Elenco AM/FM Radio Tuning Instructions? - Page 1
Forum section: electronics / rf-microwave

author: sbehnke
author_rank: Contributor
timestamp: October 14, 2019, 04:56:41 pm
content: I have soldered all of my components on the board for my semester project. The AM and FM signals are received and can be heard. They are not as clear as I would like, so I attempted to follow the tuning instructions in the manual. I set my signal generator to generate a 20 mVolt 10.7 megahertz FM modulated 1 kilohertz signal, shorted between Base and Emitter for Q2 to kill the local oscillator, connected my signal generator at TP14. I connected the signal generator and oscilloscope grounds to TP15, the common ground for the circuit and then attached my oscilloscope to TP1 as it appears in the diagram. With all of this configured, the instructions say to set the oscilloscope to 50 millivolts per division. I did this, but the signals I problem at more about 5 volts and aren't visible on the screen given this configuration.I have probed all DC voltages for the transistors based on the reference values in the manual and they are all within tolerance values for all Base Collector and Emitter on each one.I've included pictures of the assembled board, front and back, and the section from the manual that I was referring to. I'm not entirely sure if my Rigol MSO5074 is able to generate the FM modulated signal at 10.7 megahertz, but I think I had it configured correctly.Editing to add the full manual which includes the schematic:https://www.elenco.com/wp-content/uploads/2017/10/AMFM-108CK_low-res-2.pdf

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 14, 2019, 05:00:25 pm
content: If you have too much DC voltage at the test point set your scope channel to AC coupling.

author: sbehnke
author_rank: Contributor
timestamp: October 14, 2019, 05:19:59 pm
content: Thanks! I will try that this evening.

author: sbehnke
author_rank: Contributor
timestamp: October 15, 2019, 12:28:58 am
content: Thanks, that helped me see the signal. It was pretty clear at 100 milivolts and I was able to maybe sort of tune the radio better. It seems that the dial is way off the actually received frequency and that I cannot get very low in the FM band. The dial appears to be about 92 megahertz and the received frequency is 98 megahertz. I’m not entirely sure if I can adjust that lower to match the dial. The instructions didn’t really cover that.

author: Audioguru again
author_rank: Regular Contributor
timestamp: October 15, 2019, 02:10:54 am
content: Quote from: sbehnke on October 15, 2019, 12:28:58 amThe manual shows how to use the "magic wand" on P56 to adjust the FM local oscillator frequency so that the dial frequencies are accurate. The inductor L3 is adjusted for the low end of the dial.

author: sbehnke
author_rank: Contributor
timestamp: October 15, 2019, 02:08:27 pm
content: Ahh, yes, thank you. I think I have it figured out now. I got the lower range adjusted by spreading out the L3 inductor and now I need to adjust the upper range by increasing or decreasing the capacitance by turning a screw on the back of the tuning gang. I didn't see in the manual where it says which direction will increase and which direction will decrease so I probably have another evening of trial an error ahead of me and then I can go back to testing the lower end of the frequency with L3 again.

author: 0culus
author_rank: Super Contributor
timestamp: October 15, 2019, 02:23:36 pm
content: This is a fun kit, I enjoyed building one.However, the instructions are an old print that does have some errors and misprints that lead to situations that don't make sense if you take them literally. I ended up calling elenco and talking to one of their engineers to get some clarifications/corrections on these. The guy I talked to was extremely helpful and they even replaced one of the tuning slug inductor cans for FM for free (it was DOA).

author: sbehnke
author_rank: Contributor
timestamp: October 15, 2019, 02:43:10 pm
content: Yeah, I've been having fun with it. The only real issues I've had with it have been trying to tune the reception. I was hoping to use my MSO5074 for more of the tuning, but my frequency generator is only able to do up to 25 megahertz and I couldn't really see the signals vary much by turning the FM cans. I did have better luck using the multimeter and looking for the lowest voltage.

author: 0culus
author_rank: Super Contributor
timestamp: October 15, 2019, 03:01:18 pm
content: Yeah, I used an RF signal generator with an internal audio generator and AM/FM modulation which makes things a lot simpler, especially for the FM side. Know anyone who has one you can borrow?

author: sbehnke
author_rank: Contributor
timestamp: October 15, 2019, 03:09:40 pm
content: Nope, I'm a professional programmer surrounded by software only people. I did recently become licensed as a ham radio operator so it is feasible that someone in the club may have such a thing, but I don't know anyone that well yet. Do you have one you could recommend for purchase that wouldn't be that expensive? I have been looking for an SWR meter and other such analog devices, but I don't believe those include RF signal generators.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 15, 2019, 03:12:33 pm
content: Quote from: sbehnke on October 15, 2019, 02:43:10 pmJust set the generator to square waves and set the frequency to 1/5th of the frequency you want, I bet you will get plenty of signal.

author: Hank30721
author_rank: Contributor
timestamp: February 21, 2023, 07:13:49 pm
content: Quote from: PA0PBZ on October 15, 2019, 03:12:33 pmI know this is an old topic but I am trying to do the final FM alignment on my 108CK. My signal generator tops out at 30Mhz. If I use it and set it up as PA0PBZ suggests, (1/5 of 88MHz is 17.6Mhz), do I still set the deviation and tone frequency the same in the FM modulation section of the generator (Siglent 1032x)?

author: AFTORF
author_rank: Contributor
timestamp: February 21, 2023, 07:27:52 pm
content: Tone will be the same but deviation is 1/5 of 75 KHz : 15 KHz.

author: Hank30721
author_rank: Contributor
timestamp: February 22, 2023, 07:19:24 pm
content: I will give it a try and report back!

author: Hank30721
author_rank: Contributor
timestamp: February 26, 2023, 04:21:33 pm
content: Quote from: AFTORF on February 21, 2023, 07:27:52 pmThe instructions say to set deviation at 22.5kHz. Do I use 1/5 that value also?

author: Hank30721
author_rank: Contributor
timestamp: March 15, 2023, 08:51:21 pm
content: I tried the harmonic with a square wave - could not get results exactly as the manual stated when matching the upper and lower end of the FM dial to the receiver. However, it does work and tunes stations as good as any other simple FM receiver I have in the house.Here's a short video of the FM section:https://youtu.be/0Pb14emYriMI wish I could find someone to go over the radio and see how close my setup on the radio is to the ideal settings. Any takers in the southeastern US?