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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Mon 27, 2017 2:25 pm 
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ednspace wrote:
Are these kits available? How would I got about ordering one.

thanks,
ED



See Bill's post above. He will be back shortly and we can get the kit. If you don't already have one, the little transmitter is amazing.

Ed

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Mar Wed 29, 2017 5:13 am 
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Thanks I appreciate the info. It would be really nice to get this going as around here I am picking up just a couple of AM stations. I appreciate all the effort thats gone into making these available.

ED


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jul Thu 20, 2017 7:57 pm 
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Sorry folks but the last of the parts kits have been sent to members. Also, interest in parts kits is down to zero or I would somehow supply more. It's been a great run thanks due to Tom Bryant

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jul Thu 20, 2017 8:18 pm 
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Thank you, Bill, for all the effort you put into compiling and supplying the kits.

Larry

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Jul Thu 20, 2017 8:55 pm 
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bill hamre wrote:
Sorry folks but the last of the parts kits have been sent to members. Also, interest in parts kits is down to zero or I would somehow supply more. It's been a great run thanks due to Tom Bryant



Thanks for the kits Bill. I use mine and it works great. I have no am reception here, but now I pick-up broadcast at 1000kc on the dial. The station streams oldies right from the putor. I receive it with an old RCA table radio. It was built and sold in 1946. Of course it had to be completely rebuilt.

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Fri 11, 2017 6:43 pm 
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35Z5 wrote:
A VFO ain't gonna happen...

The crystal determines freq, unfortunately very limited choices in the BCB band... Besides 1000Kc there are 1228 & 1544, may possibly get lucky and snag something from ebay... but be warned, I have several older different freq that cannot be modulated...

Tom


I like this design but I don't want to be rock bound. I prefer to be closer to the top of the band where the antenna is more efficient and 1544 KHz is a bit too far off center for my liking. Soooo... I went looking for a suitable VFO to replace the crystal oscillator. I found several. The one I chose to use was designed by Richard AD7C (his design is the foundation of at least two other more complex VFOs). I'm too new here to post a link to his site but just Google AD7C and you'll find it. His VFO uses an AD9850 DDS module and an Arduino UNO. It's a fairly simple design and I found all the parts I needed for it on Ebay for less than $40. I'm using an Arduino Nano instead of the UNO because I want everything to fit on one PCB. I already have it prototyped on my bench and partially working. Can't post a pic just yet till I make a few more posts here.

I modified the Arduino sketch so that it covers only the MW BC band AND 1750 meters (160-190 KHz). I even have an EU version that covers LW and MW in 9 KHz steps. It'll be be at least another month before I completely finish it and 3D print a case for it.

Sam


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Fri 11, 2017 7:32 pm 
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Very nice.

Wonder if there is a way to get a motorized tuning unit and have the arduino control it as well so the antenna is optimally tuned to the frequency the transmitter is set at.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Fri 11, 2017 7:53 pm 
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Tube Radio wrote:
Very nice.

Wonder if there is a way to get a motorized tuning unit and have the arduino control it as well so the antenna is optimally tuned to the frequency the transmitter is set at.


I thought about that but I want to keep the cost factor down. I don't have a problem using a wafer switch with several inductors connected in series with a variable inductor and manually tune it. It's not like I'm gonna be swapping frequencies every day. The Arduino could certainly do it and I could redo the sketch to have it switch in (or out) relays with the proper inductance when the frequency hits a certain number. Sensing the SWR for an exact tune would tax the Arduino's memory. Might be something I could pull off on a Raspberry Pi...

Sam


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sat 12, 2017 1:44 am 
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I've often thought of using a pi to provide the source and processing (stereo tools has a version for the pi) then using a board built on the pi for the LM-386 transmitter.

Would be totally self contained.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sat 12, 2017 2:03 am 
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Macrohenry came up with a crystal controlled PLL frequency synthesizer that will provide any AM frequency on exact 10 kHz channel spacing:
viewtopic.php?f=12&t=82833&start=0

Simple and effective.

Edit:
Corrected channel spacing to 10 kHz. I originally had 1 kHz.


Last edited by BobWeaver on Aug Sat 12, 2017 5:28 am, edited 1 time in total.

