Dave Richards AA7EE

July 30, 2012

The Other Half Of The ZL2BMI DSB Transceiver – The Transmitter!

In the last blog post, I described the receiver part of my build of the ZL2BMI DSB transceiver and noted that I’d been having problems with the TX transmitting a constant carrier, even with no modulation.  Everything seemed to be OK up to and including when I built the driver stage. On adding the BD139-16 final though, pesky RF feedback started having it’s way.

During my early years as a radio DJ, one of the pieces of advice I received from my program director was that if I didn’t know something, it was better to not talk about it at all than admit it on the air. As a general rule, it’s probably better to spend time imparting what you do know to your listeners, than to waste time telling them all the things you don’t know.  However, occasionally admitting to holes in your knowledge, I think, increases your relatability and well, is just more honest. In the same way, after my partial success with the G3WPO DSB80 rig, I decided that I wasn’t going to keep blogging about the circuits I built that didn’t fully work. However, a very nice comment from Rogier on my last blog post about the receiver in the ZL2BMI DSB transceiver made me change my mind.  Rogier said that even if my circuits don’t work, they still look good (or words to that effect). Well, I’m not posting the pictures here because I think they look good (after all, what good is a nice-looking circuit that doesn’t work?) but for two reasons. Firstly, to share what I’ve been up to, and secondly, someone may look at my layout and know why I’m having the problem with RF from the final getting back into the earlier stages of the rig and causing it to emit a constant residual carrier (of about 3/4 watt if I remember correctly – not an insignificant amount in such a rig).

So without further ado, here’s what my ZL2BMI transceiver looks like from above.  I hadn’t yet added a TX/RX switch, so the power supply line is connected in the TX position, and the 12V supply to the receiver is disconnected:

My version includes a mic pre-amp as used by G3XIZ and detailed on the GQRP site:

I added an extra 01.uF cap from pin 8 of the NE602 to ground in order to try and stop RF getting where it wasn’t supposed to go.  I also temporarily disconnected the output of the mic amp from pin 1, which didn’t help. I’d read that some people have experienced problems with RF getting into the antenna input coil on TX, so temporarily removed that coil, but that didn’t make a difference either.

Another view of my build:

It is now sitting on a shelf until inspiration (or help from someone else) moves me to take another look. I’m taking a brief break from building but am feeling the desire to build a kit 🙂

Rogier – was it you that I heard Bill Meara mention in the Soldersmoke mailbag in the just-released episode 145?

July 29, 2012

Half Of The ZL2BMI DSB Transceiver – A Simple 80M Direct Conversion Receiver :-)

A few weeks ago, Jason NT7S mentioned the ZL2BMI DSB transceiver as a rig I might be interested in building. He was right – I had seen it in SPRAT but for some reason hadn’t seriously considered making it into a project. The mention from him somehow got me to take another look at it and, well, it was such a simple design, it didn’t seem as if I had anything to lose by giving it the old college try.

The great thing about building a transceiver is that if the transmitter part doesn’t work, you’ve still got a receiver. That’s what happened to me (or at least, until I figure out my problems with the transmitter.) Everything was working fine up to and including the building of the driver stage. Once I added the BD139-16 final, I started experiencing problems with a constant residual carrier being transmitted when no modulation was present.

However…….once I had finished the first part of the build, which consisted of building the receiver, I took a little time to enjoy listening to the receiver and generally being surprised that such a small collection of parts would allow me to listen to the ragchewing on 75M. Little things like touching a wire to the antenna terminal and hearing atmospheric noise coming out of the speaker always give me a kick.

Here’s the schematic for my (only ever so slightly different) version of the receiver part of the ZL2BMI DSB transceiver:

large

 

There are no RF or AF gain controls in this schematic.  The circuit is still on a board, not yet in an enclosure, and in the experimental stage. If I ever get it into a box, I’ll add an RF attenuator pot in the antenna input circuit. This is even easier to build than a receiver with a VFO, as there are fewer toroids to wind. In fact, there is only only one – the single antenna input inductor.  Coverage was about 3911 – 4009KHz, so I didn’t bother winding a rubbering inductor, figuring that 100KHz of coverage was already pretty good for such a circuit.

The frequency drift wasn’t very encouraging. I was expecting a little better from a ceramic resonator VXO, being around 200 – 300Hz/hour upward drift after an initial 15 minute warm-up period.  The free-running VFO in my 40M NE602 CW DC RX had a better stability – on 7MHz! This board wasn’t in an enclosure though, whereas the 40M receiver was.  I wonder if that could have made the difference?

