40 Metre - Midney Receiver Kit Construction
Introduction
Keen to make a start on HF I did consider purchasing a commercial transceiver, perhaps the well regarded FT100D. But after building the Kenwood PC interface my imagination had been fired and my thoughts turned to further construction - An HF kit.
So which kit and which band ?
Well my key requirements were.
- To learn from building it.
- Listen to the M3WEB 40 Metre Net.
- Component level kit i.e. not stick the PCB in the case, solder on leads for the controls and away!
- A first TRX project, so capable of being built in a reasonable time by a constructor with limited experience.
- Reasonable price.
- CW and SSB.
Following some fairly extensive research both on the web and in magazines for kits (Hands/Howes/Ramsey/Lake/Walford/Elecraft etc) and following some very helpful advice from a number of amateurs (Thanks again!) I decided to build the Walford Electronics Midney / Kingsdon 5Watt CW / SSB combination for 40 Metres.
Construction - Session 1
I carefully read all the detailed instructions. Starting to try and place the components was, to say the least rather puzzling, referring to the circuit diagram only confused me. The parts layout diagram did not seem to help very much either as it has little direct reference to the circuit board holes etc. After a little thought (and lunch! ) I held the circuit board up to a desk lamp with the parts layout sheet in front. Now I could see the circuit board holes shining through the schematic. Carefully checking the values, the first few components for the PSU stage were soldered in. Making the "topside" earth connections was harder, the joint and board needed to be really hot for the solder to take, but this was soon mastered.
As the kit is tested stage by stage the first test commenced! Checked the voltage at the test point - all correct. Then completed the first part of the audio stages. Wired up the headphones, finger on a screwdriver at point A1 and got a raspy buzz as expected. Getting late!!
Learning Points
- Stage By Stage construction excellent.
- I will photocopy the part list and push the components into the list before I start the Transmitter! This should make finding the parts a lot quicker !
- Use the desk lamp trick to mark up more components on the PCB before starting construction.
- Soldering practice!
Construction - Session 2
Some thought was required for the next set of components in the bottom left hand corner of the board. Working from the parts layout diagram it took me a while to correctly place them. I had to work quite a way through the list and then retrace my steps to get everything to fit correctly - There are a lot of holes here!
Referring to the reference points on the back of the board and noting that a resistor can't really have both it's legs on the same track helped! Once this resistor (R9) was moved everything else fitted. There was some brief confusion between C10 the capacitor and CI0 the connection but reading the instructions again resolved this.
Placed most of the components for this stage, but no soldering or testing.
Learning Points
- Read and reread the instructions - everything is there!
- Check and double check resistor values Red and Orange bands can look very similar!
Construction - Session 3
Soldered in the components from Session 2 and the remaining components for this stage. Next tested Pin 5 of IC2 and measured 7.5 volts (Suggested between 6.5 and 7 volts) . Connecting up the headphones and touching pin 5 of IC2 for the next test made little difference, but touching the IC with my finger changed the tone as expected, then tested with the CW filter enabled which changed the tone again. Hopefully this is OK!
Construction - Session 4 - CIO and RF Mixer / IF Filter
Rechecked my work from Session 3 and found I had got confused with the IC pin numbers *(IC PIN Diagram), The voltages were fine. Then on to a number of small capacitors, I checked them all with the meter to be sure of their values (good practice!). The earth connection on C12 was a little tricky being so close to CT1 (Although perhaps this was not helped by the splendid can of Cuban Beer I was drinking)... CIO complete. The CIO buffer was next but I did not have these parts handy and will test the CIO frequency later, so on with the RF Mixer and IF Filter. I carefully measured all the capacitors before placing them. A few questions now appeared.. Hmm.. I prepared an email for Tim.
Questions
- Should the diode (D1) right hand side be earthed on the top of the PCB, if not should it be in a countersunk hole ?
- Should the capacitor (C2) (right handside be earthed on the top of the PCB, if not should it be in a countersunk hole ?
- I have carefully measured all the capacitors before placing them. But I seem to have 3 10nf disc capacitors left, when need C10 ,C1 and C4 (68pf, 10pf and 4p7) .
- R71 (junk box), TR70 (from the TX kit), fine. But what is the function of RX C70 ?
Learning Points
- Small capacitors are not always clearly marked, so it is essential to triple check values with a meter.
Construction - Session 5 - Checking Session 4!
