So OK here is the great reveal on some of the earlier posts on this blog. I built a prototype of a stepper motor controlling the main tuning capacitor of an analog VFO.
We now have a digitally controlled Analog VFO. This is the first time that I have actually used an Arduino to control a stepper motor. Old hat undoubtedly to many of you; but a first for me with the Arduino. About 10 years ago I dabbled with a project using a PIC16F84. I was totally lost in the Assembly Language.
We will now, some 10 years later, circle back to that old project. It involved the controlling of a remote antenna tuner. This effort with the controlling of the capacitor with a stepper motor is a stepping stone to the Antenna Tuner.
See my website for more details on the VFO, the code to control the stepper motor including the LCD readout and the code for automatic zeroing of the capacitor on power shutdown. It also describes the Antenna Tuner Project approach and how the LCD will provide the readout for setting the capacitors and the tap points for the inductor using shorting relays.
Be sure to visit Yvan's website www.brainy-bits.com for the many excellent tutorials. It all started with his you tube video.
But for now as you will see the whole thrust of digitally controlled Analog VFO was to give deference to my friend Bill in recognizing the relevance of the analog VFO in today's rigs. At the same time we have the ability to add a touch of "digi" stuff to simulate the HRO dial mechanism.
In preparation for the contest I reconfigured one of my 40 Meter rigs so it will work on 20 Meters. It was a pretty simple change over. Unsolder two caps in the BPF and retune the Trimmers and then swap in a pre-made 20M LPF.
This is the two Filter, two VFO rig with a wooden front panel and of course the cool 20X4 display.
There are quite a few stations in the Caribbean that were testing their stations today. I picked a PJ2, and an HR8 using this rig with an outboard amp at 80 watts. I had my beam in line but can tell it is at times intermittent. I think it is a coax/connector problem at the beam itself. On the list to get fixed ASAP.
What I didn't mention was three lines of code changes, 5 minutes on the computer and I reset the tuning range to 20 Meters. Kind of hard to do with analog systems unless you have a bunch of heterodyne crystals.
VFO B defaults to FT8 on startup -- need to test FT8 on 20 Meters. Tomorrow.
The Red knob on the lower right hand side is the TUNE button. When the MOX switch is flipped on and the button momentarily pushed the word TUNE appears on the LCD right after the word Rig. After the 7 second cycle the word disappears and the rig returned to normal operation. During the TUNE a 988 Hz tone is generated and then pumped into the microphone circuit (following some filtering and attenuation).
Several off and on blog comments has caused me to think (something I should have done more of sooner).
My main issue was to "assure an automatic "ZEROING" of a circuit which led me down a path of trying to store a register value in EEPROM should I forget to manually Zero a control before power turn off. This quickly got complex. Then N8MN described to me how he used something I developed for an LDMOS amp control circuit to essentially do the same thing. Other commenters suggested a similar approach.
But then in a lightning moment at 3;00 AM this morning my brain said STOP!. You don't need to screw with the EEPROM! What I am trying to do is ZERO a control before the power goes off (either manually or automatically). When you power off the circuit logic takes over to automatically introduce a delay while the control is Zeroed and then power shut off. A bonus --some logic in there to provide reverse voltage protection.
Soon all will become apparent.. Pete N6QW
2/25/2019 ~ The Arduino Answer.
Some times the answer is at the end of our nose. Steve N8MN, contacted me off the blog and said he did what I wanted to do and he got the idea from me. Wow that is scary.
Several years ago I wanted to build an LDMOS amp but reasoned that the control system had to be extra "tight" so I wrote some control code using a Mega2560. I started off with the classical motor stop start circuit where a relay is latched across the contact of a momentary NO Push Button. The latching of the relay across the contact starts the motor. A similar in series NC PB once engaged drops the relay latch and juice is cut to the motor.
Soon all will be apparent...
73's Pete N6QW
Thus Steve suggests the same approach where you start the Arduino with a PB and then Break the circuit as with the Motor start only you add some delays to write once to the EEPROM before total power off. On start up passing through the setup lets you "0" the control. So I had the answer just didn't realize.
Joe, W3JDR suggested essentially the same thing in his comment. So now a bit of testing with hardware.
73's
Pete N6QW
2/25/2019 ~ Follow On Arduino Question
Rather than try to respond to the several comments I will post some additional information here. Thanks to those who made inputs.
