A 1955 Solid State QRP Transmitter using the Philco SB-100.
3/14/2017 ~ Late breaking -- I put a 4:1 transformer in the collector lead and as measured across 50 Ohms on the secondary side I am seeing 3.2 Volts Peak to Peak. If you perform the rigorous calculation that transforms into 25.6 Milli-watts or 14 dBm. Now we are cooking! That is better than the rig on Bill's blog.
See Photo addition at the end --just to posit where 60+ years have taken us --and I have personally seen the amazing change to our tools, techniques and toys!
Recently my friend Bill, N2CQR posted data on his blog ~ soldersmoke.blogspot.com about a vintage late 1950's early 1960's 10 milliwatt 10 Meter transmitter. That was quite a feat!
But given my Italian heritage I could not let that pass without building my own solid state transmitter using a transistor from 1955. My rig operates on 14.060 and produces 0.4 milliwatts with a 3 volt collector supply using a Germanium transistor from Philco. The SB-100 was one of the first RF transistors that could work all the way past the 10 Meter band. The max Pout was 10 milliwatts --so mine is just loafing along.
This was fun.
73's
Pete N6QW
It must be easy to misunderstand when someone says wire wrapped it is decoded as wire tapped. Hmm wonder who recently did that?
Almost makes you forget that you just paid $55,000 for a 9 passenger Toyota SUV. It looks cool but scary to park. The ride is no better than a bucking bronco! I am a small framed guy and my visibility is like looking at a picture framed between the steering wheel and the top of the dashboard. No I didn't buy one --just looked at one while my Avalon was being serviced. But the new smell is much like the buzz of building a new transceiver!
A special shout out to active duty US Navy Seabees and former Seabees world wide. Today is the 75th Birthday of the founding of the Seabees. Happy Birthday fellow Seabees! Our motto "Can Do" resonates even today! The first Seabees were civilian construction workers who were formally organized as Naval construction forces shortly after the start of World War II. Seabee's were instrumental in building the advanced bases that made the Pacific island hopping strategy a reality. Today that legend lives on in places like Iraq and Afghanistan. We Build, We Fight is the Mission Statement!
If you followed the prior post on Transceiver Architecture look at item #3. The circuit below IS the hardware described in number 3.
What is the best Homebrew Transceiver Architecture?
This question is almost like your XYL (or girl friend) asking you: "Do you think I am getting fat (or fatter as the case may be)? How in the world do you answer that question (in an honest manner) without getting a lot of blow back.
In some cultures a "plump" woman is highly prized while in others, almost looking anorexic enjoys the same level of adulation. But being the best begs the defining of what is a transceiver architecture?
Having built dozens and by that I mean maybe 4 or 5 dozen, describes the number of transceivers built by me over a nearly sixty year period and thus I have used various schemes. Here are a few:
The first is a bit of a hedge where the project is not really a transceiver but a trans-receiver which means you build essentially a separate transmitter and receiver that share but a few common elements such as a VFO, BFO and some TR switching. In the December 1989 and January 1990 issue of QST, Wes Hayward W7ZOI featured a project that was a 20 Meter QRP SSB/CW trans-receiver. This approach allows you the freedom of customizing and optimizing the individual transmitter and receiver blocks without being constrained by having many common elements such as the Bitx40. The W7ZOI hycas IF/AGC is definitely better suited to a standalone receiver and may be a bit more difficult to implement in the Bitx40. I did not say it could not be done as I am sure I would get a flood of comments that I was bashing the Bitx40. I actually replicated the 89/90 project and have two such trans-receivers. What comes to mind on customization is one of the rigs has an 8 Pole KVG SSB Filter for receive and a 5 pole KVG for the transmit side --now that is a nice receiver. The customization could be extended further to having separate and switchable CW and SSB filters in the receiver. Frequently SSB transceivers with a single filter when pressed into service in the CW mode are a bit wide. The down side --lots more parts, lots more circuits, more costly to build and lots more potential for errors or circuits requiring maintenance. The chance for making it a small box is somewhat less by just the sheer number of additional circuits needed.
Next is the transceiver which as the name implies is more unitized in that there are more common circuit elements that are used on both transmit and receive. A common receive and transmit mixer is almost standard as is the use of say a double balanced mixer that on receive is the product detector and on transmit is the balanced modulator. In between are IF stages and a filter that are used both on transmit and receive and only the signal steering is changed --this is the Bitx40.This now is available as a built unit for the amazing sum of $59 shipped to you--and even includes the Si5351 and LCD display.
