Please give me some basic RF pointers - Page 1
Forum section: electronics / beginners

author: VSV_electron
author_rank: Regular Contributor
timestamp: May 11, 2024, 02:49:48 pm
content: Hello friends, I badly need your advice on getting into some basic RF territory. The subject is huge and deep and I'd probably like just to dip my toes in the waters of the great RF ocean. I'm a simple digital guy and I'm afraid I'll never be able to become a hardcore RF enthusiast due to my modest IQ level but some RF experience even if it's superficial won't hurt anyone.If you don't mind please set me straight on the following as I feel this might be the most practical approach for the jump start. (I've got a ton of books on RF, including the famous 'Exp. Methods in RF Design' by W. Hayward but I would spend years with the books just to start figuring out the basics... again due to my modest IQ level).So, to the subject:Suppose I've got the following two items off Ali Express both of which receive good reviews from buyers:1. A loop antenna:https://aliexpress.com/item/1005002999325010.html2. A 70 Watt SSB amp kit:https://aliexpress.com/item/32735096030.htmlNow, I have to reveal how dumb I am, please bear with me...The question: What can I do with those two items? In other words - What is missing from the equation that would allow me to assemble the basic RF system?If you would be so kind please put those two items in context on some sort of block diagram to identify their place in the complete and functional RF system.Of course I understand that the antenna would be placed on the far end from the operator but I'm clueless on where the 70 Watt SSB amp goes and what other parts are needed to shape up the system to make it minimally functional.I foresee your clever and reasonable question:- "What do you want to do with the basic complete RF system, the two components of which you named?"Me:- To be honest, I don't know yet. I'm at the moment more interested in the process of putting the whole thing together rather than in the end result which of course is the ultimate goal. You please tell me what I can do with it.I've got some basic workbench equipment and recently I almost by accident purchased a 'NanoVNA-F V2' (I didn't plan to use it for RF specifically) which now could to be applied in the RF context where it primarily belongs to.

author: shabaz
author_rank: Frequent Contributor
timestamp: May 11, 2024, 03:12:56 pm
content: It's not legal to transmit at the frequencies that equipment is intended for.If you want a quick overview with low effort, it's probably useful to take a beginner level ham radio course (and optionally do the exam if you feel like it). It's not intensive at all, and the reading material is minimal, but will provide you with a lot of answers (or pointers at least) if you're coming from zero experience, so then you can focus more on the areas of interest.There are various RF building blocks you could create or experiment with, depending on interests. However, there's no getting around the reading up; it may well take years for a complete deep-dive into many areas of any engineering topic, not just RF, but that doesn't mean you can't do practical work as you learn. Lots of people dabbled with RF from slim beginner books on "how to make a radio" etc.

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 11, 2024, 03:27:18 pm
content: Quote from: VSV_electron on May 11, 2024, 02:49:48 pmYour question doesn't make a lot of sense, it's like asking "I have a chicken and a rose, what am I missing to complete it?"

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: May 11, 2024, 06:34:19 pm
content: That antenna will not survive anything the amp puts out.Maximum power: 250 mW

author: CaptDon
author_rank: Super Contributor
timestamp: May 11, 2024, 08:38:43 pm
content: Do yourself a favor and get a hold of one of the ARRL yearly edition handbooks. Perhaps from the mid 70's to mid 80's when they had great projects covered in detail. Just start at page one and read!!! They cover everything. The equipment you show interest in can not be used without a license and since the code requirement was dropped even a chimp can get a license. What you need to know could fill an entire college course. Seriously, the ARRL Handbook is a great place to learn about R.F.!!! I had a '50, '54, '60, and '64 and won a 1982 edition at a hamfest!! Then, for additional antenna theory they also published an 'Antenna Handbook'.

author: tszaboo
author_rank: Super Contributor
timestamp: May 11, 2024, 10:11:52 pm
content: You need a HAM radio license to be able to output anything above 2 watt of RF to any antenna.Otherwise it's not legal.Coincidently, to get a HAM license, you need to learn the answers to your questions.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 11, 2024, 10:45:25 pm
content: Seriously, at the moment, the OP has been "ripped off".As it stands, you can't do anything with the stuff you bought---it is similar to buying new tyres for an engineless car.

