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 Post subject: AM Radio Transmitter Kit
PostPosted: Jul Tue 21, 2015 7:47 am 
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I stumbled on these kits at eBay, so bought this
http://www.ebay.com/itm/1308kHz-Amplitu ... 1571421789?

and this
http://www.ebay.com/itm/Screw-Joint-Sim ... 1583705083?

For 24 bucks total. Actually the second is not really needed if one is on a super tight budget, but makes the project easier and better appearing.

So after stuffing the PCB and assembling/wiring to the chassis, I connected my MP3 player, and tried several antennas. I had also gotten a Rat Shack 8 AA battery holder, to supply 12 volts to the unit.

I got range, but could not get clear audio; it was always distorted, regardless of the modulation level setting.

I determined that the input level from the MP 3 player just wasn't sufficient, so I built an amplifier using an LM 386 circuit. It's the small PCB behind the modulator board.

I still couldn't get satisfactory audio, however, so I tried using a wall wart for power, instead of the battery pack. BINGO! Audio cleared up beautifully.
I used a wall wart with a switchable DC output voltage range, and discovered that the best sound came at around 8 to 9 volts, so I dug through my considerable pile of wall warts and selected a unit delivering about 8.5 volts.

The range varies, depending on the angle you are, away from the antenna. In this case, it's simply a dozen feet of wire thrown over the bed in the radio room, for testing. Best distance is about 80 feet or so.

With a portable set, the background hum can be pretty well nulled out. I am also able to get fairly clear sound with my Zenith 8S463 console, by rotating the Wave Magnet antenna. In fact, it sounds pretty good with it's big speaker.

Now this unit is not competition for an SSTrans, but then it's only about a quarter of the cost, and does a reasonably good job for what it was designed.

Sorry, I can't post the print; it's copyrighted, but as cheap as the kit is, there's not much point in trying to bootleg it. He uses a crystal that oscillates at 1308 Kc, easily receivable at 1310 Kc.

Here's some scans; the unit, birds eye view, and in a plastic case I've had since the '50's, and now finally has a use, eh eh!


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jul Tue 21, 2015 11:38 am 
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Location: Melbourne, Florida, USA
Hi Richard, that seller is a nice person and sometimes posts on TRB.
He recently posted that he now has his own website here:
http://sysynt.dyndns.org/D-Shop/index.htm

Thanks for sharing your project. I've often looked at his kits and wondered how well they performed.
That chassis looks nice and could be used for lots of other projects!

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jul Tue 21, 2015 10:33 pm 
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Hey Bill, I can definitely give this unit a thumbs up!

I forgot to mention that he stated a ground was indispensable, and I had tried connecting to the mounting screw of an AC outlet on the wall, but it didn't do any good.
Apparently the grounding through the AC wall wart connection is what put it over the top AFA cleaning up the transmitted signal.

Edit; I've installed it in my computer room, sitting atop my stereo, which outputs to it.

I connected the antenna wire to the mounting screw of an AC outlet plate about a dozen feet away and strung along the baseboard, and that along with wall wart power is sufficient for good range and almost negligible background hum.

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jan Thu 14, 2016 8:02 pm 
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Location: Oxford, MI
I looked into buying this , but the 1300-1310 KHz frequency in my area is kind of busy. Can one substitute a different frequency crystal for transmission on a different frequency?

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Tue 29, 2016 7:44 am 
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Location: Northern CA
Hi Fifties,

I have one of these kits also and just got around to stuffing/soldering the board and assembling the chassis today. I’m planning on using one of those little FM/USB/TF- card reader units from China that another guy on here has an extensive thread about. He installs them in radios as I recall, I’m sure you remember the thread. I have both of the type that he has and they work ok.

Was wondering, do you still use the LM386 amp? Do you have a schematic for your circuit if you think it’s needed?

I have an AMT-3000 connected to an Aluratek internet radio that’s xmitting on 1300khz, how tight is the little one from Japan? I don’t find it listed on Ebay anymore. I can change the SSTran if need be to a different freq I would imagine if bleedover is a problem.

Do you use an earth ground still? I know the SSTran here needs one to buck the hum, but I have screwy old knob and tube wiring. Sometimes the kitties out in the garage will bite through the gnd wire to the cold water pipe going to the washer and it will drop db mainly, plus get a distinct hum. A quick splice and all’s well again.

Did your cap’s come vastly different than what is shown on the blurry paperwork, besides the 2 electrolytics? I figured out most of them, that the pico-farad values (some) have a black line underneath the stampings; but am not familiar with 104,105, etc markings. Even some of the ceramics did not show the underline, like the 30 pico-farad. Better documentation would be a great help with this kit.