However, the receiver sounded pretty good, and there wasn’t much to it:

Here’s another view:

Looking at the schematic, you’ll see that as well as the 0.1uF coupling capacitor from pin 5 of the NE602 to pin 3 of the LM386, there are 2 x 0.1uF decoupling capacitors – one from pin 5 of the NE602 to ground, and the other from pin 3 of the LM386 to ground. I saw a wonderful looking version of the ZL2BMI transceiver built by a ham in the Czech Republic, but looking at his schematic, saw that he left out these 2 decoupling capacitors. There was a 0.1uF coupling cap from the output of the NE602 to the input of the LM386 and that was it. I thought that perhaps he was onto something, so I also left out these 2 caps. Well, they are quite important. The 3 capacitors between them form a kind of simple diplexer – as far as I can tell from my limited knowledge. With just the coupling cap, I was hearing stations, but was also hearing breakthrough from nearby strong in-band signals. Adding the 0.1uF from the output of the NE602 to ground cut out the breakthrough as well as cutting down on some of the higher-frequencies in the audio. Adding the second 0.1uF cap from the input of the LM386 to ground helped shape the audio a bit more and cut down on some more of the higher frequencies, making the receiver more pleasant to listen to for long periods.

I shouldn’t admit this in public, but my first thought on seeing the 3-capacitor network that connects the two chips was “How can a 0.1uF cap bypass RF to ground, when the same value is also coupling audio to the input of the next circuit? If the 0.1uF coupling cap passes audio to the next stage, why doesn’t the 0.1uF bypass cap short all the audio to ground?”

After a bit of thinking, I realized that the capacitors form RC filters with the circuit impedances which determine which frequencies they pass and which they don’t. Imagine you’re an audio signal coming out of the NE602 and heading towards the coupling cap for the input of the LM386. You are going to see that 0.1uF capacitance as well as the input impedance of the LM386, which is about 10K. The 3dB cut-off frequency of this high-pass filter is given by:

But what about those 0.1uF caps to ground? Well, they also form high-pass filters, and the impedance in this case is the impedance of the connection to ground which, if the capacitor is connected properly to the ground plane, should be very low. Therefore, the cut-off frequency of this simple filter is much higher. Audio frequencies are blocked and subsequently passed on to the LM386 AF amp, while RF is bypassed to ground.

While pondering the really nice-looking ZL2BMI rig that had been built by the the Czech ham, I decided to do some testing of my own.  Maybe he had a reason for leaving out those 2 coupling caps?  I decided to replicate this in my circuit and found very quickly that without at least one of those 2 bypass caps, the circuit experiences breakthrough from strong stations on nearby frequencies.  I made a recording with and without one of the bypass caps, and here are the results:

If I were going to build this as a simple little receiver to listen to the ragchewing and general chat on 75 and 80M, instead of using a ceramic resonator, I would use a varactor-tuned free-running VFO as with my Hi-Per-Mite DC RX so that I could cover a wider portion of the band. I’d also use a double-tuned bandpass filter for the antenna input and include an RF attenuation pot as well as possible an AF gain pot.

Naturally, these simple receivers have their limitations, and it doesn’t stop me from dreaming about owning a Ten-Tec RX-340, but I get a real kick out of receiving good-sounding signals from a handful of parts.

July 27, 2012

Using the NM0S Hi-Per-Mite Filter From 4SQRP To Make A Simple 40M DC CW RX

When 4SQRP brought out a version of the David Cripe NM0S-designed Hi-Per-Mite Filter, I noticed that it could be configured to give up to 50dB of gain. Like many others, I’m sure, my next thought was that it would make the process of building a simple direct conversion receiver even simpler. I decided that at some point, I needed to use this little filter board as the audio chain in a direct conversion receiver for CW.  I wanted to see for myself how it would sound.

