Thursday, June 23, 2016

LDMOS Amplifiers

More on the control System ~ (7/05/2016)

My initial thoughts on the switching of the low pass filters reflected on my past experience with filter switching harkening back to my KWM-4 SSB/CW transceiver built in 2013. When I built the KWM-4, this was a real challenge as my goal was to have no band switch as such; but rather to take advantage of a three digit code that could be associated with band memories that was generated in the K5BCQ kit. By using the encoder to menu change bands the three digit code associated with the bands could provide the signals to control the band pass and low pass filter banks. So why not the same here with the LDMOS amplifier?
Shown below are the BPF and LPF boards in the KWM-4. 

Below is the KWM-4 schematic that was initially used with the project which was later changed to the second circuit which was finally used in the project. The second circuit uses P Type MOSFET's and in effect used less parts. For test purposes I included the ability to manually switch band using three toggle switches. This proved beneficial  as I could bench test the LPF or BPF boards  without the need to have the frequency controller.
Interesting side note -- the concept/circuit of taking the three digit code and coming up with the band switching signal was done on my own. Finally I designed something where it worked and it was done with my own hands. I shared this with K5BCQ and he said --why didn't you use a CD4028 as you can decode and drive the relays directly. The case of the better mousetrap has once again arisen to the top. Well it was my design and it did work!!!!
So having the KWM-4 experience under my belt I started down the same path, only this time using the CD4028. Because of the availability of many more output pins on the Mega 2560, my thoughts were to have not only the LCD display what band was being used but also to have six LED indicators on the front panel that would light up depending upon which LPF was selected. Thus six Digital Pins for the LPF lights and three pins that would be decoded the via CD4028  to actually drive the relays. So that would take another three Digital Pins. When I developed the code it was with the 9 Digital Pins.
Then I got to thinking about the actual relays that would be used on the LPF which are American Zettler good for 20 Amps on the contacts. Since a pair must be put in line for each band that coil current draw would be more than what was available directly from the CD4028. This would then require additional transistor (or MOSFET) switches that could handle the current. Now we were adding a lot more parts. The relays used in KWM-4 were communication type (Omron G 5V1) and four of those (two in the BPF and two in the LPF) had a lot less current draw.
That is when the "Ben Franklin Effect" (being struck by lightning) took over. I asked why was I making this so hard? Then it became clear that I did not need the three digit encode and decode and all of the extra circuitry. The very same signal that would light the panel LED's could trigger the transistor (or MOSFET) switches. Boom there we had it! I would only need 6 Digital Pins and a lot less parts. This also dramatically reduced the code logic and freed up three Digital Pins.
One of the best parts about having only 15 or 20 minutes at a time to work on this project is that you have to think about what is the best use of that time. Breaking the project into pieces makes you "noodle" -- a lot. Below is the first prototype schematic for the LPF switching.

Pete N6QW


Control System Breadboard ~ (7/02/2016)