At least for me, I know I want to do something but often do not know how to articulate something well enough to describe it. So here is an example: not actually what I am trying to do but to illustrate the issue.
You have a digital VFO and you are tuning around and the band is dead. So you turn off the rig and turn on Fox News to get the latest real news. About two hours later you go back and turn on the rig hoping band conditions improved. In the code I use there is always a default frequency and that is where the rig starts up not where I last left it. I had an ICOM 730 a long time ago and it did the same thing only the start up was somewhere in the CW band and I wanted to operate SSB. So every time I turned it on I had to move it to the phone band. I found that annoying. wouldn't be nice to start up where you last left off? Yes most rigs today now do that...
My real application has a "0" point only this time if you do not intervene where you last left the circuit now becomes the new "0" point not the real "0" point. There is a way to mechanically "0" the circuit before turn off but if you forget to do that -- then you are stuck with a new "0" point. This results in a recalibration of hardware and software, which is not easily done. What I was asking is as follows.
The latest reading (now being stored in a register) is always stored in the EEPROM device (or some other storage device)
You turn off the rig
When you turn on the rig and before the loop starts you read the EEPROM and if it is not "0" but some other value then a correction process takes over and the hardware is physically placed in the "0" state. This is not a LO but physical hardware that must be changed much like a potentiometer that must always be dead center when you start the loop.
My question involves just the EEPROM and how to store the value of a register, how to read that register in the setup and then make a correction. The rest I know how to do as it is now being done manually. I am trying to cure a my most common problem -- I forget to do it before I turn off the power.
Now if some of the suggested hardware can do this then I am on the right path. My other alternative is to flash the screen every 5 seconds. "Hey Dummy, Before Power Turn Off, Zero The Circuit". [Now That I know how to do!]
Pete N6QW
2/24/2019 ~ An Arduino Question
For those who have the Arduino skill set here is a question/task for you:
Before powering down the Arduino I want to read some value being stored and if that value is not "0", I want some action to occur which would cause that value being stored to become "0" upon reapplying power. It is important the code to do the actual zeroing process in the setup phase. This is like "zeroing" the meter before you take any measurements. I was thinking EEPROM but that is only good for maybe 100,000 cycles and if you constantly read and write to EEPROM that makes it only 50K times. So that is a consideration as well. The bottom line is that whatever is done once the loop starts, automatically it is starting at "0".
Pete N6QW
2/23/2019 ~ Capping off that magnificent Analog VFO.
Yes that is a bit of a play on words. However stability and lack of drift are not the only two factors of import in an Analog VFO. There is the nagging issue of how to set the frequency and do this on a repeatable basis. In the late 1930's enter "James Millen" a mechanical engineer of note who designed essentially an oversized micrometer dial mechanism mated to a gear box so that you could actually read small frequency change increments and do so on a repeatable basis.
Shown below is the world famous HRO Dial Mechanism. Essentially the large dial was a Vernier dial mechanism that had numbers appear in windows cut out on the dial face and the movement of the dial was coupled to a gear box (Boston Gear Works) where a large gear ratio required many "cranks" of the main dial to achieve one full rotation out of the back end of the gear box. The variable capacitor connected to the gear box was the type so each degree of rotation resulted in a capacitance that when plotted resulted in a straight line of frequency change. Move it one increment and it was a 1 kHz chnage. I find it funny that at times I am being told I am not on frequency as my signal is 20 Hz low -- which today is 1/50 of the resolution possible on the HRO dial. We have come a long way; but it was indeed advanced technology for the 1930's
I grabbed this photo off of a current eBay listing and you can have the above on a "buy it now" basis for a mere $275. Ouch. If any one has one of these either sell it for $$$ or you can donate it to the N6QW Laboratories where I will sell it for cash and buy more radio parts so I can keep making stuff so it can be posted on the blog and website.
Bill, N2CQR has one of these very mechanisms on a homebrew receiver that he calls HRO-ish. In a recent podcast he mentioned that he was having repeatability problems with his Analog VFO coupled with this mechanical delight. It was not a stability or drift issue; but a problem that you could not come back to the same frequency for the same dial reading. The suggestion of many regarding the problem was that it was a 'mechanical problem". After all, the mechanism was long in the tooth perhaps nearing 80 years old. Bill has fixed the problem and that he will cover in our next Podcast (soon).
