More Propeller Projects

I plan to attempt to use the Propeller for both LO and BFO for a small receiver. Jeff put me onto a neat little receiver which is just begging for experimentation. The Propeller can produce multiple RF signals simultaneously, just as needed for the receiver. More information can be found on this single conversion superhetrodyne receiver kit from N3ZI

But, I am diverted to yet another project, to build an even more accurate Frequency Source for the Propeller Master Clock. The TCVCXO that I built using the Homebrew circuit board has been doing very well in all experiments. It occurred to me that if it was connected to a GPS one second tick, it could be steered to even more accuracy.

So far, only initial plans are in place, with some circuit diagrams and example code.

The strategy is to implement a Huff-n-Puff circuit and support Propeller SPIN code to "drive" the Voltage Control Pin with corrections - Results: A GPS Disciplined Frequency Master Clock.

Google: Huff-n-Puff Oscillators

Actually, this is all experimental, and I do not really know what to expect. But, this is what I have at present.

https://www.circuitlab.com/circuit/8bt74u/prop-tcvcxo-huffnpuff/

The following is a code snippet from my current GPS ISR Object (has not been tested).

PRI Huff_n_Puff | C, PrevC
  PrevC := 0
  Trend := 0

  dira[GPSPin]~              ' Set for Input, and Float high via Pullup 10K Resistors

  repeat
    Trend #>=  10
    Trend <#= -10
    pause(80 * ||Trend)    'Pause should be less than ~900ms
    dira[HnPPin]~          'Set Tri-state Mode

    waitpeq(0, 1<<GPSPin, 0) 'waiting for CPS SEC Pin to be LOW
    waitpne(0, 1<<GPSPin, 0) 'waiting for CPS SEC Pin to go HIGH

    C := cnt
    CountError := C - PrevC - CLKFREQ
    PrevC := C          'Save for next iteration

    if(CountError > DEAD_BAND)
        Trend #>= 0
        Trend--
        IF( HnPEnabled)
            HnPStat--
            outa[HnPPin]~     'Huff - Make Pin LOW
            dira[HnPPin]~~    'Output Mode

    elseif(CountError < -DEAD_BAND)
         Trend <#= 0
         Trend++
         IF( HnPEnabled)
             HnPStat++
             outa[HnPPin]~~    'Puff - Make Pin HIGH
             dira[HnPPin]~~    'Output Mode

    else
         Trend := 0

The intent is to "drive" the Voltage Control Oscillator (TCVCXO) to match the GPS. The RC time constant of the Huff-n-Puff circuit above, along with the Program logic should only gently correct the output Frequency.

What I expect for output is a square wave (at HnPPin), varying duty cycle depending on correction needed.

Obviously, more development and testing is needed.

Please comment, if you have experience with this sort of thing.

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UPDATE
I found the following interesting page: http://www.rt66.com/~shera/index_fs.htm


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Measured Success

After installing the Homebrew PCB with the 10MHz TCVCXO Frequency Standard Clock on the Propeller, I finally got it connected to an Antenna as a WSPR, QRSS and OPERA 200mW Beacon.

The results are amazing, the Frequency is measure as very Stable and the Frequency is measured to be as set.  The reporting site, and measurement that I trust the most is W1BW (Operated from ARRL HQ);  they report Zero Hertz Drift and at the desired frequency of 10.140210MHz - exactly as I have programmed the Beacon.

Note: Not only does the TCVCXO provide for a stable and accurate RF frequency, but it also provide accurate scheduling for the Beacons. WSPR requires scheduled transmittion on two minute boundaries, starting the actual beacon two seconds (+/-1) past the minute. This Propeller Beacon is on-time, every time :-).

Also, the three beacons run in quick succession, that is: WSPR starts on a two minute boundry (runs for 2 min), followed by QRSS on the top of the next minute (runs for about 3 min), followed by OPERA on the next minute (runs for about 2.2 min). Then all repeats 10 minutes later. The 10 minute schedule allows the QRSS beacon to be displayed at the same place within the 10 minute remote Grabber captures.

I am receiving many reports (spots) from around the US, no DX yet, but the night is young.

My WSPR on the Map

Note: the W1BW report (at 3939 km) in the following list (click to view).

My WSPR Spots - as Reported by WSPRNET.org

Also, the following was reported by the KK7CC Grabber, note the frequency scale, which is out side of the normal QRSS Subband, I had to pick a frequency to allow my signal to show up on his Grabber. I picked 10.139930MHz, KK7CC reports the same !

My signal is the lower trace with Propeller graphic and my Call in slash code.