Some of the schematics online for this kit show a common Gnd. This is what the short piece of bell wire is for? And for the audio input, this is common to this also? The PCB will get it’s negative from the chassis stand-off? I do build a lot of kits from China, like the digital clocks, but really I could have an AMT3000 done in the time that I spent today trying to decipher these hieroglyphics and bad spelling on this jewel.

Thanks for any info on your setup!

Hcompton79, no you cannot just sub in a xtal for a different freq. without circuit changes.

-Charlie


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Tue 29, 2016 10:36 am 
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CT707 wrote:
Hi Fifties,



Was wondering, do you still use the LM386 amp? Do you have a schematic for your circuit if you think it’s needed?

Yes, I still use it. I'll have to look for the print; if you need it, PM me.

CT707 wrote:
I have an AMT-3000 connected to an Aluratek internet radio that’s xmitting on 1300khz, how tight is the little one from Japan? I don’t find it listed on Ebay anymore. I can change the SSTran if need be to a different freq I would imagine if bleedover is a problem.

It transmits on 1308 Kc, receivable clearly on 1310. You would want to experiment to see if your transmitters cause co-channel interference. There's just too many variables involved to determine without actual testing, i.e., distance from your receivers for each transmitter, angle of reception, amount of modulation, etc.

CT707 wrote:
Do you use an earth ground still?

Yes, you absolutely need a ground for this circuit to work well.

CT707 wrote:
Did your cap’s come vastly different than what is shown on the blurry paperwork, besides the 2 electrolytics? I figured out most of them, that the pico-farad values (some) have a black line underneath the stampings; but am not familiar with 104,105, etc markings. Even some of the ceramics did not show the underline, like the 30 pico-farad. Better documentation would be a great help with this kit.

I honestly don't remember the specifics on the caps, but I had NP stuffing the board. You can do a Google search for the numerical cap markings if need be.

CT707 wrote:
Some of the schematics online for this kit show a common Gnd. This is what the short piece of bell wire is for? And for the audio input, this is common to this also? The PCB will get it’s negative from the chassis stand-off? I do build a lot of kits from China, like the digital clocks, but really I could have an AMT3000 done in the time that I spent today trying to decipher these hieroglyphics and bad spelling on this jewel.


I'm surprised that you had such a problem with so simple a board. Just stick with the print he supplied with the kit and you'll be good.

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Wed 30, 2016 5:54 am 
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Thanks for the reply Fifties,

Great tip on using Google to look up the values for the caps! I found the info for the numbers on the caps and converted from nano-farad to what he showed on the schematic to be a .1uf and a 100pf and it turns out that I had those installed wrong. The other one’s were ok.

I think part of the problem I am having with this board is these new damn progressives I’m wearing. I use a clip-on set of magnifiers which I’ve had for years, and these new specs aren’t hooking up well for me. They drive me nuts doing the bobblehead thing trying to get a sweet spot to focus through. Next pair I’m going back to bifocals with the reading lenses way down at the bottom. Plus I got glass lenses this time in case of solder splatter and they are way heavier than plastic.

Got it done this afternoon and did a final check, then briefly hooked it up to a 9V battery and it throws an excellent dead carrier. Ungrounded, with no hum. Wiped out the SSTrans on 1300khz as soon as I turned the switch on. Hope to do some checks with an input tomm.

Did your kit come with a couple of extra mylar’s with it also to isolate the mains to your old radio(s)? I thought that was nice of him to include those if need be.

I’ll PM you if I need the LM386 schematic and it’s not too hard to locate, thanks for the offer.


-Charlie


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Wed 30, 2016 6:39 am 
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Quote:
Did your kit come with a couple of extra mylar’s

I'm not sure exactly what you are referring to?

Quote:
I think part of the problem I am having with this board is these new damn progressives I’m wearing. I use a clip-on set of magnifiers which I’ve had for years, and these new specs aren’t hooking up well for me. They drive me nuts doing the bobblehead thing trying to get a sweet spot to focus through.

I just use my regular reading glasses and this mounted magnifier, which I can lower down to just above the board that I'm working on; works great!


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Wed 30, 2016 7:42 am 
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With the kit I got, it included a couple of 630v capacitors and a print on how to further reduce the hum by inserting these inline between what looks like an AC plug and the Gnd going to the xmitter. I did not really get it, that’s why I asked if you got these in your kit too. It was geared more towards a Japanese install though. Both blades of an AC plug have a .005uf connected to them, then are joined into one lead out and go to the ground midway between earth gnd and the “small power MW/SW AM transmitter”. I have the print I can scan and send if you want to check it out, since you have the same kit. (It’s copyrighted) It’s hard to understand the English translation.
“ That means it’s not enough, for reducing Ham noise, to connect Transmitter’s earth to the Ground, but actually need to connect all earth lines directly into one poetical through certain value of capacitors”

If we had a cap short, guess what goes into the xmitter and straight to ground?