Taking yet another step to assure project success the control system will be built on a bread board before it will be installed into the amplifier case. Here is the initial layout of the bread board.
The size of the bread board is 12 X 18 inches which was chosen as a  size to facilitate changes and troubleshoot problems during the initial development stages.
Starting in the upper left hand corner is the 9 VDC power supply for the Arduino Mega 2560. This supply has plenty of reserve capacity as there are many more I/O pins and thus a larger current draw. Next to that supply is the 12 VDC supply that will be used for powering on the "Hockey Pucks" shown in the upper right hand corner, as well as the relays in the low pass filter board. The small metal enclosure is another supply. This is the DC to DC convertor using the 48 VDC that powers the amp and converts that to 12 VDC that is the source in powering the In/Out TR relay and the Bias supply. The small metal plate holds a 4X4 keypad and the 4x20 LCD. The final install will most likely use a 4X3 keypad. The 4X4 was in the junk box! The vector board will house various circuits that interface to Arduino Mega and the myriad of control relays/LEDs. The terminal blocks will provide a convenient means of connecting to LEDs and external devices like sensors (heat and SWR) and relays/switches.
Stay tuned.
Pete N6QW
Control System Subtleties ... (6/28/2016)
Frequently I will install a control system to later find out --it doesn't work or work properly. Have you been there? My aim with this project is to find those anomalies and "gotcha's" before the first wire is connected to anything. That is the beauty of the Arduino Mega 2560 --lots of pins and you can simply hang a LED on any pin to see if the circuit is controlling as it should. I really like that. No smokedparts!!!
When I looked at the "critical failure path" (something left over from my aerospace days) I could see that the Arduino was really supplying two critical functions:
  1. The pure control function that in essence turns on the power supply and at the appropriate time the amplifier itself.
  2. The second is the supervisory function that should some limit be exceeded that several things happen such as turning off the supply or preventing the amp from being put in line. These could include over temperature conditions or the SWR is out of whack or perhaps that the 48 VDC supply is heading to an over voltage condition. Other conditions might include the failure to put in line the low pass filters. We certainly wouldn't want the power supply to be OFF yet be able to put power into the amp -- that would be one expensive dummy load.
I would now like to focus on one of the "conditions of concern" or as I used to say -- a COC event. Briefly here is the thought around  one of the processes and how it is addressed in hardware and soft ware. Once the amp is powered "on" (meaning the 48 VDC is powered on)  and we have the appropriate Low Pass Filter selected,  the next step would be to put the amp in line. But there are certain tests and sequences that must be satisfied for this to happen. I will now outline those steps and tests.
  • The basic mechanism for putting the amp in line is a contact closure from the transceiver that is tied to the Push To Talk Switch (or VOX). That contact closure is detected by the amp and then a series of actions take place.
  • But here is the first subtle test as there are in fact several contact closures that must be detected and the first of these is called LED16. On the rear of the amp is a standard RCA connector where the external PTT(VOX) contact closure signal would enter the amp control system. At the RCA connector is wiring that is fed to the NO contacts of a small relay (called LED16). If that relay is not closed then you cannot complete the keying circuit. The closing of LED16 has many dependencies including is the power supply on, is a LPF filter connected, is the amp in bypass or emergency shutdown? Other factors would include over temperature or High SWR. Thus many other events determine whether it is safe to close LED16. (Don't you just love how and Arduino can do all of those tasks?)  So now we have the RCA Connector , the LED16 NO contacts, a protection diode and finally ending up on analog pin A0. The second subtlety  is that A0 is constantly read each time through the loop and until it sees a low condition (from the PTT/VOX through the LED16 and the diode). Nothing happens until A0 is low and then the next series of actions take place.
