how to generate AM / FM - Page 1
Forum section: electronics / beginners

author: alin_im
author_rank: Regular Contributor
timestamp: April 20, 2015, 12:11:08 am
content: hi guys,what equipment do i need so i can generate am and fm signalsI have an oscilloscope and a 1Mhz signal generator. I can use it for the modulation signal but what type of equipment do i need to use/buy for the carrierdo you think i can use ahttp://www.ebay.co.uk/itm/10MHz-DDS-Function-Signal-Generator-Carrier-Debugging-Source-Frequency-Counter-/271634348857?pt=LH_DefaultDomain_3&hash=item3f3eab3b39or i need something else ?

author: jeroen79
author_rank: Frequent Contributor
timestamp: April 20, 2015, 12:56:53 am
content: What exactly do you want to do?The device you found is just an ordinary function generator and as far as I can see it has no option to modulate the frequency or amplitude with an external input.And 1 and 10 MHz are too low for mostbroadcast bands.Look for transmitters or transmitter schematics.Also look into the your country's regulations regarding radiotransmissions.

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 08:22:56 am
content: Adding amplitude modulation to your existing signal generator is fairly straightforward but it's not possible to do the same with FM - you need to build a voltage controlled oscillator but this isn't too difficult.

author: alin_im
author_rank: Regular Contributor
timestamp: April 20, 2015, 10:20:58 am
content: Quote from: jeroen79 on April 20, 2015, 12:56:53 ami do not want to broadcast radio, i want something like a modulating fq of 50khz and a carrier of 500khz, some basic stuff to understand better the how they function

author: joeqsmith
author_rank: Super Contributor
timestamp: April 20, 2015, 10:57:43 am
content: Lot's of ways to make this work. I bet you could make the carrier with a 7404.

author: Cherry
author_rank: Contributor
timestamp: April 20, 2015, 11:43:24 am
content: Awesome!

author: alin_im
author_rank: Regular Contributor
timestamp: April 20, 2015, 09:23:21 pm
content: what do you think about this signal generatorhttp://www.ebay.com/itm/12Mhz-Dual-ch-DDS-Function-Arbitrary-Waveform-Signal-Generator-sweep-Software-/111505341795?pt=LH_DefaultDomain_0&hash=item19f63c7d63

author: Zad
author_rank: Super Contributor
timestamp: April 20, 2015, 09:58:58 pm
content: What I think is that you would be better off buying a couple of books in introducing amateur radio, and actually build an AM and FM modulated oscillator. You learn far more about how things actually work than just buying a "black" box which you punch some numbers into.

author: Howardlong
author_rank: Super Contributor
timestamp: April 20, 2015, 10:14:04 pm
content: Not sure if you're into programming or not, but if you are you can use your sound card to generate FM and AM, although the carrier will have to be below 20kHz.If you can get an academic discount, the Analog Discovery, frequently mentioned on this forum, has a pretty decent two channel AWG as well as a bunch of other stuff. Even if you can't get an academic discount, Microchip Direct seem to have it a lot cheaper than anyone else for non-academics.

author: alin_im
author_rank: Regular Contributor
timestamp: April 20, 2015, 11:22:34 pm
content: Quote from: Zad on April 20, 2015, 09:58:58 pmthank you for your advice !!! i think this is the best way...if you have any recommendations please tell me. thank you

author: VK5RC
author_rank: Unknown
timestamp: April 20, 2015, 11:56:01 pm
content: The ARRL handbook, (the USA amateur radio society's) even if second hand, has a good introduction into rf and usually some simple circuits as well.

author: G0HZU
author_rank: Super Contributor
timestamp: April 21, 2015, 12:18:28 am
content: I'd suggest doing it two ways.1/ Oldschool. Using classic AM and FM analogue modulator circuits that date back many decades. You can find these in loads of example circuits for CB/ham radio or radio control. Don't waste too much time on either of these...2/ Modern. Make a basic vector modulator at, say, 1MHz and then learn how to drive the I and Q inputs to generate AM or FM (or SSB etc etc) from the same vector modulator.You could start off driving the VM using a soundcard (and someone else's SW) to generate the I and Q signals but then go on to create your own hardware (MCU plus DACs and V Modulator) and firmware to drive it properly for AM or FM or many other types of modulation.The webpage below from G4JNT covers pretty much everything wrt making the VM and describes the G3PLX SW. It's mainly aimed at SSB generation but it is still a useful learning tool wrt vector modulation.http://www.g4jnt.com/SDRTxSW.htm

author: miguelvp
author_rank: Super Contributor
timestamp: April 21, 2015, 03:57:45 am
content: Since no one has asked, what kind of 1Mhz signal generator do you have? model number and vendor?Just in case you missed if it has AM/FM modulation.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 21, 2015, 06:51:03 am
content: Quote from: VK5RC on April 20, 2015, 11:56:01 pmGreat book. Can definitely recommend this.

author: alin_im
author_rank: Regular Contributor
timestamp: April 21, 2015, 07:44:17 am
content: Quote from: miguelvp on April 21, 2015, 03:57:45 ami have farnell lfm4

author: alin_im
author_rank: Regular Contributor
timestamp: April 21, 2015, 07:46:25 am
content: Quote from: smjcuk on April 21, 2015, 06:51:03 ami saw that in every year it appears another one, it this year book an upgrade of the 2014 one or they have different topics in every year. if so what year do you recommend

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 21, 2015, 08:29:12 am
content: It's an upgrade yearly. Within the last 1-4 years is fine - radio tech doesn't change that much.Can usually snag a copy on amazon second hand, abebooks or ebay for not much.

author: VK5RC
author_rank: Unknown
timestamp: April 21, 2015, 10:56:18 am
content: + re smjcuk, I would go for a good priced second hand one, the updates tend to not be huge, some have a cd of some simple programs that can help design multi-pole passive rf filters.I recall the 'revelation' of understanding capacitance and inductance as a young lad reading the handbook. I have just got my first copy of the art of electronics, it reminds me a lot of some parts of the arrl book but I suspect that the art..... is probably in a higher if not different league.