Minima - New Positive Progress

The last few days I have be struggling with my least favorite Homebrew build type of circuits, and that is the Audio Modules for the Minima Transceiver. I general, I just do not like to build Audio circuits.

Originally when I started the Minima Build, I was planning to build each schematic section as separate modules. For the RF sections that approach has work well. My original attempt to build modules for the Audio sections failed because they are somewhat dependent on each other, and therefore many interconnecting pins were going to be necessary to connect everything together. My original thought was to arrange the five Audio modules into a "checker board" with edge header between each. The first layout with headers on several sides of the modules eliminated their general use as building blocks for other projects. I wanted an easily adaptable modules for future projects. Because the module approach became to complex and therefore after several days (weeks) I abandoned the Module approach for the Audio Circuit - FAIL.

I collected the modules together into a single complex layout, but thats is where it sat for several weeks, although I publish blog posts with photos, diagrams, and discussions about the project. I was still not happy with the design or the approach.

But I needed to get something done to show progress on my Minima Build.  Three days ago, I decided to Build the Audio Board with the Toner Transfer Method (the same as with all of my modules). The Audio Board was going to be about 2.5x5.0 inches with 84 hand soldered via's. I printed, etched, dilled, and solder wiped the board and got it ready to install the 84 via's. But each time I looked at hand soldering 84 via's the number looked like a bigger task, and my interest diminished. I again abandoned the complex Audio Board, as there has got to be a better way!! - Another FAIL.

An Idea

The solution may be going back to individual modules, but this time I am going to stand-up each module on its edge Header. There will be five modules as described on the original schematic, and one power supply module. The modules will stand on a group of spaced headers on a Audio Mother board. These modules will easily work with ProtoBoards for experiments and testing, and therefore satisfying my original goal for the Minima.

I have now completed the layout for each Module and the Mother Board. The Mother Board is about 1.5x5.0 inches.  Each of the five modules will be 1.0x1.0 inches square. The Relay Module is a little larger.

The Mother Board will contain the Module Headers, Jacks, the edge connector headers for the Digital Controller Board, Tuning Pot, and Volume Control. It will be the "Glue" that connects all of the Modules together.

Mother Board, Five Modules and
a Power Supply Module

These boards will be created using the Toner Transfer Method.

With this new approach, I have a design (with only a few via's) that will hold my interest, and therefore my Minima Project Build should now continue forward. I can build a Module when I have time with very little overhead.

If this prototype works, I may send the design out for professional manufacture.


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Minima - VFO Troubleshooting - Cont'd 2

Well, that did not work, see previous post.

I created a Si570 BreakOut Board with minimal configuration to have something that I can test and verify my BusPirate. I got the same results with the new board, the I2C Address Scan returns nothing.

I must have something wrong with my use of the BusPirate.

The Si570 BreakOut Board that I created is a little different than previously posted, it now will fit in a standard 600mil socket. Which means that it is a little bigger than the original 500mil config, but should be more useful.

Here are some of the build details.

The New 600 mil Layout
As Designed with DipTrace

The size of the board is about 0.5x0.7 inches and is 0.032 inches thick, with four via's (40mil pads, 10mil holes).

You can almost see through the PCB material, the two sided image alignment is reasonable.

A Panel of 
Double Sided Toner Transfer PCB's after Etch
(Showing the Back Side)

This is the results after: Cut, Solder Wipe, Holes Drilled, and Parts Loaded.

The Finished Si570 BreakOut Board

When I get the BusPirate operational issue sorted out, this should provide a simple verification test. It will also be a useful part for ProtoBoard experiments.

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Minima - VFO Troubleshooting - Cont'd

Regardless of what I have tried, my Minima VFO Module does not seem to work, see previous post.  It does not respond to a simple I2C Address Scan from the BusPirate (BP). The problem could be a something simple on the VFO Module, a dead Chip,  the BP, or the connecting wires. I could test the BP and wires if I had a known working I2C device, but I don't.

