In the World of the High Tech Redneck, the Graybeard is the old guy who earned his gray by making all the mistakes, and tries to keep the young 'uns from repeating them. Silicon Graybeard is my term for an old hardware engineer; a circuit designer. The focus of this blog is on doing things, from radio to home machine shops and making all kinds of things, along with comments from a retired radio engineer running from tech, science or space news to economics; from firearms to world events.
Sunday, December 6, 2015
Receivers and Other Radios
The topic of communications or general purpose receivers comes up a lot in our community. On a couple of occasions, I've had readers drop me an email about radio receivers; either selecting one, or occasionally helping them with one that's not behaving the way they expect it to. Since I've been designing receivers for most of my career, for everything from satellites and commercial aircraft to my home ham station, I have some experience that I'd hope would be helpful to folks. I thought I'd put some of it down.
Let's start with a couple of broad questions: should you get one jack-of-all-trades receiver, or maybe one specialized, good, receiver and one that's more "general purpose"? How do you even choose one to buy? If you're not just picking the nicest looking front panel, or the one with price and features you think you need, you're reading specifications, right?
In your mind, you can easily turn that question into another one we always hear: one gun to do everything or a couple of specialized guns, right? It's the same problem in several ways. Naturally, opinions would vary, but I lean toward a couple of different radios and a couple of different guns. Just like you may choose HF for cross-country (or around the world) comm. links, and a VHF for your local AO, you might have a "serious" transceiver and a small, innocuous radio for simple things, like a short power outage.
What about specifications? In my earliest days of studying receivers, back in the late 60s/early 70s, the criteria that people cared about were "the two S" characteristics of Sensitivity, and Selectivity. Sensitivity refers to the receiver being able to hear the weakest, just-above-the-noise signals on frequency while selectivity refers to being able to reject undesired signals. Today, we'd add a third S: strong-signal handling.
For the last 30 years or more, sensitivity has rarely been an issue. For one thing, to be blunt, we've gotten better at designing these things. For another, and it's the main advancement in the field, it's easier to get lots of gain at low prices (gain is the term for amplifying; making small signals bigger). Although Moore's Law hasn't really applied to radio circuitry in terms of increasing the number of functions in a part, the improvement in transistor performance that arguably comes from Moore's Law is one of the drivers in the producing this availability of gain. The saying is that "gain is cheap" and it has revolutionized design. Suffice it to say you really don't need to worry about sensitivity in radios designed since the 1970s. You'll have to go back to vacuum tube radios from the 60s and before - and cheap ones to boot - to find radios that need an external preamplifier to be sensitive enough.
Sensitivity is usually reported as some number of microvolts (millionths of a volt) of signal for a specific signal to noise ratio (SNR), but you'll only see that specified on radios with an antenna connector. For a portable with a whip antenna here's a simple test you can do: tune it to an unused frequency or a weak station in the shortwave band you're interested in. Now simply grab the antenna. If the signal gets better (lower noise, usually louder) the radio isn't optimized. If the signal gets weaker, the radio is well-designed. Ever seen people hang a wire off the whip antenna on a portable? That's a sign of bad design.
Selectivity remains a concern, and hasn't advanced as much as sensitivity - especially in ultra-small, portable radios. The reason is that selectivity depends on filter technology and there haven't been any major advances in that area over the years. The cliche here is that filtering comes by the cubic yard. To make filters narrower or to get better rejection of nearby frequencies requires either more parts, or higher quality factor ("Q") parts, and both of those mean "bigger". For sure, today's continually-shrinking electronics have given us smaller parts to make filters with, but to get a given ratio of bandwidth that the filter is passing to the bandwidth it's rejecting (called its shape factor) requires a number of components that's set by physics, not by fancy design tricks.
Strong signal handling didn't really start being talked about until the early 70s. Whether it was because of the change over to transistors from vacuum tubes going on around then, or whether it was because of the growing crowding in the RF spectrum, or some other factor, I can't really say. A lot of factors go into determining the strong-signal performance of a receiver, but the ultimate answer is to make the signal voltages (or currents) small compared to the voltages (or currents) powering all of the circuits, so it's possible that the higher voltages of vacuum tube circuits helped the problem, but it still might be that the denser packing of users is what caused it.
Strong signal handling is sometimes called "Dynamic Range", but that's a term that I don't like to use because it's used for a lot of different things, and that causes confusion. Because the terms aren't as standardized as pure sensitivity or selectivity, it also means you can be comparing two different radios and find different numbers for their strong signal handling, and that can mislead you into picking the wrong one. (I prefer to rank by the output third order intercept (OIP3), but I'm not going to explain what it is. For now. It could take a post of its own.)
In your everyday use, I'd argue the two most important characteristics are selectivity and strong signal handling. Improving the first makes the radio bigger while improving the second makes it harder on batteries. Clearly, pocket-sized, battery-powered receivers are at a disadvantage.
