holes 5mm diameter for placing the transistors
bfr91a, BF980 (BF960) and CF300. If CF300 is replaced by 3SK183
its hole is only 3mm diameter.

Decoupling 1nF capas for CF300 are trapezoid shaped crossing the pcb.
Drill  2 rectangular holes to put the decoupling capas inside.
These 2 capas are soldered along the g2 and source lead of CF300.

Be careful when soldering the trapezoid capas,  the ground side of capa is to be soldered
on the components side of pcb in front of  the coil 5049. The capas fixed on
the g2 and source leads must be soldered on the layer side, in front of the rf strip lines.
Once the trapezoid capas have been soldered, check with an ohmmeter, be sure that
the g2 and source of CF300 do not touch the ground.
If trapezoid capas are not available, you can put ordinary small capas, two or
three by lead, don’t let a piece of lead not decoupled.

PIN CONNECTIONS

For CF300 or 3SK183, and BF980 or BF960, lead with little rectangular piece
is source, long lead is drain, g1 is front of drain and g2 is front of source.
For bfr91A, long lead is collector, middle is emitter, base front of collector.

NEOSIDS INDUCTANCES

Cut useless pins and useless can leads. Try to solder cans all around to ground.
Be careful, 5049 and 5056 inductances have not useless pin on the same side.
 

BFY90
This transistor has a fourth lead joining its package for ground.
You can cut it or solder to ground.
 

DON’T FORGET GROUND FOR :

 -holes around the little rectangular ground plane on the layer side.
 -Pin 17 and 10 of pll TSA5511, pin 19 and 1 of MC3356.
  For pin 19 of MC3356, hole in pcb is not done, you have to cut
  the pin short and solder it on ground, on component side.
  Use a thin soldering iron tip.
-ground of crystal 48MHz, under the resistance r 8.2k
-ground hole of the middle inductance 5049
-end of the two strips lines of rf front end.
-ground of the two mar8 made like for tx with a piece of wire in U form
  solder on the component side, cut short on the mar8 side, and put the mar8 after.
 Mar8 are fragiles, to put at least, don’t let the iron too long.
 They are good when they have between 0.7v and 2.5v in the input.
 

ADJUSTMENTS

In high speed, human ears are not usefull when tuning and checking the rx.
In 38kb/s and more we don’t hear anything, not even the noise.
The oscilloscope become an indispensable tool.
Moreover, in 1.2GHz traffic and high speed, you have a very little luck that your
neighbour, in front your home, will give you the carrier for tuning your rx.
That is why the tx kit has to be built before the rx, it will be a 1.2G generator
for adjust IF parts, demodulator and rf trimmers.
 

MINIMUM INSTRUMENTS REQUIRED

-Voltmeter, with digital display.
-Oscilloscope, minimum 20MHz
-The tx kit as 1.2G generator.

OPTIONAL INSTRUMENTS

-Frequency counter up to 1.4GHz
-Modem connected to the tx kit, to see eye pattern on the rx output.
-Professional generator from 50MHz to 1.4GHz.

PRELIMINARY

-Internal bf modulation , 12.5kHz with squared signal :
 On the tx kit the deviation R 100ohms will be set on middle.
 Put a R 12k between pin 7 of tx pll TSA5511 and 5v supply.
 Link up this pin 7 to the input of db9 connector to txdatas (see electric tx diagram)
-Set TX frequency to 1240.00MHz (value on the lcd displayer)
-Set RX frequency to 1240.00MHz (value on the lcd displayer) rx vco will be 1298.700MHz
-Set squelch R 2.2kohms to open squelch, cursor near R 100k.
 

FAR WIRED LINK TX/RX KITS

For rx tuning and checking, the tx kit must be
moved away from rx.
Link the kits with a multi-conductors wire, several meters, for
13v supply, sda, scl for I2C bus and ground.
Don’t start the PA of TX, let the ptt signal off, (high level)
The few mW of tx vco is enough for the rx adjust.
To make an antenna you can put a little piece of wire (15cm) on the output
of the first mar8 of tx kit.

