Budget RF audio generator options for tuning radio receivers

[RiRaRi]

Hi. I am looking for cheap RF audio gen for tuning radios. I would like the ability to produce both AM and FM frequency. Any reccomendation is welcome.

[bdunham7]

What's the budget? 

[tautech]

Exactly what are you trying discover when this info has already been posted in other threads you have started.

https://www.eevblog.com/forum/testgear/budget-signal-generator-for-aligning-am-and-fm-radio-and-what-else-do-i-need/
https://www.eevblog.com/forum/beginners/is-scope-and-freq-generator-needed-for-repair-vtg-solid-state-audio-gear/

[RiRaRi]

I apologize for double thread. I am looking for one device that can do both FM and AM frequencys. Something like this on aliexpress but as i can see it does not reach lower freq.
And for budget: the cheaper the better but also decent quality device.
TinySA is good option. Are there some others?

[xrunner]

I'm not up to date on the budget offerings out there ( I use older hp equipment for this purpose), but I can tell you I think you need to use better terminology.

I apologize for double thread. I am looking for one device that can do both FM and AM frequencys.

You probably mean FM and AM modulation. Perhaps the unit will be able to generate internal modulation frequencies or accept an external modulation frequency. The correct way to say this is -

"I am looking for one device that can do both FM and AM modulation"

[RiRaRi]

Yes, that is correct. I am from non-english part of the world. Also, i am talking about aligning a radio. Probably tuning isnt the right word for this procedure.

[Aldo22]

TinySA is good option. Are there some others?

TinySA can do this, if the "stairs" in the audio signal do not bother you (It sounds "normal", not heavily distorted).
In the attachment you can see the TinySA, which transmits a frequency modulated signal of 600Hz on 107.50 MHz.
Below is a small FM radio, which is set to 107.50 MHz and receives via antenna.
The headphone output goes to the DSO2512G which shows the demodulated audio signal.

The AM and FM modulation is done using an 8 point approximation of a sine wave. This limited approximation does contain harmonics and has some steep level steps as can be seen in this measurement of the AM modulation.

https://tinysa.org/wiki/pmwiki.php?n=Main.MODULATION

[BrokenYugo]

If you want to work with limited gear you need to understand the typical superhet alignment processes so you can decide if you can make it work with whatever you're looking at. Like you might consider if you actually need something that will do 100+MHz in the first place. AFAIK with a typical FM radio only dial alignment (getting the LO to track the dial) needs a signal higher than the IF (usually 10.7), which you can do with known local stations instead.

IIRC you really need an oscilloscope too for hifi FM stereo type stuff, any old analog scope will do for that though.

[RiRaRi]

Thanks. Problem is that i dont have any AM signal (stations) here but want to be able to test and align AM radios. FM radios, too. Which device would you reccomend for aligning that dos not make these stairs like tinySA? Something better for this job.

[colorado.rob]

Thanks. Problem is that i dont have any AM signal (stations) here but want to be able to test and align AM radios. FM radios, too. Which device would you reccomend for aligning that dos not make these stairs like tinySA? Something better for this job.

How much are you willing to spend?

[RiRaRi]

At least as possible. But amount that is neccesary. I have the budget but just want to get cheap but okay option.

[geggi1]

If you want to build there are plenty of options.
For AM at low frequencies you can build a small amplifier from a PN2222 or similar low power transistor or an intigrated circuit.
Eksamples can be found here. https://sound-au.com/articles/am-modulation.htm
Then you can make the carrier by using a DDS module like the AD9850 or AD9851 and an arduino.
Build plans, schematics and INO files can be found on the internet.

If you need to run AM in the air band the DDS frequency can be multiplied a few times.
For the 9850 a 5 time multipllier will get you in the air band. http://techlib.com/electronics/2diomult.html

For FM generation you can find soem eksamples here: http://electronbunker.ca/eb/DDS_Controller1.html
You will probably have to use a multiplier to get to the FM broadcast band or VHF two-way bands.

Finaly you will need some kind of attenuator to bring the levels down to something that can be inserted in to the antenna of a radio.
You will probably need somet in gin the range of 120dB attenuation in total split on a few attenuators.
I would suggest 50dB, 40dB, 30dB, 10dB that would give you the posibility of 130dB in steps of 10dB.
Build the attenuators with SMD components (0,25W type)  and match the traces to 50 or 70 ohm depending on system impedanse.
Use connectors beteen the input and outputs of the attenuators with male and female on oposite ends to simplify connecting the units.
The attenuators should have some kind of shielding to prevent RF leakage.

[colorado.rob]

At least as possible. But amount that is neccesary. I have the budget but just want to get cheap but okay option.

A Siglent SDG2000X arbitrary waveform generator will do what you want. It's a decent lab instrument that has the ability to do AM and FM modulation from the low end of the AM broadcast band to the upper end of the broadcast FM band. You can buy the 40MHz version and hack it to 120MHz.

[RiRaRi]

Thank you. It is expensive but it is good tool. As i was thinking to get cheaper scope with built-in sig gen i was thinking that this could be cheaper. Around 50-100 €/$. This does not work?

