EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: chrisb741 on January 17, 2024, 12:02:01 am
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If I create a ARB waveform of 4 sin waves and set the frequency to 108.475Mhz will I get a 433.9MHz output that I can modulate and then transmit it to be and picked up by a ASK receiver?
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No.
Max sampling rate in Arb mode is 75 MHz (300 in DDS) and maximum output frequency 20 MHz.
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Inject 108.475MHz (10dBm, ASK modulated) into a (passive) frequency doubler and use the 4th harmonic to test the receiver.
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I tried using the ARB didnt work too well.
How is it normally done? Can I used the SDG2000X plus other components to create a 433.9Mhz ASK modulated signal
I can send and receive such signals with a 433Mhz ASK transmitter and receiver module with a mcu attached, but I'd like to find out how I create such signals another way
Will a spectrum analyzer such as SSA3000X-Plus with modulation analysis help with understanding and testing digital communications?
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On my Siglent SSA the tracking generator output is just that, a tracking generator. It is not a seperate discrete, tunable, frequency. source. it's output is at current frequency of the sweep. It is incrediibly useful but if your looking @ 432 Mhz , your not going to generate 144 Mhz to triple from. If you set span to zero and your center frequency on the SSA to 432, you get a variable level stead 432 Mhz signal. You would have to provide an external double balanced modulator from Mini-circuits labs [part SBL-1] to modulate the TG output.
May I suggest the book "Experimental Methods in RF Design" By
Wes Hayward Before you spend any money. Especially if designing receivers. Yes, it is for ham radio, but the principles are the same.
You can get a very nice DDS synthesizer board on Ebay or Amazon for 30$. Buy that. If you need a lab grade source buy a PTS 250, 512, 1000 etc on Ebay [Programmed Test Sources] Either with knobs or use the parallel programming input on three back. for knobless models.
it is easy with bench frequency synth and a mixer module to build a demodulator, use an oscilloscope and low pass filter on the. mixers IF port to see the signal.
The communication test mode software, on the SSA will help you, but it is receive only. That module is free for 40 hours on purchase of the SSA as a demo.
Your preferred tool is the SSA as a beginner, just put an external 10 dB attenuator on its input to protect it from You!
There are many ways to generate a ßignal from your Arb by mixing, multiplication, harmonic generator, frequency doubler etc. The simplest way is a crude harmonic generator Consisting of a 470 Ohm resistor with a 1n914 diode. It will generate a few microwatts of signal into a six and one quarter inch piece of wire that your receiver might hear within a few meters.
Ground the 1n914s Anode, pump the cathode through the series resistors, hook the antenna to the cathode. The 1n914 will act as a varacter multiplier. The antenna will radiate the signal. It's faint, and no product would ever use that method, but it's a lifesaver on the test bench sometimes.
It sounds like you have much to learn about UHF.
Steve
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You can use frequency multiplication with a 2 and 3 multiplier and get the multiplication of 6.
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On my Siglent SSA the tracking generator output is just that, a tracking generator. It is not a seperate discrete, tunable, frequency. source. it's output is at current frequency of the sweep.
The purpose of getting the SSA was to monitor and measure not generate a signal. To use it receive only.
I can easily generate digital ASK and FSK signals with various transmitter modules
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You don't know WHAT your generating till you check it with an SSA. Rule one, never assume what you can't see or measure in UHF RF.
Buy the SSA, preferably the 3 Ghz version. I have the 1.9 Ghz version and ended up building a mixer-downconverter to see WIFI. Either version is an excellent instrument.
You'll still need Haward's book and a 10 Db attenuator and good quality cabling. I'd also suggest a WA5VJB log periodic [30$] as a reference antenna or input coupler for the SSA.
Loading your low component count poorly matched remote transmitters directly with the SSA without a pad or air gap is a common beginners mistake.
Eventually, for testing Antennas with the SSA, pick up a used 20 dB directional coupler on Ebay. This for return loss / reflected power.
