Getting into RF - a few questions - Page 1
Forum section: electronics / rf-microwave

author: VSV_electron
author_rank: Regular Contributor
timestamp: June 07, 2024, 09:00:22 pm
content: I'm all on my own and only you, my dear fellow EEVblog members can set me on the right track. I'm trying to realize from which direction to enter the RF territory and I need your help on that.Before asking a few concrete questions, just a short intro on what I'm after.My interest in RF (let me not narrow down the broad RF field yet, although my choice as an amateur is of course limited) is mostly in exploring major functional blocks of any transmitter-receiver RF system, primarily the receiver side: mixers, oscillators, amplifiers, etc.However I know that exploring them out of context doesn't make much sense; these functional blocks were made to serve particular purpose, not the other way round.Here is the dilemma: On the one hand I'm not going to become a HAM adept but on the other hand I have to choose some RF subset for the target receiver system, otherwise my whole initiative as I said looks purposeless. And yet again - I'm really interested in building and exploring RF circuits.Correct me but I see that my choice of the RF receiver side is not too wide: It's either HAM or otherwise broadcast radio station.Major question:In respect to the receiver construction, how different is HAM receiver from the radio station broadcast receiver? I have a few 'DIY' books for either but without much knowledge of the analog schematics I can't successfully analyze the differences.For instance, take the ubiquitous 'superhet' - What will be the major differences in construction between the broadcast vs HAM superhet receiver?Another question:Suppose I assemble some or even a few of the HAM receivers - What am I going to do with them? Am I going to overhear some other people's talks? This sounds not ethical to me to say the least. (I hate listening to other people's private talks in general).Or are there any HAM public channels ment for anyone to listen to, not the private talks?My only other choice, if I'm correct, is the broadcast radio station receiver. I know that apart from the FM radio there are no other stations left around. So If I go the broadcast path am I left with the FM receiver only? (Funnily enough I have a few commercially made ones collecting dust in the closet... What an irony...). Nevertheless, let me stress it the third time: I want to build and explore RF circuits.My last question:While stocking a reasonable bank of RF components that I thought would be needed to explore the RF circuits (my choice was intelligent but not too knowledgeable) I got a few sets of blank CAN transformers/coils of three kinds. Please give me some guidance on where in particular these will fit in RF circuits:First type:https://aliexpress.com/item/1005003388187155.htmlSecond type:https://aliexpress.com/item/1005003604363316.htmlThird type:https://aliexpress.com/item/1005003757706854.html

author: xrunner
author_rank: Super Contributor
timestamp: June 07, 2024, 09:42:18 pm
content: Quote from: VSV_electron on June 07, 2024, 09:00:22 pmReceiver design is a big subject. But a main difference between ham rx and a broadcast rx is that the ham rx will have selectable bandwidths for the different modes such as SSB, CW, or AM reception. Also would have a decent signal strength meter and a 50 ohm antenna input for a good antenna. Plenty of things to read about on the internet regarding this.QuoteUh, listen to the hams is what you would do. There is nothing private about hams talking or communicating in various modes such as AM, SSB, CW, PSK, RTTY, FT8, or many other digital modes. It's all fair game to listen to it's really encouraged because they want more hams to get licensed.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: June 07, 2024, 10:52:36 pm
content: Most HAM radios these days are transceivers. There are also radios in HF that are just receive. The receivers are all over the price range and some are very expensive and very good.Many HAM radios are general coverage up to 30 MHZ, which means they can receive on all freq but they only transmit on HAM Bands, There are VHF and UHF bands also.Many Modern radios are computer controlled with analog digital circuitry.I do not know what you mean by broadcast band, Here in US this means lower freq, up to about 1.5 MHz, I think that commonly many European radios covered more freq than the common US Broadcast band radio.It is not hard to get a Ham license here in US, there is no longer a Morse code requirement. You can look up the testing in your country.All HAM communication is public and even the digital modes have to be public knowledge (open source)If you are looking to buy a radio. I would recommend looking at several used Ham transceiver radios with general coverage and just not using the Transmit (for a start), there are many more of these around than the HF receivers.Designing and building a receiver is a challenge. Maybe start with an old CB radio and see how they did it. Get schematics. Or maybe start by building an oscillator, or something else simple on a breadboard.Those components are just inductor things and are used for tuning circuits, You have to know what circuit you are designing and what freq is being used and what other components are involved, so that part of your question is very hard to answer.

