Tuning of Superheterodyne Radios - Signal Generator w/Modulation? - Page 1
Forum section: electronics / beginners

author: Wil_Bloodworth
author_rank: Regular Contributor
timestamp: November 06, 2023, 06:45:46 pm
content: There seems to be several terms used for, what appears to me to be the same thing, waveform generation. There is Signal Generator, Frequency Generator, Arbitrary Waveform Generator, and maybe there are others.I'm trying to purchase a tool that will allow me to align antique AM radios (i.e. adjust the IF transformers). From what I understand, I need to generate a signal at 455 KHz in order to get started. In addition, I've heard that I need (?) to modulate the signal with something like a 1 KHz tone so I can hear that tone when it comes through the output transformer and eventually the speaker.I have an oscilloscope that has an arbitrary waveform generator built in. It goes up to 25 Mhz but it does not do modulation.Here is my oscilloscope (OWON HDS2202S):https://www.owon.com.hk/products_owon_hds200_series_digital_oscilloscopeI was looking at buying a signal generator that has modulation (and I'm not opposed to this option) but the prices range widely and I'm not sure what options are "reasonable" around $400. Ideally, I don't want to buy something that is 50 years old either.Any and all suggestions are welcome. Thanks in advance!Thank you,- Wil

author: Xena E
author_rank: Frequent Contributor
timestamp: November 06, 2023, 08:06:29 pm
content: Hi willNo need to spend a fortune.I see you're in the US, so I'd suggest joining the antique radio forum there, (ARF), if you haven't already, and ask advice, you may also find somone who has what you need for sale.An AF modulated RF generator is indeed what you need.They will also be able to advise on alignment of specific sets.Good luck!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 06, 2023, 10:27:03 pm
content: I know you said you did not wish to buy something 50 yrs old, but they made signal generators specific for what you are trying to do. There were sig gen with 455 KHz dedicated output as well as their adjustable output and internal 1 KHz modulation. RCA, Heathkit and EICO come to mind.There are all sorts of more modern versions of these mini test units.that are semi conductor based also that are newer.Prices on ebay etc are getting unreasonable.IMHO. You could get a nice unit for less than $100, I think. We have one at the radio shop that works and would go for maybe $50.The advice to seek an antique radio group is really good. They will have meets for selling things like you want. The fleamarkets at Ham meets and antique radio meets sometimes look surprisingly alike.Another thing to do is to go to an Hamfest and see what shows up. Since your scope is small, you could bring it and power the signal generator and see what the generator does before buying it. Remember to bring some connectors to make it easier. The antique radio buffs are more likely to use antique test equipment than the Hams, but this is just a gross generalization.Although it would be nice to have a modulated signal so you can hear it, a CW signal from your scope generator can be applied before the IF stages and the result can be monitored on your scope at the end of the IF stage for tuning just the IF stages. Frequently the IF stages can be adjusted by injecting a modulated signal into the antenna or just listening to a good local AM station and tuning for "Max" at the RF, IF stages. just monitor at IF output or the speaker.You could get innovative and build a "Modulator" that would modulate the output of your generator. But I would go for the antique radio association or the Hamfest route. Many clubs (both antique radio buff and Ham Clubs) have on stuff for sale listed on their site by their members locally. You could even ask for advice and might find someone who has an extra unit they wish to give away.Look at this:http://vrps.org/CONVENTION2023.html