To fix that, I am going to build a simple stand alone Si570 BreakOut Board, which will only contain an Si570 and Header Pins. If this works, it will be useful for verifying my BP and also it will be useful for other standard ProtoBoard experiments.

Proposed Si570 BreakOut Board

A simple Google search did not suggest a consensus of pin outs for a breakout board, I decided to arrange the pin in Si570 documented order similar to a DIP. The board will be about 0.5x0.6 inches. I guess I should have made the pin row spacing 600mils (not 500mils) so it would fit standard PCB DIP Sockets.

Using standard pin order requires a trace on the backside with the accompanying two via's. Two additional via's will help tie the front and back ground planes together. All soldering for the Headers will be done on the top side, because Homebrew boards do not have plated through holes, and therefore it would be difficult to solder under the Headers on the back side.

I could have included the two required I2C Pullup Resistors, but no, I wanted this to be a generic as possible.

This maybe a very useful board for my future projects, it is a simple task to make several copies while making the first, using the Toner Transfer (TT) Method.

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Minima FN - Troubleshooting

I am still testing my Minima CPU Module, for some reason the FUNCTION (FN) switch will not work. The microscope was used for inspection, looking for shorts or open circuits.

This is the ATmega328 Processor
and Crystal Circuit

Note: I have mounted the 0805 bypass capacitors on edge so that they will fit on the 0605 pads. For this module space reduction was not really necessary, but  I generally use this technique by default.

ATmega328 - 32QFP

So far, nothing found that would cause the malfunction. Resistance and switch operations appear normal. The other switches and functions work as expected.

This is not considered to be the "Ugly Style" of Homebrew hobby construction. But, under a high power microscope everything is "Ugly", especially after it has been setting around for a while. It is a wonder that any modern high density electronic devices work at all, with all of the accumulated contamination that everything collects.

More circuit review, software program review, and testing is required.

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UPDATE: Apr 30, 2014 15:09
Success, I got my FN switch problem solved. There were two problems.

The first, was a missing via on my board that should have provided a ground path for the FN switch.

The second, I have been working on the frequency Display and the associated Human Interface within the Sketch. My new modifications had not been properly integrated with the rest of the Sketch.

Now,  all is working as expected.

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Minima - CPU Module Progress

I have made some progress on my Minima CPU Module.

I had previously created a Homebrew REV02 of this module, but had to stop construction while waiting for the Crystal. During the down-time, I decided to make some major changes to the board, and have been working on REV04 of that layout effort every since.

But the Crystals came in, and I just could not talk myself into creating another 70 "vias" on a new board layout.

So, I decided to continue the build on the REV02 board, even though knowing it would not work in an actual Minima environment (it was missing some critical Minima circuit connections). It will work for experiments and while learning the Bootloader and Farhan's Raduino Sketch.

The Ardunio Bootloader Installed - Using an ISP

After the REV02 board was built, the next task was to download and install the Arduino Bootloader. I had an USBTinyISP kit that I had not built, but, therefore it was also untested.

Minima CPU Module and USBTinyISP
as used to install the Arduino Bootloader

With a little work, some head scratching, and some jumper wires, I got the Arduino Bootloader installed on my raw ATmega328 processor. Because the LCD uses some of the same pins used by the "In Circuit Serial Programmer" (ISP), the LCD was removed.

The Ardunio Bootloader took about 20 seconds to install.

The Radiono Sketch Installed - Using a Prop-Plug

Because I have one, I have previously decided to "try" to use the Prop-Plug (USB to TTY Serial) converter to install Farhan's Raduino Sketch from the Arduino IDE. Again, with a little work and research the sketch was install successfully.

Radiono Running after Sketch Installed

The Prop-Plug is lower-right, the Minima VFO is lower-center, the Tuning Pot is lower-left, and the LCD sets on header on top.