author: fourfathom
author_rank: Super Contributor
timestamp: June 07, 2024, 11:57:09 pm
content: Different modes require different receiver designs. AM broadcast is the simplest: Amplitude Modulation. You can (and I did, many years ago) build one using a simple tuned circuit, a diode, and some high-impedance headphones.FM broadcast uses Frequency Modulation. This requires some circuitry to convert FM to audio. These days, both AM and FM radios use specialized integrated circuits as well as passive components, but you can still build one using basic transistors, etc.Ham radio can use AM and FM, but it also uses modes such as CW and SSB, as well as digital modes, and these typically require a "Beat Frequency Oscillator" (BFO) to demodulate those signals. Again, ICs and/or discrete components can be used in these receiver designs. Actually, a discrete-component CW / SSB receiver can be extremely simple, just a dozen components or so. Of course better performance requires more complication. Plenty of simple designs (schematic and theory) are available via internet search.And yes, hams expect people to listen to their conversations.

author: pdenisowski
author_rank: Super Contributor
timestamp: June 08, 2024, 12:32:15 am
content: Quote from: fourfathom on June 07, 2024, 11:57:09 pmI think one of the high points of my amateur radio "career" was when I got my first SWL card - not only had a 3rd party listened to my conversation with someone else, but they sent me a (paper) card in the mail to confirm it and asked for my card in reply!(SWL = short wave listener)

author: dobsonr741
author_rank: Frequent Contributor
timestamp: June 09, 2024, 01:54:50 am
content: You’d get answers on all your questions if you study for a ham exam. Even better, take the exam. Plenty of resources are available, and you’ll get a very practical, proven way of learning RF (and a bit more on the hobby and regulations)

author: Andy Chee
author_rank: Super Contributor
timestamp: June 09, 2024, 04:28:56 am
content: Quote from: VSV_electron on June 07, 2024, 09:00:22 pmA broadcast superhet receiver and HAM superhet receiver are relatively similar in principle, the differences won't be very apparent.For noticeable differences it would probably be better to compare receivers that operate using different principles. For example, compare a TRF receiver (tuned radio frequency) with a superhet receiver. Or how about a software defined radio! (the latter can be extremely simple hardware circuit wise, all the complexity takes place mathematically in software).QuoteAnyone transmitting on HAM frequencies do so with full knowledge that random people may be listening. That's why the content of such discussion is usually benign, such as talking about their latest soldering project, discussing antenna designs, computer problems, road traffic congestion, etc. That's not to say there are conversations about personal health and family issues, but they do not make up much of the content.And that's only voice speech. HAMs also use other modes of communications, signal beacons, weather telemetry, text based messaging, image communications, etc, etc. All still public obviously.QuoteYour listed parts can be usually found in intermediate frequency (IF) circuits of superhet receivers operating below, say, 300MHz. Anything above and you really need surface mount components to reduce stray capacitance/inductance.

author: radiolistener
author_rank: Super Contributor
timestamp: June 09, 2024, 08:25:26 am
content: Quote from: VSV_electron on June 07, 2024, 09:00:22 pmthey are very different.First they using different modulation. Broadcast receiver uses AM modulation (if we're talking about LW/MW/SW receiver, FM receiver uses FM modulation). While ham receiver uses SSB (LSB or USB) or CW modulation.Second they using different receive bandwidth. Broadcast receiver uses 20 kHz AM bandwidth (10 kHz audio). While ham receiver uses 2.7 kHz SSB bandwidth or 500 Hz CW bandwidth. But good ham receivers also allows to change receive bandwidth.Third, they have different sensitivity. Ham receiver is more sensitive than broadcast receiver.Forth, ham receiver usually has higher dynamic range.Also ham receiver input is usually designed for professional external antenna and has 50Ω impedance. While broadcast receivers usually have high impedance antenna input or even internal ferrite antenna.Quote from: VSV_electron on June 07, 2024, 09:00:22 pmNo, private talks are not allowed on ham bands. Usually their talk like this:- My call sign is XXX who can listen me?- XXX, this is call sign YYY, I listen you for 59- YYY, this is call sign XXX, I also listen you for 59, have nice day, good bye, 73- XXX, this is call sign YYY, thank you for QSO, have nice day, good bye, 7359 here means signal readability 5 (perfectly readable) and signal strength 9 (extremely strong signal). For CW there is also third value for example 599, where last 9 means tone quality (perfect tone).73 here is a telegraph code "best regards".When there is too small peoples on the band they can spend more time to talk about their equipment, antennas, or discuss some electronics circuit.If you want to understand what is radio, you're needs to start building from a simple broadcast receivers, then build more complicated receiver for ham band. Then when you will be familiar with circuits, you can start experimenting with transmitters, because it is more complicated and needs much more knowledge.More easy way to get in touch with ham radio is just to buyRTLSDRv4dongle and listen amateur bands. It helps you to understand difference between broadcast AM signals and SSB and how signals are looks like in spectrum domain. This digital receiver will cover almost all your needs for receiver.