  • We have a complete keying circuit but now before RF is pumped into the LDMOS amp we must first connect the antenna to the amp, then turn on the bias and finally the input RF is fed into the amp when the input side of the TR relay is activated. When the PTT/VOX is un-keyed the process is done in the reverse order with the transceiver input shut off, the bias turned off and finally the amp uncoupled from the antenna. There are delays built into the code to assure the relays are in fact closed or open.  
  • LED17 and LED18 are relays that are switched from the Arduino based on a timed sequence but another subtlety here is that their source voltage comes from a DC to DC convertor connected to the 48 VDC rail. Thus if the main power is OFF you cannot switch the amp in line. The same also applies to the amp bias circuit which is also connected to the 48VDC to 12 VDC convertor. Snubbing must be applied to the LED17, and LED18 relays.
  • A circuit diagram would look like below.
Pete N6QW
It is all in the Control Systems ...
 This project encompasses proving an Arduino Control of a hi Power Linear Amplifier. It is a new departure for N6QW as it has extensive I/O requirements which required moving to the Mega 2560  a  Arduino variant that has 56 Digital I/O and 16 Analog Inputs. The on board memory is 256K
    The current configuration uses a 3x4 Keypad as the main control element.
    Key 1 = Power On
    Key 2 = Power Off
   Key 3 = Amp Bypass [In this mode the LPF's are disconnected and the amp power is off it requires RESTART and LPF Selection the TR Relay is disconnected so No RF into the amp on Bypass.LED16 Controls                        whether the amp is bypassed BUT LED 17 and LED 18 control the actual sequencing of the connection of the amp to the antenna system and the transceiver. WE are trying to avoid "hot switching". Thus the amp is connected to the antenna first and then the transceiver is connected to the amp. This is done by a small delay on the connection of the amp to the input side. Problem solved!]
The next series of keys select the correct Low Pass Filter with 2 subsets panel LEDs light up to show which band also shown on the LCD (20X4) In addition a 3 digit binary code is generated which is decoded to select which filter: Key 4 = 160M, Key 5 = 80M, Key 6 = 40 M, Key 7 = 20M, Key 8 = 15M and Key 9 = 10M.When any of the LPF buttons are pushed the TR Relay is powered on.
Key 0 = Manual Emergency Shutdown and is different from Power Off in that a 1 minute delay is introduced into the loop so that you are forced to "noodle" about why the Emergency Shutdown was necessary. There are options of automatically invoking this condition based on events such as an over temperature situation or a high SWR condition. When the Emergency Shutdown occurs the N6QW AMP Control Box disappears from the masthead and goes blank When the timing period for Off is over it reappears -- nice touch N6QW.
    Currently Key # and Key * are not used
 Fail safes are included into the code that either detect aberrant condition or auto bypassing the amp if no LPF is selected, Over Temperature and High SWR will shut down the power supply. Logic is also provided from putting RF into the amp without the supply being in operation.
  Various Analog Sensors reads the actual output Voltage, the temperature of the heat sink and the SWR condition. Several of these parameters can trigger the power supply to the off condition. SWR uses two of the analog inputs to sense the Vfwd and Vref to actually calculate the SWR that that amp output is seeing, If it exceeds some set value like 2:1 the power supply is shut down.
 A8 is a particularly important sensor as it measures the 12 Volt rail after the latching. There is a call routine called VDC12 and there is a two part screen that deals mainly with LED 16 and the ability to trip the TR relay. Two things happen one is the ability to change any of the LPF's and second is the ability to trip the TR relay
    Revised June 23, 2016 N6QW */
    #include <Keypad.h>
    #include <Wire.h>
    #include <LiquidCrystal_I2C.h>

