FSA3157 H-Mode RF Mixer Module for HF receiver-FedEx Fast Ship SV1AFN shop

Description

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H-Mode Mixer Module
as per PA3AKE description
With DAC or Potentiometer for bias control
With DAC or Potentiometer for LO wave symmetry
During the last 5 years I have built more than 15 units of these RF mixers, for friends and myself, using my hands only,
on pieces of double-sided copper clad boards and "ugly" construction methods. Every time I had one finished, I was staying
late in the lab measuring and checking possible improvements. If to increase LO power (voltage), how to have the best
symmetry all the times, how to adjust the bias independently of the frequency range, how to extend the frequency range, etc.
That last phone-call a couple of months ago, asking for another one,  made me decide to finally prepare a small PCB this time
and thus eliminate the need for making another one from the scratch again. I haven't made the PCB before, because I was
thinking I have nothing to add or modify as this is great already! These people (G3SBI, PA3AKE) have offered Amateur Radio
with an important advancement. For those who cannot fully understand the meaning of IPO3 and IMD figues on a mixer, I have
shot a photo of a SBL-1 mixer's IF output spectrum using the same test setup as with the h-mode mixer just to compare them visually.
​The PCB dimensions are 46.7 x 63.5 mm and all SMD components are factory soldered.
L1, L2, L3, P1, P2 and the SMA connectors are not soldered in place.
L1 and L2 are wound with 6-turns of 0.25 mm copper enameled wire on a BN43-2402.
They make  a choke of about 50 uH and they filter DC power as produced by the two Micrel voltage regulators.
One is fixed for 5V and the second is adjustable, set at 7V with R7 and R8.
L3 needs 7 turns of bifilar wire and it's purpose is to double the voltage of the applied LO signal and drive the 74AC04 inverters correctly.
For making L3, cut two lengths of about  35 cm of wire, twist them together for approx 4-5 turns per inch over all their length and wind 7 turns
into a BN43-2402 ferrite core. Remember one turn is counted when the wire enters the core from one side, call it front side, gets out from the
same hole of the opposite side, makes a u-turn to enter the next hole of the opposite side and comes out from the second hole of the front side.
So after winding 7 turns, both the start and end of the winding will come out from the same side. Now, there are 4 wire ends left there.
Actually they are 2 windings. With a multimeter, identify and separate those 2 windings apart, which is number 1 (the start and end of each
winding should beep the continuity tester) and which is number 2. Separate the start of winding number 1, the end of winding number 2,
and by shorting the remaining 2 wires together, this makes the center one. Then place as in the photo, the center goes to LO input and the
other two, polarity doesn't matter, to ground and 74AC04 input. If you have an oscilloscope you can check the LO input signal at say 0 dBm,
you should measure about 500 mVpp on L3 center pin and 1 Vpp on the not-grounded pin. This way you can check if L3's winding is OK.
Then you can find a 5 Vpp LO signal at pin 6 of  U5 as amplified by its inverters.
In order to optimize the circuit to perform its best, it is needed to apply a DC bias to two points. There is a choice for setting the DC bias at
these two points, one is with a manually adjusted trimmer potentiometer or with a DAC. The DAC can be used in a mutiband receiver system,
where evey time a new band or frequency range is selected, a controller can set the optimum DC bias using the I2C interface to control the DACs.
The first point is at the LO amplifer's output, and the DC bias should be set for the best symmetry of the LO signal where it is applied to the
FSA3157 switches and this can be controlled by P1 or DAC IC, U7. If uncertain or you don't have an oscilloscope to check, adjust trimmer
P1 for 2.5VDC on pin 6 of U6. If the DAC will be used, start with setting 2.5V and don't place P1. If P1 will be used then you will need to
remove R6. The board  should not be left with R6 and P1 together, one solution should be chosen.
The second point is T2's center pin. Proper adjustment of the bias level, reduces IMD products. R11 and R12 ensure biasing at 2.5VDC
without placing P2. On this case don't place P2 and remove R13 too. If the DAC will be used, don't place P2, remove R11, R12 and keep
R13 in place. For a quick test you can only remove R13 and keep R11 and R12 to provide 2.5V DC bias. If you need to adjust manually,
place P2, remove R11, R12 and R13. Again, one solution should be chosen.
Each DAC chip (U6 and U7) has its I2C addressing inputs tight to 5V via 10K resistors and all can be shorted to ground with jumpers,
in order to select different I2C address.
Pin-header J10, has 5 pins assigned as follows:
Pin 1 Ground
Pin 2 SDA
Pin 3: SCL
Pin 4: +5V output for checking
Pin 5: +12 VDC input
See more info at www.sv1afn.com under projects or directly to
https://www.sv1afn.com/fsa3157hmodemm.html
(copy and paste to your browser to work).
ORDERS For a complete DIY KIT
The KIT includes a  high-quality ENIG FR4 PCB (63.5 x 46.7 mm) that comes with all SMD components factory soldered.
RF capacitors are used for all the circuits.  Three SMA female connectors of the vertical mount type are also supplied together with 3 pcs BN43-2402, some 0.25 mm wire, 2 trimmer pots and 2 jumpers.
The shipping is with registered mail  (your signature is required upon delivery) or with FedEx, you can choose when ordering.
Check out my
other items
! I always combine shipping.