Eagle Peaks and The Governor – part 2

Hi all,

I have had the phone fixed, and obtained some pictures from the recent trip where I activated Eagle Peaks VK3/VE-045 and The Governor VK3/VE-046. The earlier post can be found here.

On the way out, there were some good views of the south side of Mt Buller, which still good, but softening, snow cover. The picture was taken in early dusk.
Mt Buller southern side

I activated Eagle Peaks, but it was dark by the time I arrived there. Here was a look at the summit the following morning:
Eagle Peaks summit

On the way to The Governor, I headed down to Lickhole Gap. I was amazed at the amount of trees that had come down in recent months. This was a bit of a theme throughout this trip:
Fallen trees at Lickmore Gap

I eventually made it to The Governor. The first picture here shows the summit, including part of the end-fed antenna. The second picture was taken from a nearby knoll. At that stage, the clouds had lifted a little, allowing photos of more distant objects.
The Governor summit, activating with an end-fed for 20 and 40.

Snow on the southern side of The Governor

Hope you enjoy the pics. 73, Regards Wayne VK3WAM

Quick note: The correct spelling of VK3/VE-046 is The Governor, not The Govenor, so it is spelt as one would initially expect.

Eagle Peaks and The Govenor VK3/VE-045 & VE-046

Hi all,

It had been over a month since my last SOTA activation, and so I thought it time to put aside my CW rig design adventures and get my hands dirty (or is that scratched) out in the field. I had been to Eagle Peaks before, last time was on a Bush Search and Rescue Victoria expedition to help rescue a guy who had fallen off a cliff. For this trip, I would need to go near that same cliff. Better be careful.

Here is a map of the area, and my route taken in red:
Map of route taken to access Eagle Peaks and The Govenor

Eagle Peaks VK3/VE-046

I set off Thursday (20th Sept) in the afternoon, but was a little delayed. I got to the parking spot at Eight Mile Gap just before sunset, and headed off on an hour and half walk to Eagle Peaks, with the last 3/4 of an hour in the dark. The track had actually had some work since the last time I was there, with the fire undergrowth slashed back. This was a hint as to what was to come later, which made me think that my initial plan for 6 summits might be a little difficult.

I arrived at Eagle Peaks at 7:30pm and quickly set up tent and strung out a new end fed wire for 20/40 with a matchbox to 50 ohms. There is a tuning stub a little less than half way for 20m. SWR was around 1.5 to 2 around 7.03, 7.09 and 14.06. I’ll need to look into this a little later to see if I can get this down a little more. I am not into trying to get 1.00001 SWR, but I would like it below 1.5 as then associated losses are minimal. I should not expect fantastic results here, considering the wire is only a few metres off the ground, strung up by trees. I used some rope at the end insulator to attach to an end tree.

I worked 5 stations on 40m fairly quickly. Nothing heard on 20m.

The Govenor VK3/VE-046

The DSE map has this spelt Govenor, rather than Governor – so I’ll take that as ok for now, although they are not always right with place names.

After seeing the slashed undergrowth on the way to Eagle Peaks the previous evening, I thought I need as much time as possible to get to The Govenor as it might be tough going. I awoke at 6am the next morning to rain showers and in the clouds. Visibility was at 50m. There would be a lot of map and compass today. First task was not to fall off the cliff at the same place the hiker did a few years ago, so I traversed to the east of the cliff. The ground was very steep, and it would be hard to go up the other way. I was amazed, when approaching Lickhole Gap, how many fallen trees there were. Many had come down only a few months ago, some snapped halfway up the trunk. It is expected that there are fallen trees around, but this was a large number. There was a major wind storm during the winter that affected an activation of Mt Bullfight, see here, and I think that many of these fallen trees came down from the same wind event. I hope to be able to access some of the pictures I took from my damaged camera phone – but we will see.