Pete,  N6QW

Monday, June 20, 2016

Circuits on Hold

Making a Difficult Decision!

I am placing a hold on any further LDMOS RF Amplifier postings. Frankly I have limited time and I must choose between blogging or working on the project. Thanks for riding along.

Pete N6QW

Wednesday, June 15, 2016

LDMOS RF Amplifiers

LDMOS Amplifiers --Are You On Board?

6/19/2016 ~ The Power of the Arduino -- The TR Switching Sequence.

One of the biggest issues (maybe ranking near the top) are the problems with putting a RF Amp in line between your transceiver and the antenna system. All sort of problems can be encountered and mainly these revolve around protection of your precious FLEX6700 $8 Kilobuck transceiver to the issue of smoking the final. A one time permanent  tattoo that says "I Smoked a Final" is OK--but you want no more than one such tattoo in a lifetime.
So not only is it an issue of amplifier switching but amplifier protection! The Arduino is ideal in this case as there can be logic incorporated into the control functionality to add a high degree of protection.
Here are some possible cases that need addressing:
  • The Amplifier is OFF but you accidently pump RF into the amp.
  • The Amplifier is OFF but you have the amp TR switches engaged so that RF is pumped into the amp.
  • The appropriate low pass filter was not selected --so the output side is not connected but the input side is - smoked the final.
For your consideration are my initial thoughts on how to address these issues --again I would find it hard to accomplish with purely mechanical controls.
Let us now take a tour through this schematic. Well start first with the Meanwell DC to DC convertor which is a really cool box available from Jameco Electronics. The input can be anywhere from 36 to 72 Volts DC and the output is 12 VDC at 1.25 amps DC. The cost is about $13 USD. In simple terms --if the main power source (our 48VDC 30 amp supply) is OFF, then there is no power to these relays. So any action that causes the main supply to be off will cut off the source of power to these relays. Pretty cool!
Next we want to look at LED16 which controls another one of those 5 VDC SPDT Omron relays. In essence a command to put the amp in line must be seen as a grounded input passing through the LED16 relay contacts and ending up as a "LOW" signal on analog Pin A0. There is nothing special about using an Analog Pin --it could have been done with one of the Digital Pins --but I did want to experiment with the analog pins as they will play an important part with the sensors.
LED16 when closed and when a ground condition (LOW) appears from your transceiver on Pin A0, then this satisfies one of the conditions to enable LED17 and LED18 to be activated -- the 48VDC present is another.
But let's go back to LED16. There are many conditions that must be met for LED16 to close the series circuit. The first is that the Amplifier must be ON and that neither the "normal off"  or bypass" or "emergency off " condition exists. A second here about normal off and emergency off. Normal OFF lets you start the amp immediately as does Bypass. But with Emergency OFF you must wait 40 seconds (or however long you want) before you can restart the amp. This is purely so you are forced to think about the "why" this happened before you tap the "On" switch. Another constraint to the energizing of LED16 is if the LOW PASS FILTER relays for a particular band are not energized. This was done by satisfying a multiple "OR" condition represented by two parallel lines || . I guess this may be the first time I used a logical OR condition with the Arduino. Two "if statements" are needed with one to detect if any of the LPF relays are in line or to detect if none are in line. Try that with just toggle switches! 
If such a condition were it not addressed could mean you would pump RF into the amp without any load -- smoked final.
So that now brings us to LED17 and LED18. Two LED signals are used so that they can be sequenced with a small (selectable) difference in time. You want LED18 to come on first so the antenna is first connected to the amplifier and then you want to hit it with RF. This prevents "hot switching" where there is initially no load on the amp and you are pumping RF into the amp. But for LED17 or LED18 to sequence, LED16 must be activated and also you must have 48 VDC into the DC to DC convertor. As I add some features there will be other constraints such as over temperature and high SWR.

One of those features to prevent engaging LED17 or LED18 is to measure the output voltage with an "if" discriminator  such as a call void checkVolts()---where -- if( volts < 40 || volts >50){ digitalWrite(LED, LOW);}  This essentially shuts down the power supply!

To activate the LED17 and LED18 controlled relays I used a simple 2N3904 switch that is triggered when a voltage appears on the base. Just for safety in case something gets smoked with the 2N3904's I will probably add a couple of 1N914 diodes in series with the 10K resistors to prevent an voltage being back fed into the Mega 2560. Cheap insurance !
Pete N6QW
6/18/2016 ~ So OK you are not interested in LDMOS RF Amplifiers ... BUT you might find the use of the Arduino as the control function useful in other projects.

I can tell by the number of visits to the blog that there is little interest in building a 1KW LDMOS RF Amplifier and I get it. But to that, end what I will be sharing with regard to the use of an Arduino Mega 2560 has other applications like building a control system for a Beacon transmitter or perhaps switching antenna systems. So there just might be a nugget or two worth your time. I am not an Arduino expert but am simply an experimenter that has been lucky enough to get a few things to work.
Just today I saw a project from a ham in New Zealand [Dex, ZL2DEX ] who designed a circuit to scan channels in one of the early channelized FM radio transceivers. It was an elegant design using a small army of NAND circuits and mostly discrete components. There had to be a lot of noodling to get that to play. Today's digital engineers would take an Arduino and with about 100 lines of code  could achieve the same purpose. So its here and why not use it. But employing an Arduino requires thinking about things differently.
Let us start with an example using the LDMOS RF Amplifier as the venue. I could build a control circuit that would virtually use all mechanical toggle switches, lots of relays and perhaps one or two NE555 timers, a thermal switch and perhaps one or two other sensors along with a few discrete components.
Would it work? Of course it would work! But there would have to be a lot of manual intervention and were a critical situation occur, a manual intervention on your part would be required. That time period where you might see a problem, until you hit the OFF switch may be of a duration that you would smoke the final --ouch $200.
The Arduino control systems would require some manual intervention but the ability to auto sense aberrant conditions and to take the required action is faster than you -- such an approach just might save you $200.

