Spectrum Analyzer Suggestions... - Page 1
Forum section: electronics / projects

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 10, 2010, 06:56:53 pm
content: Any suggestion on what is good or not, the best and worst? cheaper, good for money, where to buy, any free to be handed down?I'm surveying in ebay for SA up to GHz frequency, but the price makes me think many many times.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 10, 2010, 08:06:24 pm
content: http://www.qsl.net/n9zia/wireless/appendixF.html#9

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 10, 2010, 11:56:20 pm
content: how about atten 500MHz SA? rigol didnt have SA, right?@nihaomike, that homebrew is quite nice, googled some DIY SA, but there are jargons that i dont understand. will need time to study it. i remember one interesting jargon... "pink noise"i want something that shows the inverted "V" graph... dBm vs MHz

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 11, 2010, 01:13:06 am
content: What frequency span are you looking for? If it's much less than the bandwidth of the oscilloscope, you could use a downconverter along with an oscilloscope running FFT. For example, if you want to look at signals in the 900-930MHz range, you could run it through a downconverter with a LO frequency of 875MHz, which would shift the signals down to 25-55MHz.

author: joelby
author_rank: Frequent Contributor
timestamp: July 11, 2010, 06:16:56 am
content: Rigol do make spectrum analysers, but they don't seem very serious about them - you can't seem to buy them anywhere and they no longer even mention them on their site. I didn't rate them anyway; no tracking generator or vector analyser options.Perhaps you could tell us what you intend to use one for?

author: jahonen
author_rank: Super Contributor
timestamp: July 11, 2010, 07:54:48 am
content: The good RF guys (and certainly not the cheapest, but you can't go much wrong with these): Agilent/HP, Rohde & Schwarz, Anritsu and Advantest. There might be others but those came relatively easy in mind.1 GHz upper frequency limit is rather low for RF, something like 3 GHz is more common.Regards,Janne

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 11, 2010, 08:45:03 am
content: Quote from: NiHaoMike on July 11, 2010, 01:13:06 amsound interesting, i can see some example in the link you have provided, need to study more? i think maybe a simple DIY can do, if..... its simple to build.@nihaomike & joelby = i'm thinking of building an RF circuit (transmitter and receiver) and i want to know how much its strongest frequency that transmitter transmitting and the receiver resonating. currently i'm trying just 433 MHz, but who knows? i might go advance and in the future want to go 800-3000 MHz? but in the mean time, 433 MHz is what i have in mind.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 11, 2010, 09:08:36 am
content: any downconverter exampe, that will read 433MHz into 50/100 MHz rigol FFT? i also need to be able to see the strength of it.

author: joelby
author_rank: Frequent Contributor
timestamp: July 11, 2010, 09:13:55 am
content: Just mix the signal coming out of the transmitter with a ~433 MHz signal using any suitable frequency mixer. Mini Circuits sells a billion different ones - here's one that comes with BNC connectors:http://minicircuits.com/pdfs/ZAD-1+.pdfTo determine the signal strength if you're using a DSO, it'd be easiest to first use a calibrated signal generator as the input and take some readings at different frequencies.The Rigol FFT is pretty awful for this sort of application, by the way. You could save the data points and analyse them in Matlab or similar.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 11, 2010, 09:20:14 am
content: Quote from: joelby on July 11, 2010, 09:13:55 amerrr. how the principle works? can rigol be input with greater than 100MHz signal and read correctly?

author: ThunderSqueak
author_rank: Unknown
timestamp: July 11, 2010, 09:27:18 am
content: Quote from: shafri on July 11, 2010, 09:20:14 amtaken from the post athttps://www.eevblog.com/forum/index.php?topic=30.30andQuote from: EEVblog on November 06, 2009, 01:48:14 amit is late... :>

author: joelby
author_rank: Frequent Contributor
timestamp: July 11, 2010, 09:37:36 am
content: Quote from: shafri on July 11, 2010, 09:20:14 amA frequency mixer will take two signals of frequency f1 and f2 and output the sum and difference frequencies, (f1 - f2) and (f1 + f2), plus a bunch of other products like (2*f1 - f2) etc.If your test signal f1 is 433 MHz and your local oscillator signal f2 is, for example, 432 MHz, the mixer will output a signal at (433-432) = 1 MHz as well as (433+432) = 865 MHz. Normally you would low-pass filter the output of the mixer, and maybe band-pass filter the input depending on the kind of transmitter. The 1 MHz signal would be easily visible on your oscilloscope.You'd get away with 125 MHz into the 100 MHz Rigol, but 433 MHz would be infeasible. Attenuation aside, you'll have some nasty aliasing to contend with.