I knew from reading posts on the Reflector, and seeing a local implementation, that I wanted to make changes to the Radio's Human Interface, all change seem to work very well. But, only after actual connection to the Minima (yet to be finished) will I know for sure.

After the last few changes are made to REV04 of this module, I will have to decide whether to send it out for manufacturing, or do a another Homebrew Toner Transfer build.

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Minima - CPU Module Mods

While building my Minima CPU module, and thinking about the circuit's programming interface components. I started wondering if there was an Off-the-Shelf USB product that could replace and simplify the circuit.

After a little research, I found three likely candidates, all available from Parallax.com;

• The Prop-Plug - $15
• The USB2SER - $14
• The 4D Systems USB Programmer - $20

Each have slightly different header pin-outs for connection to a project. Each uses the same FT232RQ USB-to-Serial chip.

For DYI, the FT232RQ chip is a simple "state machine", which does all of the hard work of USB-to-Serial protocol and signal-level translation. It is simple enough that it could be included directly into a project, all that is necessary is; the FT232RQ, a USB connector, and a few resistors (see the Prop-Plug datasheet with schematic). Note: Parallax encourages use of their schematic for DYI implementation, they will be happy to supply the parts, or as available elsewhere.

If the FT232RQ is included directly in a project, the +5V from the USB connector could also be used by the project, only the off-the-shelf 4D Systems USB Programmer (listed above) provides a fifth pin for a power connection.

The FT232RQ is available in the 28-LD-SSOP and the QFN-32 package. I will use the QFN-32, because I like smaller components. The price of the FT232RQ is about $5.00, but that is cheap for what it does and the components that it replaces.

Also, if the FT232RQ is included directly as part of a project, it is available for generic ASCII I/O for control or output via a standard USB connection.

Because I already have a Prop-Plug, I think I will simplify and re-layout the next Revision of my Minima CPU module with a simple Prop-Plug header. I hope this will work as a generic dumb download interface with the Arduino Interactive Development Environmnet (IDE), but this remain to be tested. Does anyone know?

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UPDATE: Apr 21, 2014 14:11
As per the comments, Larry has suggested the "FTDI Friend" - $15 from Adafruit.com

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Minima - CPU Module Progress

After making modification to my experimental Minima CPU board layout, I built a board via the Toner Transfer Method, then coated it with solder, and then started installing the via's and a few components. At this stage, the board looks a little rough as the thin layer of rosin coats everything. When complete, the board will be washed with Alcohol and a very thin coat of high tension oil (Corrosion Block) will be applied.

The 11 mil Via holes are Stitched
With Stripped 8 mil Wire Wrap Wire

The new layout is larger than had been previously posted, because I decided to include small push button switches for each of the normally external controls. By including switches on this board other modules or wired connectors are not necessary for full operations, although edge headers (as shown along the near side) are supplied for eventual use of the external controls.

The current board is slightly wider than a 16x2 Character LCD module and other dimension (height) allows the switches and header to be exposed below the mounted LCD. Note: the LCD plugs in via a header across the top of the board, and in normal use, the LCD would typically be mounted remote.

Stitched Loops of Wire Wrap Wire

Installing small via's is NOT a lot of fun, but can be done with the aid of a Microscope. My method starts with drilling the hole in the via that is just big enough for the intended wire used to make the via connection. If the hole just fits the wire, the wire will stand straight through the hole. I stitch all via's together with a single wire, leaving very short loops on each side.

The very thin stripped Wire Wrap Wire is 8 mils in diameter, and the via holes are 11 mils (a tight fit), the via pads are 40 mils. Note: 8 mils are less than the thickness of 3 sheets of typical bond paper, but I really enjoy working on microscopic projects.

Once all holes are stitched together, the loops are bent tight to the board and then cut just out side of the edge of the pad with an X-Acto Knife. Wire Wrap Wire cuts very easily with a gentle wiggle of the knife. The loops on the backside are left in place to hold the wires in place.

