Wednesday, October 28, 2015

Hacking the Ten Tec Model 150A to extend its frequency range to 15 MHz

Be Amazed at the Wizardry of N6QW

Hacking the Ten Tec 150A SSB/CW transceiver to extend its range to 15 MHz



Three actions:

  1. Modify the Final Amp Low Pass Filter
  2. Modify the RxTx Mixer Band Pass Filter
  3. Modify the Low Level Driver Low Pass Filter
All filter changes were simulated in LT Spice and I think it worked.

Pete N6QW

Saturday, October 24, 2015

Errata ~ Part 4 Simpleceiver

Errata in the Part 4 Discrete Audio Amplifier

 
One of the blog readers, W4JED contacted me regarding the "reversed  polarity" of the output capacitor on the discrete component audio amplifier that appeared in Part 4. The schematic error would have most like caused a smoking of the capacitor (or a very loud bang followed by the smoking). Thank you for bringing it to my attention. The corrected schematic is shown below,
Pete N6QW
 
 Soldering Surface mount can get a bit intense so what is needed is some loud music in the background to sort of calm the environment. For your listening pleasure some "Solderin Music"

 
 


Wednesday, October 21, 2015

Simpleceiver ~ Part 6

Dual Gate MOSFET Direct Conversion Receiver

 
Based on inputs I have received either in direct comments on the blog or from email messages, there seems to be a desire to better know the "why" of various choices and actions. In this particular post we will look at the Dual Gate MOSFET being used in a Direct Conversion Receiver (DCR). We will also use an LT Spice simulation to demonstrate the "why".
 
In the Part 5 we described the Direct Conversion signal frequencies and the resultant outputs. Essentially to receive an 800 Hz CW signal on the 7.030 MHz QRP frequency we would need to supply a local oscillator signal at either 7.0292 MHz or 7.0308. Again the Direct Conversion Receiver is simple to build and is quite sensitive; but does not give single signal reception. You will receive the same signal at TWO places on the dial!
 
Below is a schematic representation of a Direct Conversion "detector" using JFET's configured as a Dual Gate MOSFET. We have chosen two JFET's for this evaluation and includes the very popular 2N3819 and the 2N4393. The same circuit was used to evaluate both devices and the only difference is the device used in the test bed circuit. The incoming signal has been set at 0.3 Microvolts and the LO is 1.414 volts. The output scan is from 10 Hz to 50 kHz. [Note these photos are GIFs as I was severely criticized by one blog reader for using JPEG's the reasoning for which is still not clear to me but to stop receiving emails --they are GIF's.]
 
 
 
You only need to connect the audio amplifier to this circuit, connect an antenna to "Gate 1" and your favorite Local Oscillator to "Gate 2" and you are in business. Keep in mind the LO signal frequency must be in the same range as the incoming signal.
 
As homebrewer's the usual process is to dig into the "junque box" and find a couple of devices and heat up the iron AND then wonder why the receiver seems dead. Well this is where my term "noodling" comes into play. Turning on the soldering iron should be the very last step. Evaluating what you are doing and how you are doing it IS the first step!
 
If you start with the circuit above utilizing the LT Spice simulation you would see below the following expected response. In the first case we use the ever popular 2N3819 and in the second case is the 2N4393. The output curves are very similar BUT the 2N4393 has about a 6dB greater gain than the 2N3819. Will they both work --yes but the 2N4393 is more sensitive to weak signals.
 
 
 
 
Keep in mind that you need a real antenna to hear signals. Throwing a 10 foot piece of wire on the ground is a compromise (a poor compromise) in comparison to a 40 Meter Dipole at 30 feet. Hooking your Direct Conversion Receiver to a rain gutter may provide some signals but is not as desirable as a real antenna. Put you time and resources into an antenna and then you can remove that as a variable in the reason "why the receiver seems deaf".
 
Having a signal from a Local Oscillator is one thing but having a signal of one volt or better (1.414 Volts Peak to Peak is 7 dBm) is needed to make this play. Some of the LO devices (AD9850, Si5351) are output frequency sensitive. Thus at lower frequencies there is plenty of output; but at higher frequencies the voltage output drops off and thus may not be sufficient for the mixing process. Thus an outboard amplifier may be needed between the LO and the detector. But unless you measure the output over the frequency ranges you may not realize that insufficient LO drive is causing marginal performance.
 