Welcome to engineering, where everything is a compromise. There are no perfect solutions. If there were a perfect solution, everybody would be doing it that way and you wouldn't need to choose one.
Where is all this blather going? There are many good little amateur radios with a broadband receiver in them. I've mentioned before that my "EDC radio" is a Yaesu VX-6R, a handheld VHF/UHF ham transceiver that transmits on the 144, 222 and 440 MHz bands, using narrowband FM. It also features a wideband receiver that tunes 0.500 MHz (below the standard AM broadcast band) to almost 1000 MHz (1.000 GHz) (the last few MHz below 1000 are blocked out due to being a US cellular phone band). If you use the little antenna that comes with this handheld, you'll think it doesn't receive anything below the FM broadcast band. The antenna isn't optimized for the receiver, it's to work with the transmitter, which is fussier about the antenna. The receive side is just a broadband input. If you give it a good antenna, it's fine, but good broadband antennas aren't at all trivial to build and I think any attempt to cover 500 kHz to 1000 MHz would require a few antennas. Bottom line is that these little radios aren't going to be useful if you need to hear shortwave or below without building antennas.
As an alternative, you can grab something like this: a Kaito WRX-911. This little, sub-$20 shirt pocket shortwave radio will get AM/FM broadcasts and nine shortwave broadcast bands. It passes my antenna test: touch the antenna and signals get weaker. It's not very good at strong signal handling, but neither are handhelds like my VX-6R or its cousins. That means that if you're in an area with lots of strong local stations, you might not hear anything but them.
Posted by SiGraybeard at 4:19 PM
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Did not know about the grab the antenna test. My $20 Radio Shack close out passed. But Radio Marti on 9565 is pretty strong here this afternoon. Greenville, SCReplyDelete
On another but related subject, I read that Collins was going to stop making mechanical filters. I considered that really bad news. Is there anything else with the same performance? DSP at IF? I guess I better decide if I want one for the HFs and buy up. They have audio DSP.
This is slightly OT, but perhaps a useful thing to know. Ferfal, over at Surviving in Argentina, has run a few interviews, excerpts etc from folks in the Ukraine. Apparently if the checkpoints find a radio with a transmitter, they get very "concerned"., as they figure the owner could be calling in a fire mission on their location. So a receiver only could have some benefits.ReplyDelete
Terry - Collins is either shutting down the filter operations in Costa Mesa, or has already closed down. Very few radios are using 455 kHz IFs anymore and that's pretty much the limit for mechanical filters. Most use crystals in the "few" MHz range. As you suggest, many go into an A/D converter and filter in software.ReplyDelete
raven - I was thinking of that exact scenario. I thought I said something about it being less likely to draw attention, but must have edited that out. Or the thought evaporated before I typed it.
Just glad you didn't mention the $20 USB "dongles" that seem to be all the rage amongst those who know little about radio!ReplyDelete
One thing you might have overlooked about the VX-6R is that it's not particularly "user friendly", especially to a beginner.
I've got one, and unless I keep the manual handy, I have a hard time using it. I suppose if I carried it more I'd remember all the functions, but it's got a lot of stuff crammed into a very small box.
Nice post, SiG. Thanks.ReplyDelete
Can I ask why you chose the VX-6R and not one of those Baofeng radios from China? Your Yaesu is over $200 while the Baofengs are under $50.ReplyDelete
Funny you should mention the VX-6 as an "EDC" radio. I thought about getting one, but I questioned whether the MF-HF receive was really going to be useful. I could see no evidence of a BFO in any of the documentation, thus I didn't believe it could credibly be useful for CW/SSB/Digital reception. I ended up with an FT-60 (VHF-UHF only) instead.ReplyDelete
So this begs the question: Do (can) you use it for any of those modes?
As for the commenter asking about the Yaesu instead of a Baofeng, I can't answer for Graybeard, but I can say that I spent the extra for mine because my experience with Yaesu is that they're rock-solid tough and reliable. I've not had the same luck with other equipment. Don't know if that helps...
good intro to rx vs tx...ReplyDelete
i'd also look at various scanners, analog/digital like the uniden home patrol series, and of course ssb radios, my favorites are the tecsun pl-600 and the gp-5/ssb units...
when discussing amateur options like the baofeng uv5rs, these are entry level/throw/give away rigs for newbies and local persons...
danmorgan76/brushbeater/sparks31 all do a great job on discussing the various comms options..
don't forget sdr as well...
get a radio shack discone antenna for rx.....
the goal, imho opinion, is to have a multi layered approach to comms, for both rx locally/regionally/nationally and tx, locally and regionally...i really don't care what happens to Cali or russia for dx ....
here's a good article on comms 101..
@DrJim, why the disparagement of the dongles? There are more than a few people who do actually know something about radio who are using SDR and the RTL dongles to push the limits of what is possible. They are listening to satellites, experimenting in the ghz ranges, inventing new RDF techniques, tracking and mapping aircraft and vessels, downloading satellite imagery, and a host of other more mundane activities too.ReplyDelete
They're building down and up converters, building cheap panadapters to get more use out of older traditional gear, exploring digital modes, and other traditional ham activities.