In the meantime, my preoccupation with direct conversion receivers continued, as I embarked on building a G3WPO/G4JST DSB80. The receiver in that DSB rig uses an SBL1-8 DBM. That particular mixer package is out of production, but I used an ADE-1 and was pleasantly surprised by the receiver. I had some problems with the TX section, so put it aside and started building a ZL2BMI DSB transceiver.  I’d known about this little rig for a while from the pages of SPRAT, but a comment on Twitter from NT7S encouraged me to have a go at building it. The receiver is a simple NE602/LM386 combination with just a single-tuned filter on the antenna input. Of course, the receiver is not THAT simple, as each chip contains more complex circuitry, but the schematic at the chip level looks almost too simple to work.  As with the DSB80, I had problems with my ZL2BMI rig transmitting a sizeable residual carrier, but was surprised that the receiver sounded pretty good. The seed was sown…..

The ZL2BMI DSB rig was actually only the second time I had built an NE602/LM386 direct conversion receiver. The first was about 20 years ago when I bought a kit for the Sudden receiver on 20M. At the time, I wasn’t that keen on it and it soon ended up in pieces. I’m not exactly sure why I wasn’t taken by it, but I think it was a combination of factors. Firstly, I was living in an apartment in Hollywood with no outdoor antenna and was using just a short length of wire indoors as an antenna. It’s also highly possible that band conditions weren’t great, but I just remember not hearing many signals and also not liking the fact that a half-turn of the variable capacitor covered the entire 20M band. Because of this one not so great experience, I have since harbored a bias against using NE602’s in direct conversion receivers, an attitude that I now realize was unfair.

After achieving only partial success with both these rigs but enjoying the fact that the direct conversion receivers in both of them worked quite well, I wanted to build a simple receiver and use the Hi-Per-Mite kit that had been sitting patiently on my shelf for the last few weeks.

Look at the schematic for any NE602/LM386 DC receiver, and they are almost all the same, differing only in whether they use a crystal, ceramic resonator, or free-running VFO for frequency control, whether they have a single-tuned or double-tuned antenna input filter, or whether they use a differential or single-ended audio output.  The circuit is so simple that there is only so much room for variation, but there were a couple of things I had in mind for my mine.  While the receiver portion of the ZL2BMI rig only has a single-tuned filter on the antenna input, I wanted to do what G3RJV did with the Sudden, and place a double-tuned filter there. It’s an easy thing to do, and living in a built-up urban area, I have a lot more RF around me than ZL2BMI does when he’s using his rig in the bush, so a bit of extra bandpass filtering certainly couldn’t hurt. The other decision to be made was the method of frequency control. I was curious to see how the internal oscillator in the NE602 would work as a free-running VFO.  My apologies to you folk who have built umpteen simple NE602-based receivers and have-been-there-and-done-that.  I guess I need to get this out of my system! Another thing that I had seen in other circuits but hadn’t tried was the use of a 1N4001 diode as a varactor. Some call it the poor man’s varactor. Sounds like it was custom-made for me!

So that was my configuration – double-tuned input filter (just like the Sudden) and a free-running VFO tuned with a 1N4001 diode.  From what I’d read, I knew that I should be able to get enough capacitance swing from the 1N4001 to cover at least the bottom 30-50KHz of 40M. Here’s what I ended up with:

There’s nothing original in this schematic  but as you’ll see soon, it did turn out quite well, so I decided to name mine “The Rugster” after my cat, whose full name is Chloe-Rug, but who gets called several different variants of that name, of which “The Rugster” is one.  For the input bandpass filter, I used the vales of L and C that are used in the GQRP 40M Sudden Receiver. The pre-wound inductors in that design have a value of 5.3uH. I decided that I wanted to use T37-2 cores, so I used the calculator on W8DIZ’s site to figure out that I’d need about 36 turns on a T37-2 core to give 5.3uH of inductance. I fiddled around a bit with the values of the parallel fixed capacitors before settling on 47pF for those. I had originally thought that a higher value of around 68pF should work, but that didn’t put the peak of the filter somewhere in the mid-range of the adjustment of the trimcaps.  Some experimentation revealed that 47pF fixed caps achieved this.  Your value may vary depending on what value of trimcap you are using.  For the VFO inductor, I found a design for a 40M DC RX on the internet that was tuned by a 1N4001, noted the value of the inductance, decided that I wanted to use a T50-7 core (for stability) and once again, used Diz’ site to calculate the number of turns needed.