In the next post I will have an actual  test hardware amplifier that is based on Parts 5 & 6.Stay tuned!
 
 
Pete N6QW




Sunday, October 18, 2015

Simpleceiver ~ Part 5

The Product Detector ~ Dual Gate MOSFETS

Plots added for the 2N3819 (10/19/2015)

Data Plots for Additional JFETs Added 10/20/2015

Having covered the audio amplifier stage for the Simpleceiver (again the choice is yours) we will now move on to the Product Detector stage. As the name product detector implies, the output of this stage is a product of the mixing action of two signals.
 
Think of the product detector as a "black box" where two signals are input to the box and the single output contains two products. One product is the sum of the two input signals and the other contains the difference. Filtering at the output port can remove one of the products.
 
In its simplest form the "black box" can be the basis of a direct conversion receiver where a variable frequency oscillator (known as a Local Oscillator, LO) is connected to one of the ports and signal from the Antenna (after passing through a stage of RF amplification) is connected to the second port. The sum frequency would contain the LO + Antenna signals but the difference would be in the audio range. Now one of the down sides of the Direct Conversion Receiver is that you get the same  audio signal for two values of the LO, where the LO is above AND below the incoming signal. Thus it is not single signal reception. But that does not detract from its capability as a simplistic receiver.
 
Here is the math part of what is being said. The antenna is tuned to 7.030 MHz and one supplies a LO at 7.0292 and the difference is 800 Hz (nice CW sound). Now if the same 7.030 MHz Antenna signal is mixed with 7.0308 LO signal then the difference is 800 Hz (again a nice CW Sound). In one case the LO signal is above the incoming and in the second case it is below the incoming. BUT it is the same audio signal so you will receive the same signal at two places above the dial. [This also is important in visualizing USB and LSB.] With direct conversion you will receive the same signal at two places on the dial but for a simple receiver this is only a slight inconvenience!
 
Another example of a product detector response is when a signal is input at 12.0945 MHz ( a BFO signal) and the RF signal at 12.096 MHz( coming from a crystal filter) the two outputs would be: 1) 24.1905 MHz (sum) and 2) 1500 Hz (difference). For the product detector, the  one we want is the 1500 Hz as this is then the audio output.

Typically we add a low pass filter after the product detector so only the difference (audio signal)  is passed. This filter is a Pi type comprised of a 10 NF at either end with a 1 mHy choke in the middle which now will only pass the difference frequencies. Note in this case because the input signal is coming from a Crystal Filter you will have single signal reception which is now governed by the placement of the BFO signal. To receive the opposite sideband you would need a BFO frequency of 12.0975 MHz
 
Our "black box" can take many forms including 1N4148 diode ring, packaged Double Balanced Mixer's like the SBL-1, Gilbert cells such as the SA602 or SA612, vacuum tubes like the 12AU7, or a Dual Gate MOSFET. Of course the most famous Dual Gate MOSFET is the 40673 which today are on the unobtainable list. Some of these devices have no gain, in fact have a loss while others provide a substantial amount of gain. 
 
Since the Simpleceiver is a minimalist approach we have chosen to use the Dual Gate MOSFET, which is one of the devices that has gain in the conversion process. There are a whole new crop of RF Dual Gate MOSFETs and one in particular is from NXP and is the model BF991. Most of these unfortunately are Surface Mount Devices that for many newbie homebrewer's is an anathema. The Simpleceiver shown in an early post video now has a BF991 installed --so if a homebrewer is not shy about SMD --just drop one of those into the circuit.
 

Why use the Dual Gate MOSFET?

I would like to take just a few lines to explore the why of our choice to employ the Dual Gate MOSFET in the Simpleceiver given that there are so many new technology "black boxes" at our disposal. Many would say use the SA602 or SA612 which are also gain devices which even have a "twofer" capability wherein you can have the detector and carrier oscillator in a single 8 pin device. Simply plug in a crystal and a few caps between pins 6 and 7 where you have an instant BFO.
 
The Dual Gate MOSFET is not a black box like the Sa602 or SA612. As my friend Bill, N2CQR would say about a DGM, "you can better visualize the signals being applied to the device and have greater in depth understanding of the signal conversion process." This also satisfies his term of "more homebrewedness" with discrete components.