The dongles are just another tool, and an incredibly cheap and powerful one at that, so what gives?
I'm very familiar with the dongles, as I've tested and experimented with probably 10 or 12 of them, from the $10 Bargain Basement models through the Fun Cube Pro and Pro+ models.
Most of the $20 ones are junk, and simply fall apart when in a high RF environment, like here in the Los Angeles basin.
They only do 8-bit conversion, which severely limits the Dynamic Range they can handle.
They're very good teaching and learning tools if you want to "get into" SDR stuff on the cheap, but without adequate front-end filtering, they just fold-up. Even when you cut the RF gain way back, you'll still get strong signal "breakthrough" from other services.
I've used them extensively for APT weather satellite image reception, and even made a couple of contacts through FO-2 using one, BUT in those cases I use an M2 "eggbeater" antenna along with an SSB Electronik preamp, which has some good filtering to keep out-of-band signals out of the dongle.
I had paging transmitters that were a few miles away come up and completely wipe out an APT pass before I put the SSB preamp at the antenna.
I bought a $300 HackRF model, and dumped it a few days later as it, too, only had an 8-bit converter. Yes, the HackRF will transmit, but at an extremely low level, and won't do full duplex.
My primary gripe about them is directed at the people who claim the $20 dongles are the all-signing, all-dancing answer to all you radio reception problems.
You can only do so much with software when you're hardware limited, and while it's pretty neat you can push these things so far with some FOSS, they just don't cut it in some areas.
The whole idea that's appealing about them is "DC-to-Daylight for under $50", but to really use them, you need another few hundred dollars of antennas and filters.
I'm sure they're better in rural areas, but here in RF Alley, they just roll over and die unless you put some good band-of-interest filtering in front of them.
Thanks for the response. I've got a cheapo DV3 RTL and it is letting me look at some of the things I mentioned. The best part is finding signals with the waterfall.
I moved from the little antenna to a dual band, and got on my new RS discone this week. Had to turn some settings down, but I'm getting good reception now, in the bands I'm mostly interested in (VHF, UHF, and 800 and 900.) I'm in the Houston metro area, and not having problems getting crushed.
I'd hate to have missed out on either it or the Baofang, because I heard someone didn't like them for not being more than they are. They're cheap, they're limited, but they are a great gateway on to other parts of the hobby, and a low commitment way to explore.
I might be a little sensitive about it, because I was turned away from the hobby as a kid, by some guys who sneered at what a friend and I wanted to know. I had no way of knowing that those kind of guys are a minority and I missed out on decades I might have spent with ham radio. I see a LOT of sneering from the 'old guard' directed at new hams who have come in thru prepping, with their cheap gear, and sense of urgency. Less now than 3 years ago, as some of those guys have gotten chinese radios themselves, but there is still a lot of 'if you're not on HF, working DX with your big beam on your tower, you're not a real ham. These younger new hams are MUCH more interested in communicating, than in being 'hams.'
As long as the cheap gear gets the job done it has a place on the bench...
Yep, the waterfall is great. Ever since I've had my Flex radio 5000 I've become a believe in them. I had a panoramic adapter for my Kenwood TS-950SDX, but it just isn't in the same league as the one for the Flex.ReplyDelete
Yeah, a lot of Old Fart Hams are doing a disservice to the entire Amateur Radio community with their attitudes that "If it ain't HF CW DX (or traffic), it ain't shit".
One of the major things about Amateur Radio is that it should be a learning experience. If you find a niche you love, great. But don't knock-down the new guys because they found a different niche.
Us older guys who've been around are supposed to help the new ones, and educate them in the finer points so they avoid the missteps that we all take.
I agree about the cheap gear. If it works for what you need it to do, that's great. I just get a bit upset at some of the people that say it's better than it is without backing it up with numbers, or real-world experience.
I know that this post is almost a year old now, but I have some experience with 2 meter HT's, and while I agree that you get what you pay for, the Baofeng is to me one of the best innovations to hit ham radio in years. This is simply because it fulfills a niche that until now has gone completely empty. It is a VERY inexpensive little handheld that is useful for not only the beginning ham but can also be nice for one who has been in the game for awhile, who just wants a radio that they can toss into their bag or car as a back up. It has surprising features for such a cheap, um, inexpensive radio. I find the best thing is that it has the ability to be programmed via your computer. It makes set up a breeze, and eliminates much of the problem of the needing the manual just to run the thing. I have used a couple of the old Radio Shack HT's before, and these Baofengs run circles around them. One bit of advice and that is to upgrade the antenna, at least to a better ' rubber duck' type. It helps me to get to repeaters that I can't with the original one. Sorry, I have no numbers, so you just have to go with anecdotal tales.ReplyDelete