 Lets start our thinking differently with our motor starting example and the two switches SW and SW1. SW is a normally closed Push Button switch and SW1 is a normally open Push Button switch. So how would this be represented using an Arduino. To answer that question we will use the diagrams below.
The first diagram is of course the motor starting circuit, and the second is simulating the momentary push button switches SW and SW1 using the Arduino and two micro sized 5 VDC SPDT relays. The ones  used, the contacts are good for two amps (Omron G5V1). The beauty of the relays since they are SPDT is that you can configure them as either NO or NC.
Guys I used this same approach in my SSB transceivers when I give a momentary push to the TUNE button then there is a delay built in to create the 988 Hz tone and to keep the PTT engaged for about 10 seconds --so this is merely building on what I have used before. In passing the same code works for either SW or SW1 needing only to identify which PIN will be used, as it is how the relay contacts are wired determine NO or NC. In writing the code for the Arduino several things must occur and these include identifying that there is an integer number identifier that can't be changed. Thus the const int LED =28; means that a LED is attached to pin 28 on the MEGA 2560 and cannot be changed.
While I use the term LED because  with a LED it can actually be used to visually show an output when driven high, more importantly is that you have 5 VDC on that pin. The next piece of info is to tell the Arduino that Pin 28 is being used in the pin mode and this is done in the setup portion of the sketch with the statement pinMode(LED, OUTPUT);  --- this is just saying that pin 28 will be an output pin.
The final three pieces occur in the loop part of the sketch where some event occurs that tells the Arduino to drive Pin 28 HIGH (voltage on the pin); to hold that pin HIGH for a short period of time and then to drive Pin 28 LOW. [Two code snippets are shown the only difference is the Pin assignment, with LED = 28 and LED0 = 30.]
                                                digitalWrite(LED, LOW);
                                                digitalWrite(LED0, LOW);
Now lets get back to the event that will trigger SW or SW1. In my approach I am using a keypad with Key =1 being the Power On button which a tap of Key 1 signals the Arduino to give a momentary contact to SW1 which then goes through the latching process and the supply is turned ON. A momentary tap to Key 2 turns the supply to OFF as Key 2 momentarily engages SW.
So now the naysayers will shout --we could have done that with manual Push Button switches which is of course is true. BUT suppose there is a heat sensing device on the copper spreader and there is a temperature rise sufficient to cause concern? Separately there is code that when that heat rise reaches a pre-determined level there is internal code that essentially triggers SW and the supply is shut down. So the same basic code that normally shuts down the power supply can also be embedded into other call functions to shut down the supply. This is where we see the real power of the Arduino.
By the way similar code snippets are used to sequence the two TR relays so that the antenna is connected first before the transceiver RF is pumped into the amp. I have done that manually with the vacuum relays in the Big Dog amp which entailed some RC timing circuits. But with the Arduino a few code changes can fine tune the time duration of the sequencing. 
Hopefully, this may start you to think about the Arduino as a marvelous supervisory and control device --something not easily done with toggle switches alone.
Pete N6QW
/16/2016 ~ Motor Starting Control Circuitry

