Budget RF audio generator options for tuning radio receivers - Page 1
Forum section: electronics / testgear

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 17, 2023, 10:58:54 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: September 17, 2023, 11:45:12 pm
content: What's the budget?

author: tautech
author_rank: Super Contributor
timestamp: September 17, 2023, 11:46:34 pm
content: 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/

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 18, 2023, 12:06:45 am
content: 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?

author: xrunner
author_rank: Super Contributor
timestamp: September 18, 2023, 12:19:14 am
content: 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.Quote from: RiRaRi on September 18, 2023, 12:06:45 amYou probably mean FM and AMmodulation. 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"

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 18, 2023, 12:57:54 am
content: 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.

author: Aldo22
author_rank: Super Contributor
timestamp: September 18, 2023, 09:09:01 am
content: Quote from: RiRaRi on September 18, 2023, 12:06:45 amTinySA 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.Quote from: tinysa.orghttps://tinysa.org/wiki/pmwiki.php?n=Main.MODULATION

author: BrokenYugo
author_rank: Super Contributor
timestamp: September 18, 2023, 12:41:37 pm
content: 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.

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 18, 2023, 05:11:14 pm
content: Thanks. Problem is that i dont have any AM signal (stations) here but want to be able totestandalignAM radios. FM radios, too. Which device would you reccomend for aligning that dos not make these stairs like tinySA? Something better for this job.

author: colorado.rob
author_rank: Frequent Contributor
timestamp: September 18, 2023, 06:58:31 pm
content: Quote from: RiRaRi on September 18, 2023, 05:11:14 pmHow much are you willing to spend?

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 18, 2023, 08:36:30 pm
content: At least as possible. But amount that is neccesary. I have the budget but just want to get cheap but okay option.

author: geggi1
author_rank: Frequent Contributor
timestamp: September 18, 2023, 09:16:06 pm
content: 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.htmThen 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.htmlFor FM generation you can find soem eksamples here:http://electronbunker.ca/eb/DDS_Controller1.htmlYou 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.

author: colorado.rob
author_rank: Frequent Contributor
timestamp: September 18, 2023, 09:38:21 pm
content: Quote from: RiRaRi on September 18, 2023, 08:36:30 pmA 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.

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 18, 2023, 10:21:05 pm
content: 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?

author: xrunner
author_rank: Super Contributor
timestamp: September 18, 2023, 10:40:37 pm
content: Quote from: RiRaRi on September 18, 2023, 10:21:05 pmThe 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: ABSColor: blueFrequency: 0.5MHz-470MHzSignal strength: -70-132dBmBuilt-in 800Hz audio modulationAdd the analog digital CTCSS functionUse 8-12V DC power supply, frequency 7 digitsFor example: 439.6000MHz shows 4396000KHzSignal 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 * 2.5inItem weight: 271g / 9.6ouncePackage size: 210 * 160 * 70mm / 8.3 * 6.3 * 2.8inPackage weight: 303g / 10.7ounce

author: colorado.rob
author_rank: Frequent Contributor
timestamp: September 19, 2023, 03:19:03 am
content: 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.)

author: Aldo22
author_rank: Super Contributor
timestamp: September 19, 2023, 08:29:07 am
content: Quote from: RiRaRi on September 18, 2023, 10:21:05 pmThere are also cheap little transmitters on Aliexpress.No idea if these could be useful for you:https://www.aliexpress.com/item/1005005593130961.htmlhttps://www.aliexpress.com/item/1005004907484326.htmlhttps://www.aliexpress.com/item/1005005334451938.htmlJust randomly picked.

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 19, 2023, 01:52:57 pm
content: Acctualy, compared to 700EUR+ Siglent these cheap Aliexpress items seams greatI 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?

author: Aldo22
author_rank: Super Contributor
timestamp: September 19, 2023, 03:05:54 pm
content: Quote from: RiRaRi on September 19, 2023, 01:52:57 pmWhy 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.

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 19, 2023, 04:00:01 pm
content: 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?

author: colorado.rob
author_rank: Frequent Contributor
timestamp: September 19, 2023, 04:26:19 pm
content: Quote from: RiRaRi on September 19, 2023, 04:00:01 pmThey add harmonic distortion to the signal, making it impossible to do accurate SINAD measurements.Do you need to accurately control the RF output level?

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 19, 2023, 05:51:54 pm
content: 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?

author: tautech
author_rank: Super Contributor
timestamp: September 19, 2023, 08:06:23 pm
content: Quote from: RiRaRi on September 19, 2023, 01:52:57 pmThe model you have been recommended in this and previous threads is €475.https://www.siglenteu.com/waveform-generators/sdg2000x-series-functionarbitrary-waveform-generators/

author: Aldo22
author_rank: Super Contributor
timestamp: September 19, 2023, 08:31:50 pm
content: Quote from: tautech on September 19, 2023, 08:06:23 pmThat is probably the price without VAT.RiRaRi is from Croatia. The shop there charges575,94 € for the SDG 2042X.Apparently RiRaRi does not want to spend so much.

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 19, 2023, 10:23:52 pm
content: I mean if i need to i will, but i think tinySA is enough for my job. Dont you think?

author: Aldo22
author_rank: Super Contributor
timestamp: September 20, 2023, 08:10:09 am
content: Quote from: RiRaRi on September 19, 2023, 10:23:52 pmI can't answer that for you because I have no experience with what you are doing and because I don't know what is "good enough" for your purpose.I can only repeat the specificationsLow output mode spec:* Sinusoidal output with harmonics below -40dB of fundamental.* Output frequency range from 100kHz to 350MHz* Output level selectable in 1dB steps between -76dBm and -7dBm* Optional AM, narrow FM and wide FM modulation or slow sweep over selectable frequency span* Modulation frequency: 50Hz to 8kHz (Rem.: Amplitude can not be changed).If you want to buy a TinySA, make sure you get an original one.I got mine fromthis storeand it is original.

author: TurboTom
author_rank: Super Contributor
timestamp: September 20, 2023, 08:44:11 am
content: If you would like a full-featured AWG and 100MHz max output frequency is enough (still covers a major portion of the FM band), and you don't want to pay for an SDG2000X series instrument, you may consider Rigol's DG811 and hack it to (almost) DG992 level. That's currently probably the AWG with the best bang-for-buck ratio in its hacked condition. Don't under-estimate the advantages of a full-featured AWG: The U/I is much more comfortable than the one of the TinySA since it's specifically configured for generating waveforms. Moreover, you've got plenty of modulation options with all kinds of adjustable parameters. There are external input(s) to the modulators, so you could also use an external audio signal to modulate the AWG. And, not to forget, the output level control is more accurate and covers a wider range. With in-line BNC attenuators you can even get into the RF signal generator level range...Initially, I was joking about the DG800/900 series's funny enclosure (and I'm still...), but reagrdless of its ridiculous appearance, the case is quite rigid (not to compare with other "plasticky" bottom-of-the-barrel AWGs) and its perfomance features put it right in the place of a "serious" entry-level AWG with (IMO) a well thought-out U/I.

author: colorado.rob
author_rank: Frequent Contributor
timestamp: September 20, 2023, 03:12:07 pm
content: How much tuning do modern AM and FM receivers really require these days?

author: RiRaRi
author_rank: Regular Contributor
timestamp: September 21, 2023, 11:17:02 pm
content: Not new one. 70s, 80s receivers. Even tube ones