But I leave you with this tantalizing thought … what if there was another way to have a mechanically tuned Analog VFO that has high accuracy and repeatable frequency changes without resorting to one of those $13 SanJan frequency counters?
73's
Pete N6QW
2/22/2019
Many of the readers of this blog are aware that I participate in a podcast (almost monthly) along with the host and cruise director, Bill N2CQR. Our subject areas are wide ranging and frequently we travel a path where we use different approaches to arrive at the same end state.
One area in particular where there is great divergence is our methods of frequency generation for LO's and BFO's. Bill typically takes the analog approach using coils and capacitors. With due credit to Bill's skill and patience he has been very successful in building highly stable analog VFO's.
N2CQR as a student of Doug DeMaw's practices you often see the multiple capacitors in his tank circuits along with physical isolation of the coils (air wound no less) and tuning capacitor which are far removed from any heat generating circuits. The fact that he has many rigs using this method is a testament to his skills and understanding of the analog VFO topology. Analog VFO's can be used with today's rigs. So a tip of the cap to Bill.
But for Bill it is not just the idea of using the analog approach; but more of the technical understanding of each and every component in his VFO. He can see, in depth, the impact of component selection, physical isolation, rigidity of construction all with a measure of attention to detail. He will frequently say --you can stare at the Adafruit Si5351 all day long and learn nothing about how all of those bits and pieces work to generate an RF signal.
I on the other hand prefer the newer technologies and perhaps for a different set of reasons. I like building lots of stuff and using digital methods for frequency generation supports the rapid prototyping paradigm. In fact there is a bit of laziness as well. Many of the critical factors that affect the successful analog build are not so much of a concern with an Arduino controlling a Si5351. Frankly for me it comes down to a time factor --a really high quality analog VFO is not a simple output of spontaneous construction. I can build a Digital VFO in about an hour. For the average homebrewer the high quality analog VFO may take a whole day to fabricate.
Bill and I are not in any sort of competition and that is where I think our divergent views makes for a better podcast in that the listener has an array of options at his disposal when undertaking a homebrew rig.
In fact building an analog VFO is in itself a terrific learning tool as it addresses the electronic as well as mechanical aspects of rig fabrication. Build one, learn the details and then stand back and enjoy the wonders of those coils and caps.
I would appreciate hearing any comments on the subject of analog versus digital frequency generation.
The Building of a SSB Transceiver ~ You can do it!
2/22/2019
At Christmas my 3rd son gave me a transducer speaker that mounts to a piece of foam board and I sit here amazed at the sound reproduction. The amp driving the speaker is the 2N3904 and LM386. So it will provide more than just headphone volume (with a 100 Ohm resistor installed). I received a comment about the 100 Ohm resistor and just for fun substituted a 10 Ohm in the LT Spice simulation and saw no difference in the output curves. The short video tells much.
Pete, N6QW
2/21/2019 ~ Go Daddy Now Fixed! The audio Amp Schematic is on the website.
2/20/2019 ~ Problems with Go Daddy!!
For over 24 hours I have been trying to upload updated schematics and information to my n6qw website. It seems like Go Daddy who hosts my website has some sort of issue with a windows server. One solution that offered was for me to spend more money and move over to a Linux server OR just wait until they get around to fixing the problem. Not only is it a cost issue but also I would have to start from scratch and rebuild all five of my websites. This makes about as much sense as declaring an emergency so the emperor can have his wall.
My alternative is to wait a bit longer to see if they can resolve the problem or just post the info here. Here is one of the updated schematics. Perhaps if any of you have a Go Daddy account you may have the same problem.
Pete N6QW
2/18/2019 ~ Toroids are not self shielding!
I noted that after installing the shield on the left hand side there appeared to be a detuning of the band pass filter. Despite what many have said toroids are not necessarily self shielding.
When I installed the side piece, I thought there was a sufficient space gap between the steel based side panel and the T-68-2 cores. There was not and so the BPF was being detuned. There just was no way with the side panel in place to re-peak the BPF to the proper value unless I followed the practice espoused by Ian Roussel (Full Custom Garage on the Motor Trend Channel) which is make a hole.. The "A" change was to cut about a 1 and 1/8 inch round hole in the side panel stiffener right over the BPF. This accomplished two things. Firstly it reduced the effects of the steel on the BPF and secondly to provide access to the trimmer caps so that the BPF can be tuned with the steel side piece in place. Worked perfectly -- the hole does not affect the stiff properties of the side bracket. We are good to go. The 2nd photo below shows the side piece without the access hole. You have got to love when a plan comes together!