So ok what you all have suspected for a very long time is now being presented with evidence --Pete is a couple of cornflakes short of a full box! He now wants to talk about starting motors???
Often times we learn things in one arena that have application in another and you will see why my box is full. In the 1980's I had a life changing experience where I worked as an outside sales engineer for a company selling automated industrial controls (aka a peddler). So I would visit various client companies that had automated production facilities and my mission was to sell them many things, at times stuff they really didn't need; but it was cool stuff. I got a chance to play with hardware and got paid to do it.
One of the most basic circuits you work with in automated industrial controls is what is known as a motor starting circuit. You need something more than a $3.99 Radio Shack toggle switch to start a 3 horsepower motor thus the circuit below.
OK how does this circuit work (again more than a toggle switch)? BTW a 3 horsepower motor is like 2200 watts -- about the load of a 1KW output amplifier. The sequence of events is that there is a momentary push of SW1 which completes the circuit and Relay 1 is engaged so its Normally Open (NO)   contacts bridge SW1; but because the circuit is complete the contacts stay closed. The momentary push button SW1 is out of the circuit but the circuit is complete so the motor runs. Now to stop the motor if you push and engage SW which is Normally Closed (NC), that opens the voltage and the relay drops out and so releasing SW back to its normally closed state will not start the motor.
In practice the actual motor is not the load but a high powered solid state switch receives the start and stop commands this way. So SW and SW1 are actually controlling a "hockey puck" solid state switch or other high power contactors to power on off the motor.
Now what does this have to do with the LDMOS amplifier and how it will be controlled. In essence this motor start circuit can be used to control the application of power, which for the LDMOS amp is 48 VDC at 30 amps. Additional switches can be daisy chained with SW  to add other controls. For instance if you added a NC thermal switch in series with SW and suppose you hit the critical temperature. When such an event occurred then the thermal switch would open and the circuit would be broken and the power supply turned off. Until things cooled down you could not restart the power supply. This is where you say AHHHHH! Now suppose you had a SWR detector in the loop and if you exceeded say 2 to 1 that could supply a trigger to shut down the supply.
During the time I worked as a sales engineer we were making the transition from hard controls to soft controls. A revolutionary step forward was the Modicon Micro84 which was a programmable logic controller. [I sold a lot Modicon's mostly so the client companies could jump on the automation bandwagon and not necessarily real applications.] It was a brave new world in moving from a panel full of switches to a small box where you had wire terminals. We have that today with the Arduino.
We can actually program the Arduino to simulate SW and SW1 and essentially stand in for these hardware devices. The Arduino can actually take analog inputs and cause other actions --remember about a thermal switch or a SWR trigger. That is exactly the plan and we will include band switching of the low pass filters all under Arduino control. But we will need to move away from the Uno, Nano or Pro-Mini. This task will take a lot more I/O an thus we will be moving up to the Arduino Mega 2560. It will also involve the use of the keypad.
Stay tuned.
Pete N6QW
In a direct departure from building homebrew transceivers I am now embarking on an LDMOS Linear Amplifier project. Being almost 3/4 of century old I am now believing life is too short for QRP. So over the course of the next several months I hope to chronicle my journey as I build my dream amplifier.
My apologies to those who are not into high power amplifiers. But at this time I have about 20 homebrew QRP SSB transceivers I have built and now it is time to add some shoes. This LDMOS is intended as a mate for my KX3 as it only will take a few watts of drive for 1 KW output.
In 2001 I traveled a similar journey when I built a 3CPX1500A7 single band (20M) amp. It was a joy to operate although with its 200 pound weight is not easily moved. Today almost that same power level can be achieved with a box weighing less than 50 pounds and that includes the power supply. So indeed the technology is here so why not use it.
By the Way --a 3CX1500A7 tube costs about $600 and a BLX188XR ( 1 KW device) fits in the palm of your hand and costs about $185. Did I mention the solid state device is instant on -- no more 3 minute time delays.
I should mention my first foray into PIC microcontrollers when I built a 3 minute solid state time delay relays for an earlier 3CX800 amp. The homebrew TDR cost me about $11 --an Amperite 3 minute TDR was about $40. The 3CPX1500A7 ( I now have a pulse rated tube in there) has two microcontrollers (PIC12F675). Both circuits were designed by me. The 1st provides a 4 second step start on the 3000 Volt 1 amp DC power supply -- the effective capacitance on the supply is 60 Ufd at 4000 VDC. IF you ask to ask why the step start then never build a high power amp. Part of the answer is to not shock the filaments. The 2nd microcontroller provides a 3 minute time delay after the filaments are on for at least three minute before you hit it with plate voltage.
The base plate for the 3CX1500A7 power supply is a piece of sheet steel 1/4 inch thick and 17" X 17". You cannot build an amplifier like this without due regard to the High Voltage and the needed safety measures. There is a micro-switch interlock on the top cover that when the cover is removed you cannot start the HV power supply.
Here is a sneak peek at the LDMOS amp that will be constructed.
Some photos of the Big Dog ---
I should mention there was a good deal of homebrew in this 3CPX1500A7  amp including the manufacturing of a suitable plate choke and winding the tank coil. The main bread slicer cap is rated at 7 KV. This amp project ranks right along with the KWM-4 in terms of complexity and engineering challenges. The interlock control circuitry including Grid overcurrent protection was a real challenge. One other challenge -- the blower runs for 1 minute after the amp  is turned off.
The power supply wiring approach is based on work I did with electrical panel builders -- I think the care with which the supply was built is evidenced in the final product. This is definitely not Manhattan construction! In case you are wondering the "red wiring" in the power supply is not from Radio Shack but 30KV high voltage wire.
In SS Podcast 187 I mentioned about dial plates made from a hard disk drive. You see how these were used in the 1st photo.