author: EEVblog
author_rank: Unknown
timestamp: July 11, 2010, 09:51:21 am
content: Attn do a reasonable looking cheap model:http://cgi.ebay.com.au/ATTEN-AT5011-A-Spectrum-Analyzer-Tracking-Generator-1G-/390110997077?cmd=ViewItem&pt=AU_B_I_Electrical_Test_Equipment&hash=item5ad46d6a55A new spectrum analyser for under $1000 was previously unheard of!Dave.

author: joelby
author_rank: Frequent Contributor
timestamp: July 11, 2010, 09:55:19 am
content: The Atten does look pretty reasonable! You'd think they'd develop new products using LCDs instead of CRTs, unless they have a very big bin full of them they're trying to get rid of.As a comparison, the R&S RHS3 with tracking generator I have was something like $12000. It's a nice, portable unit though!

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 11, 2010, 06:12:22 pm
content: a frequency counter... seems alot cheaper. can it help in RF design?

author: slburris
author_rank: Frequent Contributor
timestamp: July 11, 2010, 11:31:23 pm
content: Build one:http://www.scottyspectrumanalyzer.com/Scott

author: Unknown
author_rank: Unknown
timestamp: July 11, 2010, 11:37:18 pm
content: 1GHz seems pretty limited for a 433MHz signal, if you want to measure distortion/spectral purity, I believe the standard is something like up to the fifth harmonic. But $1k (whether AUS or US) is a good deal for a spectrum analyzer, assuming it works well.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 12, 2010, 03:19:31 pm
content: fifth harmonic? is it 433MHz x 5 = 2GHz++ ? or 433MHz x 2^5 = 13GHz++ ?

author: jahonen
author_rank: Super Contributor
timestamp: July 12, 2010, 04:05:41 pm
content: Quote from: shafri on July 12, 2010, 03:19:31 pmI think it is ten harmonics (not sure though), so fundamental being 433 MHz, then the upper limit is 433 MHz * 10 = 4.33 GHz.Regards,Janne

author: chscholz
author_rank: Regular Contributor
timestamp: July 12, 2010, 04:52:42 pm
content: The rule of thumb is 5th harmonic (as in 433MHz x 5 = 2GHz++) for broadband data signals with NRZ modulation.Quote from: shafri on July 12, 2010, 03:19:31 pm

author: joelby
author_rank: Frequent Contributor
timestamp: July 13, 2010, 08:24:13 am
content: Quote from: shafri on July 11, 2010, 06:12:22 pmFor designing oscillators, sure. The difference between the two is conceptually similar to comparing a voltmeter to an oscilloscope. A voltmeter and a frequency counter aren't very useful if the signal is more complicated than a single voltage/frequency that doesn't change much in time.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 13, 2010, 02:24:50 pm
content: Quote from: joelby on July 13, 2010, 08:24:13 amas i have expected from the materials suggested here. spectrum analyzer is capable of showing all the frequency strength, but the counter only counts and show one single freq reading that might be strongest.the concept of (f1 - f2) and (f1 + f2), (2*f1 - f2) suggested by joelby and some circuitry and prescaler chip suggested by nihaomike are quite interesting, will need more study on this.... a sacrifice of time to save money...

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 13, 2010, 11:33:21 pm
content: Here's a mixer:http://www.analog.com/en/rfif-components/mixersmultipliers/adl5350/products/product.htmlHere's a PLL:http://www.analog.com/en/clock-and-timing/pll-synthesizersvcos/adf4350/products/product.htmlJust some suggestions for two of the key components.

author: ArtemisGoldfish
author_rank: Regular Contributor
timestamp: July 14, 2010, 12:52:48 am
content: Quote from: shafri on July 11, 2010, 06:12:22 pmI only found a frequency counter particularly useful for tuning a Local Oscillator, and only to tune the 8MHz reference oscillator, since if you need to measure a single frequency to a good degree of accuracy, a good frequency counter is indispensable. If you want to measure power output, definitely go for a power meter or spectrum analyzer. The spectrum analyzer is also definitely handy for being able to see how much spectrum a given signal occupies, if you really care about having a nice, clean signal that doesn't take up too much space in the frequency spectrum.