Pete N6QW
2/17/2019 ~ Be sure to visit www.n6qw.com where the project is documented and new schematics have been added over the past two days. Learning to Hem ~ No we are not sewing!!!
In keeping with trying to use stuff I already have knocking about the shack we now address a common problem with homebrew construction: making or buying a case enclosure. The problem is compounded by the fact the front panel is from the former 30M CW transceiver project that was a QRP Quarterly article. But the back panel came from a transceiver that was rebuilt at least three times.
Now for the disconnect. The front panel is 4 inches high and the back panel a mere two inches. Standing alone the front panel flexes as you spin the encoder --not a good plan. Thus to stiffen things we need to connect the front panel to the back panel to add rigidity. We essentially have a trapezoid and how to fabricate those two pieces, one for each side, and not spend a fortune on material.
One of my currently favorite TV shows is the Velocity Channel (now Motor Trend) and my new hero is Ian Roussel of Full Custom Garage. This guy uses what is at hand and often comes up with very creative solutions. In one episode he needed a round metal structure to house the odometer that was being affixed to a new dashboard. He spotted his dog's water bowl which it turned out was stainless steel and just the right size. The poor dog now drinks out of a plastic dish. But it is that sort of thinking we need to employ when we fabricate our homebrew rigs.
A trip to Home Depot yielded a piece of galvanized metal flashing that was about 8 X 11 inches. The price was $1.14 and was enough material to make two sides. But wait you are thinking that stuff is awful flimsy. True; but if you bend it over along one of the seams --it becomes rigid. A pair of Tin Snips, a metal straight edge with scribe and a bench vise is all that is needed to make these very durable side braces. The galvanized metal can be soldered as well as painted. Thus the bending over and doubling is known in the fabrication world as "hemming".
The first item on the list should be a manila folder that will serve as a pattern to overlay on the sheet metal and provides a template to scribe the outline. Keep in mind you have right and left hand pieces and thus you must flip the pattern over to draw the scribe lines for the different sides. The 1st photo below shows the template of the sides and you can see the bend line for the hemming. On either end add 1/2 inch of material that is bent over and will provide the anchor points to the front and back panel.
You might have to "play a bit" with the metal bending so get two sheets of the material. The finished rig is a far cry from the boards screwed down to work bench as it was initially built. Nice looking Rig, Pete!
Ian Roussel would be proud.
Pete N6QW
2/15/2019
2/13/2019
[2/11/2019 I have started publishing schematics for the Simple SSB on my website at www.n6qw.com. Although it is doubtful that many (if any) would take up the fabricating of this rig, there just may be one or two who have an interest.]
Just the other day I was having a very nice QSO with Gene W6QFU and we exchanged our station line up. W6QFU is lucky in that he just recently acquired a very nice ICOM 7300 and has joined the ranks of perhaps over 100,000 other hams world wide who now have that rig sitting at the operating position. Some would suggest it is an appliance rig; but at the same time it is a great sounding rig that undoubtedly is very popular and the current price point puts it in reach of many hams. Guess there is a link to price point and the numbers in shacks around the world.
On my end --yes, yet another new rig just finished and W6QFU was the third contact on that rig. So I was anxious to see how it held up. Well I might add... ARRL as previously reported will start a new podcast one month from now called "So What Now?" A possible answer to that question (or perhaps it is a challenge) is to suggest you build your own SSB transceiver. Trust me what I am suggesting you build is not in the ICOM 7300 class; BUT it puts out a respectable signal with a rock solid frequency stability and it is something you built and can be built for about $100. [YMMV depending on how much junk you have in the junk box.]
But let us go back in time to review SSB transceivers starting in the late 1950's and early 1960's. BOOM there was an explosion of technology in that time frame starting with the Collins KWM-1 and KWM-2 (the cost --read a years salary for most middle class working folk) to more modest rigs that were less costly. Heathkit did much for the hobby in offering single band transceivers that could be had for about $100. I remember being on Midway island (actually two island Sand and Eastern Island) in 1963 where a fellow Navy ham on Eastern ran one of those rigs into a 13 dB gain Rhombic antenna pointed at the US. Everyone wanted to talk to him--firstly he was DX and secondly that gain antenna took that 100 watts and made it look like more than a KW (like 2KW and you can check the math [10*log(2000/100) = 13dB]) But even the simple Heathkit rigs involved some pretty complex circuitry to receive and transmit a signal using common circuit elements.