When building receivers, I like to start with the audio chain first. It’s quite affirming to be able to touch the input and hear that reassuring loud hum and mixture of AM broadcast stations in the speaker! So I got out the 4SQRP Hi-Per-Mite kit. Close inspection of the PCB revealed a small problem that was easily remedied. There was a very, very narrow copper trace connected to the ground plane that had been bent so that it was contacting the input pad.  A DVM test confirmed that the input pad was shorted to ground. I didn’t take this picture until I was part of the way through removing the offending trace, but you should be able to see the problem:

A minute or two with a sharp craft knife and that pesky little trace was history. Here’s the finished board:

The only thing that prevented me from putting this kit together even more quickly was my own compulsion to solder the components into the board so that they line up as straight as possible. The holes for some of the capacitors were a bit larger that they needed to be so that if you just plug them into the holes and solder, they’ll be a bit off-square. It’s not a big deal, and most builders won’t be bothered by it, but I just can’t control my OCD tendencies sometimes. Anywhere, I finally got there:

Although with modern low-flux solders, there is no need to remove the flux, it sure does make a board look nicer. I recently started using flux remover on my boards so that I can show off the underside too. At the suggestion of W2EAW, I apply it with a cheap plumber’s flux brush obtained (for 19c) from the local hardware store. Look at that nice clean board!

Trader Joe’s sells Green Tea Mints in a clear-top case that fits the Hi-Per-Mite board well if you’re looking to use it as a stand-alone device. There’s also room for power and in/out connectors (though you might need to cut off the top corners of the board in order to make room for the connectors.)  The tin in this shot had been knocking around my bench for a while, so the clear-top is a bit scratched up, but you can see the potential:

The next step was to build the direct conversion receiver with the NE602 and some of W1REX’s MePADS and MeSQUARES. The most frequency-sensitive part of the VFO circuit was built ugly-style, with the help of a 10M resistor for a stand-off, to help the stability. I don’t have any pictures of the board without the Hi-Per-Mite audio filter/amp added, so here’s the finished board. In the earlier shots, you can see the VFO toroid before I decided to slather it in hot glue in a bid to make it a bit more stable. There is only one component in the final receiver that I missed from the schematic, and that is a 1N4001 diode in series with the 12V supply for reverse-voltage protection.  I’ve blown too many fuses in my shack supply to not use these little fellows in the future 🙂

Another shot from basically the same end of the board, showing the input bandpass filter on the left, VFO toroid on the left at the back and the DC input circuit nearest you on the right (reading from right to left, you see the reverse-polarity protection diode,  10uF input smoothing capacitor, 78L08 voltage regulator, and the 0.1uF DC output bypass capacitor. I’ve had those green trimcaps for a long time and it was time they were used. They don’t take solder well (I think I got them from Radio Shack about 10-15 years ago) but it seemed a shame not to use them in something:

Here you can see the varactor tuning circuit built ugly-style just to the left of the VFO toroid. The 3 connecting cables are for the AF gain pot (which is connected in place of R11 and R12 in the Hi-Per-Mite, as per the Hi-Per-Mite instructions), multi-turn tuning pot, and AF output jack. I’ve used lavalier mic cable that I bought from a local pro-audio store. It has 2 inner conductors shielded by a single outer braid and is very flexible, which makes it useful for wiring up small radios.  RF connections (which you’ll see in later photos) will be made with Belden 8216 coax:

At this point, I was very gratified to discover that the receiver actually worked, and seemed to work quite well too. That fact gave me enough inspiration to start building an enclosure to house it in.  The next shot isn’t ideal, as the back of the case is a little out of focus. You’ll notice that the front, and the two bolts sticking up on the right side are in focus, but the back of the case (and especially the bolt at the back left) isn’t. When I realized this, I was too far along installing the board to go back and take another shot and besides, sometimes I just have to control myself and keep forging ahead:

A view of the board installed in the case, with the lid:

A closer view from the top, in which you can see the VFO toroid now doused thoroughly in hot glue.  I’m not sure if it helped the long-term stability at all, though it did help to make the VFO more resistant to physical shock. Another way of securing the VFO toroid in a vertical position would have been to drill 2 small holes in the PCB and use a small nylon tie:

The coax that leads from the 1K log RF attenuator pot to the board is a little long, and that is because the one you see in the photos is a 10K linear pot. It was all I had at the time of building.  I am going to swap it out for a 1K log pot when the next order arrives from Mouser in a few days, and kept that lead a little long in case I need to chop some of the end off when changing the pot out.

