Category Archives: How-to

Video blog episode 011

I finally finished off the 6-meter Yagi project and got it on the air. I’ve actually been using it for a while, but needed the ARRL VHF contest to get enough activity on the band to shoot video in a reasonable amount of time showing me making QSOs. I was running 50 watts into the 4-element Yagi and worked sporadic-E clouds to 30 different Maidenhead grids, including two in New Hampshire, which were my first double-hop sporadic-E QSOs. Enjoy!

Video blog episode 005

Now that I’ve been working on ham radio antennas, I have a couple of projects for the video blog. The first one is a 6-meter 4-element Yagi. It is designed to be semi-portable, and for me this is particularly important because it’s not practical for me to leave up an antenna for any significant length of time. Perhaps impudently, I am posting this introduction and design video before I actually have the antenna on the air! However, I have tested the antenna itself (sans 1:1 balun) with a VNA and it seems to behave more or less as expected.
I spend a lot of time talking about various design parameters and the actual modeling procedure, so this may seem a little dry if you’ve done this before. But, I try to keep my speech pace relatively slow on these videos, so there’s always the 1.25x and 1.5x speed options on YouTube.  Part II will detail the construction process, and Part III will show testing and hopefully actual on-air performance.

Video blog episode 002

Episode 2 of my video blog has been posted to YouTube. This is the second video in the Superloop antenna series, and shows the construction of a decade resistance box to use as the terminating resistance of the antenna. The box allows you to repeatably set the resistance to the value you want, as opposed to trying to make fiddly adjustments of a potentiometer. This part of the project went well, other than it having a 2 ohm offset due to resistance in the thumbwheel switches, wires, and banana plug connectors. Enjoy!

Video blog debut!

Finally! My first Arizona Signal Watcher video blog episode is now available on YouTube. This is the first of a several-part series on the “Superloop” receiving antenna. This design was developed by Bruce Conti and this is my take on the design and construction. The antenna is very useful and convenient when needing a signal null in one direction and good reception in other directions, and when portability is important. The first video is entitled “Superloop Antenna Part I: Introduction” and gives an overview of the antenna design and some theory behind it. Subsequent videos will detail the construction of the antenna and the electrical/electronic components needed to optimize the antenna performance. Comments here or on the YouTube page are very much welcomed. Enjoy!

 

How-to: Aluminum case for new RTL-SDR blog brand TCXO dongle

The RTL-SDR Blog posts articles and links related to software defined radio. They also sell RTL-SDR dongles and accessories. Last month they introduced a dongle with a temperature compensated oscillator (TCXO). This virtually eliminates the well-known offset and frequency drift of “standard” dongles as they heat up or the ambient temperature changes. NooElec also makes a model like this, but if you don’t like the MCX connector on the latter, the RTL-SDR Blog version uses an SMA connector (and is a bit cheaper at the moment). Both brands are good products in my experience.

The RTL-SDR Blog does not sell an aluminum case for this dongle (yet), but once you get past your first RTL-SDR experimentations, this is a must have. A metal case shields the dongle from RF interference and provides a better ground plane. It is a fairly straightforward mod to get the RTL-SDR blog dongle to fit in the RTL-SDR case sold by NooElec.

Disclaimer: you can potentially ruin your RTL-SDR dongle, so attempt this at your own risk.

Tools needed: sandpaper, small metal file, small phillips screwdriver, power drill, hammer and hole punch (optional)

Here is a picture of a modified case and an unmodified case, plus the file I used, and the dongle removed from the plastic case it comes with:
IMG_1574_case_blowup

I did not take a picture of an unmodified dongle, but you want to sand down the long edges of the PCB just enough so that it fits on the rails in the case. Normal fine grit paper works fine. Also, you can sand down the PCB that sticks out from where the USB plug is mounted. Do not sand too much or you can hit conductive traces and/or solder points.

Using the file, etch smaller slots on the short sides of the existing USB slot in the case. You might also need to file down one of the long sides of the main slot to allow the plug to vertically fit. You want to do this fairly precisely to avoid creating a large hole for RF interference to leak in, so trial and error is the best method.

On the other end cap, you will drill a 1/4″ hole for the SMA plug. Note that a commercial case might have a square hole to accommodate the lip of the plug, but that it not necessary. It just means that the USB plug will stick out a couple millimeters more than usual on the other end. Use the slot end of the case as a template to determine where to drill the hole. A hole punch can be very helpful here to mark the hole location to keep it in the same vertical plane as the rest of the dongle and USB plug.

Some people claim that the paint on the case can cause electrical problems, i.e., the case will not be a unified ground plane. So, before you put the case together, use the file or sandpaper to strategically remove paint where the case pieces fit together. This does not have to be precise.

You can fill the MCX hole in the case with a short screw and nut to prevent possible RF interference from entering here.

Here are a couple shots of the end product (a little blurry, but you get the point):
IMG_1571_USB_end

IMG_1572_SMA_end

I’ve had this running for about 20 hours total since I made the mod and it works fine.