There were many complicating factors in building a homebrew SSB rig in the 1950's and 1960's
Socketry --yes you had to do all of that metal bashing and mechanical engineering to layout all of the tubes and components that had to be affixed to a large aluminum chassis
Power Supplies. You often required Filament, Bias, LV, HV and control power to operate the rig. We are indeed fortunate --12 VDC and we are there today
Front panel controls abound as does a space reservation for the Analog Dial Readout
So there was much involved aside from just a few schematics. In todays rigs none of those issues exist as many circuit elements simply solder to a few pads. Socketry is minimized so you can feel secure in selling your set of Greenlee Chassis Punches at the next block yard sale. You won't need them. A 12 VDC well regulated supply or even batteries can run your rig. You only need to cut out a rectangular hole in the front panel for your favorite display (LCD or Color TFT). If it is a touch screen then that will reduce further the number of controls needed
Fast forward to today some 60 years later and building a transceiver is much easier and uses far less components thanks to IC's, PLL's and inexpensive commercial crystal filters. Let me take a moment to discourage the use of homebrew crystal filters especially if you have not previously built one, and two if you lack some pretty decent test gear. Sure you can purchase crystals inexpensively but that is only 5% of the task. So reject all of those claims that you only have to buy 5 crystals at 40 cents a piece and you are there --you aren't! INRAD sells a nice 4 pole 9 MHz experimenter's filter for about $30 and you can also buy 9 MHz filters from the GQRP club for about the same shipped to you. Yes I do have several rigs with homebrew crystal filters so I do speak with experience. But it is a simple decision if you do not have that experience --buy the filter! So lets talk a minute about the SSB transceiver architecture. and we'll proceed first to the block diagram.
Many rigs today are bilateral or as some prefer bi-directional in that a) signals can be routed in two directions through the circuit element and b) because of (a) you can use that circuit element in both transmit and receive. Here is an example of one circuit element that I frequently use... a bidirectional IF Amplifier Module as shown above. This module has four transistors, a bunch of caps and resistors, two matching broadband transformers, a crystal filter and a relay to bias parts of the circuit to change the signal direction. The common 2N3904 and 2N3906 make up one amplifier stage and following the crystal is a second identical stage. The amplifier circuit was invented by Plessy and appears in EMRFD (just so it has street creds). Here is what is happening .. with one bias condition the two 2N3904's take on the amplifier role. With the alternate bias condition the 2N3906's are doing the heavy lifting. This circuit is good up to about the 6 Meter band and a single amp pair is good for 15 to 17 dB of gain. Here are some notable items. This is a broad band circuit --there are no IF transformers and there is nothing to peak or tweak. The resistor compliment for a single amp stage is 22 Ohms, 2 X 100 Ohms,. 2X 680 and a 1K. For caps -- six each 100 Nano Farad. The power source is actually 6 VDC but I run mine on 8 VDC through a three terminal regulator. Add in two FT-37-43 matching transformers [19 Turns solenoid wound tapped a 6 turns. The 19 turns squared is 361 and the 6 turns squared is 36 --thus 361/36 = 10. So this transformer matches the 50 Ohms of the Plessy to the 500 ohms on the GQRP filter.] Including the Linear Amp control ( another 2N3904) there are eleven transistors and FET's along with two packaged ADE-1 Double Balanced Mixer's an Arduino Uno R3 (because it was in the junk box) a 16X4 Seasick Green LCD (also a junk box refugee). BTW I was looking at some 16x4 Blue White LCD's --$8 shipped from the USA. Lest I forget the GQRP 9 MHz crystal filter. If you use the INRAD it is a 4:1 match as the INRAD's are 200 Ohms. This may be a good place to stop for now… but to whet your whistle:
Interesting note this front panel was cut out of the front panel that was used for the 30 Meter CW transceiver that originally was a QRP Quarterly article. I should tell you that I was encouraged by QRP Quarterly to design and build this CW rig so it would appeal to those QRPer's who dominate CW. I did as was suggested and did make one contact to prove it works . The rig then went into the never to use again and possible use in other projects bin. There it has sat for five years. Now is the time to use it! The panel was reversed as it was double sided PCB. The Key is now the Mic jack and where the analog dial was --it was cut out for the LCD. The audio amp stage was cut out of the original main board. There are three empty holes in the new panel. Above the red knob the audio gain control will be installed and the hole in the lower right hand corner will house the audio output jack. and the small hole next to the mic jack will be filled with a bolt and nut. The original panel was 8 inches long and with a bit of juggling and cutting material off of each end the size is now 6 inches wide. Thank you Velocity Channel for giving me some really great ideas! Yes Virginia having a CNC sure makes life a lot easier when you are fabricating radios. The part that was cut off included the former part containing the volume control and headphone jack. The two bolt holes nearest those were enlarged to house one of the toggle switches and the new headphone jack. New panel controls include MOX and TUNE button (red button), Volume control, Main Tuning, USB / LSB Select and VFOA / VFOB Select, Microphone Jack and Headphone Jack. Lest I forget the 16X4 LCD.