Thursday, June 9, 2016

Another New Transceiver from N6QW

Time for Another Transceiver!


The 60M Arduino Sketch  code is now posted on Noteworthy is that the code includes the ability to auto switch the band pass and low pass filters depending on which button is depressed


6/12/2016 ~ More Refinements

I will soon post the code in .txt format on my website I am happy to report that I now have the capability that as you change  from the 60M channels to the 40M channels that signal outputs are available to change the Band Pass and Low Pass Filters. So there is automatic band switching which makes essentially the full operation follow what ever is punched in on the keypad. USB and LSB  switching is retained.

Have received some inputs about eliminating the display entirely and by using 4 LED's the channel readout would be in binary format. Another suggestion was to eliminate the keypad and use the encoder to either act as a normal VFO or that it could have a mode to simply spin through the channels in the channel mode. I was provided seed code to start that process --so that may be the next task.

I managed to find two fifteen minute time slots so was able to build the audio amp stage a NE5534 driving an LM-380. About 6 months ago I cut the audio amp board on the CNC and thought it might come in handy --it did. You can see the audio amp board next to the main board.

Having standard designs plus having the computer programs for the CNC makes cutting boards pretty easy. Most likely the next 15 minute project will be the microphone amp. A thought-- because the board is so small is to make it a vertical board that will be soldered to the bottom of the audio amp board.

Pete N6QW

6/10/2016 ~ The Arduino Code is in initial testing!

Late Breaking News now on a 8X2 Display!!!!

Again I am following the path of using what I have and spending my time wisely as I have so little available. Since 60M is channelized with 5 channels there is not much need for an encoder and all that is needed is to select the proper channel. I made an attempt to use a couple of toggle switches and decode the position of the switches to select the channels --that did not end up too well.
Next I thought about using a keypad like in the conversion of the Ten Tec Model 150A and that led to success! I first stripped down that code so all of the "tuning" crap was removed and then set up the code so when you press Key # 1 you are on Channel #1. Having a  12 position keypad that left 7 open "channels". So then I thought about 9A2ZX's post that 60M was evidently not very exciting and so my horizons were expanded to think beyond 60M. I am happy to report we now have a 60/40M transceiver. Here is the channel line up.
Channel #1 ~ 5330.5 KHz
Channel #2 ~ 5346.5 KHz
Channel #3 ~ 5357.0 KHz
Channel #4 ~ 5371.5 KHz
Channel #5 ~ 5403.5 KHZ
Channel #6 ~ 5.0000 MHz (Check for time and propagation)
Channel #7 ~ 7.2000 MHz
Channel #8 ~ 7.2130 MHz
Channel #9 ~ 7.1850 MHz
Channel #10 ~ 7.2350 MHz (* Key)
Channel #11 ~ 7.0386 MHz (0 Key)
Channel #12 ~ 7.0300 MHz (# Key) [Or 7.078 MHz]
In examining my 40M operating habits, I find there are a couple of frequencies where I do most of my "yaking" and thus that directed my choice. Now if one desires so, it is not difficult to add back in the encoder. I did retain the LSB/USB switching capability as USB is typically used for WSPR or Digital Modes; but on 40 Meters typically it is LSB.
The coding effort was largely driven by lack of time --so working in 15 minute blocks you get what I got. I will do a bit more testing on the code and then make it available. AS of right now I am using a 16X2 display. Given the channel type operation the plan is to migrate this to a 8X2. Stay tuned --more fun to come.
Pete N6QW
We are on a roll here not so much for starting all the way from scratch as it is to take what is in the bins and making it into something new. When I made the conscious decision to cannibalize the original Let's Build Something prototype, the flood gates were opened and I found by combining other pieces I had in the junk box this provided the seed not for just one new transceiver but several transceivers. So check your junk box and see what is available.
Staring me right in the eye was the mainboard which had discrete components Plessey bilateral amplifiers and a 4.9152 MHz filter, which looked like this.
The first thought was how to use this in a somewhat different form. Since I had now freed up a 3.180 MHz crystal filter (Model XF-30A from an early Yaesu FT- 101) this would be a good fit for this board. I also convinced myself to quit using homebrew DBM's and move to the SBL-1. So now the board looks like this and in a minute you'll see the why of these changes. I used a small vertical board to mount the SBL-1 and you can see that along the right hand edge.