Here’s another view of the innards. I am quite pleased with the way this little receiver turned out. You can see one of the 4 brass nuts that are used to secure the lid to the rest of the case. I use brass, as I can solder to it with regular solder. When placing the nut, and before soldering, I screw the 4-40 machine screw through the side of the case into it so I know the nut is in the right place.  If I were to get a little over-zealous when applying solder and accidentally get solder on the screw it wouldn’t stick, as the screw is made of stainless steel:

This is what The Rugster looks like in her case with the lid on:

If you look closely at these pictures, you’ll see that the PCB panels don’t line up perfectly and that the edges are just a little rough.  I am somewhat detail-oriented, but I am not a craftsman by any means, and I know my limits.  I made a conscious decision not to spend a lot of time filing and sanding edges. After making deep scores in the board and breaking it, I ran the edges across a file on the bench a few times and left it at that. Good enough is good enough in this case, and it’s certainly good enough for me.

A view of the underside:

I’ve spent a few evenings listening to it and most of the signals that my K2 could hear, this little receiver could hear almost as well. With the very weak signals the K2 won, of course.  A small part  of this could be due to the fact that the DC receiver, even with it’s 200Hz-wide filter, is still at a 3dB disadvantage to a single-signal receiver (such as a superhet), as it is hearing on both sides of the local oscillator.  Naturally, I expected my K2 to be the better receiver (duh!) but was really surprised at what an enjoyable experience listening to this one is for such a simple circuit.  As expected, it does overload in the evenings, but all I have to do to get rid of the breakthrough is to adjust the RF attenuation pot back a little from “full gain”, and the breakthrough disappears.   Elecraft use an NE602 in the front end of the K1, and it has an attenuator for the same purpose. I’m not sure whether the breakthrough is from strong in-band amateur signals or from AM broadcasters – it’s actually hard to hear the content due to the narrow bandwidth of the Hi-Per-Mite. One small adjustment of the RF gain pot and it’s gone – then I just bump up the AF gain a bit to compensate. Volume is enough to drive my MFJ-281 ClearTone speaker.  I normally like to listen to CW with a 500Hz note, but because the response of the ClearTone drops off below 600Hz, I kept the Hi-Per-Mite filter at it’s design center-frequency of 700Hz, and the speaker sounds good. EDIT – If the AM breakthrough is from signals in the 550 – 1700KHz AM broadcast band, which I strongly suspect that it is, a simple high-pass filter with the cut-off set somewhere around 2 or 3MHz should work wonders to eliminate this.

Another point I wanted to mention is that even though the Hi Per Mite employs an LM386 for the AF amp, it is used in the low-gain configuration. Because of this, you don’t hear any of the hiss that is heard in other simple receivers that employ a 10uF capacitor between pins 1 and 8 for high gain. This is a surprisingly pleasant receiver to listen to.

The fact that the tuning rate is quite low helps a lot in the enjoyment of this receiver too.  The 10-turn pot covers 6999KHz – 7051KHz giving an average tuning rate of about 5KHz/rotation. The VFO shifts in frequency very little indeed when  the receiver is knocked or moved. Drift is not great, but manageable.  Drift in the first 10-15 minutes is only slightly worse than after that initial warm-up period,  so I’ll give you the results from switch-on, which were 90Hz drift in the first hour,  140Hz drift in the second hour, and 110Hz in the 3rd hour. All the drift was downward – there was no upward drift at all. The drift was steady, and with a little bit of compensation, I think those figures could be improved upon quite a bit. However, for casual listening (and this is all I am going to use this for) it is adequate.

This receiver is certainly not perfect, but considering it’s just an NE602 and an LM386 (oh – and a quad op-amp IC for the filtering), it’s not bad at all.

Thanks Dave NM0S and 4SQRP for this neat little audio CW filter kit.

Here are a couple of videos that I just made of The Rugster. Please excuse the poor video quality – it’s an old, cheap camera:

This one is a little shorter:

July 3, 2012

An Air-Spaced Variable Capacitor With Brass Vanes

I think I might be closing in on the ideal variable capacitor for a VFO.  This arrived in the mail yesterday from an eBay seller:

The capacitance swing is 9-50pF with wide gaps between the vanes.  Rotation is fairly smooth, though the bearings could use a re-lube. Brass is a good metal for the vanes, as it has a lower temperature coefficient than aluminum.  However, this particular capacitor interested me because the fixed vanes are brass, while the moving vanes are aluminum. Why not all brass?  This would mean that as the vanes are engaged and the capacitance increases, more of the aluminum vanes will be meshed with the brass vanes, meaning that the temperature coefficient of the capacitor will increase.

