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Softrock Lite 6.2
Adventures in Electronics and Radio
Elecraft K2 and K3 Transceivers


February 2009 Archive


19 February 2009

I built one Rev. B board for what I hope is the final revision of the Z1501B active antenna, shown below. The image shows a couple of options that not everyone may wish in their antenna. One is a transformer to match to high Z balanced input. The second is a protective relay that grounds the FET input stage when DC power is removed. This has two purposes. One is to reduce the chance for static damage when the antenna is not being used. The second is to prevent damage from induced signals when operated near a high power transmitter.

The large red device is not a ceramic capacitor, but rather an 80 joule varistor across the DC power line, with the thought that it will minimize damage that might otherwise propagate back down the coaxial cable should the antenna be subject to a nearby lightning hit. (DC power is duplexed with RF over the coaxial cable.) There's nothing that is going to prevent damage with a direct strike, unfortunately.  The white leaded device at the upper right is a "gas trap" voltage clamp across the FET input.

I am still considering how to package the amplifier. One possibility is the enclosure pictured, a Hammond aluminum "mini-box" design. The mini-box fits within a length of PVC pipe to provide weather protection. and the pipe may be extended to provide the antenna rod as well. I've provided an RCA connector for the antenna input.

The image below shows the Z1501B active antenna along with a companion Z1202A economy DC power coupler. I have a much more elaborate coupler in the works as well, but for many applications this simple coupler is all that's necessary.


18 February 2009

I've added a new page concerning my "new old stock" HP 11076B Down Converter. You may read the page by clicking here or via the navigation bar at the left of  this page.


16 February 2009

I finished building the prototype active antenna DC power coupler this morning. The PCB layout is good; no changes required and the coupler performance is quite acceptable over the range 10 KHz to 100 MHz.


As soon as I've built and verified the revised prototype PCB for the antenna section, I'll add a new page to the site and begin accepting orders.

I've also added photographs of several receivers to the FM Receivers and De-emphasis page.

15 February 2009

It's been two weeks since I've updated this site. First, I've made a small correction to the crystal test fixture documentation at Documents\Assembly and Usage Notes for Crystal Test Fixture.pdf to correct a typo.

Second, I've added a new page on FM receivers and de-emphasis. I thought this would be a simple page to research, document and write. Boy, was I wrong. I started it on 04 February and finished it this afternoon. The page is FM Receivers and De-emphasis.

Third, I'm still working on K3 transmitter intermodution distortion measurements and an associated report. In the process of making measurements, I found some inconsistencies in my transmitter's performance and I'm working on understanding why I see the results I do before completing the measurements and the report.

I can confirm that there's a clear relationship between the K3's supply voltage under  transmit conditions and the resultant intermodulation product level. That's scarcely surprising or a new discovery, of course. What did surprise me is that a relatively small voltage drop during transmit can make a several dB difference. This lead me to acquire a HP/Agilent 6652A digital controlled power supply with remote voltage sensing to run a more detailed look at the effects of voltage drop on transmitted signal quality.

In order to collect this data and other data, I wound up automating the process with about 1500 lines of code in EZGPIB to (a) control the K3 over a serial port; (b) control and read an Advantest R3463 spectrum analyzer over the GPIB and (c) read and control the 6652A power supply over the GPIB. The result is thousands of data points comprising intermodulation levels for specific frequency, power level and DC supply voltage.

I've also received the next version of the prototype active antenna and power coupler and hope to have a page set up to describe these products in more detail, as well as a schedule for their availability as kits and assembled products.

01 February 2009

I recently had a  request for an assembled Z10000 amplifier housed in an enclosure. I tried a new enclosure style and think it turned out well.


Top view
Inside the box

I've also accepted a couple of orders for my AM broadcast band reject filter discussed at Inductor Choice for Band Reject Filter. I'm not quite ready to sell hundreds of these yet (well, I can dream, can't I?) but I have a few prototype boards available for sale either as kits or as an assembled filter. Anyone interested can receive details, including options and prices by sending an E-mail message to me at the address at the top of the page. It is not a kit for a beginner without test equipment, as the inductors must be measured and adjusted using accurate test equipment. I'll have a detailed page with pricing and required test equipment capability as soon as I'm ready for larger production quantities.

The photo below shows the first completed filter ready for shipping. It's in a powder coated die cast enclosure. It turns that although the result is a very attractive, it's not the most desirable solution electrically. This is because the complete box, inside and outside, is powder coated which prevents electrical contact. I mechanically removed paint from this enclosure using a rotary wire brush, but that is a great deal of work and one slip will irreparably mar the finish and render an expensive enclosure un-salable. Future filters will use a non-painted enclosure, with painted enclosures available only on special order with a surcharge to reflect the extra work and cost of  the painted version.

Z10020 Band Reject Filter
01 February 2009

I'm still working on the transmitted intermodulation analysis of the K3, K2 and TS-940. I've written 20 pages, mostly graphs and images, and hope to finish it this week.

This project has turned out to be far more time consuming than I thought, mostly because of continuing problems with the K2.  I'm a CW and data mode operator, and I've only used the K2 in CW. There's something wrong with SSB mode, under some conditions. I think it's RF feedback, although it's an odd version of RF feedback because it's seen when operating into a dummy load and its very sensitive to the signal generator level used in testing.

01 February 2009

I have a half-dozen or so crystal test fixtures left. Any reader interested in one should E-mail me to confirm their availability. Price remains $14.00 for US domestic customers ($14.70 for Virginia residents) and $17.00 for international customers. These prices include shipping by first class mail domestically and air mail internationally.

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.

This is unlikely to be a kit that I keep in stock once the current batch is sold.


01 February 2009

As usual, I've moved the preceding month to an archive page, viewable by clicking here or through the navigation table at the top of this page.