Friday, February 28, 2014

Minima Transceiver Module Testing

Jack - WA7KMR and I spent some time in his Lab, using his Test Equipment to characterize the first few modules of my homebrew implementation of Farhan's Minima Transceiver. We tested my; RF Mixer, Crystal Filter and IF Amplifier (see previous post).
Jack at the Controls
We first connected each module as a standalone device to ensure each worked as expected.  We were both most interested in the Crystal Filter performance measurements. My previous measurement attempts with the AIM-4170B were inconclusive, other than the shape of the bandpass.

Crystal Filter
With Jack's Lab Equipment we measured the bandpass and insertion loss of the Crystal Filter. The bandpass is 6KHz, and insertion loss is about 3db, with about 2db of ripple. With some tweaking, I think the ripple could be reduced.

We later checked the operation of the standalone RF Mixer, and then the IF Amplifier. The RF Mixer worked similar to one of Jack's known mixer. The amp provided about 30db of gain at 20MHz.

We connected all three modules together and I very pleased with the results.

RF Mixer, Crystal Filter, and IF Amplifier
Output of the IF Amp
Horizontal = 20MHz Center,  5KHz / Div
Vertical  = -30dbm at top line, -110db at bottom, 10db / Div
LO was 200mV RMS

The RF Signal was Detectable down to -90dbm
The Results: I am a very Happy-Camper.

More of my "Minima" module implementations will follow.

Thanks Jack, for the measurement help.

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Tuesday, February 25, 2014

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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Sunday, February 23, 2014

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 :-)

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.


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Thursday, February 20, 2014

CQ with AIR

My Son and I are working on a project to automate; 20 air driven punches, with a similar strategy that was used by the old "pin printers", but our project will be on a much larger scale.

The planned punch printer will be much larger and much more powerful.

Air will be used to drive the punches and will be controlled via 12Volt air solenoids. I have previously posted the a description of the single test FET Driver that will be used, and which will be controlled via a microprocessor. The planned circuit for the finial product will consist of three stacked boards with 8 FET Drivers per board. The Toner Transfer of  the Prototype board is shown here.

Eight Circuit FET Driver Board
a Toner Transfer Prototype

To test the FET Driver, I needed a microprocessor to produce a test signal that would be easy to use.

From a previous project, I have an "Adafruit Trinket" microprocessor programmed to produce a "CQ" on one of it pins. A simple jumper was used to connect the Trinket to the FET Driver.

Trinket Sending CQ

The results was "CQ" being taped out by the air valve.

Air Valve Sending CQ

Once the air valve was connected to the cylinder,  . . . things got MUCH more interesting, and VIOLENT!

For this test, the air pressure was set at about 5 psi (34.5 kpa), for actual or normal operation the pressure will be about 40 psi (275 kpa). (I think I have the unit conversions correct)

Believe me, the following video does NOT fully capture the loudness or intensity of being - "ON THE AIR with AIR".

Pounding Out - CQ

Sorry for the rotated video (I will avoid that mistake with my future videos).

The test of the FET Driver? - It works great, . . . and I now know what it really means to "pound out" CQ.   :-)

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Tuesday, February 18, 2014

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.


Friday, February 7, 2014

The Farhan Minima RF Mixer - Cont'd 2

If you look at the schematic of the Mixer shown as used with LTSpice (see previous post), you will see the center of the lower transformer is not grounded. The original Farhan circuit grounds this point. When I first copied it, that is, created the circuit within LTSpice, I inadvertently forgot the ground connection.

But the LTSpice simulation worked as expected so I assumed the circuit was correct. Later while cross-checking the circuit for another issue, I noticed the forgotten ground. But, then when the transformer ground was connected, the LTSpice simulation did not show the expected 20MHz output via the FFT. Now I am really confused.

To allow the created circuit on the PCB to be tested with and without the transformer grounded, I inserted two Zero Ohm resistors that will be left out of the ground path for initial testing. I am sure they will be needed as I am sure Farhan knows his circuit much better than I.

Without the DC ground path I wonder how the LTSpice solution is discharging the electron build up from the effects of rectification at the junction of the JFET. Perhaps the other JFET junction provides a DC leak to ground. Regardless, I have something to do experiments with.

Also, I laid out the circuit board for smaller coil forms (BN-43-2402), but I could not find my 36 AWG wire to wind the cores.  When found, I plan to load another PCB with the small cores.

UPDATE: Feb 14, 2014
I found a role of #26 AWG wire and decided to try to wind a tri-filer winding on the very small BN-43-2402 binocular core. I was only able to get about three turns on the core, I needs 8 turns for this project. I will continue looking for my much smaller wire.

I had previously mis-posted the part number of the Binocular Cores that I have used. the number and links are now correct.


Thursday, February 6, 2014

The Farhan Minima RF Mixer - Cont'd

With a little work, I was able to shrink the PCB for my mixer (see previous post). The smaller coils, smaller JFET foot prints allow for optimization and part placement. The PCB has be reduced to 1.0 x 1.4 inches.

