Radio W4KAZ

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Retroactive Filter Tuning with NanoVNA

W4KAZ version of BCB filter. Built using NP0/C0G leaded capacitors, t-80-2 torroids, and a 220uh choke.

NanoVNA

Recently this NanoVNA product popped up on my radar, and like normal, I was a bit behind the group in discovering it. It is relatively newly available, but seems to be rapidly becoming known because it is both inexpensive and very functional. What a wonderful and useful project. There is a group devoted to the project. There is also a secondary product fork recently begun. The second fork will have a larger screen. Software will not be compatible between the two. (update….maybe more than one fork, rapidly changing).

The NanoVNA itself appears to well suited to the home hobbiest, both in price and utility. As an open source hardware design, being produced by various vendors, it is not coming out yet as a mil-spec “ruggedized” product. It is also not $50,000 USD. Also, caveat emptor. The calibration dummy load supplied with the units I obtained measured an intermittent 50K ohms instead of 50 ohms. A second unit supplied a load that measured 43ohms. [I used a known 50 ohm load for the calibrations.]

Dummy loads aside, it appears I wound up with a cheap copy of the cheap copy of the open source hardware. Yet both units appear to function, at least well enough for the 30Mhz of spectrum of interest here at W4KAZ. All images below were captured on a Samsung Galaxy S7, rather than spend a lot of time dorking around with rapidly developing beta software. Truth is – I was in too much a hurry […]

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2019 IOTA de W4KAZ From Cape Lookout NC

2019 brought another solo operation for IOTA, but return to Cape Lookout for the event.  Weather was much better than 2018, the only WX challenge being the winds.  Normal for the islands on the NC coast, and very agreeable for comfort, but it caused the only bit of trouble for the antennas.

Antennas were set up on Friday.  This year two folded dipoles were used, one for 40m and the second on 20m.   A hy-gain AV-18VS vertical was set up in the unlikely event 15m or 10 would open. (Neither did for me)

Checking the tuning on the antennas had me chasing shadows for too much of Friday afternoon.  After sorting out the feedlines, there was still an SWR problem on the 40m folded dipole.  These had been tested at home before the contest, but had been tugged on quite a bit trying to straighten the mast in the high winds.  So as a fallback measure I hoisted the 40m/20m trap dipole, and tabled the folded dipole problem.  In the end it turned out to be a problem with the antenna analyzer rather than the antennas.  Since it was already in the air, I just re-positioned the trap dipole to be at right angles to the folded dipoles.   But that was after all too much walking from shack to antenna several times looking for problems.

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Experimenting With Trap Dipoles- Part 2

see: Experimenting With Trap Dipoles – Part 1

Those coil and cap experiments described in part #1 eventually led me to the ‘best’ compromise solution for my situation. In the end I chose to build traps that were resonant below the higher band. I also chose to use cap values on the smaller end of the capacitance value range.

#gallery-12 { margin: auto; } #gallery-12 .gallery-item { float: left; margin-top: 10px; text-align: center; width: 33%; } #gallery-12 img { border: 2px solid #cfcfcf; } #gallery-12 .gallery-caption { margin-left: 0; } /* see gallery_shortcode() in wp-includes/media.php */ Sample of original 20m trap using 7 turn coil. This trap experienced SWR shifts under xmit at 100w in CW contest. Revised traps for 20m/40m dipole. The traps use three of the TDK capacitors in series for a total value of 23pf. The 14 turn coil used resonate the traps at 12.65Mhz. Inductance calculated as approx 7uh. Revised trap for 20m/40m dipole. The trap use three of the 2KV TDK capacitors in series for a total value of 23pf. The caps are mounted in series on a small bit of PCB for a cap value of 23pf. Joints were soldered slightly long with a bit of excess solder in the hopes of a bit of extra heat sinking.

Sadly the Panasonic capacitors are no longer available. Possible TDK replacement are being tested. These TDK caps are physically smaller, and only 2Kv rated. I intend to use these in series/parallel groups once I […]

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Experimenting With Trap Dipoles- Part Numero Uno

Revised traps for 20m/40m dipole.

Experimenting with trap antennas, selecting the resonant frequency for the traps, notes on capacitors and coils. […]

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