Author Topic: Inexpensive RF Signal Generator?  (Read 3753 times)

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Offline jgalak

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Inexpensive RF Signal Generator?
« on: December 12, 2017, 08:30:28 pm »
Are there any inexpensive rf signal generators out there that can reach into the 440MHz range?  New or old, doesn't matter.  At least sine and square waves, but AM/FM modulation would be a big plus.  USB is fine, old analog units are fine if they are available, aren't enormous, and won't require tons of work to maintain.  Looking at Rigol/Siglent, the 500MHz AWGs are too much money right now.

Basically something to test UHF filters and maybe recievers with, in the absence of a SpecAn with a tracking generator.

If the answer is "no, you need to spend money", that's not unreasonable :)
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Offline taydin

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Re: Inexpensive RF Signal Generator?
« Reply #1 on: December 12, 2017, 08:46:07 pm »
Are there any inexpensive rf signal generators out there that can reach into the 440MHz range?  New or old, doesn't matter.  At least sine and square waves, but AM/FM modulation would be a big plus.  USB is fine, old analog units are fine if they are available, aren't enormous, and won't require tons of work to maintain.  Looking at Rigol/Siglent, the 500MHz AWGs are too much money right now.

Basically something to test UHF filters and maybe recievers with, in the absence of a SpecAn with a tracking generator.

If the answer is "no, you need to spend money", that's not unreasonable :)

Here is a project that I recently ran into:

https://www.crowdsupply.com/era-instruments/erasynth

ERASynth: 10 MHz to 6 GHz
ERASynth+: 250 kHz to 15 GHz

Notice how well it compares to a $18,000 Keysight unit.

Already 210% percent funded, and I ordered mine too :)
Real programmers use machine code!

My hobby projects http://mekatronik.org/forum
 
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Offline taydin

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Re: Inexpensive RF Signal Generator?
« Reply #2 on: December 12, 2017, 08:49:28 pm »
This unit does basic AM/FM modulation. I was researching this type of equipment because I wanted to be able to generate a WIFI reference signal for testing purposes. Unfortunately, this unit doesn't do such complex modulation, so I am currently researching an SDR that will do the job.
Real programmers use machine code!

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Offline Tony_G

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Re: Inexpensive RF Signal Generator?
« Reply #3 on: December 13, 2017, 07:24:21 am »
You might want to look at a HP 8657B as they can be bought on Ebay US for around $300 at times.
 
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Online bd139

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Re: Inexpensive RF Signal Generator?
« Reply #4 on: December 13, 2017, 08:19:01 am »
Depends how much of 440MHz you need and how cheap you want to go and how stable you want it to be. My father used a Heathkit RF-1 for this stuff and built a slightly de-Q'ed tuned UHF amp to tune the harmonics. He believed you could solve any problem for under £20. Crap solution but it worked.

Power measurement at 440MHz is more of a problem I would suspect.
 

Offline tggzzz

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Re: Inexpensive RF Signal Generator?
« Reply #5 on: December 13, 2017, 09:02:56 am »
He believed you could solve any problem for under £20.

Excellent engineering attitude. And if you can show that it can't work, then you are in a good position to know exactly what you really do need.

Quote
Power measurement at 440MHz is more of a problem I would suspect.

That's like using a voltmeter to measure a bench power supply. It is trivial to get a reading of 10.00V. If you have two meters, then to get them to both show 10.00V only needs a screwdriver. If you want to get someone else's meter to agree about the 10.00V reading, then get out your wallet.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline chrisl

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Re: Inexpensive RF Signal Generator?
« Reply #6 on: December 13, 2017, 09:12:51 am »
...... At least sine and square waves, but AM/FM modulation would be a big plus. .......
The square wave requirement will cost you. Otherwise an old HP sig gen can be had for at a fairly low price.
 

Offline jgalak

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Re: Inexpensive RF Signal Generator?
« Reply #7 on: December 13, 2017, 10:10:26 am »
...... At least sine and square waves, but AM/FM modulation would be a big plus. .......
The square wave requirement will cost you. Otherwise an old HP sig gen can be had for at a fairly low price.

I may be ok without square.  Are there specific model numbers I should look for?
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Offline CJay

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Re: Inexpensive RF Signal Generator?
« Reply #8 on: December 13, 2017, 10:32:15 am »
Specifications are everything, It's entirely possible to assemble a workable homebrew signal generator for ~£50 these days, it won't compete well with a HP, Aeroflex, Tek, R&S etc.etc. on the more 'finessed' specs but it will work and it will get you going, it may also be a useful learning experience.

