If you need an amplifier, [Hans Rosenberg] has some advice. Don’t design your own; grab cheap and tiny RF amplifier modules and put them on a PCB that fits your needs. These are the grandchildren of the old mini circuits modules that were popular among hams and RF experimenters decades ago. However, these are cheap, simple, and tiny.
You only need a handful of components to make them work, and [Hans] shows you how to make the selection and what you need to think about when laying out the PC board. Check out the video below for a very detailed deep dive.
Old radios often had selenium rectifiers to convert AC to DC. The problem is that the old units, dating back to 1933, are prone to failure and to release dangerous chemicals like hydrogen selenide. [M Caldeira] has a new board made to fit a particular rectifier and also allows a varying voltage drop. The circuit consists of a few diodes, a MOSFET, and a pot for adjusting the voltage drop. An IRF840 MOSFET provides the adjustment.
Did it work? It did. The good news is that if it fails — which shouldn’t happen very often — it won’t release stinky and noxious fumes
We wondered if he should 3D print a fake case to make it look more the part. If you haven’t seen a real selenium rectifier, they were made of stacks of metal plates coated with bismuth or nickel. Then, a film of doped selenium was annealed to the surface to form cadmium selenide. Each plate could handle about 20 V and the more plates you used, the more reverse voltage the device could withstand.
For as useful as computers are in the modern ham shack, they also tend to be a strong source of unwanted radio frequency interference. Common wisdom says applying a few ferrite beads to things like Ethernet cables will help, but does that really work?
It surely appears to, for the most part at least, according to experiments done by [Ham Radio DX]. With a particular interest in lowering the noise floor for operations in the 2-meter band, his test setup consisted of a NanoVNA and a simple chunk of wire standing in for the twisted-pair conductors inside an Ethernet cable. The NanoVNA was set to sweep across the entire HF band and up into the VHF; various styles of ferrite were then added to the conductor and the frequency response observed. Simply clamping a single ferrite on the wire helped a little, with marginal improvement seen by adding one or two more ferrites. A much more dramatic improvement was seen by looping the conductor back through the ferrite for an additional turn, with diminishing returns at higher frequencies as more turns were added. The best performance seemed to come from two ferrites with two turns each, which gave 17 dB of suppression across the tested bandwidth.
The question then becomes: How do the ferrites affect Ethernet performance? [Ham Radio DX] tested that too, and it looks like good news there. Using a 30-meter-long Cat 5 cable and testing file transfer speed with iPerf, he found no measurable effect on throughput no matter what ferrites he added to the cable. In fact, some ferrites actually seemed to boost the file transfer speed slightly.
Ferrite beads for RFI suppression are nothing new, of course, but it’s nice to see a real-world test that tells you both how and where to apply them. The fact that you won’t be borking your connection is nice to know, too. Then again, maybe it’s not your Ethernet that’s causing the problem, in which case maybe you’ll need a little help from a thunderstorm to track down the issue. Continue reading “Ferrites Versus Ethernet In The Ham Shack”→
[MIKROWAVE1] claims he’s not a radio repair guy, but he agreed to look at a malfunctioning Hallicrafters S-120 shortwave receiver. He lets us watch as he tries to get it in shape in the video below. You’ll see that one of his subscribers had done a great job restoring the radio, but it just didn’t work well.
Everything looked great including the restored parts, so it was a mystery why things wouldn’t work. However, every voltage measured was about 20V too low. Turns out that the series fuse resistor had changed value and was dropping too much voltage.
When you think of Sony, you probably think of a technology company that’s been around forever. However, as [Asianometry] points out, it really formed in the tough years after World War II. The two people behind the company’s formation were an interesting pair. One of them was a visionary engineer and one was a consummate businessman.
While it is hard to imagine today, securing a license to produce transistors was difficult in the early days. What’s worse is, even with the license, it was not feasible to use the crude devices in a radio.
With as cheap and versatile as RTL-SDR devices are, it’s a good idea to have a couple of them on hand for some rainy day hacking. In fact, depending on what signals you’re trying to sniff out of the air, you may need multiple interfaces anyway. Once you’ve amassed this arsenal of software defined radios, you may find yourself needing a way to transport and deploy them. Luckily, [Jay Doscher] has you covered.
His latest creation, the SDR SOLO, is a modular system for mounting RTL-SDRs. Each dongle is encased in its own 3D printed frame, which not only protects it, but makes it easy to attach to the base unit. To keep the notoriously toasty radios cool, each frame has been designed to maximize airflow. You can even mount a pair of 80 mm fans to the bottom of the stack to really get the air moving. The current design is based around the RTL-SDR Blog V4, but could easily be adapted to your dongle of choice.
In addition to the row of SDR dongles, the rig also includes a powered USB hub. Each radio connects to the hub via a short USB cable, which means that you’ll only need a single USB cable running back to your computer. There’s also various mounts and adapters for attaching antennas to the system. Stick it all on the end of a tripod, and you’ve got a mobile radio monitoring system that’ll be the envy of the hackerspace.
The Hackaday comments section is generally a lively place. At its best, it’s an endless wellspring of the combined engineering wisdom of millions of readers which serves to advance the state of the art in hardware hacking for all. At its worst — well, let’s just say that at least it’s not the YouTube comments section.
Unfortunately, there’s also a space between the best and the worst where things can be a bit confusing. A case in point is [Bryan Cockfield]’s recent article on a stealth antenna designed to skirt restrictions placed upon an amateur radio operator by the homeowners’ association (HOA) governing his neighborhood.
Hiding an antenna in plain sight.
Putting aside the general griping about the legal and moral hazards of living under an HOA, as well as the weirdly irrelevant side-quest into the relative combustibility of EVs and ICE cars, there appeared to be a persistent misapprehension about the reality of the US Federal Communications Commission’s “Over-the-Air Reception Devices” rules. Reader [Gamma Raymond] beseeched us to clarify the rules, lest misinformation lead any of our readers into the unforgiving clutches of the “golf cart people” who seem to run many HOAs.
According to the FCC’s own OTARD explainer, the rules of 47 CFR § 1.400 are intended only to prevent “governmental and nongovernmental restrictions on viewers’ ability to receive video programming signals” (emphasis added) from three distinct classes of service: direct satellite broadcasters, broadband radio service providers, and television broadcast services.
Specifically, OTARD prevents restrictions on the installation, maintenance, or use of antennas for these services within limits, such as dish antennas having to be less than a meter in diameter (except in Alaska, where dishes can be any size, because it’s Alaska) and restrictions on where antennas can be placed, for example common areas (such as condominium roofs) versus patios and balconies which are designated as for the exclusive use of a tenant or owner. But importantly, that’s it. There are no carve-outs, either explicit or implied, for any other kind of antennas — amateur radio, scanners, CB, WiFi, Meshtastic, whatever. If it’s not about getting TV into your house in some way, shape, or form, it’s not covered by OTARD.
It goes without saying that we are not lawyers, and this is not to be construed as legal advice. If you want to put a 40′ tower with a giant beam antenna on your condo balcony and take on your HOA by stretching the rules and claiming that slow-scan TV is a “video service,” you’re on your own. But a plain reading of OTARD makes it clear to us what is and is not allowed, and we’re sorry to say there’s no quarter for radio hobbyists in the rules. This just means you’re going to need to be clever about your antennas. Or, you know — move.