The same day I received a very helpful reply from Tim. As advised I checked again!! C3 and C6 are black tipped!!! They I are not 10nf's!! So the problem is solved. I had already got the 2 caps from Maplin and a solder sucker which will now be needed to remove the 2 caps!!! Only the stated components should be earthed and RX C70 is an optional part for the RIT. Sorted.
Learning Points
- Come back to the board later and check it again!
Construction - Session 6 - VFO
Removed C3 and C6 and replaced with the correct values, fitted the remaining parts to complete the VFO, prior to the Band dependent parts.
Learning Points
- Come back to the board later and check it again!
- The solder sucker works magically.
Construction - Session 7 - VFO Band Dependent Parts
Soldered in the band components and started drilling the front panel. Must remember to fit the couple of remaining TX specific parts!
Construction - Session 8 - Front Panel
Fitted remaining TX transistor, then soldered on front panel, which was quite fiddly, but perhaps it was just getting late. Also attached the rubber feet, which I had forgotten!!
Construction - Session 9 - Front Panel, Finishing and Wiring
Fitted the controls and soldered on all the wires. This took a while! Soldering the wires on to the board proved difficult, certainly for the TX I will get some veropins then solder on to the pins. Once again the solder sucker was handy to remove misplaced joints! Well I have finally finished the construction, so I hooked up the power and headphones just to see what would happen! The volume works, tuning I get a loud tone in the middle of the tuning range, the fine tune works and the CW filter changes the tone. So a good start. Now to look at setting it up!
Learning Points
- Use veropins for mounting the wires on to the board!
- The solder sucker works magically (Again).
Testing - Session 1 - Contact!
Encouraged by the beeps and buzzes, I decide to connect up a short length of wire to the antenna connection and earth the earth (!) More noises. Longer wire required, so I carefully prepare and connect up a tuned antenna for 40 Metres (Attached one end of a reel of cable to the Midney then drop the reel out of the window) Back to the one headphone. I tune.. yes it's alive, masses of CW greets me. Tuning further, then through the haze.. "CQ DX CQ DX this is United Tango Four United Ocean" I look him up on QRZ.com it is VALERY GOYKO from the Ukraine.. Splendid..
Testing - Session 2 - Of VFO's and Scopes
Adjusted the fine tune pot so the centre of the range is uppermost and soldered a pin on to VFOB which will be used to set up the VFO range. It seems to tune from high to low, Emailed Tim about this and he promptly replied to say that you can just swap the connections to the tuning pot around to have it tune in either direction. As with most questions it is in the notes!!!!
Keen to progress, thoughts turn to my PHILIPS PM 3263X scope (!) and how I can use it to measure frequency. Unfortunately I don't have a manual for it, but reading various articles on the web and the "Hands-on guide to Oscilloscopes" book encourage me! Much reading, probing and button pushing later I understand more about the scope and have a waveform display but no luck with the Gamma T control [ Update - Delta T Control!] which would enable me to measure wavelength and hence to work out frequency. So I post a message to the very helpful Yahoo QRP group..
Testing - Session 3 - Of VFO's, Delta and Ypres
Got some very helpful replies from the QRP group this morning regarding setting up the rig.. Basically I need a frequency counter. Fortunately I was able to borrow one from a fellow club member (Thanks Sean!) I adjusted the CIO (Carrier Insertion Oscillator) to 6001.5 KHz using the CT1 trimmer, very straight forward.
Then I checked the VFO frequency, it read just under 1Mhz (?) I was expecting it to be 7.0Mhz to 7.1Mhz, very puzzling. Somewhat lost by this I returned to the next task, reversing the tuning so it runs clockwise (low to high) simply by swapping round the outer connectors on the main tuning control.
Reading the notes again, the VFO should show 1.0 to 1.1Mhz, effectively an offset, It makes sense now! So following the notes VFO adjustments are made using L52 (Toko - carefully with a matchstick) and RT1 (Preset) to cover an indicated 1.0 to 1.1Mhz.
Listening in, the band was very very busy I had hoped to hear the M3 Net, but no luck. However, I did hear the Ypres special event station ON7FF who was being kept very busy..
Another email from the QRP group clarified my confusion with Gamma T it is Delta T, I just got things mixed up!!
Learning Points
- Read and reread the instructions - everything is there!
Testing - Session 4 - RF Band Pass Filter
The two inductors needed very little adjustment.
Conclusions
The Midney works splendidly. I learnt a lot, had great fun building it and Tim always provided helpful answers to my questions. Highly Recommended !