My QRSS on KK7CC Grabber - Las Vegas

I am a Very Happy Camper !!   :-)

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UPDATE
New DX report at 7049km with only 200mW:

Timestamp	Call	MHz	SNR	Drift	Grid	Pwr	Reporter	RGrid	km	az
2012-03-17 03:54	WA0UWH	10.140204	-24	-1	CN88xc	0.2	WA2YUN	RK39hh	7049	270

And, Two more:

Timestamp	Call	MHz	SNR	Drift	Grid	Pwr	Reporter	RGrid	km	az
2012-03-17 10:04	WA0UWH	10.140208	-14	0	CN88xc	0.2	VKFRG	QF44np	12766	244
2012-03-17 10:04	WA0UWH	10.140199	-26	0	CN88xc	0.2	VK4TMH	QG56fj	11758	252

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Strategy for My Homebrew Projects

I have used protoboards (white plug boards) for as long as I remember, in fact most of my Homebrew projects start-out on a protoboard, and from there usually end up on a custom Homebrew PCB.

In the past, I only had a few expensive (typical $30) protoboards to share with new and old projects, and therefore dismantling older circuits was always necessary. My typical protoboards were the fancy ones with a metal backing plate and banana plug terminals, and of course all of which is un-necessary. Actually, only the raw protoboard is necessary, see a previous project.

My previous final Homebrew projects rarely resemble the original; rats nest of wire on the protoboard, nor the required 1/10 inch spacing for headers. Therefore, once prototyping was complete all further circuit development or testing was done directly on the target Homebrew PCB.

That is going to change:

All  of my new Homebrew PCB projects will be laid out with the protoboard in mind as the potential target usage. All headers will be laid out on 1/10 inch non-overlapping grid (i.e., along each side) as required for use with the protoboard. In the final project, the headers holes can be filled with Male pins on the top or bottom side, or with Male-Female stacking adapters as seen in some Arduino Shield products. This strategy will allow interesting combination of assorted projects on a single protoboard or as stacked sets (again, similar to that of the Arduino Shields).

I foresee a future Homebrew Transmitter, Receiver and maybe a Beacon Controller all stacked together to make a fun combined project.

Note: I will still continue my overall strategy of creating the smallest Homebrew projects that I can for as long as I can, but the projects may now be a little bigger to allow for the new header placement strategy. I still enjoy building very-very small and dense projects, the smaller the better!

In support of this Strategy:

Recently I discovered a relatively inexpensive (~$8) source for full size (clear) protoboards from Adafruit (their nomenclature is: breadboards), see:

https://www.adafruit.com/products/239

They also have half size (white) boards, for $5:

https://www.adafruit.com/products/64

UPDATE: I found the half size (clear) protoboards at SparkFun for $5.95:

http://www.sparkfun.com/products/9567

Bulk Male-Female (stacking) headers or more difficult to obtain, I have only found them available from the Chinese manufacture in lots of a million. But they are available in a package of; 2 each 8 pin and 2 each 6 pin headers for $1.50, also from Adafruit and SparkFun. They can be carefully cut apart, or joined to create other size headers as necessary.

https://www.adafruit.com/products/85
http://www.sparkfun.com/products/10007

Male pins are also available as:

https://www.adafruit.com/products/392

https://www.adafruit.com/products/400
or
http://www.sparkfun.com/products/10158

I found jumper wires with Female ends attached, I cut them in the middle, using each end for battery and other device connections:

http://www.sparkfun.com/search/results?term=jumper+wire+-+0.1&what=products

Coin cell holders are useful on small projects:

http://www.sparkfun.com/products/10592

I have looked for other similar sources for all of the above, these are easy, and the links are provided here for my future reference.

Note: I am not a agent or associated with Adafruit nor SparkFun, I just need/use their products.

UPDATE: My Friend Larry - KB7KMO thinks he has a link (somewhere) to bulk Male-Female (stacking) headers, I am waiting his search.

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Move Over SA612, for a Newcomer

There may be a newcomer on the direct conversion receiver block, check it out.

LTM9004 - 14-Bit Direct Conversion Receiver Subsystem

• Integrated Dual 14-Bit, High-Speed ADC, Lowpass
• Filter, Differential Gain Stages and I/Q Demodulator
• Lowpass Filter for Each ADC Channel
• RF Input Frequency Range: 0.8GHz to 2.7GHz
• 50Ω Single-Ended RF and LO Ports
• I/Q Gain Mismatch: 0.2dB Typical
• I/Q Phase Mismatch: 1.5 Deg Typical

Now:

• if we can only figure out how to use this at lower frequencies, 
• if the price and availability is right, 
• if we Homebrewers can figure out how to solder this thing

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