My transceiver approach that I use most frequently is to have a double balanced mixer on the front end which is always fed by the VFO and on the back end, after the bidirectional IF amps and filter, another double balanced mixer that is always fed by the BFO. On receive the signals go from left to right and out to the audio amp. On transmit the microphone amp inputs a signal to the DBM, the signal is steered to the other direction right to left through the IF amp/Filter to the mixer stage and now we have a signal that is sent on to the further transmit stages. A bit of signal steering and powering on either the audio amp or microphone amp and we have a bare bones transceiver. See the 1st figure below which is the shirt pocket transceiver block diagram.
A variant to the approach in 2 above is to have the same modules DBM, IF/Filter, DBM. Only in this case on receive the a band pass filter is connected to the RF port the VFO to the LO Port and the mixed signal passes through to IF port on to the IF amps and filters. The output of the 2nd IF amp is fed to the RF port on the 2nd DBM and the BFO is connected to LO port and the IF is at audio and on to the audio amp. Now on transmit there is a bit of signal switching frequently done with diodes or relays. The rig goes into transmit and the RF port that was formerly connected to the Band Pass Filter is now connected to the microphone amp and the port connected to the LO is now connected to the BFO . This mixing process creates a DSB signal that goes on to the IF Amp /Filter chain. After passing through the filter we have either a LSB or USB signal depending on the BFO frequency which now enters the second DBM via the RF port. The LO port is now connected to VFO and the IF port now connected back to the band pass filter. This essentially means the IF amp is working in one direction --but for me too much steering of the VFO and BFO signals and too great of an opportunity for signal leakage given the routing of the RF carrying signals.
Another variant to the trans-receiver is what I did in my JABOM transceiver (Just A Bunch Of Modules). See figure 2 below. This circuit use three double balanced mixers --here we go more parts. We start again with a double balanced mixer stage that on the front end is fed the LO input so that it is both a receive and transmit mixer. On receive the output of this stage is fed to a post mixer amplifier with a 6 dB pad and then on to the crystal filter. But on transmit the input to the post mixer amp is connected to the balanced modulator DBM so here the filter is only operating in one direction.. After the signal passes through the crystal filter on receive it goes on to the hycas IF amp and AGC stage and on to the product detector (3rd DBM) and finally the audio stages. But on transmit the output from the crystal filter is routed to a 2N2222 amp stage and back to the original Rx Tx Mixer stage. You can think of this like a hybrid trans-receiver and transceiver.
No transceiver topology discussion can be complete without paying homage to another Peter and that is VK3YE and his Knobless Wonder.VK3YE's approach was no LO which essentially means a single channel SSB transceiver and only uses 10 transistors. Basically the homebrew filter is on a frequency in the 40 Meter Band (I think 7.190 KHz) and the BFO is tweaked (slightly higher) to give LSB. There is no need for a transmit mixer as the output from the filter IS 7.190 KHz. Thus you always know what frequency you are on, no undesirable mixing products and minimum part count. I think he has a BD139 in there for a final which gives several watts to the antenna. What a great emergency rig! I did find 7.2 MHz crystals and have purchased a batch --so I may someday have a KW in my shack.
The real answer to my posed question is that it depends on what are the initial expectations. If you want absolute control and a great deal of functionality the trans-receiver may be ideal. If you are looking for bare bones, low cost, carry in your pocket then the Knobless Wonder is the best. Middle ground would be the Bitx40 Bilateral approach.
While I try to keep current with the technology trends, regrettably I was born in the Dinosaur era of this hobby and it is hard to shake the past.
A connective story for you (meaning you have to connect the dots) and for this we go back to 1967 when after serving four years in the US Navy, I had my first real job. Should digress that while you would think at this time (Vietnam War) that here I was a degreed EE with his military service behind him that job offers would be a cinch! I applied at Collins Radio thinking my degree, having a ham ticket and military service out of the way would be a plus. Well it wasn't, as serving my country for four years was a handicap. Basically Collins said you have not done electrical engineering for four years and we can hire a new college graduate who has the most current skills AND we can pay him less! Thank you Collins!