Etched, Solder Wiped and Drilled,
Ready for Cut and Parts
The Completed Mixer
The Two J310 JFETs are located in the Center

JFET Bias Circuit is on the Left
The Two Coils are, of course, Obvious 
Testing will follow as tests are devised.

I spent some more time with LTSpice. I changed the LO from a small sign wave to a 70mV square wave, it works much better. Then I could correctly observed the results via an FFT plot. For the simulation I used a frequency of 27MHz for the LO and 7MHz for the input signal. As can be seen in the FFT plot, the output contains the desired 20MHz signal and lots of higher harmonics. The 20MHz peak is the difference (27 - 7 = 20) and the 34MHz peak is the sum (27 + 7 = 34), the 27MHz LO is suppressed, as it should be.

Lower Left is the Farhan Mixer Circuit
Upper Left is the Full FFT Plot
Upper Right is the Expanded FFT Plot Centered on 27MHz
Lower Right is the Output Plot at the 50 ohm Load
Note: I think a normal Diode Ring Mixer requires about 700mV P (~7dbm) of LO input, or something greater than the 0.6v to turn on the diodes. I think for this mixer the JFETs can use a much smaller LO signal.

I really like working with LTSpice.


Wednesday, February 5, 2014

The Farhan Minima RF Mixer

I have been wanting a simple Mixer Circuit for experiments in my electronics shop, and most recently for use with my Small Signal Amplifier (see previous post).

Alan - K6ZY at the last Puget Sound QRP (pQRP) meeting mentioned he was considering building a Homebrew Farhan VU2ESE Minima Transceiver project.  After looking at the schematic for the Mimina, it appears that the Mixer Circuit would work very nicely as an stand-alone mixer for my experimental use. Very good documentation of the mixer's operation is provided by Farhan. The mixer used in the Minima has been dubbed the “KISS Mixer” by Chris Trask in his paper.

Minima Mixer Circuit in LTSpice
(See file below)
To play with the idea of building an experimental mixer, I created a LTSpice simulation circuit to start my understanding of it operation.

So far I have not gleamed much information from the LTSpice simulation, but maybe I have something wrong with my circuit; bias, configuration, signal levels or expected output. Or, maybe LTSpice can not deal with mixed signals correctly, but  I will continue working with LTSpice to learn more.

In preparation for my experiment and use of the Mixer Circuit, I have started the initial design of a PCB using DipTrace. Keeping with my ever present Goal of building electronic projects as small as I can, this initial design is larger than I think the final design will be, as I have currently configured it to used larger components than necessary. I think I can find small SOT-23 J310 JFET packages and smaller transformer cores. But this is a start.

Mixer Layout in DipTrace
 I have configured the PCB as a single-sided circuit as it can be produced with simple Homebrew Toner Transfer Method. But perhaps, using double-sided will be best for reducing the over all size.

This mixer as a stand-alone device will be very useful in my electronics shop - Thanks Farhan.

UPDATE: Aug 7, 2014 07:46

Here is my "SpiceMixer01.asc" file that I have been playing with.