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 11, 2024, 11:21:30 pm
content: Quote from: tszaboo on May 11, 2024, 10:11:52 pmHi tza, I doubt that level of 2 Watt antenna power is correct for EU. Maybe you can check local regulations and update your post?In USA FCC power to antenna for "Low Power Unlicensed Transmitter Part 15" is mostly less than 1 milliWatt, from "DC to Daylight", with some exceptions eg ISM bandsIn USA Refer to FCC OET Bulletin 63 for power by band tabulations and penalties. Other jurisdictions will have similar regulations.

author: Bud
author_rank: Super Contributor
timestamp: May 11, 2024, 11:31:26 pm
content: As other posters said, 1- you cant use these components together because they are incompatible, 2-you need a license to transmit, 3- an early years ARRL Book is a good start if you still want to understand RF at entry level.Edit: 4- even with a license you cant use what you bought to transmitt, because you do not have a transmitter. An amplifier and antenna will not magically transmit on their own.

author: 807
author_rank: Frequent Contributor
timestamp: May 12, 2024, 10:40:23 am
content: As already mentioned, your best bet is to do a bit of further reading on amateur (ham) radio. Start off with a beginners book on ham radio. As well as the ARRL, the RSGB in the UK produce suitable books too. To start you off, you could probably find some basic info on the internet.The item you linked to is a power amplifier. It can be used to boost the output from an existing, low power, transmitter. It won't do anything on it's own, without a signal to drive it.If you do build your own transmitter you can legally use it without a license, as long as you connect the output to a dummy load (high wattage resistor), and not to an antenna.

author: tszaboo
author_rank: Super Contributor
timestamp: May 12, 2024, 10:50:07 am
content: Quote from: mag_therm on May 11, 2024, 11:21:30 pmYour phone, and a Wifi router can output 2W easily. Some other frequencies are less. Feel free to look it up yourself, or ask chargpt. That's not the point that I'm making.

author: CaptDon
author_rank: Super Contributor
timestamp: May 12, 2024, 11:49:49 am
content: Haven't looked lately but the Part 15 spec was 100mw not 1mw. Nearly all toy walkie talkies and nearly all musical instrument wireless equipment as well as garage door transmitters and so forth are 10 to 50mw. One part of the clause is that no matter the frequency an operator can not cause willful or harmful interference to licensed services which caused the banning of some very expensive UHF wireless mic equipment after the repacking of UHF television. After making that rule the FCC should have been required to make restitution for all the equipment which was suddenly illegal for use and headed to the landfills!!!

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: May 12, 2024, 12:15:16 pm
content: An RF amplifier specifically for SSB doesn't make sense to me. i thought SSB was a mode of modulation.

author: xrunner
author_rank: Super Contributor
timestamp: May 12, 2024, 12:19:15 pm
content: Quote from: VSV_electron on May 11, 2024, 02:49:48 pmWhat can you do with it? Build the amp and test it. No license required to test on a bench into a dummy load. You'd have to test it anyway before using it "live". So buy the amp, build it, and test it on the bench into a dummy load. Play with it and check it's operation. You will learn a lot from doing that.

author: wasedadoc
author_rank: Super Contributor
timestamp: May 12, 2024, 12:54:05 pm
content: You can learn a great deal about RF by building and studying receivers. There are lots of transmitters legally operated by others that you can do receiving experiments with. Even getting an AM band crystal set working will be educational for the OP.

author: Andy Chee
author_rank: Super Contributor
timestamp: May 12, 2024, 08:55:34 pm
content: Quote from: Ground_Loop on May 12, 2024, 12:15:16 pmRF amplifiers can be non-linear Class C amps, or linear Class A or B amps.For amplifying SSB you need a linear amplifier. For amplifying FM, you could get away with a non-linear amp.Of course, there’s way more to it than I can summarise in three sentences, far beyond the scope of this thread, but within the curriculum of most ham radio licence study guides.

author: Andy Chee
author_rank: Super Contributor
timestamp: May 12, 2024, 09:05:05 pm
content: Quote from: VSV_electron on May 11, 2024, 02:49:48 pmThe kit that you linked is a small transmitting amplifier. As an RF n00b, I’d suggest staying away from transmitting stuff for now, and focus on receiving. If you want, you could get a receiving amplifier.As a digital guy, how familiar are you with analog to digital conversion in audio systems and/or analog sensors like potentiometers?RF can also be sampled with an AD converter! Instead of 20kHz audio, you’d be sampling a 200MHz radio signal!This is how modern software defined radios work, and building an SDR radio might be one way to dive in the deep end.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 12, 2024, 11:31:14 pm
content: Quote from: Ground_Loop on May 12, 2024, 12:15:16 pmIt is a linear mode, so the linearity of the amplifier is more important than it is for CW or FM.