author: jonovid
author_rank: Super Contributor
timestamp: June 09, 2024, 10:16:35 am
content: the chicken or the egg?befor building a superhet receiver some suggestionsradio signals are invisible so seeing what your doing needs the right equipment.already have a receiver or transceiver for the radio frequencys your interested in.already have or get a radio frequency signal generator for the radio frequencys your interested in.start at the low end of the radio spectrum before starting projects for the high end.a pcb receiver project kit is a good place to start.radio transmitters transceivers & getting a licenseget to know an amateur radio operator nearby where you live or go to the local radio club.then your have or know someone to communicat with. walkie talkies are more fun with a buddy.radio transceivers that do not need a license like citizens band radio are for uneducated normiesthat know how to hold a phone & communicate with one hand. without the technical side of it.broadcast radio or any professional job in radiostart with amateur radio for experience & add to the technical side of your resume or to master the mic skills of a radio disc jockeystart podcasting or get good at any MC public speaking.

author: dobsonr741
author_rank: Frequent Contributor
timestamp: June 10, 2024, 03:25:50 am
content: I love superhets, however their time has passed. Superhet parts no longer available, the direct digital conversion took over everywhere.With that, the once complicated RF design is diminished, and the functionality moved to algorithm/software, implemented on DSPs or FPGAs. Should it be your phone, your ham radio, or a radar station the first order of business is to get the antenna signal digitized, if possible as baseband or if not then after an immediate downconversion without much else. At that point it’s no longer RF design, it’s digital signal processing. Same idea with transmitting.Of course, you can still build superhets, just as many on this forum build tube circuits. If you think about a career in RF design, then best to complement it adding something else, like signal processing or mixed signal or power electronics.

author: iMo
author_rank: Super Contributor
timestamp: June 10, 2024, 07:19:49 am
content: Quote1. most ham radio operators today use SSB, FM or digital modes (FT8 for example). In SSB and FM there is not much difference in the analog superhet design except the detector. For SSB you need a beat oscillator to demodulate SSB (USB/LSB) or CW, or special FM detector. A standard broadcast receiver could be easily modified for SSB/CW.2. there is none private talk in HAM radio. HAM operators have to follow the specific rules of communication, they have to posses a license from the authorities they have to comply with. So you may listen to the ham traffic.3. There is a lot of AM, SSB, digital in HF bands (up to 30MHz). FM is usually used in 145/430MHz bands and above.4. best way to start is to start small. Your questions are too general, almost like AI generatedBuy radio kits from ali/ebay, build them, play with it and slowly get in. It takes many years to get somehow fluent with radioelectronics technology..

author: stretchyman
author_rank: Regular Contributor
timestamp: June 28, 2024, 11:18:13 am
content: Just purchase a 2nd hand Ham Transceiver, have a listen around and see what you like. You can listen to SW broadcast too. You may get inspired and get your ham license?Designing and building stuff is a whole other level.J.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: June 29, 2024, 05:28:48 pm
content: Depends on how much you want to do hardware vs software.If you just want to do software, you can get an SDR, which would let you listen to any frequency up to maybe a few hundred MHz, and you could reconfigure it for any modulation too (as long as the data rate is low enough).If you just want to do hardware, you could build a few diode ring mixers, a few crystal based oscillators for driving the LO of the mixer, an antenna, a low noise amplifier, and some filters to build a superhet receiver. If it's a simple modulation scheme like AM, you can demodulate in hardware, but anything more complicated and you're better off just digitizing the signal and using software to figure out what was sent. I would build everything separately in modules so you can test each part separately. If you're not a purist most of these parts can be bought as a premade chip.In real life people either use a superhet with an RF PLL for the LO (so you can change the frequency on the fly), or they use direct downconversion at high frequency.