When I applied at AT&T Long Lines --they couldn't wait to hire me and that was much different --the HR guy was an ex-Naval Officer like me. First day on the job and I was shown a "semi-company classified" movie about a new product. This was a hush hush movie about a new product called "a cell phone". (That was 50 years ago!). The movie started out by saying "someday everyone will have a cell phone." I couldn't help but snicker a bit as the "cell phone" looked like a made over BC611 Walkie Talkie --yeah everyone!
Well some day is here. (Did you connect the dots?) While I had a cell phone when I worked as far back as the mid 1990's, it was bulky and the battery life sucked. Being in an executive position with one of the aerospace companies --had to have it with me at all times. Almost dropped in the toilet once! But todays' cell phones are small, light weight and have great battery life. I have had personal cell service for about the last 13 years so I am a bit late in coming to the party.
But wait to call them a cell phone is a misnomer. I have a moderately priced Samsung mobile device that is a cell phone, an mp3 player, a streaming video device (Netflix, YouTube), a computer, word processor, email/text message device and a device chock full of applications. It has only been recently that I have been texting and even more recently added binge watching so I can watch Netflix movies and even TV programs from CBS. Using the CNN application (provider of Fake News as has been charged by one high ranking government official) I can keep track of what you know who, has just said as gospel but not quite true.
Then just today I discovered there are ham radio applications. Now all the dots can be connected. Some are more useful that others and there is even a rating as to their usefulness. I downloaded and installed one called "Ham Radio Tools". This one is useful as it contains tools for calculating the lengths of a dipole or vertical, an ERP calculator (have just convinced myself that my shack being under the beam is not a good idea to run 1500 Watts PEP on 20 Meters --that close), Ohms law Calculator, LC Resonance, and Grid Square locator . I tested several of the apps and they really work --and fast.
My XYL is not in the best of health so we spend a lot of time in doctor waiting rooms -- now with my mobile device I can evaluate/design circuits using my "cell phone" -- wow a lot has happened in the last 50 years. I am sure I will get a flood of comments that many of you have been doing this for years and even are operating you rigs at home from your phone while sitting in a Starbucks having a Latte. Bear with me --I am the dinosaur just catching up.
(A note from Pete -- I can see the number of hits on each post and was somewhat surprised that the secrets of homebrewing got nearly 500 hits and the troubleshooting one just over 150. So that is helpful and very telling --we like to build stuff; but don't like to fix it. That is the last time that troubleshooting will be discussed by me. I know how to do it --do you?)
How to make your Rig do TUNE?
So you asked has Pete been in the house too long because of all the rain in California and now has gone bonkers? Everyone knows for SSB only rigs (like the stock Bitx40) you simply whistle into the microphone or yell the standard "HOLA" into the microphone! Others will ask why do you even want to tune your radio? VU2ESE's Bitx40 instructions basically say plug in the microphone and talk it up.
Well having your SSB only rig be able to TUNE has some very practical and necessary applications. The CW ops are smiling now as they think --just hold the key down for about 10 seconds and you are in TUNE.
The "why" is now unveiled. Firstly if you have homebrewed your own rig, then you need to make adjustments so that the performance is optimized such as tuning the Band Pass Filter or setting drive levels to intermediate stages or even adjusting the bias on your IRF510. Of course you would never do this "on air" but into a dummy load. That is a lot of whistling or shouting HOLA. CW ops are still smiling!
Thus rig adjustment for best performance is probably the 1st use and the second after that is the adjustment of the rig to the antenna. So OK, you have one of those fancy auto tuners and you let the tuner do the hard work. But if you are like me and have no such devices, then you need to be able to provide a tune signal to make the adjustments -- thusly reason #2. Perhaps a third is maintenance --suppose you suspect you are not getting full smoke to the antenna --then you would want to put your rig in TUNE and see what the output looks like.
So how does one generate a TUNE signal. Mind you the TUNE doesn't have to be at full power but just enough to put a couple of watts of RF into a dummy load or into your antenna system. So how is it done?
Method #1. In an SSB only radio if there is a way to unbalance the carrier in the balanced modulator then a simple unbalancing will output the carrier. This seems like an antithesis of its purpose. We work hard in our rigs to make the carrier "go away" --we get nervous when the carrier suppression is only 65 dB down and now we want to undo that. Well many of the old boat anchor radios had a carrier balance control right on the front panel so you could make that adjustment. Now with our packaged Double Balanced Mixer a bit harder to do. The SBL-1 however can be unbalanced --read EMRFD for a way as described by W6JFR (yes me in another life). But you cannot do this in a casual manner --so not for everyone.