I found a track cut to Mt Darling which came in from the west. I used this for a bit, but it started to go down the hill to the north west. I presume it comes from somewhere near Sheepyard flat, but I was not going that way. It is not marked on any of the maps I had seen, but it is clearly intended to be there as the undergrowth had been slashed. In any case it only helped me out for a few hundred metres. 😦

From this track, I made my way down to the saddle between Mt Darling and The Govenor. Funny that there is a track to Mt Darling, but not The Govenor; it is a much higher summit. I arrived a little late to plan and began to activate. I quickly got 10 contacts on 40m SSB. I put out a number of calls on 20m, CW. I heard NS7P come back very weakly, it would have been a 219 contact. I got his call sign wrong with the QSB, he sent it back and I was good to go, but then he was gone. Either he had to stop operating or conditions had turned.

My observations about this end fed antenna so far is that it is much better for local contacts on 40. A good 2 S points or above, looking at my logs based on reports. That is nominally 12dB, but given the “compression” many rigs give on their S meter reports, I’ll take it to be about 6dB above my vertical. Where my vertical is streets ahead is on DX. I would say a good 15dB or more ahead. Shame that the vertical is not as convenient – particularly stringing out all of the radials.

Onward I say

So running a bit behind schedule, I decided to drop the attempt to go to VK3/VE-075 and head for Mt Sunday instead to camp for the night. I thought it would take about 7 or so hours to get there. I headed down along a route to quickly get to the river and then access a track about 200m up the other side.

I then hit the bad undergrowth, and this was a shocker. Progress became very slow, and with the saplings 4 to 5m high, I had to continuously use the compass to have any sense of direction. I was using a phone as a GPS, but all the spray from the undergrowth got into the phone holder, and water damaged the phone. No more GPS. Lucky I had a print out of the map on board, because that was now my only reference with the compass. I have done plenty of rogaines, so I am quite comfortable navigating by map and compass.

The undergrowth was so bad, I decided to chance it going down a watercourse that was quite open. You can see where this happened on the map where my track heading down from The Govenor heads to the north. The first part was ok, but once at the valley floor, it was bad. I expected it to be bad, but I thought it could not be as bad as the undergrowth up top. It was even worse. I have done these kinds of creek traverses on BSAR searches before, but this one would easily be the worst. It was made particulally bad by all of the recent tree felling by that wind storm. There were hundreds of mature living trees fallen. I have never seen anything like it. I expect dead trees burnt by fire to come down, but not many living mature trees. The shame about this was that these trees might have been spared by loggers over one hundred years ago, but many are taken out just a few months ago.

After more than 7 hours, I finally made it to the river at 7:30pm, completely exhausted. I was to watch an “Australian Story” about John Cantor’s traverse of the Brookes Range in Alaska when I got home. When conditions were against him, he had a meltdown at one point. I must admit that I can relate, as I had a meltdown when I was about 400m up from the river where I began to wonder if I could actually get out of this trap, or if I would be getting out my radio to call “MAYDAY MAYDAY this is VK3WAM”. Of course, with food and the rest on board, I would only be able to do this if I had broken a leg, but out of the many times I fell over trying to get down to the river, there was one time I thought, oooh that was close.

Moral of the story: Even if it is bad up on the ridge top, stay there, because the creek will be worse.

Getting out

After making the river, I set up camp, had some dinner. I put up the end fed antenna, but in a steep valley on both sides, not too much signal gets out. It might work during the day when the skip on 40 is not so bad, but signals are well down at the bottom of the valley compared to the mountain top. I could not work anyone from down there, but I could at least listen to Sydney vs Collingwood football game.

I awoke early for the next day, with the first priority simply to get out of here. I still hoped to activate Mt McDonald, but a fall back option could be The Bluff. The first task was to cross the river. The level was quite high and I had to abort my first crossing attempt. After going up stream for 200m, I found a suitable crossing point where it was only about 80cm deep, even if fairly fast flowing. The walking pole helped enormously here as it had been doing most of the trip. It was tough to get out of the immediate valley area, but then the forest opened up. There was still plenty of undergrowth, but there were actually bare patches from time to time, and even grass on the ground! Actually seeing the ground was a moral lifter! It took another hour to get to the road.

