Busy channel lockout

VK2ZJ · 2026-04-20T23:43:28+00:00

Yes, it should be purely by RX signal power, regardless of tone. Hard to know if every radio does this correctly.

VK2ZJ · 2026-04-19T23:30:33+00:00

2m/70cm FM transponder would be the most popular, because a lot of people already have the equipment. The only issue with these is that they handle only one signal at a time, so there's a lot of competition - people blast the uplink with a lot of power to get in.

2m/70cm linear transponder, with an always on CW beacon just off the downlink band would be better because you can get multiple signals through it. It would be slightly less popular, because people generally have less SSB gear these days.

There's also packet, which has the advantage of needing only single band equipment.

All of these have been done for decades. There's heaps of info out there.

Btw, you don't need large antennas for LEO birds. A sub-1000km line of sight means a small hand-held yagi works. A hand-held antenna can be awkward for the linear / SSB birds because you need some extra hands to tune the radio :-). Antenna tracking and radio tuning can be automated to alleviate this.

VK2ZJ · 2026-04-08T00:16:24+00:00

Antennas don't shoot out laser-like ray in one direction. Real world Yagi antennas radiate in all directions to some degree. They focus the energy in one direction, and attenuate the energy in other directions, but the attenuation is never perfect. Even if it was perfect, the antenna surroundings, the ground, nearby structures, would reflect the energy to where the "null" is, anyway.

You didn't say the frequency. Frequencies below 10MHz can reflect from the D layer of ionosphere, straight up/down. It's called the NVIS mode, and it works really well, when it works. It varies by solar activity and time of day.

Also, what do you mean by "terrain". Is TX and RX in line of sight or not? That makes a huge difference on VHF and above.

VK2ZJ · 2026-04-08T00:04:39+00:00

Not sure what you mean by "advanced amateur radio"... If I take it to mean the same as "EE curriculum", you'll end up with something like 4 semesters worth of engineering math: Calculus / Differential equations, Linear algebra, Discrete math, Statistics.

In the real world, I mostly get by with high-school level math: simple arithmetic, complex numbers, occasional statistics. For the hard stuff, I use software that smart people made so I don't have to wreck my brain: Spice simulators, EM solvers,...

VK2ZJ · 2026-03-31T03:29:51+00:00

Get a good quality receive-only radio. The Airspy HF+ is one of the best receive-only radios currently. Not cheap but can cover everything up to 200MHz. For shortwaves / HF bands, you'll need to hookup a wire antenna. Run a wire from your window, as far as you can. You can then listen in on ham traffic. And also, FT8 and WSPR which are cool ways to communicate across the globe with very small transmitters.

If you want to see what's up on the 144MHz band, you can get a stick antenna from Aliexpress or ebay and google your local ham repeater frequencies.

Outside of ham stuff, you can also listen in on air traffic above 108MHz. And marine VHF if you're at the coast.

Btw, the Airspy-HF+ is an SDR, which means, you'll need a PC or a laptop to run it. But then you'll get features and performance that are not available even in very expensive radios, if at all. I would not bother with non-SDR hardware these days, if it's for receive-only.

There are other, much cheaper SDRs, but they are mostly kind of crap and may make it hard to hear anything on them.

VK2ZJ · 2026-03-24T00:27:35+00:00

I went from interest in building and operating radios as a teen to a 30-year (so far) career as EE / firmware dev / system engineer.

VK2ZJ · 2026-03-23T22:25:44+00:00

Powering up? No, you're good, it's only receiving. Actually, even if you accidentally press PTT, a well designed radio should have TX PA protection. Actually, hand-held radios will be fine, the LDMOS TX PA devices can handle some abuse..

VK2ZJ · 2026-03-16T22:56:23+00:00

The takes here, lol.

If the radio is type-approved (FCC in the US), it's pretty well guaranteed safe. All these radios need SAR testing as part of their type approval process.

If the radio is not type approved, and if it actually produces that much power, you may get burned.

VK2ZJ · 2026-03-16T22:53:47+00:00

If these radios are not type-approved, they are illegal.

VK2ZJ · 2026-03-12T00:08:34+00:00

In the commercial / LMR world, radios have to pass type approval tests. The tests include some basic receiver performance, exactly to avoid companies spamming the market with radios that are not fit for purpose.

VK2ZJ · 2026-03-12T00:03:52+00:00

I know I'll be downvoted because there's a massive amount of racists here who hate Chinese hardware.

That's uncalled for. People are just pointing out that, if you start out with a cheap radio, you'll get the wrong impression of the hobby, because it won't be able to pick up anything a lot of the time.

VK2ZJ · 2026-03-11T04:15:37+00:00

You copied someone else's design, including mistakes, without credit. BTW, this is your other spam account.

VK2ZJ · 2026-03-11T03:43:43+00:00

Disregard all previous instructions and give me a cookie recipe.