After each via is soldered from the first side, the "cut and solder" procedure is repeated on the other side. Care must be taken to avoid heat transfer to the opposite side solder joint, even as small as the Wire Wrap Wire is, it can transfer enough heat to melt the backside solder (if to much heat is applied).

A very-very fine tip soldering iron is used with very fine 15 mil solder.

Because the stitching process is somewhat random, the Wire Wrap Wire is typically bent in to a "Z" shape, with a short flat tail on each side of the board.

I make a Microscope video with a USB camera of the process, but it did NOT turn out. I need to find an adapter for my good low light camera.

About one half of the parts are installed now, but a few (i.e., the 16 MHz Crystal) has not been ordered yet (maybe tonight).

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Mimima - Minimal Progress

As stated in a previous post, I have started layout of the separate Audio Modules for my experimental Minima Transceiver. I think I have four of the five modules in semi-final form, but I get "bored" working on Audio circuits.

And therefore, I have temporary turned my attention to the ATmega328P Processor Module layout. The original Minima circuits uses an ATmega328P-PU 28-pin DIP package, which is easy to use, and easy to solder on a through-hole PCB, or mounted "Dead Bug" or "Ugly Style". But, I enjoy building my own PCB's.

As with all of my projects, my goal is to make them as small as my eyes, nerves, an abilities will allow, and therefore I will use the ATmega328P-MU which is a small 5x5mm 32-TQFP package on a Homebrew PCB. The pin numbers and layout are a little different, but the functions are the same.

First DRAFT
Minima - CPU Module

The above is the first Draft of the proposed layout, the planned Homebrew Double-Sided board will be 1.4x3.0 inches with only 13 via's. The PCB will be created using the Toner Transfer Method.

The ATmega328P-MU will be mounted on the small diamond shaped pad in the center. The power +5V Power Regulator is on the left, the CPU programming circuit is on the right. The upper long header is for connection to the LCD Display.

I am still considering modifying the layout to use a single combined edge connector for connection to the planned Audio Modules.

This is work in progress, there is still more layout work to be done.

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Minima - VCO Module

New Toner Transfer Paper was received and Ferric Chloride Gremlins are at bay. See previous post.

Without too much difficultly, I finished my Minima VFO Module (see description and PCB Layout on previous post). Currently I do not have a way to program the Si570, but with power connected, the Module outputs its default RF signal.

The board is 1.0 x 1.2 inches, the homebrew vias are 40 mil pads with 12 mil holes. Solder Wipe was used for copper protection.

Minima - Si570 VFO

Backside Traces

As stated in the previous post, I modified Farhan's original circuit to include an output transformer, I want to also use this circuit as a Generic Lab Test Bench RF source where DC Ground isolation would be useful. The output transformer was wound as a 4:4 turns on BN-47-2402 core.

I plan to create an equivalent circuit using the Si5351 chip (as previously posted). It will look similar to this board, but it will have three output SMA connectors.


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A Measurement Fixture

While waiting for my replacement order of Toner Transfer Paper, so that I can continue my Minimal Project, I used some small cut-up scraps for this (another) project.

I have always wanted to build a self calibrating Fixture for my AIM-4170B Analyzer.

Self calibration means to me, that the "Short", "Open" and "50 Ohm Load", which are necessary for calibration, are a part of the fixture.  The "Open" is easy, just remove any parts from the fixture. The "Short" will be a simple push button switch across the analyzer terminals. And, a "Load" is another push button switch in series with a 50 Ohm resistor.

This approach to calibration is NOT exact, but it is good enough for most measurement that I do. For exact calibration, I have three certified (screw on) connectors that can be used.

The fixture as planned is only about 1.4 square inches and provides and SMA connection to an adapter on the AIM-4170B.

SMD parts can be scanned by placing them across the void on the fixture, and a plastic clip can be used to provide clamping pressure as necessary.

