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 Post subject: Crystal Osc. For AM Broadcaster
PostPosted: Jul Tue 28, 2020 7:25 pm 
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Joined: Mar Sun 29, 2009 3:34 am
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Location: chancellor al.
I recall seeing a post somewhere about a 4 pin solid state xtal osc to drive a low power AM broadcaster. Can anyone tell me where to find one in AM freq. band.
A surplus elec. co. has an ad now-25 of those 4 pin osc. for less than $10 but no freq. is listed.
Tempting to get them and hope one will be in BC band.

Harold


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Tue 28, 2020 9:24 pm 
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The most common Dip Packaged oscillator is 1.00 MHz. If that's a clear frequency in your area your good.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Wed 29, 2020 1:30 am 
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They are available at Mouser Electronics for 1228KC and 1544KC in addition to 1000KC.

Dale


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Wed 29, 2020 3:23 am 
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Thanks Dale.

Harold


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Wed 29, 2020 7:27 pm 
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rxradio wrote:
They are available at Mouser Electronics for 1228KC and 1544KC in addition to 1000KC.

Dale

Outside of the 1000KHz part, those frequencies aren't on a 10KHz channel spacing multiple. If the oscillator frequencies can be trimmed to, say, 1230KHz or 1540KHz you'd be good to go. Of course being slightly off frequency wouldn't be a problem for any older radio. A digitally-tuned set would have a problem though.
John

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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Wed 29, 2020 9:41 pm 
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OldWireBender wrote:
rxradio wrote:
They are available at Mouser Electronics for 1228KC and 1544KC in addition to 1000KC.

Dale

Outside of the 1000KHz part, those frequencies aren't on a 10KHz channel spacing multiple. If the oscillator frequencies can be trimmed to, say, 1230KHz or 1540KHz you'd be good to go. Of course being slightly off frequency wouldn't be a problem for any older radio. A digitally-tuned set would have a problem though.
John

How many "digitally" tuned radios do most people who build AM transmitters transmit to :?: The other freqs come stronger than needed on "Antique radios"

Dale


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Jul Thu 30, 2020 4:56 pm 
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Location: chancellor al.
Thaks to all-good info.

Harold


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Thu 03, 2020 5:47 pm 
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Location: Beaver Falls, PA. USA
There was a nice AM frequency synthesizer described here a few years ago. I built two of them, and they work well. The desired output frequency is set with a DIP switch, using a lookup table.

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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Thu 03, 2020 6:38 pm 
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Quote:
There was a nice AM frequency synthesizer described here a few years ago. I built two of them, and they work well. The desired output frequency is set with a DIP switch, using a lookup table.
+1 on this. Built two as well.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Thu 03, 2020 6:58 pm 
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Joined: Sep Tue 30, 2014 6:08 am
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Location: Norfolk, VA
The Ramsey AM25 was Synthesized and DIP-switch controlled:

https://user-e3pxopj.cld.bz/Ramsey-Cust ... itter-Kit#

Attachment:
AM25.jpg
AM25.jpg [ 148.49 KiB | Viewed 825 times ]


And complies with FCC part 15 at the time of kit availability:

Attachment:
AM25FCC.jpg
AM25FCC.jpg [ 321.74 KiB | Viewed 825 times ]

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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Thu 03, 2020 7:05 pm 
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Location: Norfolk, VA
The Synthesized AM transmitter discussed previously:

viewtopic.php?f=12&t=344806

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Brian
"Capacitor Cosmetologist since 1979"
USN Retired 1984-2006 (Avionics/Cal)


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Sun 13, 2020 1:53 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: St. Louis, MO, USA
Are there any crystal manufacturers left in the USA? I did hear of one (international crystal?) that might start maki g them again. Anyone else know of any?
Thanks,
Dennis


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Sun 13, 2020 4:52 pm 
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Joined: Mar Thu 01, 2018 1:30 am
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I once used a 20MHz crystal and 4060 divider chip to drive a 2n7000 mosfet with square waves. Its drain was series modulated by a LM386. With some antenna matching to 6ft wire I got a range of 300 feet on 1250KHz. Sound quality was FM like. A series resistor on pin 5 of LM386 may be needed to limit input power of 2n7000 to 100mW. t's a simple circuit. Add a 33K resistor from gate of 2n7000 to ground. It's not shown in the schematic. RFC1 is 100uH and RFC2 is 1 - 1.5mH readymade choke.


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image1.JPG
image1.JPG [ 424.92 KiB | Viewed 618 times ]


Last edited by Dare4444 on Sep Sun 13, 2020 7:03 pm, edited 3 times in total.
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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Sun 13, 2020 5:27 pm 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 624
Location: Montreal, Quebec
International Crystal closed down three years back. It's unlikely to get back into business.

There was some story earlier this year that a long existing crystal company was getting back into custom crystals, maybe it was Bowmar? But it seemed hazy. Note also that custom crystals were expensive fifty years ago, when they were common, and will be even more expensive now.

Hobbyists used to rely on surplus crystals, and there were an endless supply. But you had to make do with what frequencies were available, ir grind them a bit (easy to do since the cases could be opened). For very specific frequencies, or specs, you had to have one custom ground. Commodity crystals were limited to very useful frequencies, like 100KHz for calibrators, and color subcarrier crystals. CB and then scanners boosted that. But the real change was digital electronics, a lot more cheap off the shelf crystsls, as long as it was a frequency you needed.

I can't believe attrition has eliminated all those surplus crystals. Who didn't have their own box of oddball crystsls? Many must still be out thrre, somewhere.

The idea of using a higher frequency crystal and dividing down isn't a new thing. It can be done with any transmitter circuit, best to focus on that rather than the output circuit. Ken Cornell wrote a lot about medium and low frequency license free operstion, including a famous book about LF, and his articles in "73" were the first that I remember that used a digital divider for mw and lf transmitters.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Sun 13, 2020 8:44 pm 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 158
Location: Colorado Springs, CO 80917
If anyone's interested, I can get hold of a few BCB frequency crystals, HC-6 size cases.
Local surplus store had some & they're thinking of closing up shop. Can get for really
cheap if I buy a whole boxful of stuff in one trip.

Also, I recently snagged a small lot of those crystal modules in frequencies 1544 & 1120 KC
and a very few at 614.4 and 1536 KC. Will keep an eye out for more if folks want them.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Wed 23, 2020 12:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1032
Location: St. Louis, MO, USA
Hi Hwall. Would you have a 1430 Kc crystal. I have a Gonset super diver that uses one.

Thanks,
Dennis


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Wed 23, 2020 3:16 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 158
Location: Colorado Springs, CO 80917
I don't have one in my junkboxes but I'll look in the surp store. Was planning to go plunder
around tomorrow.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Wed 23, 2020 12:58 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1032
Location: St. Louis, MO, USA
Thanks,
Dennis


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Sep Sat 26, 2020 6:18 am 
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Joined: Jan Sat 25, 2020 5:23 am
Posts: 158
Location: Colorado Springs, CO 80917
>>Would you have a 1430 Kc crystal. I have a Gonset super diver that uses one.
>I don't have one in my junkboxes but I'll look in the surp store. Was planning to go plunder
around tomorrow.

Struck out. Sorry.


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 Post subject: Re: Crystal Osc. For AM Broadcaster
PostPosted: Oct Fri 02, 2020 1:43 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1032
Location: St. Louis, MO, USA
In a pinch, I could use a 1420 or a 1440 crystal.
Dennis


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