Method #2 which offers some bonus features in that you effectively can add CW to your SSB only transceiver. In my KWM-4 I added CW by having a separate CW oscillator tuned to the center frequency of the filter and that signal was fed to a keyed buffer stage. This CW oscillator was only turned on when you hit the key and was held on for a short period of time. The output from the keyed buffer was fed to a relay where it was injected into the 1st bilateral IF stage bypassing the filter. From there the signal went to the RxTx mixer stage. Sorry CW ops this is not QSK and is like semi-break in with delay. Clunky for the ardent CW op --yes but it would do CW with an offset since on receive the Rx was set to USB. This same approach could be used for TUNE. Just hold down the key. The real hard part of this was the control and sequencing circuitry. But it did work. I have made one CW contact on the KWM-4 and it worked flawlessly. I had to do the CW contact for proof of concept.
Method #3. Since my primary interest is SSB --- how would you do this? Many early transceivers used a tone for generating CW and that same tone keyed the VOX which put the rig into transmit. The Collins KWM-2 used this approach as did others. Staring me in the face was the Arduino and I said why can't I let the Arduino do all of the heavy lifting. I researched generating tones with the Arduino and it was possible to do just that. For the earlier IDE's there is a library called "toneAC" that must be in your library section of the Arduino folder. Now the rub --you will have to find a later version of this library to work with the IDE 1.6.0 and above.
So that is step one. Next you will have to include the following in your sketch: #include <toneAC.h> Now I picked a tone that was close to 1000 Hz and the best I could do was 988 Hertz. That to needs to be in the sketch in this form #define NOTE_B5 988 Finally you need to designate a tone pin --where will the output be on the Arduino and you will need this statement const int tonepin = 4; //tune up tone We will also need to start the cycle and thus an input pin --in the set up you must write code for the pinMode and to define a status for the pin so that it is HIGH. We picked pin 12 and called that SW1 which is really a push button.
#include <toneAC.h>
#define NOTE_B5 988
const int tonepin = 4; //tune up tone
const int SW1 =12; // provides the TUNE function
const int LED = (some free pin number); //attach mini relay to parallel PTT contacts
So how does generating a tone work and how does this cause a TUNE signal? Essentially the sequence is to momentarily hit a panel mounted Push Button which we call SW1. There is a call function in the loop that constantly looks to see if the push button has been pushed which would be a signal that Pin 12 is LOW. From there the call function starts and the main loop is on hold. In the most current use I have pretty much used up all of the Arduino pins so had to come up with a bit of a work around.
When I first used this approach I was not constrained for pins and here is the sequence of what happened. The PB is engaged and the loop takes over and recognizes the button was pushed and immediately moves to the call function. Another free pin was designated as a Push To Talk pin and so upon initiation would go HIGH to which a 5 VDC mini relay was connected whose contacts were in parallel with then normal PTT contacts --the rig would now be placed into transmit. Next a message would appear on the screen, that the rig was in TUNE. Finally the tone was generated at 988 Hz, But there was a loop counter inside the loop that would turn the 988 Hz tone on and off for a specific number of cycles and thus a pulsed tone. That was the "if" part of the call function. The else part is where the word Tune is once again painted on the face of the display only it is the color of the background and thus "disappears". The pin driving the 5 VDC mini relay goes low and the PTT un-keys and the receiver comes to life. The pulsed tone is better than a constant tone as it is easier on the finals and is helpful during a antenna tune where the SWR is high. Below is an example of the rig in the TUNE mode. Pretty cool?
In one of my current projects I was short of pins so I just paralleled a panel mounted switch that is in parallel with the PTT. After engaging the (MOX) switch the rig is in transmit and I simply press the momentary PB and we are in tune. The "MOX" switch on the panel is nice if your are testing microphones so you don't have to hold down the PTT.
But wait you are NOT done. That beautiful 988 Hz tone is a SQUARE wave and perhaps a bit hard on some of the circuitry downstream. On the internet I found a square wave to sine wave RC network that uses three 1.5K resistors and three 10 NF caps. --almost like a phase shift network --well it does knock of the corners but is no pure sine wave.