author: radiolistener
author_rank: Super Contributor
timestamp: May 13, 2024, 12:54:15 am
content: Quote from: VSV_electron on May 11, 2024, 02:49:48 pmThese things are incompatible, this antenna is designed for receive only mode. If you use connect it to 70W transmitter, it will be burned out.You can use this antenna for receiver.For transmitter you're needs to use proper full size antenna. For example if you're want to use it at 3.5 MHz band, this is 80 meters wavelength, so half wavelength dipole antenna will be 40 meters length, usually it is feeding (connected to the coax cable) at center.It is also possible to build small antenna for transmitter, but it will be less efficient and using it with powerful amplifier is dangerous for your health, because it will produce extreme high electric and magnetic field strength near antenna which will exceed all safety limits. This extreme field strength is required for small antenna to compensate it's small size, as result it works with extreme high current and extreme high voltage, so it needs high voltage components for matching and good and thick conductor to reduce heating loss. The cons of such small antenna are low efficiency, danger for your health and very narrow bandwidth, it needs to be tuned every time when you want to change frequency. Also such small antenna is very sensitive to any nearby object within wavelength distance (hundreds times more sensitive than usual full size antenna), so it needs to be placed far away from any building, mains wires or other objects. Also it will suck hundreds times more noise from nearby electronic equipment or mains wires in receive mode.Also note that using incorrectly tuned antenna with powerful amplifier with no protection (like one from your link) leads to damage your amplifier output transistors. Such amplifier needs to be connected to a proper tuned 50 Ω impedance load, otherwise it will be damaged

author: 807
author_rank: Frequent Contributor
timestamp: May 13, 2024, 11:30:07 am
content: Quote from: xrunner on May 12, 2024, 12:19:15 pmProblem is, he will need more test gear & equipment to test it. It's designed to boost the output from a low power transciever, so he will need something to drive the amplifier (approx 0.5 to 5W). A high wattage 50Ω dummy load is needed to dump the power. A 6-10A PSU is needed to power it. Some means of measuring the output power is needed, either a high wattage power meter, or a more modest power meter in conjunction with an attenuator. A spectrum analyzer is needed to check for spurious & harmonics. If a clean output on a certain frequency is required, then a low pass filter is needed.The kit also doesn't come with a heatsink, so that is another requirement, and possibly a fan too.Considering that this is the OP's first step in the RF world and he says that he has "basic" workbench equipment, I would consider something less ambitious to start with.

author: pdenisowski
author_rank: Super Contributor
timestamp: May 13, 2024, 12:37:53 pm
content: Quote from: Ground_Loop on May 12, 2024, 12:15:16 pmOh, there are plenty of amplifiers designed for SSB -- I've spent considerable (work) time hunting down a few that were being operated illegally (CB bands)

author: CaptDon
author_rank: Super Contributor
timestamp: May 13, 2024, 01:42:18 pm
content: Pdenisowski, Someone (FCC) should track down the dimwit on C.B. ch19 that appears to be somewhere in the central northwest area of Pennsylvania. I travel Rt80 from the Ohio border to the exit for rt220/99 Penn state area and I can hear this idiot for roughly 100 miles of the 160 mile trip. Blah, blah, blah all day long every day mostly talking to himself!! His latest kick is talking about transexuals and truckers with 'butterbox' radios and how wonderful his radio is. Often he ends his individual transmissions with "back to the bench". Seems sad that the FCC no longer seems to care about 27MHz unless they interfere with police or military. They are even slow to respond when given the operators exact address and times of day to be most likely active!! I do know of two folks who got jail time for threats of violence on the air and illegal power / antenna height. In both instances I assisted in triangulating to 1 city block, then zeroing in on foot!! One was a C.B. operator and the other had a ham license and was jamming repeaters and their control frequencies and control DTMF codes. The F.C.C. brought in the State Police agency for the threats of violence charges!! All illegal on air activities were digitally recorded and sent to the F.C.C. gathered over several months by local ham radio clubs.