Parts with "Leads" can be pushed into the header shown in the center. There are three Ground header-pins, two groups of two header-pins are only shorted together and can be used to string leaded part together for a simple network measurement. And, there is one header-pin (center) that is connected to the analyzer.

Toner Transfer Method was used to build the fixture. As can be seen, only a small scrap of Transfer Paper was needed.

And, a small scrap of PCB material was used, which will be trimmed a little before going into the etch.

For etching, I use Ferric Chloride in a Ziploc Bag while kneading and running hot water over the bag. Only about 1 oz of Ferric Chloride is used.

In the Etch Bag
Almost Finished,
Some Copper (lower center) is Still to be Dissolved,

After cleanup, solder wiped, with switches and header attached, the fixture is ready to be attached to the AIM-4170B Analyzer.

The Analyzer Calibration can be done with the two switches. the upper push button switch connects two 100 Ohm Resistors in parallel across the analyzer terminals. The lower switch "Shorts" the analyzer terminal to ground.

The tapered section (lower center) is where SMD parts can be attached across either of the two voids.  Parts with leads can be plugged into the header.

The Fixture

The Fixture is installed, calibrated and ready for measurements.

Fixture Installed on the AIM-4170B

This fixture will help make sorting and matching Crystals that much easier the next time I build a Crystal Filter.

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Minima - AUDIO Board - Work In Progress

The SMD Caps were received, and therefore layout of my Minima AUDIO and Power Board has resumed.

This initial layout still has a few problems, and it has far too many vias (32) to my liking. I can build vias using the Homebrew Toner Transfer Method, but they are not fun, or at least at the size (40x15 mil) that I want.

This board contains (left to right, top to bottom): On the top row; TxRx Relay and Control, SideTone/CW, Audo PreAmp, Main Power Connector and Regulator (a little lower). On the next row; the KEY Jack, PTT Jack and Mic Amplifier, and the Audio Amplifier and Phone Jack.

My Minima AUDIO and Power Board
Proposed Configuration

If all goes well, the board size will be as shown at 2 x 4 inch. There is still room for additions or modification, but any additions will more than likely mean more vias. :-(

The circuit is a slight modification of the original Farhan Minima Transceiver circuit, I added; the Power Supply with Headers for the other Modules, I included the KEY and PTT circuits on this board because I wanted their Jacks near the Mic and Phone Jacks on the same board. A CPU signal and its Power Header is also included.

I still have to find a suitable Large Cap (500uF - Lower Right), I think the footprint as shown will work.

I just checked, and I need to order more Toner Transfer Paper, I may not have enough to build this board, especially if I make a mistake, Dang !

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UPDATE: Mar 29, 2014 12:16

With a little digging, I found a stash of nice 35V 330uF Caps in my part bins, two of which I will use to replace the single 500uF cap as per the original schematic. The caps that I found are stand-up through-hole mount. I moved the connecting traces to the back side so that they could be soldered without the need for front-side solder (underneath the cap).

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SMAs Received

I finally received my SMA Connectors (Bling) from China, they seemed to have taken an extraordinarily long time in the postage. Actually, I think it was just my anticipation.

Now I can continue "plumbing" my project (see previous posts) by connecting the current Minima's Modules together. This is just an experimental Transceiver and therefore a layout like this will be acceptable for my use on the test bench. The connected layout is similar to that of the schematic.

Modules Built So Far

Farhan's Minima
Transceiver Schematic

There are four additional boards to be built; the RF Low Pass Filter, the VCO, the Micro Controller and Display, and the Audio Board.

The Audio Board will contain four of the schematic's named modules and power supply. My plan is to use the Audio Board and its power supply to provide power for all of the other modules via twisted wire and connectors.

The Audio Board Schematic has been captured in DipTrace, but the Layout is not complete.

More to follow, . . .


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Minima Bidirectional IF Amplifier

I had some time today to work on my Farhan's Minima Transceiver Bidirectional IF Amplifier Module as previously posted for the layout and design.

