Project Introduction

General

Background

This kit, designed by Jan G0BBL and implemented and distributed by Tony KB9YIG, is a plug-in board for the Softrock Lite + Xtall RX V9.0 which down-converts VHF signals in the 2m and 6m bands to HF signals that can be received on the V9.0 RX. Also documented here is a 4m version (four metres, for our EU friends), courtesy of Bob G8VOI. The parts for the 4m version are included in the kit, with the exception of two capacitors (2.2 pF and 120 pF ceramic) which the builder must obtain. In addition, the schematic calls for band-specific parts C15 and L5; however, these were subsequencly dropped from the final design as unnecessary.

The builder will find invaluable information at the website of Fred PE0FKO, especially the setup of the software and firmware, as documented in the excellent users manual from Bob G8VOI.

Theory of Operation

Block Diagram

Relationship to Lite + Xtall RX V9.0

The converter plugs into the Softrock Lite + Xtall V9.0 RX at the on-board jacks J1 and J2. Power comes from the V9.0 RX’s 12 Vdc bus (on pin 3 of J2). The down-converted VHF signals are fed to the V9.0 RX QSD circuit via pins 7-9 of J1/P100.

Input.

The incoming signal from the Antenna terminal (or, via a jumper wire from J1/P100 Pin 1) , e.g., 144MHz, is pre-amplified by Q1 and fed to a double-balanced mixer, U1.

Mixing

U1 also receives a Local Oscillator signal via pin 4 of V9.0 RX’s J1. This local oscillator signal must be at a frequency (e.g., 115.2 MHz) which, when mixed with the incoming 144 MHz signal, will produce both a difference (144 - 115.2 = 28.8MHz) and the sum (144 + 115.2MHz = 259.2MHz). Fred PE0FKO's Firmware handles this translation. See notes below on how to program the Local Oscillator to result in an IF frequency that is equal to the V9.0 RX’s quadrature clock frequency.

Intermediate Frequency (IF)

The output of the mixer at U1’s pin 2 is filtered to remove the sum (image frequency). The (difference) IF is transformed into two anti-phase signals by T1 and fed to the V9.0 RX’s Quadrature Sampling Detector via pins 7-9 of J1 (in lieu of the usual BPF output for normal HF RX).

Tuning

Tuning the band is then done in the V9.0 RX on signals centering around the quadrature clock frequency (converted in software to the corresponding VHF frequency display values.

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Calculating the LO Frequencies

Care must be taken to calculate the LO frequencies so as to arrive at an IF that is exactly equal to the quadrature clock frequency. This is done using a multiplier factor that is specific to the band. This multiplier for 2m is 0.8; for 4m and 6m it is (4/3).

Calculation of LO frequency for 2m band

To determine the correct frequency for the SI570 for the 2m band, multiply the Desired VHF frequency by 0.8 - see following table:

VHF	LO=0.8*VHF	Quad = LO/4	IF=VHF-(4*quad)	Shortcut = 0.2*VHF
144.00	115.20	28.80	28.80	28.80
145.00	116.00	29.00	29.00	29.00
146.00	116.80	29.20	29.20	29.20
147.00	117.60	29.40	29.40	29.40
148.00	118.40	29.60	29.60	29.60

Calculation of LO frequency for 6m band

To determine the correct frequency for the SI570 for the 6m band, multiply the Desired VHF frequency by (4/3)- see following table:

VHF	LO=(4/3)*VHF	Quad = LO/4	IF = VHF - (4*quad)	Shortcut = (1/3)*VHF
50.00	66.67	16.67	16.67	16.67
51.00	68.00	17.00	17.00	17.00
52.00	69.33	17.33	17.33	17.33
53.00	70.67	17.67	17.67	17.67
54.00	72.00	18.00	18.00	18.00

Calculation of LO frequency for (EU) 4m band

To determine the correct frequency for the SI570 for the (EU) 4m band, multiply the Desired VHF frequency by (4/3)- see following table:

VHF	LO=(4/3)*VHF	Quad = LO/4	IF = VHF - (4*quad)	Shortcut = (1/3)*VHF
70.00	93.33	23.33	23.33	23.33
70.15	93.53	23.38	23.38	23.38
70.30	93.73	23.43	23.43	23.43
70.50	94.00	23.50	23.50	23.50

I/Q Swapping

For the bands below 2m (i.e., 6m and, in the EU, 4m) the LO frequency will be higher than the desired VHF frequency. This calls for swapping the I and Q leads from their normal ring/tip orientation.