Version 4
SHEET 1 880 680
WIRE -224 -352 -704 -352
WIRE -160 -352 -224 -352
WIRE 144 -352 -80 -352
WIRE 256 -352 224 -352
WIRE 256 -336 256 -352
WIRE -224 -320 -224 -352
WIRE -704 -288 -704 -352
WIRE 304 -288 224 -288
WIRE 144 -272 144 -288
WIRE 256 -272 144 -272
WIRE -224 -224 -224 -240
WIRE 144 -224 48 -224
WIRE 256 -224 256 -272
WIRE 256 -224 224 -224
WIRE 464 -224 256 -224
WIRE 544 -224 528 -224
WIRE -704 -192 -704 -208
WIRE -576 -192 -704 -192
WIRE 48 -192 48 -224
WIRE 304 -192 304 -288
WIRE -704 -160 -704 -192
WIRE -224 -144 -352 -144
WIRE -352 -128 -352 -144
WIRE 0 -128 -32 -128
WIRE 400 -128 352 -128
WIRE 544 -128 544 -224
WIRE 608 -128 544 -128
WIRE 544 -96 544 -128
WIRE -352 -80 -352 -128
WIRE -224 -32 -224 -64
WIRE -144 -32 -224 -32
WIRE 48 -32 48 -96
WIRE 48 -32 -64 -32
WIRE 176 -32 48 -32
WIRE 304 -32 304 -96
WIRE 304 -32 176 -32
WIRE -224 0 -224 -32
WIRE -352 32 -352 0
WIRE 544 32 544 -16
WIRE 400 128 400 -128
WIRE 400 128 224 128
WIRE 144 144 144 128
WIRE 256 144 144 144
WIRE -32 192 -32 -128
WIRE 144 192 -32 192
WIRE 256 192 256 144
WIRE 256 192 224 192
WIRE 320 224 320 192
WIRE -224 256 -720 256
WIRE -176 256 -224 256
WIRE 144 256 -96 256
WIRE -224 288 -224 256
WIRE 224 304 224 256
WIRE -720 320 -720 256
WIRE -224 400 -224 368
WIRE -720 432 -720 400
WIRE -560 432 -720 432
WIRE -720 448 -720 432
FLAG 176 32 0
FLAG 224 304 0
FLAG -352 32 0
FLAG 256 -336 0
FLAG -224 -224 0
FLAG -224 400 0
FLAG -352 -128 Bias
FLAG -224 -352 SigIn
FLAG -224 256 LO
FLAG 608 -128 SigOut
FLAG 544 32 0
FLAG -704 -80 0
FLAG -720 528 0
FLAG -576 -192 SampleSig
FLAG -560 432 SampleLo
FLAG -224 80 0
FLAG 320 224 0
SYMBOL ind2 128 144 R270
WINDOW 0 40 34 VTop 2
WINDOW 3 65 78 VBottom 2
SYMATTR Value {Lo}
SYMATTR Type ind
SYMBOL ind2 128 208 R270
WINDOW 0 34 32 VTop 2
WINDOW 3 60 86 VBottom 2
SYMATTR Value {Lo}
SYMATTR Type ind
SYMBOL ind2 128 272 R270
WINDOW 0 35 38 VTop 2
WINDOW 3 63 77 VBottom 2
SYMATTR Value {Lo}
SYMATTR Type ind
SYMBOL ind2 128 -336 R270
WINDOW 0 38 38 VTop 2
WINDOW 3 63 78 VBottom 2
SYMATTR Value {Ls}
SYMATTR Type ind
SYMBOL ind2 128 -272 R270
WINDOW 0 34 29 VTop 2
WINDOW 3 60 76 VBottom 2
SYMATTR Value {Ls}
SYMATTR Type ind
SYMBOL ind2 128 -208 R270
WINDOW 0 32 38 VTop 2
WINDOW 3 61 80 VBottom 2
SYMATTR Value {Ls}
SYMATTR Type ind
SYMBOL njf 0 -192 R0
SYMBOL njf 352 -192 M0
SYMBOL cap 160 -32 R0
SYMATTR Value .1uF
SYMBOL voltage -352 -96 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMBOL voltage -224 -336 R0
WINDOW 3 24 44 Left 2
WINDOW 123 24 72 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value SINE(0 10uV 7Meg)
SYMBOL voltage -224 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(0 70mV 0 0 0 {PulseWidth} {Period})
SYMBOL res -176 -336 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -5 56 VBottom 2
SYMATTR Value 50
SYMBOL res -192 272 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 -5 56 VBottom 2
SYMATTR Value 50
SYMBOL res 528 -112 R0
SYMATTR Value 50
SYMBOL res -720 -304 R0
SYMATTR Value 100K
SYMBOL res -720 -176 R0
SYMBOL res -736 304 R0
SYMATTR Value 10Meg
SYMBOL res -736 432 R0
SYMBOL res -160 -16 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 0 56 VBottom 2
SYMATTR Value 4.7K
SYMBOL res -240 -16 R0
SYMBOL res -240 -160 R0
SYMATTR InstName R10
SYMBOL cap 464 -208 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR Value 10n
TEXT -512 -280 Left 2 !.tran 0 10uS 9uS
TEXT 392 -416 Left 2 !.param Ls = 10000nH\n.param Lo = 10000nH\nKo L1 L2 L3 1\nKs L4 L5 L6 1
TEXT -800 -408 Left 6 ;WA0UWH
TEXT -272 448 Left 2 !.param Freq = 27Meg\n.param Period =  1 / Freq\n.param PulseWidth = Period / 2 * 1.05

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Monday, February 3, 2014

Small Signal RF Amp - Rev 03 - Cont'd

Update added at end of post.

I connected a reasonably calibrated 100uVolt RMS 50 ohm RF source to the input of my Small Signal RF Amp (see previous post). The output of the amp with a 50 ohm load was 20mVolts P, for a Gain of about 43db. Similar gain was seen at frequencies from 1 to 26 MegHz, with more on the lower frequencies, and less gain on higher frequencies. Currently, I do not have proper equipment to do a complete characterization of the amp.

Test Setup Show 20mVolts  RMS
With 50 ohm Load On the Left
100uVolt  RMS Source from Sig Gen on the Right
I am a happy camper !

I think this amp will be used in several of my future projects, stay tuned!

The amp was originally designed for 12 volt supply, but I think a local zener diode regulation at 9 volts (or battery) will be useful for use within an actual project. Regulation will help avoid supply side noise from effecting the performance. The above test was done with a 9 volt battery.

UPDATE: Feb 04, 2014

I checked with the LTSpice Simulation, it suggests with 100uV RMS at 10MHz as input, I should only see 5mVolts P at the output. I am measuring about 4 times that as reported above, I wonder why?

More investigation needed.


Sunday, February 2, 2014

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.

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?


Saturday, February 1, 2014

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.