Why would you need a variable capacitor that has a (positive) temperature coefficient that increases with decreasing frequency?

According to the seller this was a National Radio part, so I’m sure there was a good reason.  I need to put my thinking cap on. I should have cleaned it up a little more for it’s photo op, but it’s still quite a looker:

July 2, 2012

The DSB80 Part 2 And A New Addition To The Shack

Filed under: Uncategorized — AA7EE @ 7:40 pm
Tags: , , ,

I did make some progress on the DSB80 a couple of weeks ago and then put the project aside.  I became a bit sidetracked by other things, some of them non-radio, so want to provide an update in case the DSB80 project gets shelved for a while.  I received a wonderful e-mail from Frank Ogden G4JST, co-designer of the DSB80. He sent me a picture of his prototype DSB80 with my letter to him alongside. What a thrill! He said that he powered up this fine little rig, and it was still putting out 4W of DSB on 80 with fine audio and a stable VFO:

Frank told me that when he designed the DSB80, he scratched the circuit out on a piece of paper and sent it straight to Tony G3WPO, who came up with the PCB design. It was never bread-boarded.  Amazing!  Frank has many happy memories of making many QSO’s with southern England and northern France from his brother’s boat on this rig.  As I’ve mentioned before, the DSB80 I built from the kit supplied by WPO Communications worked fine.  How I wish I still had it 🙂

If you recall from the last post, I had been having some problems with the buffer amp in the VFO not buffering too well.  Jim K4AHO suggested that I capacitively couple the output of the VFO to the input of the buffer instead of coupling it resisitively. He also suggested a high-value resistor from the gate of the buffer JFET to ground to act as a self-biasing resistor. This cured the problem nicely – on terminating the output of the buffer with a 51 ohm resistor and touching it with a screwdriver, there was no noticeable shift in VFO frequency (unlike before). The output from the VFO transistor was a nice sine wave:

Here’s the output from the buffer transistor when terminated with a 50 ohm resistor:

The above waveform is about 0.9V pk-pk which, by my calculations, across a 51 ohm resistor, translates into around 2mW – just +3dBM, which is a little low for a level 7 diode ring mixer. Also, that waveform – I don’t know how important it is that the VFO buffer outputs a clean sine wave into a 50 ohm load, but I’d sure like to see it.

I decided to press on and see if I could finish the transmitter. This is where I got:

If you saw the earlier iteration of this board from a previous post, you’ll see that I have removed the on-board VFO.  In it’s place is the mic amp for the TX section. I also built the TX driver and TX final. The TX seemed to be generating a pretty nice-sounding DSB signal from the driver using a 2N3904 in place of the originally-specified BC238 device. G4JST very kindly offered me a VN66AF (the device originally specified for the final) for my experimenting, but I wanted to adapt the circuit to use the commonly available IRF510. Heck – you can even get ’em at Radio Shack.

I’ve had a couple of problems with the IRF510 final. The first was solved with the help of NT7S. Jason did a bit of brainstorming with me and we found that there is a choke in the collector circuit of the driver transistor that is designed to resonate with the input capacitance of the MOSFET final.  It turns out that the input capacitance (Ciss) of the IRF510 is in the range of 135 – 180pF, while that of the VN66AF (the final in the original DSB80 design) is around 50pF. Changing the choke from 33uH to 12uH increased the output from the final from 3/4W to something like 2 – 2  1/2W (I didn’t write it down). However, I also noticed that the rig was putting out significant carrier in the absence of modulation. I don’t think this was due to poor carrier suppression – rather due to a spurious response somewhere in my circuit layout.

This is where I’m at with my version of the DSB80. The receiver sounds good and has given me fresh inspiration to build some more direct conversion receivers. I almost wish that I had not built the TX section, as I don’t do a lot of transmitting on phone anyway, and this is the only part of the circuit I’ve had a few problems with! I’m sure that it’s my layout, or my use of different active devices, as my original kit back in 1983 worked well.

So my DSB80 board is sitting up on the shelf for the time being while I give it a rest.

By the way, there’s a new addition to the shack, which you may have noticed from the pictures above. It’s a Tektronix 465 oscilloscope. A very generous local ham gave me his old Tek 465.  I’m not sure whether he wants to remain anonymous or not but he knows who he is, and to say that this was a generous gift is a huge understatement. Thank you very much – you know who you are!

Create a free website or blog at WordPress.com.