Project Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

Project Bill of Materials

See Project Bill of Materials

Project Expert's (terse) Build Notes

• Verify BOM
• Install Components
• Test the Kit

Project Detailed Build Notes

For the non-expert builders among us, this site takes you through a stage-by-stage build of the kit. Each stage is self-contained and outlines the steps to build and test the stage. This ensures that you will have a much better chance of success once you reach the last step, since you will have successfully built and tested each preceding stage before moving on to the next stage.

Each stage is listed below, in build order, and you can link to it by clicking on its name below (or in the header and/or footer of each web page).

• Inventory the Bill of Materials
• Build and Test the Power Bus Stage
• Build and Test the Inductors Stage
• Build and Test the Remainder Stage

Background Info

Tools

Winding Inductors

To learn how to wind coils and transformers, please read the

• tips from the experts and then
• view the excellent videos on KC0WOXs Website
• or take a read of Dinesh's VU2FD guidelines.
• You can review the common construction techniques for inductors for details on toroidal and binocular inductors.

Soldering

If you are not experienced at soldering (and even if you are somewhat experienced at soldering), refer to Tom N0SS's excellent tutorial on basic soldering techniques.

The video below describes techniques for soldering SOIC 14 (and 16 and 8) SMDs

View the above in full-screen mode on Youtube.

For the more adventurous, there is a process using solder paste and an electric oven called the reflow process, which can be used to install all the SMT chips to one side of the PC Board. This is documented by Guenael Jouchet in the following Youtube segment:

• Read the Primer on SMT Soldering at the Sparkfun site.  It is a very good read and it speaks great truths.  Then take the time to watch the video tutorial on soldering an SOIC SMD IC.
• Solder Stations. Don't skimp here. Soldering deficiencies account for 80 percent of the problems surfaced in troubleshooting. It is preferable to have an ESD-safe station, with a grounded tip. A couple of good stations that are relatively inexpensive are:
  • 
    Velleman VTSS5U 50W Solder Station (approx $20 at Frys)
  • 
    Haakko 936 ESD Solder Station (under $100) 

ESD Protection

• Avoid carpets in cool, dry areas.
• Leave PC cards and memory modules in their anti-static packaging until ready to be installed.
• Dissipate static electricity before handling any system components (PC cards, memory modules) by touching a grounded metal object, such as the system unit unpainted metal chassis.
• If possible, use antistatic devices, such as wrist straps and antistatic mats (see Radio Shack's Set for $25 or the JameCo AntiStatic mat for $15)).
• Always hold a PC card or memory module by its edges. Avoid touching the contacts and components on the memory module.
• Before removing chips from insulator, put on the wrist strap connected to the ESD mat. All work with CMOS chips should be done with the wrist strap on.
• As an added precaution before first touching a chip, you should touch a finger to a grounded metal surface.
• If using a DMM, its outside should be in contact with the ground of the ESD mat, and both leads shorted to this ground before use.
• See the review of ESD Precautions at this link.

Work Area

• You will need a well-lit work area and a minimum of 3X magnification (the author uses a cheap magnifying fluorescent light with a 3X lens. This is supplemented by a hand-held 10 X loupe - with light - for close-in inspection of solder joints and SMT installation.
• You should use a cookie sheet or baking pan (with four sides raised approximately a half an inch) for your actual work space. It is highly recommended for building on top of in order to catch stray parts, especially the tiny SMT chips which, once they are launched by an errant tweezer squeeze, are nigh on impossible to find if they are not caught on the cookie sheet.

Misc Tools

• It is most important to solidly clamp the PCB in a holder when soldering. A "third-hand" (e.g., Panavise or the Hendricks kits PCB Vise) can hold your board while soldering.   In a pinch, you can get by with a simple third-hand, alligator clip vise. Jan G0BBL suggests "A very cheap way is to screw a Large Document Clip to a woodblock which will clamp the side of a PCB."
• Magnifying Head Strap
• Tweezers (bent tip is preferable).
• A toothpick and some beeswax - these can be used to pickup SMT devices and hold them steady while soldering.
• Diagonal side cutters.
• Small, rounded jaw needle-nose pliers.
• Set of jewelers' screwdrivers
• An Exacto knife.
• Fine-grit emery paper.

Project Testing

Each stage will have a "Testing" Section, outlining one or more tests that, when successfully completed, provide you with the confidence and assurance that you are heading in the right direction towards a fully tested and built transceiver.  

When you perform a test, you should always record the results of the test where indicated in the Testing section. This will make troubleshooting via the reflector much easier, since you will be communicating with the experts using a standard testing and measurement regime.

This kit can be built and reliably tested using nothing more than a common multimeter. Tests assume that the builder has a decent digital multimeter of sufficiently high input impedance as to minimize circuit loading issues.  Measurements will be taken of current draws, test point voltages, and resistances.

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