But the SA602 or SA612 can be used equally as well with the choice is left to the builder. BUT we do have as a goal for the completer Trans-receiver project to use the Dual Gate MOSFET in many of the circuits and given we bought them for 20 cents a piece (delivered) that is far less expensive than the Gilbert Cell SA602's/SA612's which cost about $3 USD --each!
 
At this point I will leave it to the reader to further explore the pros and cons of the Dual Gate MOSFET (DGM). Some will argue noise figure issues, while others will argue tendency to overload and lest I forget phase noise issues. There are always better mousetraps; but on the continuum of choices, for a simple project, the DGM passes muster as a viable candidate.
 
But realizing that those new to homebrewing do not have 50 years experience soldering their fingers together on a routine basis,  we offer the alternative of making a Dual Gate MOSFET from two individual leaded type J310 JFET's. These devices are plentiful and recently a 50 piece quantity J310's was purchased with shipping for around $10 USD.

In one of the earlier posts we mentioned the use of LT Spice to simulate the circuit that will be used in the Simpleceiver and so it is with our "homebrewed" DGM. Initially I missed the selection for JFETS and used MOSFETS. You certainly can get some interesting results using two IRF510's in Cascode (Source of one device connected to the Drain of the second device -- Read up on Cascode circuits using a Google search). Actually I think it will work -- but a better choice is the U309 which is close to the J310. The 2N3819 resulted in less gain for the same set of circuit values. So below is my simulated DGM using two JFET's in a Cascode Circuit. In the audio range -- the simulation shows about a 19 to 20 dB of gain.


This is the circuit that was simulated for our homebrew DGM (U309's in Cascode) and below is the output plot. This works!! In our next post (or an addendum) we will build the circuit and mate it up with the audio amplifier stage. Stay tuned.

73's
Pete N6QW


 In this post we mentioned that for the same circuit the use of the 2N3819 had less gain for the same set of circuit values. It is about 6 dB less and the plot for that is shown below. Do we now rise up like those who bash the Si5351 phase noise claiming that it is 6 dB worse than the Si570. NO is the answer! The 2N3819 is a viable device --it just has less gain. This is the value of LT Spice --no soldering is involved in the evaluation and we now can expect less gain with the 2N3819. Our frequencies of choice between 300 Hz and 3 kHz for the 2N3819 vary by only about 1.5 dB.

 
10/20/2015
 
The added value of the LT Spice simulation aside from assuring that a device will work in the circuit is the cost factor. The U309 is about $6 USD ( remember we are using the J310 which is 20 cents) and another good candidate is the 2N4393 which is about 1/3 the cost. So how would these stack up in an apples to apples comparison. I re-ran the plots for these two devices and the results are shown below. The striking difference is about 1/2 of a dB (your ears will never know) improvement at 3X the cost.  Gain variation as well as maximum gain must also be considered and the 2N4393 has slightly better overall gain than the U309 in this circuit. So this makes it an easy choice to go with the 2N4393 for this application.

The 2N3819 would be "Good Enough" but has about 6 dB less gain. The J310 is less expensive and when used in this circuit works better. I am trying to locate the data factors for the J310 so I can run this same plot. What I have now is practical data of how the J310 works versus the 2N3819 -- but for some who read this blog -- that is not good enough. [Usually I get an email that someone read on the EMRFD or BITX reflector that the J310 was not a good device yet they have no practical experience with the specific device!]

Pete N6QW


 

Friday, October 16, 2015

Belthorn (Bell Thorn) III Moved to 20 Meters

Belthorn III Moved to 20 Meters and Making QRP Contacts!


Several months ago I resurrected a project that was built some 12 years ago and updated the rig with a Si5351 + Arduino Controller, a color display and a new box. This radio had some innovations like using a Motorola Gain Block amplifier (CA2818C) which happens to be a 24 VDC device and led to embedding a DC to DC Convertor (MeanWell) into the project. It is a single conversion at 9.0 MHz and uses a GQRP Crystal Filter. The Arduino sketch includes a built in tone oscillator to provide a 988 Hz tone for tune up purposes.
 
The RF AMP is an IRF510 but I wished I had used a real RF Transistor like a 2SC3133 as the output on 20 Meter is slightly less than on 40 Meters. I am seeing about 7 watts on 20 Meters where I got close to 10 Watts on 40 Meters.
 
