RF Signal Generator w/ Sweep for ham radio projects

[HighVoltage]

Thanks, it does not have sweep function.

I'll keep an eye on Ebay maybe something good pops up.

Cio
Can you explain to us exactly what you what to do with this sweeping
What frequencies do you want to sweep and how fast ?

[cio74]

The main idea is to use the sweep generator to check filters response and have a visual diagram, one example here

another example with detector 


A spectrum analyser with tracking would probably be better but it's more expensive and not very useful as a stand alone RF signal generator?

In term of frequency, for instance I plan to build a HF transceiver with 2 IF stages, one at 8.2Mhz (because I have a 6KHz bandwidth crystal filter at that frequency from an old Yaesu transceiver) and the second at 455KHz.

[uncle_bob]

The main idea is to use the sweep generator to check filters response and have a visual diagram, one example here

another example with detector 


A spectrum analyser with tracking would probably be better but it's more expensive and not very useful as a stand alone RF signal generator?

Hi

Here's the problem with looking at a filter that way:

You do not have enough dynamic range to get a useful plot. With a network analyzer, you can fairly easily look at 120 db of range on a filter. Tracking generators on SA's will get you into the 80 db range with most of them. Without a proper detector, you will be lucky to get 20 db. It's simply not worth doing. The information you get is not good enough to be of use.

Bob

[Carrington]

A NWT500 maybe? Same 80dB problem, but at least relatively cheap.

[cio74]

Another very useful thing would  be to see frequency response of the band pass filters and image rejection filters. Another one check the mixer response by feeding a fixed frequency from a LO and use the sweep generator on the other entry then see the mixer output.

I have one oscilloscope that can display spectrum analyse, the OP here wants the same thing I want https://www.eevblog.com/forum/beginners/testing-a-low-pass-filter-with-a-spectrum-analyzer-with-no-tracking-generator/

[cio74]

...The information you get is not good enough to be of use.

Bob

You want me to break the bank and buy one of those VNA's, do you

[uncle_bob]

Another very useful thing would  be to see frequency response of the band pass filters and image rejection filters. Another one check the mixer response by feeding a fixed frequency from a LO and use the sweep generator on the other entry then see the mixer output.

I have one oscilloscope that can display spectrum analyse, the OP here wants the same thing I want https://www.eevblog.com/forum/beginners/testing-a-low-pass-filter-with-a-spectrum-analyzer-with-no-tracking-generator/

Hi

A good filter will have skirts or notches that are at least 60 db down. You simply can not "see" that far down with a sweeper and an oscilloscope. The "FFT" on your scope is not fast enough to follow the sweeper. The range of the linear display is not enough to show more than about 20 db without driving you a bit nuts.

Bob

[cio74]

Thanks for the explanation, if I read it right it seems that

1. I need a RF signal generator that is accurate enough at low signal levels for the usual signal injection into RF pre-amp and other places where a known frequency, modulation and amplitude is required.

2. I need a spectrum analyser with tracking generator to accurate see the frequency response of various filters.

I have a feeling the above are going to be an expensive purchase for a hobby.

[Nuno_pt]

For filters why not just buy one MiniVNA Tiny or Pro or one DG8SAQ, or N2PK, or one from Array Solutions.

[uncle_bob]

Thanks for the explanation, if I read it right it seems that

1. I need a RF signal generator that is accurate enough at low signal levels for the usual signal injection into RF pre-amp and other places where a known frequency, modulation and amplitude is required.

2. I need a spectrum analyser with tracking generator to accurate see the frequency response of various filters.

I have a feeling the above are going to be an expensive purchase for a hobby.

Hi

Yes, a signal generator is mainly used for creating accurate level signals at a fixed frequency with or without modulation.

A spectrum analyzer (by it's self) is used for checking harmonics and spurs (and modulation) out of things like transmitters.

A network analyzer is the proper tool for checking filters and circuit passbands.

A spectrum analyzer plus a tracking generator is a low(er) cost / low(er) performance substitute for a network analyzer.

