Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com
 

I've revised  the active antenna printed circuit board layout and sent it, along with a simple DC power injector printed circuit board out for prototypes. I believe these should be final, but it's always possible for an error to surface.

Since Monday, the 26th, I've been making transmitted intermodulation distortion measurements of my Elecraft K3 and, for reference purposes, my K2 and my old Kenwood TS-940. The measurements include IMD versus DC power supply voltage.

I have some non-expected results and need to work through some open issues but I hope to have the report finished in the next few days. I have well over 100 spectrum analyzer plots, oscilloscope photos and the like to work into a coherent form. (I don't intend to use all 100!). I probably will write this as a report using Microsoft Word and convert it to a PDF file, with only put a short linking page on this web site. If I can find a way to use the same Microsoft Word file for both the web and PDF versions, I'll do both. In theory, what I write in Microsoft Word should be usable as an HTML page, but my experience has not been the best in moving text from Word to HTML whilst retaining formatting and embedded images.

The crystal test fixture kits are in the hands of the Clifton Post Office and should be delivered over the next few days, or, in the case of the international shipments, the next couple of weeks.

I've added a new page 518 KHz Bandpass Filter presenting the predicted and measured results for a 518 KHz center frequency, 20 KHz bandwidth filter I designed and built for K8AQC  to reduce intermodulation interference when he is listening to NAVTEX signals.

The last three days have been consumed in getting  the second run of crystal test fixture kits ready to ship.

The photo shows  the boxes ready for a trip to the post office.

I have a few extra crystal test fixture left. Drop me an E--mail if you are interested in purchasing one. The price is $14.00 for domestic US customers, $17.00 international. (And, if the destination address is within the Commonwealth of Virginia, an extra $0.70 sales  tax.) These prices include shipping via First Class Mail domestic or Air Mail international.

I've also revised the crystal test fixture notes to reflect the current version 1.2 printed circuit board. These notes should be read in conjunction with my crystal motional parameters measurements observations.

The second run of crystal test fixture kits are ready to ship. I've updated the assembly notes to reflect the small changes to the version 1.2 printed circuit board.

I've made a couple of small changes to the Elecraft K3 AGC and S-Meter web page and PDF version. The new PDF file (dated 15 January 2009) replaces the old and may be ready by clicking here.

I've had several requests for a printable version of my page Elecraft K3 AGC and S-Meter. I've reformatted the page contents slightly and added higher resolution graphics to the printable version which is available for download by clicking here or via my Documents page.

Thanks also to Tom, N0SS, for redrawing one of my hand sketches with a computer graphics program. I've replaced my sketch with his drawing.

I've added a new page Elecraft K3 and Manual RF Gain Control presenting an analysis of how the K3's overall gain varies with changes in the RG (RF Gain) parameter.

This is almost certainly of limited interest, but it was a curiosity that wanted to better understand. My analysis is based only upon measured data and I don't know how well I've deduced Elecraft's gain control strategy. I think I'm reasonably close, but have no way to verify my analysis.

Göran, SM6PPS, has pointed me to a site with a great deal of information on the German low frequency  time station, DCF77, I mentioned on 03 January 2009. http://www.ptb.de/en/org/4/44/442/dcf77_1_e.htm is the site, run by Physikalisch-Technische Bundesanstalt, the German government agency responsible for standards and the operator of DCF77.

DCF77 operates with an ERP of 30 to 35 Kw, depending on whether the main or backup antenna system is used.

DCF77 uses an interesting modulation scheme, with simultaneous amplitude and phase modulation. The amplitude modulation is similar in concept to that used at WWVB where a power reduction of 12 dB is applied for either a 0.1 or 0.2 second interval, once a second, to transmit time of day information.

DCF77's phase modulation is more interesting. WWVB maintains a steady transmitted phase, except for the 45°phase advance at 10 minutes past the hour and a return shift at 15 minutes past the hour used to identify the station. DCF77, in contrast, modulates the carrier phase  ±13°with a binary pseudo-random sequence, with the mean phase being zero. The pseudo-random sequence is repetitive, with the details published. This allows a receiver to generate its own identical pseudo-random sequence and to compare it with the received DCF77 signal. The receiver can slip or advance its local sequence until it aligns with the received sequence. This permits considerably more accurate timing to be generated, compared with a simple phase comparison of a phase-stable signal such as radiated by WWVB.

WWVB's effective radiated power is 50 Kw, only about 1.5 dB above DCF77's 35 Kw. Using the same antenna and instrument bandwidth, I measure WWVB as 27.9 dB stronger, which, after adjustment for ERP differences, makes the propagation loss 26.4 dB greater for DCF77 into Northern Virginia.

I have a small new kit available, of rather specialized interest, however. It's a test fixture used with a vector network analyzer to measure the motional parameters of a quartz crystal. I'll add a new page describing it, and you can read the associated documentation at Documents\Assembly and Usage Notes for Crystal Test Fixture.pdf and the associated Documents\Crystal Motional Parameters.pdf.

If you are interested in one of the test fixture and can't wait for my web page with details, drop me an E-mail and I'll fill you in.

I've made a few further modifications to the Z10000 buffer amplifier construction and operation manual and uploaded the revised manual.

The revised manual is version 3.2 and may be downloaded by clicking here, or from my Documents page.

The most recent version, as of 05 January 2009, is 3.2.1, dated 05 January 2009.

Larry, N8LP, is close to releasing a version of his LP-PAN panadapter for Elecraft's K2. More details can be found at www.telepostinc.com. To obtain the necessary isolated, buffered IF signal sample from the K2, he recommends my Z10000-K2 buffer amplifier.

Larry has suggested an alternative connection point for the Z10000-K2 buffer amplifier moving it closer to the antenna to reduce BFO leakage. I've revised the Z10000's instruction manual to provide this alternative connection point as "Option 2." The revised manual is version 3.2 and may be downloaded by clicking here, or from my Documents page.

I'm still working on the new design active antenna and today tried observing signals below 100 KHz.

The image below shows the signal from the German low frequency standard time/frequency station DFC77 operating at 77.5 KHz. It's about 10 dB above my local noise level in the plot, made with an HP 3562A dynamic signal analyzer, operating with a  resolution of 0.0186 Hz/FFT bin. The frequency span is 10 Hz, or 1 Hz/division.

DCF77 is located near Frankfurt/Main and covers most of Europe and parts of North Africa. Its signal is far too weak here, compared with my local noise level, to decode its time code modulation.

I've searched the Internet and have been unable to find many details on DCF77, such as a coverage map or even the effective radiated power.