Now that I have a new beam antenna I decided to move the Belthorn III to 20 Meters and one of the first QRP contacts was with N0TUX/KH6. Thanks to Ron Taylor G4GXO for the original Belthorn design. Thanks Ron -- the Belthorn still perking along after 12 years!
 
There are two videos and the second is of the QRP contact. Check http://www.n6qw.com/ for more info on the Belthorn III.
 
73's
Pete N6QW
 
 
 


Sunday, October 11, 2015

Simpleceiver ~ Part 4

Audio Amplifier Stage

Addendum 10/13: You Tube Video of  a Test Amp.

 
In our last posting we gave some advice about starting from the back end and working your way forward through the build. Not only does this chunk the project into manageable  pieces but also enables test as you go. Thus the completed assemblies in effect become part of the test system. You may argue with that approach; but it is a sound practice. Somehow soldering all of the project parts to a circuit board and hoping it works is only asking for trouble!
 
We received an input in our last post about the LM386 audio amp IC and the issue of distortion when run at 200X gain. At this point it is uncertain that this excellent input, by the way, is based upon an individuals experience or just information floating around reflectors. But we did want to further explore the input and to give our response and take on the subject.
 
By design the Simpleceiver is just that --a project with minimum part count and easy to replicate. The audio amp stage is what I call "Good Enough" to get you started and is a totally viable circuit. That brings up the other aspect of the Simpleceiver and that is the circuit block module approach. Once the radio is built the homebrewer is encouraged to test new circuits and devices.

Thus the Simpleceiver IS an experimenter's platform. So if a builder finds the LM386 an objectionable device then by all means substitute your favorite circuit or one that has been approved by some reflector like the BITX or EMRFD groups. The LM386 can easily be changed to an LM380 ( 8 pin or 14 pin version) which of course can put out as much as 2+ watts. You can also try the TDA7052 -- like I said I smoked six of those in the recommended circuit. Or you can use just the pre-amp stage (2N3904) and feed an external audiophile style amplifier. The important thing to note is experiment and adjudge for your self.
 
For those who would like to build a discrete version of an amplifier a circuit is presented below. It is the same pre-amp stage followed by a complementary amp stage (straight from the Internet). I do know that several hams have tried simulating the complementary circuit in LT Spice and were unsuccessful -- I am no help there --other than I have built and it works. While it has more Pout than the LM386 I would say it is on par with the LM386 insofar as perceived or real audio distortion. You will note --lots more parts and the need for an isolated output.
 
 
 
 
Discrete component audio amplifier stage

In the spirit of providing alternatives for the audio amplifier for those still skeptical about the use of the LM386 then we offer the following additional circuits. These have been built and used in several radios at N6QW. But I keep coming back to "simple and good enough".
 
The first uses an op-amp as the preamp and the device of choice is a low noise version of the NE5534 followed by the LM386 (Oh oh here we go again about distortion at high gain.). This audio amp circuit was used in my 2009 Tri-Band Solid State version of the Heathkit HW-100. You can see this as one of the links at http://www.n6qw.com/
 
The only reason this is being shown is to demonstrate how this circuit was later converted to use the LM380N. Important point again about experimentation and circuit improvement. In this case the real improvement with the LM380N -- 2+ watts Pout.
 
 
 

The next schematic is the same circuit as used in the KWM-4 transceiver project in 2012 and the changes involved replacing the LM386 with the LM380N. Known for its greater output power it also has less distortion than the LM386. In passing take a look at the specification sheet for the LM380N and the "innards circuit schematic" is not unlike the discrete component amplifier shown at the beginning of this post. Hmmm there is a story here.

 

Below is a photo of the LM380N amplifier as used in the KWM-4 transceiver project. There are island blocks in the center of the board and this is where the 10K audio gain pot connects. (I am just heading off any questions that there doesn't appear to be any connections to some of the blocks. Having a CNC mill sure makes it easy to crank out prototype boards like this. )
 
 
To recap the audio amp stage should be the first item built and get working! We have presented options and hopefully have addressed the input about distortion in the LM-386. My take it is good enough and if you find it objectionable then you have the option of even taking the 2N3904 pre-amp stage and fitting that to the LM380N. It is all about experimentation!
 
Please note that unless you solder the ground pins of the LM380 directly to the circuit board and have good contact with the body of the LM-380 to the copper board you will need to add a heat sink to the LM380. (Such as the case should you use a DIP socket.)
 