CHRONOLOGICAL ADJUSTMENTS

The adjustments must respect the following timing :
1)  Fine tune vco by reference frequency crystal trimmer
2)  48MHz oscillator, by 5049 inductance core.
3)  Demodulator, discri, by 5056 inductance core
4)  First 58.7MHz IF filters, by the three 5049 inductances cores.
5)  Front end rf input, by the three trimmers on the strip lines.
6)  Deviation, by the R 100ohms on tx kit.
7)  Squelch threshold, by adjust R 2.2k, optional, only if dcd signal is used.

FINE TUNE VCO

We have the same problem for the kit tx, if frequency counter
is not available, it we be not easy to know frequency.
You can put the trimmer near the 6.4MHz crystal to middle position
and you will take back tuning when you will adjust  the demodulator.
Otherwise, if you have a frequency counter, adjust this trimmer
after 5min :
For tx kit  at 1240.00MHz with +/-1kHz, (remove 12.5kHz bf modulation)
For rx kit  at 1298.70MHz with +/-1kHz (remind that displayer will be 1240.00MHz)

48 MHz OSCILLATOR

Put oscilloscope to pin 3 of MC3356 and unscrew the core 5049
near the oscillator BFY90. You must see a green strip.
The tuning will be good when the oscillator always start after multiple power on and power off.
We will take back this tuning after IF adjusting.

10.7 MHZ DEMODULATOR

Approach the tx kit modulated with square 12.5kHz.
Put the oscilloscope in dc position to the pin 13 of MC3356, (analog data output.)
Unscrew the 5056 inductance core to see the 12.5kHz square. This square must get the
maximum amplitude.
Reduce deviation, via 100ohms R on tx kit, the square on output rx must decrease.
Take back the 5056 tune to centre the square. The tuning will be good when
the up line and down line of the square have the same noise thickness.
If up line is clean and down line is noisy, the square is too high, inversely
the square is too low.
If you find difficulty to centre the square, and no disposal frequency counter,
may be the tx carrier and  rx frequency  do not coincide,
now you can take back the two trimmers (tx and rx kit) near the 6.4MHz crystals .
 
 

58.7 MHZ IF TUNING

Put back the 100ohms r adjust for deviation on middle.(on the tx kit)
Oscilloscope always on pin 13 of MC3356 but in ac mode.
Move away the tx kit from rx to reduce the received level.
First tune the last inductance 5049 near the MC3356, to reduce the noise
and increase the square amplitude.
Same with the 2nd 5049 inductance.
At least the first 5049 inductance, but this tuning has a little effect  because
the output of CF300 is damping this filter.
When the square seems clean, retire the oscilloscope and put the digital
voltmeter on pin 14 of MC3356 (S-meter pin).
Take back the three IF filters to maximise the tension on pin 14.
A good value is a dc tension between 2v and 3v on pin 14.
48MHz level oscillator can give more sensitivity of the MC3356
You can take back its tune by the core of its 5049 inductance
to increase tension on pin 14 of MC3356.
Be sure that this 48MHz oscillator will always run after multiple power on and off.

RF FRONT END TUNING

To do with the three trimmers fixed on the hf strip lines.
The effect of this tuning is tangible only if the rx kit is shielded inside its metal box.
It is to canalise the received hf to the mar8 amplifier. If the rx kit is not
in its metal box, the tx carrier will pass directly to the input of the mixer CF300
and the three trimmers will not get effect.
Put a piece of wire (15cm) on the input bnc antenna of rx kit.
Put the oscilloscope in mode ac at the pin 13 of MC3356.
Move away the tx kit and remove its antenna wire.
The received square must be maximum noisy, if not enough noisy
remove also the rx antenna wire.
Tune the three hf trimmers to minimise the noise.
If noise disappear totally, take again the digital voltmeter
on the pin 14 of MC3356 and tune the three trimmers for a maximum level.
 