author: AG6QR
author_rank: Frequent Contributor
timestamp: May 13, 2024, 03:51:58 pm
content: Quote from: VSV_electron on May 11, 2024, 02:49:48 pmSince your profile says you're in Finland, you should probably contact Finland's Amateur Radio organization for information on licensing and ruleshttps://www.sral.fi/But briefly, to make use of your 70W amplifier and antenna, you will need:A licenseAn HF transceiver (the documentation suggests a Yaesu FT-817 or an Elecraft KX3, or similar low-power transceiver. Notice these are much more expensive than the amplifier kit.)A low-pass filter for each band you want to use, to reduce spurious harmonic emissions to a legal level. Most commercial amplifiers would come with a switched bank of low-pass filters for all of the supported bands built-in as a standard part of the amplifier.An antenna matching network, sometimes called an "antenna tuner", so that the amplifier will see a load of approximately 50 ohms resistive at the frequency you want to useWhen you have a transceiver, you can use it without the amplifier. Low power transceivers like the FT-817 and KX3 can be used directly to contact other stations, but the amplifier will make it easier for you to be heard over long distances.You'll also need the test equipment and know-how to adjust the antenna matching network, and to validate that you've assembled the amplifier correctly, and that it is functioning properly.If you can use the web address above to find a local group of amateur radio enthusiasts, they are likely to be very helpful. Most amateur radio operators mostly use their equipment to communicate with other amateur radio operators. Some know a great deal of electrical engineering, and build and test their own equipment, while others know very little of the technical aspects, and purchase off-the-shelf equipment. There are many who are somewhere in between these extremes.

author: Andy Chee
author_rank: Super Contributor
timestamp: May 14, 2024, 07:08:16 am
content: As an aside, there are several build videos and tests of this amplifier kit on YouTube, with varying degrees of detailed testing:

author: pdenisowski
author_rank: Super Contributor
timestamp: May 14, 2024, 09:53:10 am
content: Quote from: CaptDon on May 13, 2024, 01:42:18 pmHaving done direction finding and interference hunting for many years: FCC has some very talented and dedicated people working for them, they're just severely understaffed. Even cellular network operators whose (very expensive) licensed spectrum is being interfered with usually resort to self-help when it comes to interference issues, most of which are non-malicious. My guess is that the threats of violence is what caused FCC to devote resources to the cases you mention - they have some very nice equipment and are very competent when it comes to documenting activities and locating emitters.CB radio interference has been around since licenses were required to use CB. Harmonic suppression is almost non-existent in many (homebrew and purchased) "linear" amplifiers, so the biggest "threat" is usually harmonics and intermod: pretty much no one cares about people using "excessive" power within the band. There also are (well, were) plenty of freebanders who viewed CB as a kind of redneck* amateur radio, but they also rarely got any scrutiny from FCC.*I've lived in the Carolinas almost my entire life and don't consider the word "redneck" a slur - it's just an .. unconventional .. way of doing things

author: tszaboo
author_rank: Super Contributor
timestamp: May 14, 2024, 05:45:40 pm
content: Quote from: pdenisowski on May 14, 2024, 09:53:10 amWhen you are understaffed, you can just employ the:The AGM-88 HARM (High-speed Anti-Radiation Missile) is a tactical, air-to-surface anti-radiation missile designed to home in on electronic transmissions.Solves the unintended radio transmissions in less than 5 minutes.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: May 15, 2024, 01:17:44 pm
content: Getting back to the OP's equipment:The Antenna is a small loop designed for primarily Rx. It will probably survive a few milli watts of TX, More than that would burn something.I built a small loop for over 100 watts and it is quite expensive. You need good components that can survive perhaps 10,000 Volts. They are very good antennas but require re tuning for even a few KHz change in freq.The amplifier is intended to be used with a QRP transmitter Radio that puts out a few watts. perhaps 5 Watts. This is a common thing, used by lots of people who have QRP transmitters but sometimes want higher output. The quality of these amps varies greatly as does their spurious outputs. Some are quite good, others not so good.About SSB vs AM transmitters.....you can run an amplifier at higher PEAK output on SSB because you do not have a constant AM carrier present. This is a common feature in normal HAM transceivers. This varies with the robustness of the final stage amplifier especially the output transistors.It used to be that CB radio 2nd harmonic would interfere with the TV Band, Freq have changed and signal is also now digital (making the chance of any possible interference much less). Also most people use some version of cable rather than Over The Air signals.A big danger of CB interference is in the 4th Harmonic which is in the Aeronautic Band 118.000 to 136.975 MHz. You can get into big trouble for this.There are CBers who put outTens of Thousands of Watts, More than most commercial AM stations. Some CBers even have 440 volt three phase electricity to their house for these illegal transmitters.These folks usually only interfere with the use of the CB Band, since they can "STEP ON" or overwhelm lesser stations and the FCC does not seem to be interested.

author: VSV_electron
author_rank: Regular Contributor
timestamp: May 16, 2024, 06:22:06 pm
content: Thank you all for your thoughtful replies.No - I didn't buy that amp kit and that antenna I posted the links to. That was just a conversation starter and believe me or not - I've already learned some things from your helpful answers!I especially appreciate your suggestions to get some early ARRL books from the 1980-s with complete RF projects. Please mention a few specific editions if possible.... Just located couple ARRL handbooks in pdf (1986 and 1989) - is that what I need?