Great pic of your bench! I’ll pick up one of those magnifiers for here, used to have an older one at work which worked good, but would never stay in one place.
I have the same Weller soldering station, MCM sells replacement sponges for them dirt cheap. They're made by Tenma and last longer since they don't have the cuts in them.

Take care,

-Charlie


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Mar Wed 30, 2016 8:12 am 
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I don't remember getting any 630 volt caps with mine, nor instructions to reduce hum; just the print of the transmitter board circuit.

Yeah, that's my second Weller; first one only lasted 19 years... :wink:

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Apr Mon 04, 2016 7:52 am 
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This actually works a lot better than I thought it would. Pretty impressive for 24 bucks! 9 volts seems to be it’s sweet spot, and it will work without a gnd, although doing that seems to attenuate the clarity and treble somewhat.
It definitely needs a lot of push in the input but that can be overcome with an amplified cheap Ebay FM tuner that has an SD card input and USB port on it. At 12vdc the modulation control seems to work ok to tame distortion as long as you have enough signal coming in.

No qualms with it other than it’s hard to read the schematics and understand the broken English, but definitely worth the time to build.

I run a couple of charge controllers out in the garage that are connected to 4 cigarette lighter sockets and 4 USB also, so was looking for something that I could run for free 24/7 off the solar panels and get rid of a couple of wal-warts. This fits the ticket perfectly. No, it's not an SSTrans but does work. :wink:

-Charlie


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Apr Tue 05, 2016 5:14 am 
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Glad to hear that it's working well for you. Yes, it definitely seems to require a boost in the input, and a ground for a clean output signal. Frankly, mine works damn near as good as my SSTrans.

With a kit that just requires board stuffing, all that's really needed is a schematic and/or a pictorial diagram. No need to worry about broken Engrish, eh eh!

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Thu 02, 2016 12:05 am 
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As long as this is only used during the day in an area where there are no local stations at 1310 kHz, old (that is non-PLL) radios won't care that the transmitter is on a non-standard frequency. At night, there will be heterodynes.

I noted that there is also a shortwave version of this circuit, which ships with a crystal for the 25 meter band (11.7 MHz). http://www.ebay.com/itm/DIY-11-7MHz-DC1 ... 1571421789


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Thu 02, 2016 12:50 am 
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Alfredo_T wrote:
As long as this is only used during the day in an area where there are no local stations at 1310 kHz, old (that is non-PLL) radios won't care that the transmitter is on a non-standard frequency. At night, there will be heterodynes.

I noted that there is also a shortwave version of this circuit, which ships with a crystal for the 25 meter band (11.7 MHz). http://www.ebay.com/itm/DIY-11-7MHz-DC1 ... 1571421789

Actually I've found it to work just fine on digital readout radios; dunno if they have PLL circuitry, however.

The S/W version would be fine, but unfortunately it limits reception to only S/W capable receivers, and that leaves out an awful lot of AM sets.

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 9:42 pm 
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Location: Buffalo, NY
I built one of these today, and have it connected to my satellite receiver.
I have the Satellite receiver tuned to a satellite transponder that has a hospitality music service on it
(~ 100 diff audio programs to choose from).
Makes a great source of random audio programming for your little AM transmitters.
Sounds pretty good on the 1935 Philco...


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 10:05 pm 
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I have a Sirius Starmate satellite receiver (bought it activated off eBay just about 10 years ago and it still receives their stations for no cost) that I can have running through my stereo, connected to the transmitter. The broadcast from this little transmitter is excellent with that source.

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 10:12 pm 
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Sure does sound pretty good.
have you experimented with your antenna length to minimize range?
I really have no need to go any further than my house...
Sounds pretty good on the radio in my car in the driveway too.

I did have to reduce the volume from the STB, so as not to over modulate.
At max STB volume, was well over 100% modulation.
Somewhere around 50 - 75% volume looked pretty good for music on the Communications Test Set's modulation meter..


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 10:22 pm 
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Being on two acres I really don't have any major concern about the range, but I have found that it maxes out at about 100 feet in certain directions, and less in others.

Yes, both the modulation control and the source's input volume have to be adjusted for best clarity.

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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 10:39 pm 
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yeah, I just took the wife's car for a spin, and find it will go either side of my house, not much further.
This setup will work for me... Just a random length of magnet wire strung in the basement for an antenna.


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 Post subject: Re: AM Radio Transmitter Kit
PostPosted: Jun Sun 05, 2016 10:49 pm 
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I had forgotten how mine was set up.
The antenna lead goes for about a dozen feet near the floor, and connects to an opposite wall AC outlet ground screw.

Oops, I had posted that above, lol, but this arrangement seemed to work the best for me.

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