73's
Pete N6QW





Thursday, October 8, 2015

Simpleceiver ~ Part 3

Secrets of Homebrewing Revealed

How to build a project

 
Heathkit had it right and much to their credit they had a very high success rate with their kit projects. Let us examine the difference between the Heathkit approach and today's kits. Much thought went into a Heathkit project so that there was a logical and progressive build concept that frequently is missing in today's kits.
 
Typically a kit today, as received, is a bag of parts with an internet address and perhaps an link to a you tube video. Ben KK6FUT has called this solder smoke --you solder all of the parts and then watch it smoke when power is applied. The Heathkit approach was to chunk the overall build into logical and manageable small sized tasks and to test as you go. In effect the portions of completed work enable the builder to verify a circuit is working before proceeding to the next phase.  In essence the portions completed become a part of the overall test system. We strongly believe in this approach and Ben and I in the many articles we co-authored have adopted that principle.

 A friend in the UK Nick (G8INE) sent in the following which adds a bit to the decode about today's kits and kits building practices.

·         A lot of kits arrive as either a single bag of bits, or the components divided by type, not section so there’s a tendency to press on once the bag is open.

·         The received knowledge in many instances is to build from the lowest components up, its easy to start putting ALL the Rs in, then ALL the Cs, and that is encouraged in many places.

·         Some “kit” building starts with the bare board, and then building once you get all the parts – it needs a lot of self-discipline to break that sort of build up into testable stages, especially as by the time that you get to being confident working that way, one tends to be confident that it’ll work, or that you’ll be able to debug it … 

·         The whole kit building culture has shrunk, so the pool of wisdom extolling the virtues of a staged approach isn’t there as a part of the landscape, just Pete and Ben shouting the message !!

·         There’s a sort of instant gratification culture where people don’t expect to embark on long projects anymore, so the expectation is that you can just settle down and blast through the process in a single sitting.

·         There’s a lack of building culture, so people tend not to have all the right tools which includes patience and the attitude that encourages you sit and look at what you’re doing  then think it through as well as the hard tools.

[Thanks Nick --many really excellent points about the why of today. Pete N6QW]

 
Another piece to the puzzle is something Bill, N2CQR and I frequently hear arising from the SolderSmoke podcast is: "How do I know something is working?" We are frequently amazed that many new to homebrewing just don't know. By chunking circuit elements into small pieces this enables the homebrewer to really delve into each circuit element and to understand what is occurring in that part of the circuit. No collector voltage is a sure sign of two things: 1) the circuit is wired improperly and 2) no collector voltage, it follows no output. Pretty simple but often overlooked.
 
In the LBS* project a person emailed me with a photo of the audio amp circuit he built from the project and had included voltage measurements. The subject of the email was of course "Your Circuit Doesn't Work!" At one point the measurement was 3.0 Volts and another point it was "0" volts and yet these two points were supposed to be connected. Thus both should  read either 3.0 Volts or "0" volts. Close inspection of the photo showed the points were not connected. The individual had the answer in hand but never looked at the why of the data. Connecting the points made the circuit perform as it should. Homebrewing is more than Solder and Smoke. Now if this person forged ahead simply built the whole radio and had the same result (no audio) where do you start looking for the problem?
 

Where to Start?

 
The first step is to start from the back end and work forward. Below is the block diagram of the Simpleceiver. This is slightly different than the original post as the audio amplifier has been changed to a 2N3904 driving an LM386. Appropriately this is the back end and the starting place. Build the audio amp and get that working. A simple go no go test after making sure of the following is to simply connect power (see caution) and a speaker. Then placing your finger on the input should result in a large hum from the speaker --you will know if it is working. If there is no output then you will only have to deal with a small portion of the overall project to find out the why.

Steps before "Power On"

  1. Check all wiring to insure the wiring matches the schematics.
  2. Look for poor solder (cold) solder joints --this is soldering not welding!
  3. Look for any shorts or solder bridges.
  4. Insure all parts are the parts to be installed
  5. Insure that transistors and diodes have been installed with the correct polarity.
  6. Install a 1N4002 in the Plus power lead with the arrow pointing toward the circuit. (This prevents the circuit from going up in smoke when you hook up the power leads backwards.)
  7. Avoid the use of Wall Warts!
Once you have gone through this list apply power and hope there is no smoke.
 