[xrunner]

Thank you. It is expensive but it is good tool. As i was thinking to get cheaper scope with built-in sig gen i was thinking that this could be cheaper. Around 50-100 €/$. This does not work?

The specs for this unit are shown below. It is for FM transceiver testing (or it could put out unmodulated RF (CW) ) . This is stated even more clearly in other product descriptions for it. So it doesn't do AM modulation. It also only has 800 Hz modulation for FM, and doesn't state the deviation the FM output is set to. You said earlier you wanted AM modulation too. So you tell us - is that what you really want? 


Features:
Suitable for FM walkie-talkie debugging.
Built-in 800Hz audio modulation, with the analog digital CTCSS function.
The unit is DBM. General hand sensitivity is -120DBM to -130DBM.
The greater the sensitivity to a negative number, the higher the sensitivity.
The signal source cannot input power.
It is absolutely forbidden to press the intercom button to transmit when testing. (self-matching power supply 8V-12V power supply polarity is positive and negative)

Specifications:
Material: ABS
Color: blue
Frequency: 0.5MHz-470MHz
Signal strength: -70-132dBm
Built-in 800Hz audio modulation
Add the analog digital CTCSS function
Use 8-12V DC power supply, frequency 7 digits
For example: 439.6000MHz shows 4396000KHz
Signal strength -70-132dBm valid, other values are invalid.
Audio modulation is only about 800Hz, other values are invalid.
Item size: 155 * 120 * 63mm / 6.1 * 4.7 * 2.5in
Item weight: 271g / 9.6ounce
Package size: 210 * 160 * 70mm / 8.3 * 6.3 * 2.8in
Package weight: 303g / 10.7ounce

[colorado.rob]

You need a signal generator that can go from 500kHz to 110MHz to cover AM and FM broadcast bands. This is required for testing and adjusting AM and FM receivers. And you need a signal generator that can do CW, AM and FM modulation. The SDG2000X is the least expensive piece of test equipment I know of that can do the frequency range and modulation types you need, unless you start looking at used test equipment.

You can do it with an inexpensive FY6900 signal generator for the AM band. And a HackRF with the Portapack can cover FM. But I think once you purchase both items, it will cost the same as the 40MHz SDG2000X.

Deals can be found on used RF equipment. If you can pick up an older HP, Marconi, Rohde & Schwarz, etc RF signal generator that meets your needs, you'd have a much better tool for the work you are doing. There are a number of inexpensive (~$200) Wavetek RF signal generators available on Ebay in the US right now that would meet your needs. (I know that this does not help you, outside the US. It's just an example.)

[Aldo22]

i was thinking that this could be cheaper. Around 50-100 €/$. This does not work?

There are also cheap little transmitters on Aliexpress.
No idea if these could be useful for you:

https://www.aliexpress.com/item/1005005593130961.html
https://www.aliexpress.com/item/1005004907484326.html
https://www.aliexpress.com/item/1005005334451938.html


Just randomly picked.

[RiRaRi]

Acctualy, compared to 700EUR+ Siglent these cheap Aliexpress items seams great 

I think the best solution would be tinySA for FM modulation.
For AM modulation to use tinySA as spectrum analyzer to check the precise frequency when transmitting with shown aliexpress item. Would you agree?

[Aldo22]

Acctualy, compared to 700EUR+ Siglent these cheap Aliexpress items seams great 

I think the best solution would be tinySA for FM modulation.
For AM modulation to use tinySA as spectrum analyzer to check the precise frequency when transmitting with shown aliexpress item. Would you agree?

Why not?

But the TinySA can also do AM, just like FM with stairs in the audio signal.
In the attachment 2kHz on 10MHz directly into the DSO2512G.
Below 8MHz carrier.

[RiRaRi]

Nice. So what is disadvantage of these "stairs"? If i can see freq on scope and if i can hear the sound on my receiver on the same freq i cant see any disadvantage in terms of aligning the radio, or am i wrong?

[colorado.rob]

Nice. So what is disadvantage of these "stairs"? If i can see freq on scope and if i can hear the sound on my receiver on the same freq i cant see any disadvantage in terms of aligning the radio, or am i wrong?

They add harmonic distortion to the signal, making it impossible to do accurate SINAD measurements.

Do you need to accurately control the RF output level?

[RiRaRi]

I dont think i need. I need it for testing receivers and also after servicing receiver to check or align the radio. So transmit the sound on needed freq and then moving the screws on receiver to align it properly. Can you do that with tinySA?

[tautech]

Acctualy, compared to 700EUR+ Siglent these cheap Aliexpress items seams great 

The model you have been recommended in this and previous threads is €475.
https://www.siglenteu.com/waveform-generators/sdg2000x-series-functionarbitrary-waveform-generators/

[Aldo22]

The model you have been recommended in this and previous threads is €475.
https://www.siglenteu.com/waveform-generators/sdg2000x-series-functionarbitrary-waveform-generators/

That is probably the price without VAT.
RiRaRi is from Croatia. The shop there charges 575,94 € for the SDG 2042X.
Apparently RiRaRi does not want to spend so much.

[RiRaRi]

I mean if i need to i will, but i think tinySA is enough for my job. Dont you think?