Given all of the effort, Mt McDonald was going to have to wait for another trip. Instead, it was time to head for the car. This still took about 5 hours walking on the track. I was pretty tired with the backpack on. If I was to activate something, it would need to be with just a small light pack. I made the car, and then drove to Refrigerator Gap underneath The Bluff. Unfortunately, the track head is not at the saddle, but a little further up along the road. I was a little too tired to realise this at the time, so perhaps it was best just to head for home. In the end, I had two summits and 22 SOTA points in the bag. Now to get the phone fixed, and perhaps I can put up some photos. Looks like the remote locking on my car key does not work either!

Regards 73, Wayne VK3WAM

Designing a 20/40 band CW rig – Part 3

Hi all,

This is a continuation of Designing a 20/40 band CW rig – Part 2.

Too many harmonics

After the last post, that looked at the TX circuitry and filters, I went back and looked at the TX efficiency. I was also a little unhappy that there was quite a bit of power in the harmonics, which were being shunted to ground. One effect of all of this was the BS170s were presenting a variable input impedance to the previous BJT driver stage. Now both MOSFETS and BJTs are current sources, the former voltage controlled and the latter current. The voltage that is present on the output of an active device is not generated by that device directly, rather the device generates current. The voltage is a function of that current and the load. Now if the load is variable, then the voltage is going to change, even if the current output from a device is a nice clean sine wave, the voltage will not be so if the load is changing. We could kind of get away with this if the load device is a BJT as it is current controlled, but MOSFETS are voltage controlled.

The answer is not more filtering, the answer was to go back and look at the design. I first tried to lower the resistances in the BS170 bias network to swamp out the impedance changes. This worked to some degree, but it was not a final solution:

  1. More current in the bias network is overall power efficiency loss. We want to keep bias currents lean.
  2. My driving device, a MMBR941 has a maximum mean collector current of 50mA and I was within 20% of this. In the words of a well known Star Trek character “I cannot give her anymore power capt’n”.

Replace the MMBR941 with another device

It takes a long time to search around for suitable devices, and they also need to not be expensive. Instead of a long search, BS170 devices are nice and cheap, so I began with using another one of these to drive the 3 BS170 finals. It was easy enough, I already have a bias divider network to set the bias, and by moving this up and down, I can control the drain current. All of the stuff on the collector and emittor of the BJT can go, except for what is now the drain inductor.

This approach gave me more drive, and allowed greater 2nd network bias currents, but the additional losses here about matched the gains post BS170 finals. Not too good.

True Class C design

The general idea of Class C is that the active device is operating for less than 50% of the cycle. This is true, but a tank circuit is needed as well. My initial design had one of these, but on the output. The literature that I saw has the tank network between the voltage supply rail and the drain. So I needed to change what is basically a resonant low pass filter on the output to a tank at the traditional spot, between supply and the BS170 drains.

This approach certainly worked, and the output was much cleaner, but not near perfect. One thing that is needed is that the resonant tank circuit needs very low values of L and high values of C. Being a shunt, it is still presenting a very low impedance to the finals on harmonic frequencies. Because the fundamental load frequency also has a lowish impedance of around 10 to 12 ohms, the shunt network needs to have a net reactance well below this on the harmonics. A bit tough to do, and still we have the problem of variable impedance being presented to the driver stage.

Class E design

I decided to go for an alternative approach, a Class E design. The circuit I showed in the previous post has a bit of a change:

CW dual band 40m 20m transceiver with Class E finals

As can be seen on the circuit, a BS170 is being used as a driver. I have also gone from three BS170 finals to two.

A Class E amplifier uses a shunt capacitor across the transistor to complete the waveform, along with a series resonant circuit. This presents high impedance to harmonics, while passing the desired frequency. Actually, one of the tricks with Class E is that this resonant circuit is not centred on the frequency of interest, but a little below. A calculator is available here, thanks to Alan G3NYK. That site has a LF orientation, but the principle certainly works on HF or higher.