Here is the call function code: //For Check Mode --ie TUNE If you have added the 5 VDC relay to one of the pins you need to add digitalWrite(LED, HIGH) in the "if" part and digitalWrite(LED,LOW) in the "else" part. I simply called the PTT pin LED and you will also have to declare the LED pin number and the initial setup() add pinMode(LED, OUTPUT); and initial state digitalWrite(LED, LOW);
void CheckMode(){
buttonState = digitalRead(SW1); // creates a 10 second tuning pulse train50% duty cycle makes TUNE appear on the screen
if(buttonState != lastButtonState){
if(buttonState == LOW){
tft.setTextSize(2);
tft.setTextColor(WHITE); // This puts a white TUNE on a black background
tft.setCursor(126, 110);
tft.print("TUNE");
delay(12);
for(int i = 0; i < 100; i++) {
tone(4, NOTE_B5);
delay(50);
noTone(4);
delay(50);
}
}
else{
tft.setTextSize(2); // This prints a black TUNE over the white TUNE and makes it disappear from the screen
tft.setTextColor(BLACK);
tft.setCursor(126, 110);
tft.print("TUNE");
noTone(4);
}
delay(50);
}
73's
Pete N6QW.
This is a useful tool but does require some noodling.
What, are you kidding? There simply are no three easy steps. So get over it! That indeed is the heart of the problem --we all want to slide into home, take the easy way out, do the minimum work, send out 100 emails in hopes of having someone else resolve your problem. It just doesn't work that way! I repeat there are no three easy steps! No fellow hams, this is not Fake News!
That said there is however a process for troubleshooting a project and that is what I will share with you. A long time ago I came up with my process after observing how heathkit was successful in the kit market until they became a dinosaur and were overrun by the black boxes from the land of the rising sun. Heathkit's success was build and test a portion of the circuit before moving on to the next element. In effect the portions completed actually became a part of the test system as you added new elements. How simple!
I like to scratch build my radios and avoid the many kits that are currently on the market. Here is the rub --current kits --you get a board and bag of parts. Some suggest installing all the resistors first and then the capacitors. Or the reverse, caps first. Next install the devices, hook up the wires and give it the smoke test --often it not only smokes; but catches fire too!
So now you have this semi-burnt mess or if it hasn't burned it plain don't work! How in the world do you methodically go about isolating the problem areas? There was/is no testing of what you built as you progress through the bags of parts. One notable exception was the 'softrock" kits from KB9YIG. This was the heathkit model. See the video below --where do you start troubleshooting this jewel?????
So here is my process:
Turning on the soldering iron is weeks if not months away. The first steps are to get smart about your project. I call this noodling! Do your homework and research the hell out of it. Be wary of the "Internet Boasts". There is no way you can run an IRF510 with 12 volts on it and from a single device have a 500 Watt PEP linear stage. Ain't gonna happen!
Collect data on similar projects and set up a system that is easy to use so when you need the data it can be readily found. Think in terms of circuit chunks such as an audio amplifier block, a microphone amplifier block, a product detector/balanced modulator block, an IF block, a Mixer stage block, a receiver and transmitter RF amp stage, Band Pass and Low Pass filter blocks. Most of my transceivers are just that, a collection of blocks. An article I wrote for QRP Quarterly on a SSB transceiver was entitled JABOM (Just A Bunch Of Modules).
Using the modular approach serves the purpose of ease of trouble shooting as well as providing a pathway for circuit improvements. Want a Digi VFO instead of that drifty analog VFO --pull the analog module and install the Digi VFO? Want a better audio amp --Boom same drill! The module approach serves another purpose --simply flexibility in how to cram, stuff, and/or shoehorn the boards into that neat metal tin that formerly housed cookies.
I often make card board cutouts that are the same size as my module boards and using these cutouts can move them around the enclosure to determine a best fit --all the while mindful of minimizing circuit interaction and unwanted coupling of signals. I can't think of one of my projects that is just a single circuit board. I have over 100 you tube videos of my projects and you can confirm this for yourself
Backing up from the troubleshooting side is the decision you made early on to homebrew something and with that brings the other side in having suitable test equipment. Don't begin a homebrew effort if you have no means to verify if it is working. Bill, N2CQR has a monthly podcast where I just ride along and have lots of fun talking about radios. Almost two years ago we started an effort to encourage homebrewing a simple 7 part 80M CW transmitter, known as the Michigan Might Mite. We even supplied 3.579 MHz crystals (mostly Bill) for the project. That seemed to be a hit with the listeners.