It's possible to AM a simple sig gen, FM is a little more difficult but can be done, measuring output power is pretty simple, programmable attenuators that were intended for WiFi and Cell use are cheap and available as are wideband amplifiers, there are also I/Q modulators out there which can enable you to produce pretty much any modulation scheme you choose, it's potentially a great fun project if you know a little Arduino coding and can dedicate the time to it.

You might also want to consider that a Specan with a tracking generator can often be pressed into service as a sig gen so a Rigol 815TG or the Siglent 3021 (IIRC) might do all you need.

The 'communications testers' like the R&S CMU200 come with a  sig gen built in as well as offering a decent enough spectrum analyser and other facilities that sound like they could be useful to you if you're intending to work with UHF gear in the ham bands, I have two CMU200s and paid less than £500 for the pair (possibly close to £400, I'd have to check the invoice)

There's always a decent supply of second hand sig gens for sale on eBay as well, you can occasionally get a bargain or you can buy a turkey (I paid just shy of £400 for a *very* nice sig gen that's faulty and parts are essentially unobtainable, took a chance and lost, a project that's 'on the list')

 

Offline tggzzz

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Re: Inexpensive RF Signal Generator?
« Reply #9 on: December 13, 2017, 10:43:01 am »
Are there any inexpensive rf signal generators out there that can reach into the 440MHz range?
...
Basically something to test UHF filters and maybe recievers with, in the absence of a SpecAn with a tracking generator.

If you want to skin that cat cheaply and with limitations, consider https://entertaininghacks.wordpress.com/2015/08/10/measuring-rf-filters-with-a-homebrew-1-5ghz-scalar-network-analyser-costing-3248/
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
 

Offline jgalak

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Re: Inexpensive RF Signal Generator?
« Reply #10 on: December 13, 2017, 10:52:54 am »
This got me thinking - can an antenna analyzer be used as an RF source?  I have a Rigexpert AA-600, which can go to 600 MHz, can that be used somehow?
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Offline VK5RC

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Re: Inexpensive RF Signal Generator?
« Reply #11 on: December 13, 2017, 11:04:26 am »
An antenna analyser makes a not a bad RF source, might not be really stable, constant level and have a few harmonics but at 440MHz band pass filters are easily made -check out the amateur radio sources eg ARRL.
Whoah! Watch where that landed we might need it later.
 

Offline danadak

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Re: Inexpensive RF Signal Generator?
« Reply #12 on: December 13, 2017, 11:09:27 am »
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 
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Offline Teledog

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Re: Inexpensive RF Signal Generator?
« Reply #13 on: December 13, 2017, 03:33:08 pm »
Low buck?
Use a VCO (ie: Z-Comm).
Might have to wait a bit for the right one to show up on fleabay, but sometimes you can buy an entire lot for a few bucks.
FM modulation via a cap on the tuning voltage.
They typically have bit of phase noise.  (a plus for filter testing??)
and..cheap like borscht!
« Last Edit: December 13, 2017, 03:36:28 pm by Teledog »
 

Offline CJay

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Re: Inexpensive RF Signal Generator?
« Reply #14 on: December 13, 2017, 04:56:45 pm »
Low buck?
Use a VCO (ie: Z-Comm).
Might have to wait a bit for the right one to show up on fleabay, but sometimes you can buy an entire lot for a few bucks.
FM modulation via a cap on the tuning voltage.
They typically have bit of phase noise.  (a plus for filter testing??)
and..cheap like borscht!

I've got a bag of assorted VCOs up to a couple of GHz from a seller in the UK, think it might have been ECL80, I used them to test a frequency counter before I had a decent sig gen, keep meaning to do something more with them.
 

Offline David Hess

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Re: Inexpensive RF Signal Generator?
« Reply #15 on: December 13, 2017, 11:16:55 pm »
I usually end up using an all mode transceiver of the appropriate RF frequency range with a function generator as an external modulation source and stepped RF attenuator.
 

Offline jgalak

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Re: Inexpensive RF Signal Generator?
« Reply #16 on: December 14, 2017, 12:02:11 am »
That could work.  My main radio is a Flex 6500, it should be possible to have some sort of software audio source stream data into the virtual sound card it uses. 

I was actually just thinking that maybe a LimeSDR could work well for this, it's apparently been done.
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Offline David Hess

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Re: Inexpensive RF Signal Generator?
« Reply #17 on: December 14, 2017, 01:18:15 am »
The usual limit when using all mode transmitter as a low level source is leakage around any attenuators and through patch cables even when the lowest output power is used.  It may be necessary to place the transmitter inside a shielded enclosure with a fixed attenuator and then use double shielded cable outside of the enclosure.
 


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