Class E amplifiers also have a reputation for higher efficiency than Class C, and I am finding this to be the case. I was almost able to get 5 watts RF output from a single BS170 on 20m, and could do it easily on 40m. We want 5W on both bands, with a bit of margin on the devices, so I am still using 2. By designing for a specific Q on the resonant circuit, and the selection of the shunt capacitor, various power levels are achievable for a given input to the transistors.

With the change of circuit design, I also had to review how I could dampen the oscillator input when not TXing. Unfortunately, I have found that the leakage currents on the various MOSFET devices I have used are too great to effectively shut it out. I also tried using a NDT2955 device to cut the power to the finals when not TXing. This device has a very low voltage drop across it when used as a switch, even at several amps. Unfortunately it sets up some strange oscillation in the Class E circuit, so no success there. It really didn’t make much difference, because the BS170 will act the same way on a small signal, allowing it to leak through, regardless of the gate bias set well below cutoff, or the power being cut from the drain. In the end, it was back to a simple 4401 to sink away the unwanted signal when not TXing, and this had the best effect between the driver and the finals.

What was the effect of all of this: I achieved a efficiency on the finals of 81% on 20m and 85% on 40m. I had to tone down the circuit on 40m, because the circuit adapted directly from 20m at 5 watts produced 7.5 watts on 40m. I also would not want to change the biasing networks based on the band, so the flexibility of being able to control power gain in the components of the Class E amplifier itself was nice.

I also was able to significantly reduce the current on the final bias network. The load impedance presented to the driver from the finals is still quite variable, but with Class E, it does not matter as the output is remarkably clean. Some Class E approaches are fed directly with a square wave and this can allow for even greater efficiency. I could look into this, but I think I have captured all the low hanging fruit. I still had to allow a moderate level of current on the first bias network, but it is only about 2mA. There is about 40mA spent on the driver and less than 1mA on the second bias network. This is a total of less than 45mA, for around 550mW. In total, including the driver and bias networks, we should be spending less than 7W to drive 5W of RF on 20m and less than 6.5W on 40m. These levels are well below half of a FT-817 (not counting the FT-817’s draw for other things like the screen, activating the coil on the rear connector, etc).

The RX circuit needed some adjustments to deal with with the change in the output signal. I adjusted the bias on what is now Q12 up to about 11V, as the peak to peak voltage of the TX output here. I also need the base of the signal at least around 0V, otherwise the body diode of Q12 will begin to conduct. We will still be well within the breakdown limits of the device. Both the BS170 and 2N7002 have 60V drain source breakdown

Side note: What is this body diode on the 2N7002? It is what comes with the territory with MOSFETS, it is part of their nature, and for a N channel, it means that the drain will get passed through to the source if the drain is below the source, like a forward biased diode. Also, when reversed biased – the normal usage of a MOSFET, the diode acts like a zener diode, with the drain to source breakdown voltage being the zener voltage.

Speaking of zener diodes, I will be putting one across the BS170 finals, at somewhere in the high 40V, I’ll just need to select the device. Of course we never want to see the MOSFET put to its breakdown voltage. One impact of Class E design is that there are higher voltages than what would be possible with Class A or even Class C.

The Class E matching reactive components are of course band specific, so the location of the relay will need to change, with it being right up on the BS170’s. The peak current across the relay is about 1A, or 700mA RMS. This is well within the limits of the G6SK-2F unit I plan to use.

Latching relays

One other thing I should mention is that I am using two coil latching relays. These will only use power when I need to change the relay orientation. I’ll use 5V relays with the supply fed by a 5V regulator.

Next time, I’ll look at the audio part of the circuit.

73 de Wayne VK3WAM

Designing a 20/40 band CW rig – Part 2

Hi all,

This is a continuation of Designing a 20/40 band CW rig – Part 1.

Shown below is a schematic of the TX and initial RX parts of the rig. I have been successful in simulating all of these parts, and have a reasonable amount of flexibility if the real world performance of the components does not match the simulated performance.