One ham who competed his MMM emailed Bill and asked how to know if it was working --as all he had was a crystal set and couldn't hear any CW notes. Yes a crystal set --no meters, no O' Scope not even a receiver that could tune to 80 Meters. This clearly illustrates the issue --what a downer to have built the MMM and not know it was working.
Another ham put a Bitx20 on the air and while he could readily hear other stations --no contacts. He asked how would he know if his rig was working as he had no other receiver in his shack so he could listen for a signal. Bill suggested he look at his SWR meter and see if the meter moved in concert with the voice peaks (about 1/2 scale from tune). Yes, No SWR Meter in line and simply didn't have one. So acquiring some test equipment is very much in order if you want to homebrew your own rig and is mandatory when you have to troubleshoot same.
There are about 6 or 7 pieces that I would put on the list including an SWR meter [Note one of the reasons for low output or oscillating finals is too high an SWR but you would never know unless you knew how was the antenna (load).] Next would be a DVM (Digital Voltmeter) such as the ExTech series from Jameco Electronics and a frequency generator/counter such as the Feel Tech which can be had for around $50 on eBay. An LC meter (Marlin P Jones is selling one for about $40). To that I would add a DSO (Digital Storage Oscilloscope) such as Bill has the 100 MHz, Rigol about $400. For the ham with the Bitx20 who didn't know if it worked -- if he had DVM, he could have built an RF probe (three parts) where he could see if there was an RF voltage when the rig is fed into a 50 Ohm dummy load which is another item to the list. Dummy loads are easily homebrewed! Take twenty 1K 1/2 watt resistors in parallel --Boom 10 watt, 50 Ohm resistive load which is good for QRP levels.
OK come up for air and swallow hard -- that comes to around $700. The biggest item is the DSO but the others can be acquired over a few months of time and are far better than just a crystal set. Should not forget about finding an all band inexpensive shortwave radio (Sanjean) and that would give you a radio where you could at least find your signal.
To that I would add an isolated low wattage soldering iron-- that Radio Shack 80 watt iron helps heat the shack but not good on surface mount soldering or repair. While we are at it, throw out all of those $1.95 12VDC WalWarts --they are noisy and will make it seem like your project is not working! Get yourself or build a 12VDC, 2 Amp Linear power supply (one with a real transformer). Hand tools are still more items to the list. Trash those crappy Harbor Freight screwdrivers and pliers. I could go on an on -- but why try to do brain surgery with nothing more than a rusty spoon is the message.
This is a really good example of what I preach I should practice as earlier today I was testing the new board and Boom the radio went dead. Jostling the board made it come back to life! That could only be an intermittent connection --where was my quality control? See the yellow wire --well when I built this radio almost four years ago I thought I had properly soldered the wire to the pad. But instead the wire was just resting on the pad, caught under the resistor so it was making contact. By my handling the board that wire came loose and thus the intermittent nature based on the flexing of the board. I have several pairs of tweezers -- after cooling I should have "tugged on" each wire to assure there was a good mechanical connection --had I done that --the problem would have been found 4 years ago. Good lesson for me and good lesson for you
The build philosophy is the next part of my process. Bill, N2CQR and I have talked about this several times. Bill likes to start with what he considers the "tough nut to crack" and since he is partial ( I should say very partial) to analog VFO's --he always starts there. My approach is to start at the back end and build the audio amplifier stage wherein I have a couple of standard designs. [I have committed these designs to circuit boards that are cut on my CNC mill. If I want more "poop" out of the audio I use the NE5534 driving the LM380. A less demanding application would be a 2N3904 driving an LM386-3.]
I know these designs work AND I know how much "poop" they will deliver. So once built I can easily tell if they are working properly! The next element is the Product Detector/ Balanced Modulator. I favor the use of the SBL-1 or TUF-1 DBM for this application. Again I have templates in my CNC files. Once installed I can hook up to the audio amp and being careful to not exceed 1.414 Volts Peak to Peak (7dBM) inject that signal into the LO port --you can tell if it working -- any LO signal (any frequency at this point) will give you that test.
At one time I had a small single transistor test oscillator using a 2N3904 and a socket built from a SIM socket ran various crystals into the LO port. The Feel Tech generator will do the same BUT watch the 7dBM --you'll smoke the DBM otherwise. Now with these two stages working build the IF amp stage (consisting of the IF amps and crystal filter) and when that is completed hook that up to the product detector.
