Bandpass Controls for HF Digimodes

When working PSK31 or other "digimodes" on HF (high frequency) radio, we commonly use computer soundcards to analyze and transmit data. I like to use the Linux program fldigi for this, along with my Ten-Tec Orion transceiver.

The soundcard takes in the entire audio output from the Orion, typically 100 - 3,000 Hz. Fldigi (and similar software) allows you to point to a transmission of interest on a "waterfall" spectral display. This automatically sets the decoder to analyze data in a small band around the cursor using digital filtering.

This works well when the bands are relatively quiet, but when you have a band crowded with strong signals, the signal of interest can be strongly affected by "out of band" signals (but still in the 3 kHz audio region) that key the receiver's AGC (automatic gain control).

In this case, we need narrower IF (intermediate frequency) filtering than 3 kHz. Fortunately, a DSP (digital signal processing) rig like the Orion provides "infinitely" adjustable IF bandpass characteristics, so it is possible to "zoom in" on the signal of interest, largely rejecting any signals outside the small IF passband.

I have written a small Python/wxPython application "oFilter.py" that puts up a panel to allow Orion bandpass control from the same screen as fldigi. (Since fldigi communicates with the Orion via Hamlib at the same time as oFilter, there is a small potential for I/O conflict, but this is not a serious problem.)

Here are a few screenshots to show what is going on. Ultimately, it would be great to integrate the oFilter functions into fldigi or a similar program, using convenient mouse controls.

The PSK31 band at 14.070 MHz with many Europeans

coming in the 3 kHz default bandpass.

"Zooming in" the IF bandpass to 200 Hz,
more-or-less centered on the signal of interest.

Zooming in to a 100 Hz bandpass (minimum available).

The oFilter.py application.

Report from DCC 2007

About 200 hams and friends gathered at the 26th TAPR/ARRL Digital Communications Conference for 2007 was held in Windsor Locks, CT, Sept. 28-30, 2007.

Many great papers and conversations. I presented my talk (PDF), "SourceForge, Hamlib, and Rigserve: Free Beer, Free Speech, and Rig Control", which is also printed in a somewhat different form (PDF) in the Proceedings.

A few cheap photos from my Treo 650 phone:

A typical session

Gerry Youngblood explains the Flex-Radio SDR-5000

Steve Bible, N7HPR, TAPR Vice President

Banquet speaker Bruce Perens, K6BP

Bruce had many fine insights into the state of the amateur radio world. For one thing, he noted that the average age at DCC is about 10 years less than at Dayton. "We are the future of amateur radio."

SourceForge, Hamlib, and Rigserve... DCC'07

My contribution for the TAPR/ARRL Digital Communications Conference, Sept., 2007 appears here, as a PDF.

DCC is always a good show for advanced Amateur Radio technology. This year, it will be in Windsor Locks, CT, not too far from me. Previous Conference Proceedings are available.

New Rigserve Project on Sourceforge

Some of you know that I've been working on "Rigserve", which is meant to be a much streamlined server-style application providing much of the functionality of Hamlib. We avoid most of the cross-platform problems by defining our API over an IP connection, which is human-readable and even testable over Telnet. Rigserve is implemented in object-oriented style using Python, which should allow it to run on many platforms. I am not sorry to jettison low-level C, the GNU Automake stuff, SWIG, and all that!

We have talked about the relationship of this development to Hamlib. Should we think of it as a candidate for "V2 Hamlib"? Well, Rigserve is not a library, and there is no backwards compatibility. Rigserve does share some philosophy with Hamlib, but that's about it. I have concluded that it should stand on its own, but we should give full credit to the many folks who have brought us Hamlib as we have it today.

[There are some alternate approaches, too, such as XML rigCAT descriptions at http://w1hkj.com/xmlarchives.html . These may be useful to both Hamlib and Rigserve down the road.]

There is now a project at http://sourceforge.net/projects/rigserve with a slightly updated version 0.21 available for download. The files are managed in the Subversion (SVN) repository.

I would welcome anyone who wants to contribute to rigserve to join this project. There shouldn't be a conflict of interest here, because the intersection of hotshot C and Python programmers is probably limited. Though I am neither(!), I will continue to support the TenTec Orion for Hamlib.

It has been interesting to start a Sourceforge project and to learn Subversion and the other tools. Frustrating, too, because SF's shell server and compile farm chose this week to go into meltdown. The project web page is at rigserve.sf.net.

73, Martin AA6E

Hamlib, reloaded

The Hamlib project has been working on a rig-independent API for software developers that will allow them to connect to a wide variety of ham rigs without worry about their individual interface quirks.

Lately, we have begun discussing how this project can envolve into a "version 2". There is a new blog at hamlib-developer.blogspot.com to support development of Hamlib. If you want to take an active part in the Hamlib project through this blog, please contact me.

The Hamlib project is supported at sourceforge.net/projects/hamlib, which provides a mailing list, CVS, and other amenities.

Hamlib QST Stray

My little article about hamlib finally came out: QST, Feb., 2006, p. 101.