Below is the rig screwed down to the top of the work bench. In the very bottom is the IF module, Audio amp and Microphone amp. To the left of the IF module is the BPF and above the IF the bidirectional J310 amp and the single 2N2219 feeding the IRF510. To the right of the IRF510 and the microphone amp is the LPF. The junk in the center is my power buss and some relays used for TR. The RCA plug/cord above the J310's is the linear amp control. The "T" line feeds a 1K resistor into the Base of a 2N3904 with the Emitter grounded at the collector goes to the control line in the follow on linear amp. Take a good look --aside from looking like crap --there are not many parts. I did use it on WSPR and FT8 as well as a few SSB contacts. the future work will involve some packaging to sanitize the look. !
It is a shame that many hams think building a rig is too difficult. Drop me a comment if you would like to see more detail on this project. Oh should mention portions of the design are LT Spice simulations so there is solid science behind the modules. These include the BPF, LPF, the J310 Bi-Directional amp, the 2N2219 driver stage and the microphone amp circuit. Oh --the mic amp design is now the same design used in the audio pre-amp stage. The circuits not simulated are the Plessy amps (from EMRFD) and audio final stage LM386 and the IRF510. I was asked a question about how the Simple Transceiver compared to the Sudden Transceiver Project. There are two areas of comparison the first of which is performance and the second the circuit elements themselves. Performance is equal and thus I am pleased; but the circuit elements do differ and the following explains the differences.
There is some circuits which are alike and some not so. Physically the Sudden is a
smaller footprint. Some circuit differences include:
The IF Module uses the
Plessy amps and external DBM’s. The Sudden using the NE602 provides the mixer
stage and the balanced modulator on the input side and the mixer and product
detector on the output side. The LO & BFO are switched whereas in the Simple SSB rig they feed the same DBM regardless of T or R. The Sudden is a
single pass whereas the Simple is bidirectional.
The simple SSB takes the
pre-driver used in the Sudden and makes it bi-directional so it is the Rx
RF Amp on receive and Tx pre-driver on transmit. The Sudden has a separate Rx RF Amplifier stage
Only one BPF versus two in the Sudden
The Driver and Linear
Amp are the same
The Mic Amp is the same
but the Audio Amp different
The Sudden uses a Color
TFT and Nano and the Simple the Uno R3 and the 16X4 LCD
The LPF’s are the same.
Bottom line ~ not a lot of parts! For those who wonder this is not a Bitx40 repackaged. The Dual J310bi-directional stage configured as a Dual Gate MOSFET has some interesting possibilities. The stage has a manual gain control pot built into the circuit board so that stage gain can be adjusted. This opens up some potential for adding AGC and ALC to this stage so now we can add more additional refinements. One comment I made arising from the Sudden Transceiver fabrication was the opportunity for experimentation. With a change in the BPF and LPF the Simple SSB Transceiver can traverse to other bands. A simple DPDT toggle switch on the front panel could with 1/2 the switch controlling the VFO range and the second half controlling 4 SPDT relays would switch in the proper BPF's and LPF's for each band. One switch, four relays and a few more toroids and caps and you are on two bands.
Turning an Old Boat Anchor into a Silk Purse. Yes it involves the Arduino!!!!