author: fourfathom
author_rank: Super Contributor
timestamp: June 29, 2024, 06:33:20 pm
content: The simplest practical receiver to build is the "direct conversion" design:https://www.dl6zb.de/minimal_art_receiver/2-bjt-001_sm.pngA workable one just has the antenna feeding a mixer, with a local oscillator driving the other mixer input. The mixer output goes into a simple low-pass filter (R/C) and then into a high-gain audio amplifier. This isn't a high-performance receiver (far from it!), but it will pick up AM, SSB, and CW. You can improve performance with input filters, but these can be added later.But if you just want to listen without building your own receiver then a modern SDR is probably the easiest way to go. Something like the SDRplay is a good place to start:https://www.sdrplay.com/rsp1a/

author: stretchyman
author_rank: Regular Contributor
timestamp: June 30, 2024, 09:50:18 am
content: Yes, I agree. Just get an SDR. SDRPLAY ones are fine as are many others but there's seem the best for reasonable cost.J.

author: radiolistener
author_rank: Super Contributor
timestamp: June 30, 2024, 04:57:36 pm
content: Quote from: stretchyman on June 30, 2024, 09:50:18 amSDRPLAY is very expensive, it has many issues and it's low performance doesn't cost it's money. In addition it needs to use proprietary software with closed source code and many bugs.I bought one and never using it due to many issues and bad performance. Instead I'm regularly using RTLSDRv3 and RTLSDRv4.The main issue of SDRPLAY is that it is build on msi2500/msi001 chipset which is a piece of crap, the secoind important issue is that it requires proprietary drivers and software which is bad written and has many issues with thread safety, etc. Also SDRPLAY software and drivers requires more powerful machine to run.If you want to get cheap, good performance and universal solution with open source tools, then RTLSDR is the answer.For short wave RTLSDRv4 is better because it has SA612 mixer, don't require to switch direct sampling mode and allows to use LNA gain below 24 MHz. But RTLSDRv4 requires to install more modern driver which may be complicated for novice.For VHF and UHF you can get RTLSDRv3 or even usual RTLSDR dongle which will be even more cheap.

author: fourfathom
author_rank: Super Contributor
timestamp: June 30, 2024, 11:23:34 pm
content: Quote from: radiolistener on June 30, 2024, 04:57:36 pmFWIW, I've used the SDRplay and it works well enough. Yes. if you want to use it under linux then you might have driver issues, but I've never tried that.The RTLSDRv4 looks very interesting. I've build some HF JS8Call gateways with the earlier "RTLSDR-Blog", and this used direct sampling with a clock frequency of 28 MHz (which required that I put some serious front-end filtering ahead of the SDR). The RTLSDRv4 includes an up-converter, which in theory makes it a much better HF receiver. I've not tried it though.

author: stretchyman
author_rank: Regular Contributor
timestamp: July 01, 2024, 09:20:14 am
content: Wow an SA612, that makes it good does it?Maybe I should rephrase my original reply and recommend the purchase of ANY SDR will allow simple access to the RF spectrum and allow anyone to look into the hobby without trying to design and build stuff, which btw is no simple task.To design and build anything your soldering skills must be decent, you're best to use PCB design and have some test equipment too.A lot to learn!.Just get (any) SDR and have a listen first.J.

author: fourfathom
author_rank: Super Contributor
timestamp: July 01, 2024, 03:46:59 pm
content: Quote from: stretchyman on July 01, 2024, 09:20:14 amI generally agree, but the cheaper SDRs are designed for VHF and aren't going to give you easy reception on the HF bands without external upconverters or heroic anti-aliasing filters. That's why I suggested the SDRplay (and the RTLSDRv4 sounds promising). And there are plenty of other SDRs that are HF-capable.And way back in the mists of time (say 45 years ago) I was building very simple transmitters and receivers using "dead bug" techniques. In fact, more like "dead transistor", since I didn't use ICs. But these days I would certainly make a PCB for any design.

author: radiolistener
author_rank: Super Contributor
timestamp: July 01, 2024, 07:54:07 pm
content: Quote from: fourfathom on June 30, 2024, 11:23:34 pmYes, it works better on shortwave, now there is no need to enable direct sampling, upconverter is automatically enabled when you go below 28 MHz. And now there is no images across 14 MHz border, and you can use LNA gain tune on shortwave. For VHF/UHF it works the same as v3, just a little less hot, the developer said that it has improved power regulator. Also developer said that it has several filters and separate RF path for different band.