mb1504 pll module

[radionortheast]

Don’t know if this is any good for someone out there, seems to only tune between 88-108, has an audio input you wouldn’t normally get in these types of module, don’t know weather it produces a clean carrier or not.

You would want to get it with the control board, it wouldn't be much use without the screen unless you can interface with it.

https://www.aliexpress.com/item/1005007 ... ry_from%3A

[Albert H]

With a layout as shown, the output is unlikely to be especially clean.

[radionortheast]

Its buyers own risk, not much use if it doesn’t to tune from 87.5 -88 though, (suspect the only frequencies which are clear are below there) don’t know if that is an audio signal thats been injected into seems to have carriers either side on the spectrum, might be some close in view, as I like to see a tall thin carrier. It would still be quite hard for someone to make a tx from this, you’d have to know the rf output level of it, assumming it was clean. If you have a clean source, audio input, the rf output level was known, someone would have all they need.

[EFR]

Hmm, link seems to be dead.

[radionortheast]

The best thing to do is to go onto the website to find it, you’ll have to search through it, they are still there, not saying its any good. There are other modules that put out a clean carrier wave, they have no audio input you have to mess about with, delicate soldering is needed to get audio in requires an op amp buffer, to pass bass frequencies, you have to encode your own stereo make your own encoder, unlike those chips they don’t interfere with other stations on fm, good for a low power transmitter of a few watts, but might start to get issues with higher power.

[Albert H]

Forget it. Look at the specification - the power consumption is 30 mW. Assuming that includes the carrier energy generated from the IC, you'd be lucky to see a milliwatt or two. Looking at the datasheet for this IC, the manufacturer suggests that it can be used for data transmission - audio isn't mentioned.

It's ridiculously expensive for a PLL IC that needs an external microcontroller which I can get a TSA5511 (which will work up to > 1GHz) and a PIC to tune it for <£8. Getting spectral purity from a home-made VCO isn't too difficult. If you use the Kallitron oscillator you see on the NRG boards, you can get a very pure carrier - as long as you follow the basic rules.

Just for the sake of amusement, I examined the possibility of using a ½f Kallitron, self-doubling to the output frequency, tuned by a dual varicap, with a second dual varicap for the modulation. It would be just the two transistors in the oscillator stage, as I would sample the output frequency from a subsequentt amplification stage to feed to the PLL IC. A couple of stages of amplification could get the output to >10 Watts (using modern FETs), and the whole thing - including the PLL Logic - would fit into a small diecast box. Spectral purity would be exemplary, and the whole thing would be very cheap.....

[radionortheast]

Could be a misleading listing I suppose, I once got a dds module it was worst than chip, a data transmission at band II frequencies would be unusual, it does say audio input. data can be put on any carrier, dosen’t tell us if it can produce wideband mod, it could be just like some crappy signal generator in a box, not in a box I suppose, alot of those do not produce mod and have too many spurs to be used.

You can actually get little black amplifiers that amplify 1mw up to 1-2w, I had one put 5-6mw through it and blew it, went back to read a review, someone said don’t put more than 1mw through it.
The only problem if you get a difference at different frequencies, my pll puts out 5.8mw whatever frequency you choose so dosen’t cause a problem to the amp.

A more traditional transmitter pll may have more variation, usally puts out more mw, causes a problem for an off the shelf amplifier. Obviously its much easier to make something from off the shelf modules, take an amplifier for instance, someone to get a tradistional amplifier using a 2n4427 transistor, the likely hood of getting it working unlikely, an off the shelf, 1/2w amp or 2.5w one will work, obviously the cost will be more.

[Albert H]

My commercial designs use a VCO (controlled by a PLL) and its output goes through a gain-controlled buffer stage. Further on in the circuit, there is a level sampling circuit which is used to control the gain of the buffer stage, so that I get the same RF voltage irrespective of frequency. This approach is quite common in commercially designed transmitters, to ensure a constant drive level to the PA stages.

[BlackBeard]

Here's what I found
https://a.aliexpress.com/_EHTi8U0
https://a.aliexpress.com/_Eu4Dho8

Couldn't upload everything, so you'll find the rest on Imgur.

[radionortheast]

I suppose maybe the frequency coverage dosen’t matter so much, bound to be some clear frequencies between 88-108. Maybe i’ll get one to see I don’t know, maybe it will go to the ball after all and gets its tap dancing shoes on.

I manage to break mine that uses the 2780, or I manged to get audio in without the op amp, there are few spurs close to the carrier on afew frequencies, a low hum, which I can take out by using a higher value capacitor unforuantely it takes too long to lock, a couple of 100nf is all it can take. It used one with the oled display

Photo on 21-12-2024 at 08.33 #2.jpg

I’m abit to lazy to get the back up out solder the wee tiny wire, I don’t use this stuff much, I have an old max pro, something else used at a low power level. You can see in the other thread what I made viewtopic.php?t=3858 the original transmitter here that users the op amp is completely clean

[radionortheast]

My error with the above appears the signal is still good, just the little amplifier was not connected properly loose connection, i’ve remade the encoder in the other thread but since have had a problem with, have had to switch it off hopefully I can get it working again.

