So I want to build a 1-2 watt FM Transmitter. I looked at Kage's list but the 1 watt he has on there he says shouldn't be amplified and I want to build something that I can later add to a 4-5 watt amp maybe more. I can find schematics all day long on the internet but I am not knowledgeable enough to know if they are crap or not. Every single one is different so they're hard to compare too. I have a solid background in electronics but I haven't done anything with RF since the military more than a decade ago and even then what I learned was limited. I was hoping some people could point me to schematics or plans for solid ones.
I did find the lulu and have heard decent things but I'm looking for a bit more complicated build as that's half the fun.
I'm also not looking for a kit or anything, I just want schematics, as I can probably source most components cheap if not free.
I should have replied to this ages ago but been busy. These days there is no excuse not to use PLL circuitry bare minimum. Hand tuned VFOs just aren't acceptable anymore except for toy transmitters when we have all in one chip solutions even on the cheapest end. Of course I wouldn't recommend that either given the noise cheap all in one chip solutions cause, but it's still a step up. Think older Ramsey kits that were synthesized, but build around the idea rather than use it as an end means.
I actually regret my old FM transmitter I worked so hard on. It is still a champ and puts out a nice pure harmonic free signal but these days with modern digitally tuned car radios and house stereos getting pissy over even the slightest maladjustment of transmitted content I often see modern radios simply refuse to lock on to the stereo pilot or cause other bizarre issues in received audio if I don't constantly monitor a frequency counter to make sure I am within the tight tolerances they want to see now.
There isn't a lot of FM transmitter info here compared to www.radionecks.co.uk , I need to give credit where due. Those guys over in the UK can build a stable PLL synthesized FM exciter out of bubble gum wrappers and bread toasters. Okay I joke, but they have a long history of whipping transmitters up that are rock solid with no harmonic or spur issues way better than we have in the US because we here often focus on shortwave more.
It is possible to use some of those all in one chip solutions but disguard the built in MPX generator junk and filter the output well to get a clean signal and feed them a proper MPX stereo to composite generated signal using oversampled circuitry built out of basic logic chips. Thing is as annoying as it is to get a decent acceptable stereo signal through a nice clean RF circuit that is just the beginning of the issues. When you introduce RF amplification you will find harmonic filtering becomes a serious endeavor, then even when the TX side is squeaky clean comes the audio processing to further refine the audio so to keep within acceptable FM deviation. It's a hell of a project but I commend you for wanting to attempt it.
Hope I don't sound discouraging. It never stopped me from attempting these things and I feel I got pretty darn close, and enjoyed the low power and VFO drifty circuits I made anyways. Heck some of them came pretty close to PLL stability but I feel I lost a lot of hair from pulling it out in frustration by not biting the bullet and going the PLL route. Much of that was simply because of the learning process, something which we never succeed at because there is always something to learn!
I'll try to think of some circuits to post to you here. These are black arts in electronics for a reason, there is no one size fits all circuit when RF is involved.
Post by ogrevorbis on Apr 17, 2019 10:31:39 GMT -6
I know I am also late to see this, but thought I would reply anyway.
The all-in-one chip radios are starting to get pretty good. Most of them are garbage, but the QN8066 and QN8007 are worth using as long as you don't think you'd be doing KWs. The spurs are down -50 and -45 at the absolute worst points.
The QN8007 is very hard to solder though. If you're going to build your own board, what I would do is get a TSSOP-16 to DIP converter and get some QN8066s. The hardest part is going to be getting the thing programmed, but all you need is that and an arduino. There is some chinese sourcecode for it over at pudn for a small fee.
It's clean and to amp it up probably use an MMIC like PHA-1+ and then use a normal FET for the second stage. Like C1971 or RD06HVF1. You can find plenty of schematics for these transistors on google images. Another great and hard to find secret resource is: www.3-mtr.info/sales/
Most of their stuff is only photos, but if you keep looking, you'll find a lot of schematics and even PCB files for Sprint-Layout. If you want to make PCBs, that is the thing to use BTW.
Doing an FM transmitter the traditional way is a huge undertaking and will probably lead to more frustration than it's worth. Those that do it have usually perfected their skill over many years, so if you're getting into it more for the getting on air experience, then I would go the route I just talked about, however, if you are really interested in electronics, then go the traditional route.
The traditional route would involve building your own VCO and then using a TSA5511 or an MC145170 to PLL it (lock it). The nicom VCOs are apparently very good and I believe one of the PKbee kits has them. Look up PKbee kits or check out this site if you want a kit of a traditional transmitter: www.amateurradioshop.nl/webshop/bouwkits/fm-broadcast/
Post by hastycroke on Mar 31, 2020 10:55:26 GMT -6
Hi...Its antenna is connected directly to its tuned LC circuit so its radio frequency changes when something moves toward or moves away from its antenna. It does not have a voltage regulator so its radio frequency changes as the battery voltage runs down, and its preamp transistor is saturated with a new battery and is cutoff with a used battery. It does not have pre-emphasis (treble frequencies boost) like all FM radio stations have but instead it has treble frequencies cut so it will sound awfully muffled.
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