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 14, 2010, 01:36:50 am
content: A crystal oscillator module is likely accurate enough. (Most of them cannot be adjusted anyways.) Especially if it's temperature compensated.Of course, the sure way to check is to divide it down and compare it to something like a GPS receiver.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 14, 2010, 11:01:23 am
content: @nihaomike: thanx.@artemis: isnt the power output as simple as P=VI? isnt it just like, tuning the circuit using freq. counter until it shows the exact frequency we want, and then feed it with maximum acceptable voltage for maximum output?@nihaomike: actually i want to build something like the pictures below, the second is more preferable due to lower cost and simplicity in the design and application. what i found out, changing antenna length/type will make the transmitter ineffective, the receiver is not receiving anything even at the closest distance in the worst case (antenna length). so i'm wondering if different antenna length will make the freq off. and 2nd thing is that, i'm worried if that i put different capacitor and inductor size and off'ed spec a little bit.. pcb track length etc, will reduce the rf effectiveness or even shift the frequency.

author: joelby
author_rank: Frequent Contributor
timestamp: July 16, 2010, 04:07:42 am
content: Quote from: shafri on July 14, 2010, 11:01:23 amIn principle, yes, but what you've suggested doesn't make much sense. Normally wouldn't just amplify an RF output as much as you possibly can. Increasing the input voltage isn't a matter of turning up your power supply. More amplification may result in more distortion and unwanted harmonics, so you'd need a spectrum analyser to properly observe this.Quote from: shafri on July 14, 2010, 11:01:23 amThe antenna length's may be related to its design frequency. If you attach a 900 MHz antenna to a 2.4 GHz receiver, it will probably not be very effective, but it shouldn't affect the actual frequency response of the transmitter, unless it is presenting a different reactance to the antenna it was designed for. To investigate circuits like this you really want something like a vector network analyser to make sure that impedance matching is achieved between the antenna and the output, do many simulations, read the radio's data sheet and application notes, study advanced RF engineering, etc.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 16, 2010, 12:16:43 pm
content: yup i know. i'm still far off behind on this RF tech, more reading need to be done. the funny thing is the 433MHz antenna that comes with the TI's chip on the 1st picture, is somehow making the chip/circuit ineffective (better not to attach it to). but when i played around to install it in the 2nd pictured Chinese Designed RF, it improves the circuit transmission alot!vector network analyser? well..... thats the new thing

author: Zad
author_rank: Super Contributor
timestamp: July 16, 2010, 05:12:00 pm
content: I'm wondering if the antenna is faulty, possibly shorting somewhere. Usually even a piece of damp string is a better emitter than the raw board with no antenna!Some 'black box' radio transmitters are very crude, and basically connect the output of the oscillator to the antenna, so any incorrect impedance can result in the oscillator being loaded, and the frequency drifting off. Having said that, most designs have a separate oscillator and output amplifier and shouldn't drift with load. The matching receivers are usually quite wide band, and will tolerate inaccurate transmitters.If you want to match an antenna to a transmitter, the usual method is to use a voltage standing wave ratio (SWR) meter. This is basically a simple scalar network analyser which measures the transmitter power into the load, and the amount being reflected. You then adjust the antenna to minimise reflected power. 433MHz is right in the 70cm amateur radio band, so any equipment designed for that should work ok, but check the minimum power needed by the meter.http://en.wikipedia.org/wiki/SWR_meterIf you are interested in building a Vector Network Analyser, have a look at this guy's design:http://n2pk.com/There is also quite a busy forum for builders and users herehttp://groups.yahoo.com/group/N2PK-VNA/It only goes up to 60MHz, which is usually sufficient for characterising filters and matching networks. Above that frequency, and things start to get very expensive, very quickly!