If you have that single transistor test oscillator use that to supply the BFO signal to the SBL-1 and the Feel Tech can supply the signal into the 1st IF. Caution, Caution, Caution!!!! Loosely couple into the IF stage and run the signal level way down like may 50 Millivolts. Loose coupling means using a small value capacitor like 10 PF. The signal generator can be used to sweep the filter about the center frequency. If you hooked a voltmeter up to the audio amp output and if you were using a homebrew crystal filter --this is now a test system! By sweeping the filter and noting the audio output readings you can plot the voltage versus the frequency and this will tell you much about your filter!
Do you get the point? What you built becomes part of the test system and when you add a circuit and it does not work --the problem is pretty much confined to what you just added.
Most problems with a circuit can be traced to some common roots, especially when you are dealing with a proven design and what is replicated simply does not work. These root tracings include: wrong component installed, bad component, improper wiring of the circuit, cold solder joints, wiring not connected (see the photo above). To digress I love receiving emails that start by saying "Your Circuit Doesn't Work!". One chap who generated such an email sent me a photo of the circuit and had marked voltage levels at every location on the module. At one transistor (a 2N3904) the collector had a "0 Volts" reading which quickly caught my eye. Hmmm 0 volts tells me there is a problem at the collector. Upon close examination of the photo --there was absolutely nothing connected to the collector --it was just sitting there soldered to a pad. Well here is the rub -- the chap had all of the data in front of him --Clue 0 volts, Clue nothing connected, Clue why it doesn't work. I politely responded that he hook up the circuit as designed and then it would work. Never heard back from him. But this illustrates the point of how the taking of simple data can often provide the answer.
Another similar email/ photo from another ham reflected the need to improve soldering skills --yes it was a cold solder joint. Many of the components are surface mount and that opens the door to solder bridges shorting out pins or worse hot pins to ground. My process therefore before applying power is to reaffirm: right components right place, tracing the wiring to assure correctness and to observe polarities on diodes and electrolytic caps, checking the quality of solder joints especially grounded connections and to look (with a headband magnifier ) for any solder shorts! Needless to say --is the power connected with the proper polarity.
More Troubleshooting Wisdom:
I have a stable of proven horses (circuit modules) so I well know their level of performance. I know what works and how well it works. Some argue I would never try anything new -- no --it is simply I will try a new circuit in an existing well understood design. Then if that new circuit adds to the performance it will now become one of the horses in the stable. A friend is building a project where he is utilizing the Simpleceiver project that was featured on this blog as a part of his project. For the front end RF amp he was using the Dual Gate MOSFET (two J310's in a cascode circuit) developed with the Simpleceiver but he wanted to compact things.
I suggested the use of a single 2N3904 as an RF amp (have used this over and over). Both provide about the same level of gain BUT the J310's offer a way to apply AGC-- but for his application not needed thus the 2N3904 choice. He reported back the 2N3904 was not as good as the J310's --well 15 dB of gain is 15 dB. So that is a clue that there is something needing further attention with the 2N3904 build (not the design). I further suggested simulating both circuit in LT Spice and if you get the same answer on gain then it is how it was built.
Soldering skills must be learned! We do not weld our projects (that is a different hobby)! Many problems are encountered that are traced to lack of soldering genes. If the joint looks like it is welded there is a good chance the parts being "welded" have suffered heat damage. Too much solder can lead to poor connections --cold solder joints and often a large welded joint spills over and shorts out other parts. There is also the problem of how to "unsolder" the welded joint. Take time to learn how to flow solder on to joints and how to do it without overheating the parts being soldered. This is where a temperature controlled iron is vital. Grounded irons are important to prevent static discharge to very sensitive (CMOS) electronic parts. Like I said the soldering part is like the last thing you do!
So OK you bought a kit and as usual soldered all of the caps (or resistors) first and then did the wiring, added the devices and are just about to enjoy your new toy(and with out additional checks) when you hit the power and it smokes and nothing more. Before you power up that new radio that took three weeks to come from India (or China) use this process to review what you have done. Are the right wires to the right controls and/or connections, is the power supply polarity correct, etc.? If you go to my website and follow the link or go direct http://www.n6qw.com/Bitx40.html you will see embedded in the building of the Bitx40 all of what is described in this blog post. So while the focus has been on homebrew the information applies to kit projects too!
73's
Pete N6QW
PS: One reader has suggested that analog scopes are available at very cheap prices as many hams have moved to the DSO and these older analog units can be had for pennies. An analog oscilloscope works FB for troubleshooting!