Back a long time ago (I was in school ...) people rigged up systems with sweep generators and log converters driving CRT displays. Effectively what they did was build a simple scalar network analyzer out of a bunch of different pieces of test gear. That all became a lot less popular in the 1970's when vector network analyzers began to come into the mainstream. 

Bob

[sanman]

What about one of these from mRS:

http://miniradiosolutions.com/54-2/

[uncle_bob]

What about one of these from mRS:

http://miniradiosolutions.com/54-2/

Hi

That takes care of the filter stuff. It does not give you the accurate levels or the modulated signals for checking a receiver.

Bob

[cio74]

I have been looking long time before at those miniVNA usb based tools for filters. Admittedly, did not know about the other listed by Nuno.

I am currently installing the software and see if I can get an idea of how to operate it, how easy is the UI without actually having a device.

[Nuno_pt]

The MiniVNA Tiny will be my next buy after the Signal Generator.

[cio74]

FedEx came first thing in the morning with a very big package that I was not expected.

[cio74]

Found the Anritsu we've been talking at the beginning of the thread. It came from Finland over the weekend, I have not even paid for it but they have sent it anyway.

[cio74]

Nice warning label

[cio74]

According to the label is had been tested in 2003, would that be the manufacture year? It seems to have some add-on, the W-CDMA transceiver performance test, whatever that is

[cio74]

And finally the other connectors at the back, may be useful to synchronise with an oscilloscope



I am a little concerned about some previous post made by bob I think who has said they may have been used to sweep the output level and the mechanical attenuator may have been worn out.

Could someone please suggest a good test procedure to make sure everything is  fine, I have an oscilloscope that I can use.

Thanks.

[msraya]

Very nice equipment, Indeed...

For test FM and SSB ham radio receivers for SINAD, for example...
For drive mixer to make experiments..
To make sweeps..

The external modulation input is on the front panel.. nice touch...
You would need it calibrated.. but if you not paid for a calibrated generator and only use it for repair ham radio gear, that is not as important...

I buy one refurbished Stabilock 4032 calibrated, They send me all paper with all measures on different levels and frequencies that are stated in service manual and They test if these measures are into the allowed tolerance level. Happily my equipment pass all the test and they send it to me along with the report...

I can use these references in the report to calibrate (with some tolerances, of course) other of my test gear that I buy second hand and uncalibrated.. This is nice, that I can rely on some test gear in my bench... 

If you have a good friend with calibrated gear, you can send the 18Kg gear to him and take a report of calibrated measures.. or You can send it, at your cost, to a calibration service to get this information.

Manuel

[uncle_bob]

And finally the other connectors at the back, may be useful to synchronise with an oscilloscope



I am a little concerned about some previous post made by bob I think who has said they may have been used to sweep the output level and the mechanical attenuator may have been worn out.

Could someone please suggest a good test procedure to make sure everything is  fine, I have an oscilloscope that I can use.

Thanks.

Hi

The normal "quick test" is to run the generator into a good spectrum analyzer and make sure the level on the SA agrees with the level on the generator. What you find is a relay that does not close (or open ) on say, the section that takes you from -100 dbm to -120 dbm. You step down the output 3 db on the generator and it  miss tracks on the SA (-120 is -100 or -150). Exactly where the breakpoints are for this or that generator and how many there are is very much a "that depends" sort of thing.

If you don't have an SA, a calibrated receiver can do the job. A scope will let you look at the first section or two of the coarse attenuator.

Bob

[cio74]

Thanks Bob, I have done some tests early in the afternoon, it has many relays inside. Each stage has some control with no relay involved but that's small range.

I don't have a good SA, just some oscilloscope with FFT.

I will do more tests tomorrow, I am very pleased after the initial test, everything seems to work just fine, have connected a small wire at the RF output and received modulated AM/FM signal using a ham radio receiver located few yards away.

Have also managed to activate the reverse voltage protection by using low frequency and mismatched output connector.

I can't fault it, it may need to be calibrated and I still have to fully check the attenuator relays.