 

DEVIATION ADJUSTMENT

The definitive adjustment for deviation (R 100ohms on tx kit)
must be done with the modem connected to the tx.
This tuning is not critical in high speed and wide band traffic.
We have just to put it to the maximum before distortion
of the demodulated signal.
With a big deviation we are more protected against BER (bit error rate)
but we wide the channel, there is enough place on 23cm band, it is not a problem.
If you go higher in speed (76kb ore more) deviation must be greater.
The demodulator will give its maximum for +/-75k Hz to +/-100kHz deviation.
This maximum eye pattern amplitude will be around 2v pep on pin 13 of MC3356.
Tuning :
Remove the internal 12.5kHz square modulation and connect
the modem in db9 input of tx kit.
Put the tx kit near the rx.
See the eye pattern with the oscilloscope in dc mode at pin 13 of MC3356.
Adjust the deviation 100ohms on the tx kit to maximum amplitude of received signal
just before distortion.
If the eye pattern is include within 1v to 2v pep, it is good.
 

SQUELCH THRESHOLD ADJUST

For hams who want to use dcd signal they can adjust the r 2.2k on the rx kit
for strong received carriers or medium carriers. It is up to them.
If  you don’t use dcd, put this R on the open squelch position, cursor
on the side near the r 100k.

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RX PART LIST

SEMICONDUCTORS
1 pll Philips TSA5511 package dil 18 pins
1 demodulator wide band MC3356
2  amplis MAR8 or ERA3
1 transistor CF300 or BF966S or 3SK183
1 transistor BF980 or BF960
1 transistor BFR91A
1 transistor BFY90
1 transistor BD136
1 transistor BD262   or BD680
1 transistor BC547   or BC548
2 diodes pin BA479    (standard or smd)
1 diode varicap BB405 (standard or smd )
1 diode zener 7.5v  low power
1 regulator 7805
1 regulator 7808

Inductances, filters and crystals
3 selfs choke axials  50 to 100 µH
1 coil to built  0.3mm lenght of wire 6cm, diameter 1.5mm
4 Neosid inductances model 5049 0.33 µH
1 Neosid inductance model 5056 2 µH or 10.7Mhz coil
1 ceramic filter  Murata 10.7MA5 pass band = 280khz
1 crystal  6.4Mhz
1 crystal 48.Mhz

FIXED CAPACITORS
1    100 µF 25v   radial
3    6.8 µF 25v   radial
2      1 µF 25v   radial
3    150nF ceramic
2    100nF ceramic
14    10nF ceramic
1    3.3nF ceramic
4      1nF ceramic
2    0.5nF a 1nF trapezoid
4      1nF smd lenght 3.2mm
2    220pF ceramic
3    120pF ceramic
1     33pF ceramic
3     27pF ceramic
1     22pF ceramic
1     15pF ceramic
1     12pF ceramic
1    2.2pF smd  lenght 3.2mm
1    1.8pF ceramic
1      1pF smd lenght 3.2mm

ADJUSTABLE CAPACITORS
3 capas 3pf piston to fix on pcb
or 3 capas 2pf teflon, philips CO50, diam.5mm, 2 leads

1 capa  10/47pF
 

FIXED RESISTANCES  1/4watt
1    180k
1    100k
2     47k
3     15k
1     18k
11    10k
1    8.2k
1    4.7k
3    3.3k
1    2.2k
1      1k
2    470 ohms
1    390 ohms
2    330 ohms
1    270 ohms
1    150 ohms
1    120 ohms
4    100 ohms
2    100 ohms smd lenght 3.2mm
1     68 ohms
1     56 ohms
1     10 ohms smd lenght  3.2mm

ADJUSTABLE RESISTANCES
1   2.2k flat position

OTHERS
1 pcb 160mm x 100mm, epoxy FR4 double side 16/10eme
 with one side totally coppered, side for components.
 Most holes are 0.7mm diameter and isolated with 2mm diameter on the components side,
except for ground pass holes.
1  metal box 102 x 162 x 30 mm
1 bnc female 50 Ohms
1 by pass 1nF
1 db9 connector male

ACKNOWLEDGMENT
I thank Bernard F6BVP for his encouragement and his help for creation of my web pages.
Bas PE1JPD who built the original kit.
Laurent F5SOH who built the printed  vco and make the pcb design.
And all the others hams who helped me with material or finance to achieve this project.
I hope that my contribution will encourage hams to start the high speed packet.

Mes 73 de Victor F1BIU

packet address F1BIU@F6RAC.FRPA.FRA.EU