A Radical Departure & Proposal ...

So ok let's talk a minute about 60 Meters. The 60M band here in the US has been in existence for some time; but has some significant limitations including 5 specific frequencies (or channels) and a rather low power limitation --no kilowatt stations here. But given its position between the 75/80 Meter band and the 40 Meter band, 60 Meters  has some interesting propagation attributes. Did I mention not many problems with QRM. Also most operations are USB (or CW).
The FCC is kind of picky about using the specific channel frequencies and this is where the Si5351 can really shine. In fact the Si5351 was intended to generate specific clock frequencies but the ham community figured out how to turn the PLL into a VFO.  So why not use three of the Arduino Pins to program the 5 channels. Two of the switches would give 4 channels and the 3rd switch would give the 5th channel. For VFO operation three Arduino pins are used so there is no loss of pins.
By using five specific channels there would be no need for an encoder although one could be included to provide a "clarifier" function on receive only. The transmit side would be locked to the 5 channels. Notionally it appears that the Arduino programming would be greatly simplified if only 5 channels were required. NOTE: At this point I have not even done one line of code so don't ask for the sketch.
The simple 16X2 LCD  (or maybe even a 8x2) display shown in an earlier blog entry could provide a display for the channel and mode information. I would use my proven modules for the other blocks. A single 2N3904 Microphone amplifier coupled with a NE5534 and LM380 would be for the Audio output. The 2N3904's in the bidirectional amp stage would handle receive RF amplification and the transmit pre-driver. The standard 2N3904 and 2N3866 would once again be used for the transmit driver and the IRF510 for the final stage. I figure 10 watts would be a good starter for this band.
Right now this is all at the noodling stage but it does look feasible. I am unaware of many homebrew 60M transceivers but given that almost the exact same circuitry has been used successfully on 80/40/20 Meters it is reasonable to assume it would work. But we may be plowing some new ground here.

Frequency Noodling: Since I will be placing the LO above the incoming frequency there will be a sideband inversion and thus the normal LSB BFO frequency will be used for USB. Thus with a 3.180 MHz filter the 3.181500 BFO frequency would be used for USB reception and transmission. In calculating the channel LO frequencies we must add the 3.1815 MHz to the 5 specific channel frequencies and that is how the Arduino/Si5351 would be programmed

Channel #1    5.3305 MHz  LO set to 8.512 MHz
Channel #2    5.3465 MHz  LO set to 8.528 MHz
Channel #3    5.3570 MHz  LO set to 8.538.5 MHz
Channel #4    5.3715 MHz  LO set to 8.553 MHz
Channel #5    5.4035 MHz  LO set to 8.585 MHz

From my initial look see the 3.180 MHz  harmonics don't fall within the Band Pass Filter range and the Low Pass Filter cutoff could be set at 5.8 MHz, which should make everyone happy.
Share your thoughts on this project and email me at
Pete N6QW

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