Schematic of the TX and initial receive sections of the rig

TX Driving

This being a CW orientated rig, all that is needed is a oscillation on the desired TX frequency. CW merely turns it on and off. I did mention that I wanted to retain cabability of PSK and FSK modes. PSK needs the phase of the oscillation to be changeable, while FSK modes need the frequency to be changeable. An Analog Device AD9834 fits the bill. Steve KD1JV is using this in his Mountain Topper. This device is not a PLL and VCO combination, rather it generates the output digitally, and then feeds a DA convertor to generate the waveform. The output is needed for two things – it is the Local Oscillator for a mixer, and can be used directly for a TX frequency. The AD9834 has a number of capabilities that I plan to use, but this will be for another post.

Unlike Steve, I have decided to take the analog output of the AD9834. This output will drive the initial mixer, and the device selected has a 50ohm load. I’ll talk about this device on another post, but I will be using a different approach to the other designs I have seen because I want more dynamic range and better inter-modulation distortion performance.

The input to my driver is going to be taken off this output. The AD9834 can provide a balanced or unbalanced output. I need unbalanced. This signal is shown as OSC. It then feeds the base of a MMBR941, Q1. This is a RF BJT device in common emittor configuration. One of the nice aspects of BJT devices in common emitter is there is a fair degree of flexibility in setting the input impedance and the output impedance of the device. I decided on a 150ohm input impedance. I am also driving the device fairly hard, but not too close to device limits. The gain on the device is 26dB.

To save power when not TXing, I use Q2 as a switch. This 4401 device is being used as a current sink, switched on during TX, and off when not. It deprives Q1 of its DC ground, so no DC current will flow through the device. The bias network is shut down, but is still kept alive on AC so that the load presented to the AD9834 is not significantly changed. The effect of Q2 kills nearly all of the output power from the collector of Q1.

TX Power

My objective is to deliver 5W into a 50ohm load (antenna). There are quite a lot of choices to go about this, but I want to keep things as simple and as cheap as possible. I considered initially using another BJT in emitter follower mode, by using Q1 to deliver the desired peak to peak voltage AC signal and then the emittor follower would supply the current. I used an inductor on the emitter to improve the efficiency, but at the end of the day, it is still being used in Class A mode. This is a CW rig, so Class C amplifiers await!

The schematic shows three BS170s that are driven by the output of Q1 on their gates. These are N-channel MOSFETs that can dissipate about 800mW of power. If they are run 66% efficient, then that means that each one can deliver 1.6 watts. The efficiency is a function of the peak to peak voltage supplied by the MMR941, and what level the bias is set at. The bias mid point needs to be below the pinch off voltage on the BS170’s for Class C operation. The further away, the better the efficiency, but it cannot be set too far away, as there are limits to the peak to peak output I can get from the driving device. After a fair amount of experimentation, I set the bias level using a voltage divider resistor network. R9 and R10 (the R10 going to ground) form this network. (The other R10 nearby on the base of Q3 has a new identity as R18). This level ends up being around 1.2V, around a volt below the BS170 cutoff to ensure Class C operation.

The job of Q3 is to act as a switch, on during TX, so that R9 and R10 do their job as described. Off during RX, so R9 is taken out of the circuit, and R10 pulls the base of the BS170’s to ground so that they are cut off from doing anything. The BS170s then act as open circuits.

Presenting the output to the load

Class C waveforms have less than half of the initial sine wave present. The BS170s also present a changing load to Q1, so what it produces is not a great looking sine wave either. We actually have quite an ugly looking waveform on the output of the BS170s. This needs to be cleaned up. Also, the load is not 50 ohms. It can’t be if this circuit is going to operate off 12V. The best that can be hoped for, in terms of an output wave form is 24V peak to peak, due to the action of the inductor L2. I used the complex model of L2 in my simulators, rather than using a perfect inductor. The complex model output was practically indistinguishable from the ideal model. Coilcraft make some good inductors, and I plan to save builders of this rig from having to wind their own inductors, by using these Coilcraft chip inductors.