 

Simpleceiver Audio Amplifier Schematic Diagram

 



This is the schematic that will be used for the receiver. In an earlier post we mentioned that the free simulation software was a handy tool. The 2N3904 pre-amp stage was simulated in LT Spice and the addition of the 1000 Ufd bypass cap was a result of that simulation. In case you are wondering this circuit has been used and reused many times in our projects. It works --so keep things simple and just use it!
 
 
* LBS s shorthand for Let's Build Something which was a two part article in the January and April 2015 Issues of QRP Quarterly co-authored by Ben, KK6FUT and Pete, N6QW. This project started with a direct conversion receiver and by utilizing most of the block modules from the direct conversion receiver ended up with a 40 Meter SSB transceiver. The Simpleceiver and companion Simpleciter is like the LBS in that it ends up being a working transceiver but uses a different approach.
 
73's
Pete N6QW

Monday, October 5, 2015

Simpleceiver ~ Part 2 Continued

The Art of Homebrewing --- Continued

 
In our previous post we outlined some "homebrewing get ready" actions such as setting up a filing systems and securing certain publications. We now want to continue that journey.
 

The Hardware Part of Homebrewing

 
  • Homebrewing tools and equipment can make or break project and so often even basic test instruments have not been secured and the question I frequently get "How do I know it is working?" You will only know if it is working is by testing and if it is not working then a troubleshooting  procedure needs to be in place.
  • Basic tools include a good quality pair of needle nose pliers,  wire cutters (nipper), screwdrivers (various sizes of flat head and Phillips), a small adjustable wrench, flashlight, and exacto knife. Add to that a pair of forceps and tweezers. Also don't forget a suitable workspace with good lighting and last but not least a temperature controlled grounded soldering iron.
  • Test equipment is a must! Some can actually be homebrewed and works just as well as commercial units. A Digital Voltmeter (DVM) is a basic item of equipment needed in the shack. There are all kinds and varieties and some have functions beyond measuring resistance, voltage and current. Some will check transistors and diodes, while others can also measure frequency, as well as inductance and capacitance. Another tool which used in conjunction with the DVM is an RF probe which contains only 3 parts and thus easily homebrewed. An SWR bridge is another handy tool for checking RF output. Don't forget the dummy load which can be made from twenty 1K Ohm 2 watt non-inductive resistors which are connected in parallel. Effectively you have a 50 Ohm, 40 watt non-inductive resistor "dummy load" which is perfect for testing QRP transmitters.
  • Moving on to more sophisticated test equipment entails being able to see and accurately measure your signals. The two most frequently used items are an Oscilloscope and Frequency Counter. Many of the current crop of Digital Storage Oscilloscopes have a built in counter so it is a two for one. In the interim and in lieu of an oscilloscope (you will eventually need one of these) and frequency counter (you eventually will also need one of these) a General Coverage receiver with a BFO becomes a critical piece of test equipment. Many of these can be found in the $50 range. use of such a receiver enables listening to say an oscillator (verifying it works) and secondly it will tell fairly accurately the frequency of oscillation --it is a two for one test.
  • A "Junque Box" is one of the most critical pieces of the Homebrewing Art and having the right parts at the right time enables rapid prototyping as well as saving money. In time the seasoned homebrewer will find that buying a single part costing 15 cents often results in a shipping charge of $6.50 USD. But you can buy 100 parts for the same shipping cost. There is a message here and that is "buy in bulk". Most circuits we use tend to have common resistance and capacitance values ( such as 100 Ohms, 1 K Ohm, 10 K Ohm, 10 NF, 100 NF, 10 Ufd, 100 Ufd) buying these in bulk is a good start. The same for solid state devices such as 2N3904, 2N3906, LM386, etc. The Simpleceiver will use JFETS (J310) and I recently purchased a 50 piece quantity for 16 cents each and with shipping was less than $10 USD --that is 20 cents a piece delivered in my hand. One of the auction sites recently had a listing of 1200 pieces (20 pieces each of 60 resistance values) of 1% resistors for $6 USD. True it will take 3 weeks for shipping but at that price -- 1/2 cent each --it is worth the wait. Ferrite cores such as the FT 37-43 are used virtually everywhere from homebrew double balanced mixers to RF chokes. The Toroid King has amazing bargains on these cores. Diodes such as the 1N4148 bought in bulk can be had for 'pennies a piece" and these are used literally everywhere from homebrew double balanced mixers to "snubbers" on relay coils as well as their intended use in diode switching.
  • Enough of the boring but vitally necessary stuff and I will end here. 73's Pete N6QW

Thursday, October 1, 2015

Simpleceiver ~ Part 2

The Art of Homebrewing, A Disciplined Process!