There are excellent 3rd party apps for the Siglent SSA that can reduce your need to buy Siglents options. You can also quickly calculate VSWR with a calculator if you have a return loss bridge.
I would not want to tune UHF RF receiver front ends off just a remote. Works great in the near field, sucks when you can't measure SNR / sensitivity/ bandwidth / approximate noise figure in the far field. Especially if your antenna is built into/onto a PCB.
Oh, he's insulting my intelligence, I'm not listening to Lasersteve
Think again, I started with using TV tuners for my SSA. I'm trying to hammer home that you need good gear for what your doing, going cheap can equal failure fast. Especially if you have to certify your device for RFI.
I would never assume the transmitter designer did his homework. Many of the transmitters are just poor copies of reference designs from data sheets, often made with the wrong dielectric in the pcb. Often with parts omitted. On PCB "F" antennas are notoriously tricky / often just horrible.
When you design your pcb, remember to bury in some test points in the RF front end. There are plenty of freeware microstrip simulators out there such as HP AppCad etc.
I have 30 years in RF, some as amateur, some as professional. trust me.
Why be totally blind when you can own the Swiss Army Knife of
RF tools.
Mine , much to my suprise, paid for itself in one week on an unexpected ultrasound [1,5 Mhz] driver development project.
Steve
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For monitoring stuff like this it might be better to buy a mid range SDR than a spectrum analyser. I've not used the Siglent analyser, but the analogue and digital demod modes in many analysers are fairly limited in what they offer. You may eventually find you want to do things the analyser doesn't support.
SDRs are much more configurable. I'm not sure what SDR to recommend, but some platforms are very versatile for both Tx and Rx modes. Maybe someone can suggest something. The only SDR I have here is the little £100 RSP1-A receive SDR. It's fine for casual viewing of the spectrum of ASK waveforms in spectrum analyser mode as long as you don't expect it to be calibrated.
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If he's designing I'd argue he needs the SSA with TG as a source and receiver with acurately calibrated levels and the huge dynamic range.
He keeps flip flopping between TX and RX, so the SSA tests both.
Does the SDR tx/rx combo have enough dynamic range? How does he impedance match it? Can it transmit and receive at the same time? Does it have enough front end protection ? Lots of tough questions.
Last post he flipped to designing his own RX front end.
I've been waiting for some one to pop in and tell him all he needs is a 99$ 0-300 Mhz EBAY cheap VNA running off third harmonic. That would be a disaster. I know, I own one. You have to be one highly skilled designer doing a lot of cut and try on the bench to make that work.
We have no idea what hes using for RX input filter / tuned front and how he's getting to baseband... He needs to define the problem better. What's the Baud rate? What's the topology? Superheterodyne? Direct IF? What Chipset?
I have a feeling an SDR with TX might be a good learning tool at this stage, as would a harmonic generator off his signal generator But if this is wide scale commercial product, SSA all the way.
One way or another, a copy of Haywards book should be in his hands. Even a bootleg pdf at this point.
Steve
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Yes, I don't really know what I'm doing with the RF side of things. I've only used them in projects.
Sorry, just thought to clarify a few things.
That's a lot of information to unpack, can we focus on one thing at a time? Would it be good to start testing the quality of the existing transmitters, I have the receivers, so they do their job. I can measure the digital and power side but not the other transmission side.
I do have a simple USB SDR I used to monitor ADS-B years ago. I also have tinySA device. All the other equipment I have is better quality Siglent gear on the similar level as SDS2000X+
I have very basic understanding of an SA and virtually nothing with VNA
So to start I need:
Haywards book
SSA 3+ Ghz
10db attenuator
Antenna
BTW I live in Australia buying stuff of eBay is very hit and miss, lot of people don't deliver here
I have BNC to sma adapter's, cables and 50ohm load, numerous ASK/FSK 433Mhz and 2.4Ghz transceivers.