23cm VLNA
Kit assembly notes
These notes refer specifically to the kit offered by G4DDK.
The PCBs are 1.6mm, FR4, double sided with plated through holes. The board is coated with immersion silver. Leaded or unleaded solder can be used on the board. The kit components that are supplied are all RoHS compliant.
The boards are solder resist coated (the green stuff) and silk screened to show component designations, i.e. R1, C1 etc.
1. File the small slots on the two corners of the PCB, as shown.
2. Temporarily, assemble the two sides of the box inside the bottom lid. Do not solder. Place the PCB inside the box so that the tin box side corners with the overlaps are in the same corners. Identify which is the rim of the box nearest the groundplane. You now need to mark a line (use a caliper/vernier) 10mm up from this rim. When the PCB is soldered in place this line marks the lower edge of the groundplane. TAKE CARE WHEN HANDLING THE BOX. THE EDGES CAN BE SHARP.
3. Offer up the PCB to the inside of the box with the input. Mark a point immediately above the gate position of Tr1 and 10mm down from the top rim. This is where the RF input connector goes. It will be about 8mm above the PCB.
4. Offer up the PCB to the other side of the box with the groundplane of the board against the 10mm line marked previously. Mark a point 12.5mm above the rim and level with the centre of the RF output pad. Also, mark a point immediately above the supply pad and 10mm down from the top rim. The points corresponding to the RF input and RF output connector should be drilled through with a 4mm drill. The hole for the feedthrough capacitor should be drilled to accept the size of feedthrough capacitor chosen. Drill with a high speed drill with the tinplate box sides held firmly against a piece of softwood to ensure a clean hole.
TAKE CARE WHEN HANDLING THE BOX. THE EDGES CAN BE SHARP.
5. Do not solder the PCB into the box yet.
From this point onwards, observe antistatic precautions. Better still, use them all the time!
6. Solder tantalums C14, 15, 16 and 17 onto the board USING 28SWG fast flux solder. Observe the tantalum capacitor polarities. Observe C14 in particular. These are all 20V working, as supplied in the kit. This gives slightly more room for soldering the caps down if you forgot before soldering the PCB into the box.
7. Solder the IC1 D-Pak regulator in place. There are only two leads and the tab. Keep the tab and capacitors as far from the edge of the board as you can to allow enough room to allow the fine point soldering iron to seam solder the board to the tinplate box. Also solder in R14 and D1.
18. Solder the PCB into the box. The top of the board behind the regulator should be soldered to the box end.
TAKE CARE WHEN HANDLING THE BOX. THE EDGES CAN BE SHARP.
9. Solder the RF input and output connectors to the outside of the box, ensuring the RF output connector centre spill doesn't short to the box. A reasonable seam of solder should ensure that the connectors are firmly mounted to the box. The RF output connector spill should be cut such that it doesn't interfere with C13. The RF input connector spill should be cut so that the spill protrudes no more than about 1mm into the box. Solder the feedthrough capacitor into the hole previously drilled. You should fit a suitable size hole solder tag between the feedthrough capacitor and the box before soldering.
10. Solder the remainder of the components (except Tr1, Tr2) onto the PCB. I find the best way to do this is to lightly tin ONE of the pads to which the SMD part will solder. Pick up the part with a small pair of stainless steel tweezers. Hold the part in place and solder the part to the tinned pad. Use 28swg fast flow solder and a fine point soldering iron. Very little solder is required. Once the part is soldered at one end, solder the other end of the part to the other pad. If it has more than two leads, solder the other leads to their respective pads. For Wartons fast flow solder (Rapid Electronics) I find that the soldering iron temperature is best set about 360C. When soldering parts to the larger ground pads the iron temperature might need to be increased to, say, 400C. Double check all component values. All resistors, inductors and capacitors are colour coded except R14 (trimmer) and the tantalum capacitors. Note that most components are 0603 size. The same colour code is used for the same values irrespective of whether SMD 0603 or 1206 size. Take care. 1206 is the larger size. USE ONLY 28SWG FAST FLOW SOLDER or similar. Small amounts of this, enough for the pre-amplifier board, are available from Rapid Electronics of Colchester as part of the SMD re-work kit (85-6276). 22swg solder can be used for the seam soldering and box seams.
11. Wind L1 and L2 as shown and tin the ends with a hot iron to remove the insulation. It is not a good idea to breath in the fumes from the hot wire insulation. Ensure you use a fume extractor or solder out of doors! You need only tin about 0.5mm of the insulated wire.
12. Carefully solder the low loss microwave-rated input capacitor C1 to the end of the RF input connector spill. Use 28swg fast flux solder and solder quickly.
13. Solder the other end of L2 to the end of C1 away from the connector.
14. Solder L1 as shown with the 'top' end to the junction of C1 and L2. The 'free' end should be orientated near to where Tr1 gate lead will be when Tr1 is fitted (later).
15. CAREFULLY check the board for poor joints and wrongly placed components.
16. Apply 12V (20V max) power and check that the output of the regulator IC1 is +5 V. Check the output of IC2 is -5V
17. Remove power and solder Tr2 in place. Make sure you have the correct orientation of the device. The curve of the D (on the NE32584/6) SHOULD BE TOWARDS THE INPUT. On the 36077 gate is marked by a small dot.
18. Carefully bend up the gate lead of Tr1. Use antistatic precautions.
19. Solder Tr1 in place. Solder the free, lower, end of L1 to the gate lead.
20. Remove the backing paper from the absorber material and press it into the inside of the top lid of the box. It should be nearer to the RF input end of the box, rather than the regulator end.
TAKE CARE WHEN HANDLING THE BOX. THE EDGES CAN BE SHARP.
This completes construction.