[BlackBeard]

Bought the little MB1504 module. Power is quite low, maybe a miliwatt. No in-band spurs, no China-chip - a true PLL-VCO. The carrier is at -42dBm (including attenuation). 1st harmonic is at -22dBc, no 2nd harmonic. I have to say though, that there's no LPF on the board.

Oh yeah and you can set the frequency to less than 88 MHz, I think even 70MHz is possible and up to 110MHz on the higher end of the band.

The spectrum I posted is unmodulated. Span is 1MHz, RBW 7kHz. When modulated to about 70% the signal ('spike') widens to about 100kHz if I recall it right. On the other hand the TinySA is not a Rhode & Schwarz spectrum analyzer

What do you think? Needs some amplification and low-pass filtering for sure.

[BlackBeard]

Some additional measurements as the first one was not really precise.

Only downside I noticed is the frequency accuracy which really needs to be improved. On the low frequencies you can simply add +40kHz to your desired frequency - in the settings you can change the freq very precisely up to 1kHz. On the high end this doesn't seem to work anymore. The frequency is always 40-50kHz too low.

Probably need to solder in a lower value capacitor next to the quartz.

[radionortheast]

Sorry for not replying sooner, good to know it can tune to all frequencies, maybe I might go get one. There was a 2w amp that had 1mw input, its quite a low level, they sometimes write in on the reviews of them, something I didn’t know when I first connected it up to the 2870 I blew it.
Did you check it was the same output level on 87.5 that it was on 108?, I suppose a little one transistor amplifier could be made to get it to the 5.8 db level, i’m not sure i’d want to messing about doing that, like going back to some 90’s thing were you’ve have mess with different transistors in a veronica, I prefer plug and play type thing.
It could be tricky to solder low value capacitor to a crystal but not impossible I suppose, 40khz seems like alot to me, would loose alot of the signal, i’d not be able to pick it up on my pocket radio. I did manage to solder one to those not so great lcd little chip transmitters, which put it on the correct frequency, (it was after I saw a youtube video found it was too awful to use with an amplifier) the only problem might be too high value might cause the mb not to lock?

I managed to get the stereo encoder working again, when I modified one of the other signal generators to work (mentioned in the other thread) without the op amp, it adversely effected the stereo, leading to not much separation or too much. Its taken ages to get it to work again, now it sounds really nice again, as nice as it did with the op amp, its the nicest thing i've ever heard coming over fm, can ajust the frequency more without it effecting the signal to noise ratio too. Couldn't help just listening was mesmerised by it

Alot of times I do scans with the tiny sa from default 50mhz to I think it is 350mhz then you can see the harmonics too, theres also visual confirmation, been able to see other radio stations, I suppose its not how their usually used, you don't want to be bunging anyone like dane bowers.

[BlackBeard]

No problem. Thanks for your detailed reply!

About the 2w amp (manufacturer claims 4w): I tried exactly this one with the little MB1504 module. Worked like a charm. I uploaded the spectrum analysis. Still need a lowpass or bandpass though. I reached about 2W @ 8,5V. Didn't test higher voltages though. The amp already got quite warm after half an hour but not too much. Screwing the heatsink to a metal case with some heatsink compound and adding a little fan should suffice. This would be pretty much plug n' play.

I uploaded some more spectrum analysis of the amplified signal (about 2w) that also show the harmonics (unfiltered of course). Somehow they're upside down in the preview - click them to get the normal imags.

About the capacitor next to the crystal: It's capacitance is too high, thus the frequency is too low. I'd guess that soldering a variable capacitor allows you to lower the capacitance and fine tune the oscillator like this. Should work because you don't need to raise the capacitance additionally which indeed could cause problems I suppose.

Nice that you got the stereo encoder working! So you're not using the op-amp circuit anymore? I really like analogue circuits and actually prefer hardware st & rds encoders but as I'm very familiar with computers & SBCs, using those is usually the easiest solution for me. Your solution is quite sophisticated and surely takes some time and fine soldering skills to execute

Rn I'm working on "hacking" a cheap little TV box for 25€ on Aliexpress (T95 Max, 4Gb RAM, 64Gb eMMC, H618 CPU 4x1,4GHz Cortex-A53) by flashing Armbian to use it as a stream receiver & MPX encoder. The little box has a 192kHz sound card so it's basically got everything you need. Works fine so far using NanoRDS and VostokRadioLite (new little CLI software for stereo encoding & sound processing). I'll upload a tutorial here next month, when I finally have time.