I frequently tour eBay looking for bargain "Boat Anchors" that can be easily retrofitted to work the bands with rock solid frequency stability. Most of these old boat anchors suffer from drifting "ANALOG" VFO's. Yesterday I came close to acquiring such a rig. Early on Yaesu marketed some rigs that pre-date the highly successful FT-101 series of transceivers.
One such model is the FTdx-100 and I had one of those about 7 years ago and you can see how I "worked on that rig" on my website www.jessystems.com. Recently I spotted a Sommerkamp FT-100, virtually the same gear marketed by Sommerkamp in Germany along about 1966.
My complaint about the FTdx-100 was that it lacked DFMA.
[ For those who did not spend half their life in aerospace manufacturing DFMA is defined as Designed For Manufacturing & Assembly. Bottom Line you can service what you build without a total disassembly of what is built. I go into detail on my jessystems.com website about how I was unable to replace the HV electrolytic caps because it meant removing a significant part of the under chassis wiring. Guess in true Japanese fashion they reasoned this will never have to be repaired because the quality was built in. Well caps get old and need replacing!] But is was a marvel in that it was a hybrid rig that used HF Germanium transistors in the lower level stages and three tubes for the output stage. A 12BY7 driver and a pair of 6JM6's are in the output stages. BTW you can buy a matched pair of output tubes for about $25.
The FT-100 was particularly appealing in that it had a panel switch to select an external VFO or you could have crystal control of the receiver and transmitter.(Same for FTdx-100)
Now for the bonus part (and the Arduino). The primary analog VFO had a range of 8.9 MHz to 8.4 MHz. Yes it was a backward tuning VFO! There was a circular analog dial that had two sets of markings and these were 0 to 500 and 500 to 1000. On 80 and 10 meters you used the 500 to 1000 dial reading and on 40, 20 and 15 Meters you used the 0 to 500 scale. Thus if the dial real 250 that meant on 40 Meters you were on 7.250 MHz or on 15 Meters then the dial read 21.250. But at the same location if you were on 75/80 Meter you would read 3.750 MHz and for 10 Meters that would be 29.250 MHz for the reading.
So now the trick is how to do that with an Arduino and an LCD display. Actually the effort involves building an external VFO that would have a 5 position band switch. The use of the band switch does two things: first is to signal and display what band it is on and secondly to choose one of two constants to perform some math functions. The only interconnect to the Boat Anchor rig is a small chunk of coax.
So how can we make the display (I chose an LCD) read 0 to 500 on some bands while reading 500 to 1000 on other bands. Keep in mind no matter what band, the VFO is on a constant range (8.9 to 8.4 MHz) and secondly works backwards (for the newbies that means at the low end of the band the VFO is at a higher frequency).
A little time with an excel spreadsheet reveals the two numbers 8900000L and 9400000L. (The "L" is for large numbers that you identify in the sketch).
So if you were on 40 Meters and wanted to read 250.000 (7.250 MHz) you would subtract the actual generated VFO frequency from 8900000L. Since .250 is half way between 8.9 and 8.4 the actual VFO frequency is 8650000L. When you are at 7.0 MHz then the subtraction is 8900000L - 8900000L = 000.000. So for three band positions the constant is 8900000L.
Now for the problem with 80 and 10 Meters. There we have to have a higher reading on the LCD for the same actual VFO frequency. Let us pick 3.750 MHz for our example. Yes the actual VFO frequency is the same as for our 40 Meter example 8650000L. But our LCD would have to display 750.000. Thus our constant would now be 9400000L. Thus if we take 9400000L - 8650000L the answer is 750000.
So our sketch logic would be to generate frequencies in the range of 8.9 MHz to 8.4 MHz and to limit the tuning range to that 500 kHz segment. There is a range limitation code in the software but you do have to make it 1 higher and 1 lower so that the display will in fact subtract and essentially read 0 to 500 and 500 to 1000. The other aspect is to decode the band switch so that the proper band is shown on the display and that the correct constant is used for displaying the range. As you tune the encoder the top line will show the operating 80 Meter frequency and the 3rd line the actual VFO frequency. As you change bands the 80M will change to the band selected and as you tune the encoder depending upon the band the top line will range between 0 to 500 or 500 to 1000.
Too bad I was not the successful bidder as the addition of the digital VFO would have made this a great boat anchor. The reason for the last line --later on Yaesu did make an FT-100 in a solid state version. I do not think it was around for very long.