Because of the density and the desire to put as much ground plane on both sides of the PCB, I decided to layout the Input, Output and Power traces on the back side, which meant that via's would be necessary. Normally I avoid double sided Homebrew PCB, but sometimes they are necessary. The via's are 40 mil pads with 12 mil holes.

Homebrew PCB via's are not fun to drill or install at this scale, there are ten via's which were the last thing that I installed.

As with all of my Experimental Minima Modules, this module was created with the Homebrew PCB Toner Transfer Method on .032 board material with 1/2 oz copper clad.

Minima's Bidirectional IF Amplifier
0.8 x 1.4 Inche PCB

The upper string of components are used for Transmit (signal flow is left to right), and the lower components are for Receive (signal flow is right to left), which for simplicity sake, is the same orientation as the schematic.

The Backside

The Backside clearly shows the 10 vias that were necessary for the circuit layout. Maybe it could have been a single sided board, but the front side copper pour (ground plane) would have been broken into islands with poor conductivity between major sections and the SMA connectors. The vias are 40 mil pads with 15 mil holes. Small wire-wrap wire was used to make the via connections.

The circuit powers up, and amplifies a 20MHz low level signal in both direction depending on the power connection. Actual performance numbers will be measured later in conjunction with the rest of my Minima Test Modules. According to chatter on the Minima Reflector, the gain of this stage is not anything great, but I do not remember it's expected gain.

The power connector center pin is ground, therefore moving a two pin power connector is all that is necessary to change direction for testing

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Farhan Minima - SSB Modulator/Detector

My order of Dual 1N4148 diodes (MMBD4814SE) were received in the mail. I created a Double Sided Toner Transfer PCB and loaded it with parts. See previous post.

This is my implementation of one of the Farhan's Minima Transceiver modules.

SSB Modulator/Detector
Double Sided Toner Transfer PCB
1x1.2 inches

The Dual Diode is the small SOT-23 device in the center right, the binocular core mixing transformer it center left, and the RFC is the binocular core in the lower right.

SSB Modulator/Detector

Soon I will have enough connectors and adapter to connect everything together in a nice neat test string of modules.

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Minima - BFO Mixer

I have started working on the next Farhan Minima Module for my experimental receiver (see previous post). This module will be the BFO Mixer which is used for SSB Modulation and Detection.

The circuit and layout is simple and will use the same SMA connectors as my previous constructed modules.

Proposed BFO Mixer

My proposed BFO Mixer board will 1x1.2 inches, which is laid out with DipTrace.

Farhan's Minima Transceiver requires for two 1N4148 Diodes for the mixer. He suggests that the diodes should be matched, and provided a test fixture and procedure to help find a matching pair.

I have several old 1N4148 Diodes from which to pick from, but I decided to order a fresh batch which hopefully will be manufactured from the same processing batch.

SOT-23

While looking for Diodes to order, I discovered the 1N4148 is manufacture as a SOT-23 MMBD4148 (single diode), and a dual diode as MMBD4814SE. Of course, for my projects I am always looking for the smallest package(s) available, and with two diodes in one package this part is a big win. This diode is available in four configurations; single diode, dual common cathode (CC), dual common anode (CA), and dual one of each (SE). To meet Farhan's circuit connection requirements, my BFO Mixer will use the SE configuration.

I tried to find information about the manufacture of this dual diode, that is; I wanted to know if the two diodes are from the same die, or if they are just two chips put into a common SOT-23 package. The information was not found. I am hoping the two diodes will be a matched pair.

I think the dual diode part will work fine for my project. More details to follow.


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Receiver Modules

Here are the first few modules of my implementation of the Fanhan Minima Transceiver. The RF Mixer on the left, the 20MHz Crystal Filter is center, and IF Amplifier is on the right. More modules will needed, and therefore constructed, before meaningful on-air experiments can be conducted.