24V peak to peak really only allows for 12 ohms load impedance directly on the finals. This needs to be transformed to 50 ohms at the antenna connection. All rigs need to do this transformation. Steve’s Mountain Topper Radio provides a network for each band. The FT-817 provides one for each of its bands that it can TX on, and they are switched by relays. The FT-817 set of finals are operated in a push-pull configuration, but off a 8V rail. This means that the load impedance that these are driving will be lower than 12 ohms, perhaps about 9. I should analyse the inductor/capacitor networks for a given band that Yaesu have put in there. If you were to look at the circuit diagram, these matching networks take up most of the power board module schematic.

I reckon a bit of convenience is a good thing, so I am going to use a relay to switch between the two bands. This relay is K1. It is DPDT, so I can use the one relay for both ends of the matching network.

The match network has a LC tank which does most of the job of restoring a clean sine wave, and then a LC series, presenting a high impedance to remaining harmonics. This second LC series begins the process of impedance matching, where I only need two more capacitors to complete the job. This is per band of course.

Now reality bites, and there is the need to use real world components. Also, for these networks, X7R dialectic is not acceptable, but for cheap capacitors, 1nF or above tends to be X7R. So to get around this, I have paralleled up some caps to get the values I want, and to continue to use NP0 dialectic caps in 0805 SMT size. There was one cap where this approach was too long in the tooth, so I use a 3.3nF ATC cap that is 1111 size. It’s a much more expensive cap, but I’m only using one!

After these matching components, I have a sine wave output at 50 ohms supplied to the antenna. It is the job of the operator to take it from there.

Receiving

I have to receive as well, this is a transceiver after all! Now, approach 1 could take the signal straight off the antenna jack, but there is the matter of the TX output to deal with. At 50 ohms, this is not going to be a 20V peak to peak output any more. It is closer to 83V peak to peak. Of course, all of the caps need to have dialectics rated to 50V, as 83V gets 41.5V from ground, each side.

Now, I could use a relay to switch between RX and TX, to shut out the TX signal from going anywhere but out the antenna jack to the antenna. The FT-817 does. One problem – full break in on CW. It is not too good to have a relay clatter (twice) every time you send a dit or a dah. I want full break in capability on this rig, so this means using a transistor approach. A transistor is going to have to hold back this 83V, but that is too much.

Instead, I have taken a similar approach to Steve KD1JV, by putting a blocking circuit at the 12 ohm area. This cuts down the voltage that the blocking network needs to resist on TX. It also has the benefit of providing a filter through the same LC networks that dress the TX output for the antenna.

The main transistor to block is Q9, a N-channel MOSFET 2N7002. I have used a biasing network, that is assisted by BSS84 Q10 and a 4401 Q11.

Q11 is a current sink. When switched on, it takes the gates of both Q9 and Q10 to near ground. Q9 is a NMOSFET, so a ground on its gate will block any signal that is about 0V or higher. Near ground on Q10 is a PMOSFET, so it is switched on, there being nearly -12V between its gate and source. Q10 switched on takes R15 out of the circuit, leaving a voltage divider of R13 and R14, meaning Q9 is biased over 10V. The input signal is going to swing between 0V or so and 20V on the drain of Q9, with 0v at its gate. If something makes it to the source of Q9, it won’t be much below the gate, meaning Q9 should stay switched off, switching off TX signal from sensitive RX circuitry.

When wanting RX, Q11 is switched off. This then means the gates of Q9 and Q10 are pulled to 12V by R17. 12V on Q9 gate will tend to switch it on. Q10 will be switched off, meaning that the bias network is now R15+R13 against R14. The drain of Q9 will be biased at around 1V. There is 12V on the gate now, and around ground on the source. Q9 will be switched on as hard as I can make it, so get as much of the RX signal through.

