N5ESE's Version of Norcal BLT Tuner Kit 2000
(click on any picture to see larger version)
(click on any picture to see larger version)
| NOTE: 'N5FC' is my former call. This project was constructed while that call was valid, and you may observe references to it. |
The Norcal SMK-1 Kit ia a great novelty rig and a wonderful learning experience in Surface Mount Technology. With the popularity of that kit, NORCAL asked Charlie Lofgren, W6JJZ, to design a matching tuner. At just $25, this has got to be one of the bargains of the decade in QRP accessories!
While the BLT kit has been retired, you can still get information and manuals on it at the Norcal QRP website. Just navigate to the retired kits section (via the sidebar on their home page)
The tuner usesa Z-match circuit, which provides some bandpass filtering in addition to impedance matching. It uses a BNC connector at the input, and binding posts at the output, to connect to a balnced-feed antenna. The Z-match is best suited for balanced antennas, but I also modified mine to add a switch at the output (which grounds one side of the balanced output) and a BNC connector for connecting to coax antennas.
The schematic with my mods can be seen -here-.
The designer tested the tuner with a field doublet using balanced feedline, on 40 through 10 meters. I was unable to match my twinlead-fed 40 meter doublet on 10, but I had no problem with 40 through 15 Meters, although the tuning was a little touchy on 20 and 15. I attempted to match the Notebook and DCTL antennas on 40 Mters, but was unable to get a match at any setting.
I'm a little concerned with the N7VE SWR bridge. When comparing my matches on 40 meters with my Radio Shack SWR meter and my MFJ Antenna Analyzer, I found that the Rad Shack and MFJ agreed, but the BLT Tuner's null was a little off. Typically, when the BLT's LED nulled, the actual SWR was 1.2 or 1.3-to-1 (but still usable). I could, however, with the BLT in "operate", adjust the BLT tuning controls to obtain 1-to-1 SWR (as indicated by the Radio Shack SWR meter and Antenna Anayzer), but then the BLT's LED indicator was off-null. Wondering if this was a systemic problem with theis type SWR bridge, I attempted the same test with the Emtech ZM-2, and got similiar disparaging results. This may bear some looking into.
The pictures below are offered as visual aids to those building the BLT. Enjoy!
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