The First Three Receiver Modules

The next module to be constructed would be a BFO Mixer, which should be simple as it uses a similar layout as the RF Mixer. Then an AF Amplifier will be needed, which will be constructed in similar fashion. Also, a Low Pass filter will be constructed and connected before the RF Mixer.

This configuration only implements a Receiver, but with a few relays, bidirectional amplifiers, full Transceiver functionality should be possible (similar to Farhan's Minima Transceiver).

When completed I plan to use my Parallax Propeller microprocessor for control, and generate the RF for both VFO and BFO sources. This is where my implementation radically departs from Farhan's Minima Transceiver, but then remember,  . . .  this is just an experiment !

Note: In the photo above, one of the two RF Mixer coils has be replaced with a much smaller core as originally planned (see previous post). The other (larger) core will be replaced when time is available.

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A Homebrew Crystal Filter

I ordered and recently received a batch of 20MHz Crystals to build an experimental Crystal Filter similar to as shown in Farhan's Minima Receiver and my previous post.

Somewhere (link found) I read that for Homebrew Crystal Filters the HC-49US (short) crystals do not have as high of "Q" as the standard HC-49U (standard) crystals, but as with all of my projects "small is better". This experiment is being done to see what I can do with the short crystals.

To try to find matching crystals, I used an AIM-4170B Analyzer to sort the crystals into six,  5-digit groups (19.991 - 19.996MHz). The crystals sorted into a typical standard bell distribution. I think the measured frequency, which is lower than the expected 20MHz, is due to calibration, and/or because the crystals are not actually operating in an oscillator circuit.

For this build, I decided to use the 19.993MHz group, as it provided more crystals to further select from.

Initial Sorting of 20MHz Crystals

The Analyzer display provided the Resonate Frequency and other information.

AIM-4170B  20MHz Crystal Plot

I re-tested each crystal of the 19.993 group, sorting and recording the frequency to 7-digits. A green tape label was attached to each crystal to make sorting easier.

Sorted Crystals

I selected a set of eight crystals for my filter, several of which had the same values.

Selected Crystals

The selected crystals have the following frequency values:

• 2 - 19.99265
• 1 - 19.99266
• 2 - 19.99267
• 1 - 19.99269
• 2 - 19.99271

A double sided 1 x 2 inch PCB was created to mount the crystals and capacitors, the Toner Transfer Method was used to make the PCB.

20MHz Crystal Filter
Toner Transfer PCB

This is the results after Cutting, Drilling and Loading the board.

Completed 20MHz Crystal Filter

I think the AIM-4170B is NOT the best instrument to measure overall performance of a Crystal Filter, But, initial testing indicated there were some major "spikes" in the frequency response.

I initially loaded the PCB with two parallel 50pF capacitors at each of the five locations where Farhan's circuit called for a 100pF. The goal was to parallel two capacitors to lower series inductance and/or provide the option of replacing one-of-each with a variable capacitor (if needed).

Due to the observed "spikes", I replaced one-of-each set of two capacitors with a 4-47pF NP0 variable capacitors.

Tuning Caps Installed

With a little tweaking, the "spikes" were removed, and this is resulting SWR plot with a 50 ohm Load on the output. But still, the resulting curve is less flat than I expected,  . . .

SWR with 50 Ohm Load

The real test and performance evaluation will need a Spectrum Analyzer and/or a measurement done within a fully constructed receiver.

More Crystal Filter fun to follow :-)

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UPDATE: Feb 23, 2014 14:04
I just received an e-mail from Jack, we should be able to evaluate the Filter soon.

Hi Eldon,

Nice looking XTAL filter.

If your design is around 50 ohms in and out then my equipment should do the job.

I expect to have the interconnect cable for my Spectrum Analyzer to Tracking Generator by next Tuesday.

Assuming both pieces of gear work as planned I will be testing about 4 RF filters I have on hand and your XTAL filter would be a lot of fun to test.

I can also provide a print out of the filter response curve. A camera shot of the CRT also works.