Unfortunately, when TXing, quite a bit of the signal still makes it through Q9. Too much by itself to be safe. The transistor itself is ok, it is not being used anywhere near maximum limits, but the mixers awaiting later will not like what gets through. I want to block this signal, so I use another LC series resonant device to block the harmonics. This is because what does get through Q9 is horribly mangled with most of the power in the harmonics, not the fundamental. This cuts things down nicely. Also this network starts the process of impedance matching from 12 ohms back up to 50 as the mixer I want to use wants 50 ohms as a source impedance. Now this matching network is band specific, so this means a second relay. This relay, like the TX relay is only switched during band changes, so there will not be any relay clatter here. Q12 and Q13 are little helpers. They are switched on during TX to shunt away any TX signal that still makes it through this far, but because of the LC network, it ain’t much. The job of Q9 is also easier to block the TX signal when it is mostly high impedance sitting behind it.

Wrapping up

This about wraps up this post. Next up I will look at the audio processing part of the rig. The other major parts are the RX mixing and filtering and the microprocessor. I’ll look at these with later posts. My plan is to get one of these rigs built in about a month to two months as a prototype, and we’ll see how it goes from there.

Regards, 73, Wayne VK3WAM

This topic is continued at Designing a 20/40 band CW rig – Part 2.

Designing a 20/40 band CW rig – Part 1

Hi all,

I have been spending some time working on the design of a ultra portable CW rig. I’ve been spending time looking at various kit designs from Steve KD1JV, Ramsey Kits, You Kits, the Elecraft KX1 and others. Some rigs are quite simple, others have a more sophisticated approach.

Goals

In setting down to design a rig, I was wanting something that would work well in a SOTA activation context. I would want the rig to do the following:

  • I did not want to be limited to a narrow band of frequencies around a crystal, but wanted the whole band to be available.
  • The power output needed to be around 5W – full QRP. 500mW CW can be tough going in VK. One attraction with SOTA activations is working the DX chasers, so 5W is nice, while keeping the QRP endorsement intact.
  • I’d like to keep open the option of some digital modes, even if the rig would not do these directly itself.
  • The rig would need RIT.
  • If possible, to switch bands without needing to use external switches.
  • Deliver near 5W from a 12V source, safe for 12.6V – a three series LiPo cell, usable down to 9V.
  • Do all of this in a kit that would cost less than US$200, good, $150 better, $100 best – but no promises!

Overall rig design

The rig could basically be broken down into a number of sub-sections.

  1. Power – a cut-off for low input voltage, and regulators for 5V and 3.3V
  2. Audio frequency – RX audio and sidetone
  3. TX – SSB rigs mix up, but this being a CW rig, I only need to switch an oscillator output and amplify up to 5W. I also need to impedance match for 50ohms at the RF connector
  4. Oscillator – Given my tune the whole band requirement – I’m going to need a PLL and VCO or equivalent circuit, such as a DDS.
  5. RX – Taking the RF connector, I need to either use a relay to switch away the TX, or a transistor switch. I then feed a mixer to an intermediate frequency for filtering, and then can feed a second mixer to audio frequency
  6. Control – Need to use an embedded controller – I am familiar with the PIC line, so I’ll use something there. This will need to set dividers for the PLL or DDS, take button input from the user for tuning, band selection, RIT, provide a keyer facility (I won’t be using a straight key) – with the ability to configure at least the wpm send rate

I’ll go through these in greater detail over a number of posts. I have been influenced by some of Steve KD1JV’s ideas, but also want to do some of my own things. I have already mentioned that I want internal band selection. I also want a volume control, with the rig able to drive at least a 16 ohm speaker, along with low impedance head/ear phones – like the ones supplied with mobile/cell phones. I also want it to be capable of driving 200 ohm headphones.

Above, I floated ideas of how to switch TX/RX. A relay could be used, but if full break-in is going to be supported, relays are a pain. Relays are good for things like band switching – ’cause you don’t switch band 100 times a minute, but to keep the power down, they will need to be latching.

At time of writing this post, I have most of the sub-section circuits designed and thrashed through simulations and a bit of bread boarding. I’ll hopefully put up some posts over the next few days or so looking at TX, the audio section and some of the RX.

This design is going to be largely SMT, but to keep things sane, I’ll use 0805 or larger size components. I could make it thru-hole, but the physical size would be much larger, and it would be significantly more expensive.

73 de Wayne VK3WAM

Continued in Designing a 20/40 band CW rig – Part 2