I may buy another one, to check mixers I'll need two sources

[uncle_bob]

Thanks Bob, I have done some tests early in the afternoon, it has many relays inside. Each stage has some control with no relay involved but that's small range.

I don't have a good SA, just some oscilloscope with FFT.

I will do more tests tomorrow, I am very pleased after the initial test, everything seems to work just fine, have connected a small wire at the RF output and received modulated AM/FM signal using a ham radio receiver located few yards away.

Have also managed to activate the reverse voltage protection by using low frequency and mismatched output connector.

I can't fault it, it may need to be calibrated and I still have to fully check the attenuator relays.

I may buy another one, to check mixers I'll need two sources

Hi

Ok, so how about:

Drive one side of a mixer with a handy 10 MHz OCXO.

Set the generator to 10.01 MHz and drive the other side.

Feed the mixer output into a sound card and watch the level change at 10 KHz.

Bob

[cio74]

Thanks Bob, I have done some tests early in the afternoon, it has many relays inside. Each stage has some control with no relay involved but that's small range.

I don't have a good SA, just some oscilloscope with FFT.

I will do more tests tomorrow, I am very pleased after the initial test, everything seems to work just fine, have connected a small wire at the RF output and received modulated AM/FM signal using a ham radio receiver located few yards away.

Have also managed to activate the reverse voltage protection by using low frequency and mismatched output connector.

I can't fault it, it may need to be calibrated and I still have to fully check the attenuator relays.

I may buy another one, to check mixers I'll need two sources

Hi

Ok, so how about:

Drive one side of a mixer with a handy 10 MHz OCXO.

Set the generator to 10.01 MHz and drive the other side.

Feed the mixer output into a sound card and watch the level change at 10 KHz.

Bob

That could help but the product of mixing is more than just |F1-F2| in the mixer's output. Two RF signal generators and a SA will do a better job.

Speaking of a secondary generator, how good are these new digital generators such as Siglent SDG2042X or Rigol. They do not feature the a very low level output nor their chassis is built with RF shielding in mind so it would be safe to assume they are not suitable for the RF tasks I have explained earlier?

[uncle_bob]

Thanks Bob, I have done some tests early in the afternoon, it has many relays inside. Each stage has some control with no relay involved but that's small range.

I don't have a good SA, just some oscilloscope with FFT.

I will do more tests tomorrow, I am very pleased after the initial test, everything seems to work just fine, have connected a small wire at the RF output and received modulated AM/FM signal using a ham radio receiver located few yards away.

Have also managed to activate the reverse voltage protection by using low frequency and mismatched output connector.

I can't fault it, it may need to be calibrated and I still have to fully check the attenuator relays.

I may buy another one, to check mixers I'll need two sources

Hi

Ok, so how about:

Drive one side of a mixer with a handy 10 MHz OCXO.

Set the generator to 10.01 MHz and drive the other side.

Feed the mixer output into a sound card and watch the level change at 10 KHz.

Bob

That could help but the product of mixing is more than just |F1-F2| in the mixer's output. Two RF signal generators and a SA will do a better job.

Speaking of a secondary generator, how good are these new digital generators such as Siglent SDG2042X or Rigol. They do not feature the a very low level output nor their chassis is built with RF shielding in mind so it would be safe to assume they are not suitable for the RF tasks I have explained earlier?

Hi

The output of the mixer would be:

10 KHz from F1 - F2

10 MHz from feedthrough (at least 30 db below the OCXO output)
10.01 MHz from feedthrough (more than 30 db lower than 10 KHz)

20.01 MHz from F1 + F2 (same level as 10 KHz)

The sound card should have input filtering that takes out anything above 40 KHz. That filtering will be pretty effective at >= 10 MHz. If not, put in a simple lowpass filter.

====

The light weight / low cost generators are a great upgrade from a function generator. There are a lot of things they will let you do. One example is driving the mixer in the above setup. They are indeed pretty much useless for receiver sensitivity testing or stuff like IP3.

Bob