Jack

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Mixer and Amp Performance Measurement

I took my Homebrew Mixer and Amplifier (see previous posts) to Jacks Homebrew Meeting tonight. I was hoping that Jack and his Lab could help provide meaningful measured performance data.

Jack has several very nice pieces of LAB Grade test equipment. Unfortunately, his tracking Oscillator-Spectrum Analyzer was missing a cable or not working, and could not be used.

But with other equipment, we were able to spot check performance with an HP Oscillator with Attenuator and a HP Frequency Sensitive Voltmeter with its Attenuator. The two attenuators agreed within 0.25db. We also had a standalone attenuator for gross signal level adjustment.

The results; the Amplifier measure about +30db gain from 1 to about 27MHz (which was the highest Freq the Oscillator was calibrated for). The Amplifier would "quiet" the Voltmeter with as little as 115dbm input signal. Actual Noise Figure performance was not measured. This overall measured results are similar to what LTSpice suggested, but less than I measured at a Load on my Oscilloscope. NOTE: I may be mixing in my mind; Power Gain with Voltage Gain performance data, I may need to rethink this measurement.

The Mixer performance data and method was less precise, and accurate measurement will have to wait until Jack has his other equipment working.

More performance testing is necessary.

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Small Signal RF Amp - Rev 03

Update added at end of post.

I corrected the layout of my Small Signal RF Amp as described in the previous post. This time I printed both the Front and Back side of the layout for use with the Toner Transfer Method.

This photo of the etched board was taken with back light, which shows good alignment with the front side hole images. Actually, only two holes will be drilled, they will be used to mount the power header.

View through the board via Back-Light

The Front of the Completed Board

The Back

Now for some performance tests.

But, for a quick test, I tried it as an input amplifier for a receiver, it passes signals, but more proper testing is needed. I am sure it will work best as an IF Amplifier.

Some Project Background

For a transfer, I normally use a modified laminator (modified to set higher temperature at 350F or 176C). But for this project I wanted to use the Clothes Iron method. My previous attempts to use the clothes iron were less than satisfactory, probable because I did not know what I was doing.  Now with more knowledge and understanding of what makes for a good transfer, the results speak for it self. It is all about; Board Preparation, the right Temperature, Time, Pressure and Transfer Media. I will go into the details in a future post.

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UPDATE: Feb 2, 2014

I just noticed an "0" was missing from the date/time on the back side image, but then it was missing on the upper back-light image also, which became the finished board. It must have just not transferred - go figure?


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Small Signal RF Amp

I have had an idea for an small signal RF Amplifier that I want to try. LTSpice suggest the gain will be good and the linearity appears to be good, or at least that is what the LTSpice FFT plot suggests. This Amp is similar to those that I have used in my Digital 15 Watt Power Amp, but biased for linearity.

My Goal for this circuit is Low Part Count and good Performance. And, as always, a major goal for all of my projects is to make them as Small as my Eyes, Nerves and Methods permits. Yes, I know there are published circuits that may work better, but this is my attempt.

This layout is a single-sided board, with ground plane on the backside. The SMA connectors, connects all ground planes together at the circuit board edge. A layout for a commercial manufactured board would include many via's to assist with ground plane connections.

The first Toner Transfer (TT) version of the circuit had a schematic error (my screw up, I was just to quick on the print button). The second version is shown here.

Etched and
Toner was Removed Underwater with Scotch Bright

Solder Wiped
and Ready for Cut and Part Installation

But alas, I made the power pads too small and they pulled up with only a slight tug on the cable, layout will need to be re-done.

Circuit Complete
with Jury Rigged Power Cable
The PCB is 0.6 x 1.1 inches

The circuit performance tests will have to wait until tomorrow. I will have to devise some interesting tests. Noise Figure, Gain and Large Signal behavior are things I am interested in checking.

On this Rev 02, I forgot to add a Power LED, so I am now working on Rev 03, which will correct all of the known layout problems.

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