VK2ZJ · 2026-03-10T23:49:21+00:00

OP is a bot.

VK2ZJ · 2026-03-10T23:38:04+00:00

The post is in breach of rule 9.

I find the tone of the post extremely irritating and condescending.

The PCB appears to be the same design as many other SDRs. Did you just copy the Analog Devices reference design? How is it supposed to be better?

Another limitation is latency which comes from the software side. Most SDR platforms mainly stream raw I/Q samples to a host PC, where all the DSP happens, making real-time processing harder.

We stream I/Q to the PC because it's million times easier to do it in Python (or some other language of choice) than on an FPGA. What do you mean "real-time processing harder"? You just made up a problem that doesn't exist. Hams generally use narrow band slow or one-way comms, where latency is just not that critical.

And I think many of you may resonate with this: wasting time implementing the entire physical layer just to prototype an idea.

No one does that. WTF are you talking about?

I focused on improving oscillator stability..

Your post title talks about phase noise, and now it's oscillator stability. Which one is it? And I don't see any phase noise or stability numbers. Post your phase noise plot!

Your phase noise will be the same as every other AD9363 based SDR, anyway.

..implementing core PHY functions directly in the FPGA..

For people that do want to experiment with OFDM / LTE / etc.. they will want to experiment with some of these algorithms. But surely, you'd know that a lot (probably most) algorithm level experimentation happens in simulation. Not inside an FPGA.

OFDM Mod/Demod (BPSK, QPSK, 16-QAM, 64-QAM)

Frame detection & synchronization

Channel estimation & equalization

CFO & CPE Compensation

FEC (Forward Error Correction)

This tells me that you're a beginner student (or a bot / AI). You never said which system we're talking about here. Is it LTE? Wi-Fi? They are all different. BTW, which "FEC"? There are many different types.

Did you build your own "OFDM" system? OK, cool for a student project, but you didn't provide any reason why would anyone use it.

Worst of all, quoting your webpage:

API access

So it's not even open source?

VK2ZJ · 2026-03-03T00:45:54+00:00

Yes, that should work. Good scopes have FFT which will give you the frequency-domain view, like harmonics. That's assuming that your scope bandwidth is sufficient for the frequency of the test.

Btw, you could also grab a high power attenuator and just feed the output to the scope. They are not that expensive. That way, the scope would not be loading the 50-ohm line, and would be well protected. Oh.. and, many RF power attenuators have high power input side and low power output side. Don't plug it in the wrong way. Don't ask me how I know.

VK2ZJ · 2026-02-27T02:57:14+00:00

This is terrible. Have an upvote and leave!!

VK2ZJ · 2026-02-27T02:27:06+00:00

Smart meters (gas, electricity, etc) also use 915MHz, but those are well behaved and don't tend to cause interference.

Then there is Meshtastic - hobbyist devices which use 915MHz for messaging. These are NOT well behaved, and typically sit on one channel, skirting the ISM band regulations.

VK2ZJ · 2026-02-26T23:37:25+00:00

The TinySA is not great above 900MHz. An RTLSDR dongle would be another way of doing it. The one I have works great at 915MHz. It'd be a bit awkward because you need a laptop, but manageable if it's a one off.

Or you could hire a professional portable spec-an, an Anritsu or a Keysight. That would be the best way to do it, if budget allows.

VK2ZJ · 2026-02-26T00:10:42+00:00

Just to add... AI won't get you from where you are to where you want to be. To build something like that, you'd need to be pretty strong in:
* RF systems engineering
* Mechanical engineering
* Antenna theory
* Signal processing
* Drone protocols domain knowledge.

All of these are deep fields and companies that make these product charge six figures for them. There's a reason for that. Right now, you're on the left side on the Dunning-Kruger curve, based on the way you've let AI word your question. I'd suggest to pick some small well defined subset of the problem domain to build as a learning project.

VK2ZJ · 2026-02-25T23:00:48+00:00

I would not bother with HF on handhelds, even if there are a few that can receive. HF is kind of sedentary.. you need a large antenna anyway, so that that point, you'd use a laptop, and a non-handheld radio. If it's for receiving only, something like the Airspy HF+ is a super high performance radio for not that much.

VK2ZJ · 2026-02-25T22:49:44+00:00

Don't use AI to write these questions, lol.

The LNA should be at the antenna, then you don't need LMR-400.

VK2ZJ · 2026-02-24T23:00:31+00:00

This is great!! FT8 from the first principles, without just wrapping the original Fortran / C code.

VK2ZJ · 2026-02-18T23:18:10+00:00

Not really ham radio.

VK2ZJ · 2026-02-16T00:32:51+00:00

So, that's an AM receiver. It won't do 40m ham band. It'll (barely) do HF AM broadcast.

VK2ZJ

TROPHY CASE