Addendum 10/2/2015~ Schematic
 
Having spent most of my working life in the aerospace industry I can tell you first hand that having disciplined processes is paramount to producing high reliability products. It is only through disciplined processes that one can achieve consistent outcomes. That same logic applies to our wonderful hobby. Randomly  tack soldering a bunch of parts and wires could be successful but that most likely is a rare exception rather than a consistent outcome. Thus having a disciplined process for approaching homebrewing will move you way up the success curve.
 
The very minute someone mentions a process there are all sorts or rigorous rules that are envisioned and that not is not what is meant. A disciplined process in our context is more so  an organizing effort that enables doing tasks in a logical, sequential and measured manner. We are lucky for today with just a few mouse clicks we have much of the information needed to build our disciplined process and be successful at homebrewing a radio project.

Every process must start with two critical pieces of information: where to start and the desired end state. This may sound simplistic but often the failure to accurately identify these two pieces results in a major disaster. Starting by turning on the soldering iron and 'welding" parts together says it all. You will often hear me repeat lighting up the iron is one of the last steps in the process.

  • Deciding on what project is a really good starting point --and start with a small project. The Michigan Mighty Mite, 80 Meter CW transmitter is a great example. About 12 parts including the Low Pass Filter and the level of complexity is ideal for a first project. One creative ham lacking the tuning capacitor built his very own cylindrical capacitor from two beer cans and some electrical tape. So don't overlook the possibility of homebrewing all of the parts. Another might be building a simple dipole antenna. Or maybe a crystal set. But don't light up the iron yet --- there is much more to do.
  • Information gathering is the next step. Simply downloading a bunch of information on to your computer, tablet or Smart Phone without a thought about how to organize the data is a huge mistake. In the future you will want to retrieve the data you collected and having a process to store and retrieve data is key. I have several file folders on my computer where I organize my data. These include: Specification Sheets (pin out data, power ratings for various devices, etc.), Receiver Projects, Transmitter Projects, Transceiver Projects, Design/Technical Notes, Antenna Projects and Software.
  •  Start by "Googling" Michigan Mighty Mite and do a similar search of You Tube. You will be absolutely amazed at how much information exists on this project. Do overlook the SolderSmoke Blog and other blogs that are searchable. Save the information in the appropriate folder.
  • Find, beg, borrow or steal the following publications: Solid State Design for the Radio Amateur (Hayward), W1FB Design Notebook (DeMaw), QRP Power (ARRL). You can bypass the ARRL Handbook and EMRFD and this is just a personal opinion. While these two publications are good in their own right, the ones suggested are more practical in nature and written for those just starting out. There are two quarterly publications that are useful: QRP Quarterly from QRPARCI and the SPRAT from the GQRP club. I am more inclined toward these magazines more so than QST because of my bent on homebrewing. If you wanted to read about the zillion radio contests or see a review on the latest $12000 radio then by all means jump to QST. In particular two of recommended publications (Solid State Design and W1FB Design Notebook) form the basis of much of the background circuits that are used in the Simpleceiver.
  • Download and install the following free software. EZNEC for antenna modeling, LT SPICE for circuit simulation and Arduino IDE (you will need this later). We have a favorite single transistor amplifier circuit that has been used as an audio preamp and as a microphone amplifier. We have simulated that circuit using LT Spice and are presenting that below. Mouse clicks and no soldering irons were used to evaluate the circuit properties. This is the real power of the software as it lets you run various cases so that you can optimize the performance. I found a "notch" in the output and this was fixed by adding a larger size bypass capacitor.




The simulation software not only gives you a quick look at circuit performance but also enables a bit of tinkering to perhaps stretch the Frequency Response or increase the Power Output. Mouse clicks not soldering irons (at least at this stage) is the order of the day.

Stay tuned for more information on the Art of Homebrewing Process.

73's
Pete N6QW