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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sat 12, 2017 2:08 am 
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Nice


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sat 12, 2017 7:31 pm 
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As long as it doesn't constantly wonder, freq stability has never been one of my concerns... Most tube radios will drift a KC, maybe two on warmup and usually isn't all that noticable... My tube Tx(s) get turned on and often run for weeks at a time, never really drift enough to be a concern, I usually "center 'em up" after a few hours(or maybe days)... I do have a Tek Scope with freq counter that serves as modulation & freq indicator, takes maybe 30-40 seconds to verify and adj if necessary...

BTW in area with lots of adjacent stations, sliding 5Kc generally reduces interference...


Tom


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sat 12, 2017 11:30 pm 
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Oops. I forgot we were talking about modulated crystal oscillators. Macrohenry's PLL wouldn't work for that.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Sun 13, 2017 4:07 pm 
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It might work provided the oscillator drove a transistor and the transistor was connected to the LM-386 like the oscillator was.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Mon 14, 2017 2:56 pm 
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BobWeaver wrote:
Macrohenry came up with a crystal controlled PLL frequency synthesizer that will provide any AM frequency on exact 10 kHz channel spacing:
http://www.antiqueradios.com/forums/vie ... 33&start=0


I saw that design and he even provided the PCB design and instructions on how to etch the board. It's also designed to replace a crystal. It's small, stable and programmable, but you have to open the case and flip some switches to change the frequency. It was posted in 2008 and you can still get all the parts from Mouser or DigiKey, though with inflation you might spend a little bit more than the $12 he stated to get all of the parts.

Fast forward nine years to 2017 and now you can get a micro-controller and a DDS module combo for about the same price. Also designed to replace a crystal and also small and stable. My project (when I finish it) has a display that shows the frequency and lets you change it on the fly (on MW or LW) without opening the case.

Attachment:
AM Xmitter Proto5.jpg
AM Xmitter Proto5.jpg [ 157.89 KiB | Viewed 362 times ]


When I finish this, I'll post it as a new thread. Until then, if someone else wants to play with something like this, I have the Arduino sketches ready for both North America (1750 Meters and MW) and Europe (LW and MW).

35Z5 wrote:
As long as it doesn't constantly wonder, freq stability has never been one of my concerns... Most tube radios will drift a KC, maybe two on warmup and usually isn't all that noticable... My tube Tx(s) get turned on and often run for weeks at a time, never really drift enough to be a concern, I usually "center 'em up" after a few hours(or maybe days)... I do have a Tek Scope with freq counter that serves as modulation & freq indicator, takes maybe 30-40 seconds to verify and adj if necessary...


There's nothing wrong with hybridizing a tube transmitter. In fact, I'd like to try it with this VFO. I like the warm sound of tube transmitters and receivers....

And back on thread.... Digikey now offers programmable crystal oscillators for way less than the $15 mentioned in this and other posts. You can have them do it or program it yourself.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Mon 14, 2017 7:48 pm 
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There is a DDS VFO

http://www.pongrance.com/DDS2016.html

That with a slight modification will allow it to produce an amplitude modulated output.

It involves a mod to the circuitry of pin 1 of the DDS chip which is a 6.8K resistor to ground.

http://www.analog.com/media/en/technica ... AD9834.pdf


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Mon 14, 2017 8:16 pm 
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I did the same thing, but used a PIC instead of an Arduino. I kept the controller board separate from the DDS/modulator board so that the DDS could be shielded more easily.

This is the controller:
Attachment:
DDS_Controller.jpg
DDS_Controller.jpg [ 54.05 KiB | Viewed 343 times ]


This is the modulator/DDS board:
Attachment:
DDS_Modulator.jpg
DDS_Modulator.jpg [ 39.15 KiB | Viewed 343 times ]


Tube Radio wrote:
There is a DDS VFO
It involves a mod to the circuitry of pin 1 of the DDS chip which is a 6.8K resistor to ground.

I tried that modification, but wasn't satisfied with how it worked. It wasn't possible to get the modulation even remotely linear unless you kept it below 30%. I concluded that it was easier to modulate the output of the DDS directly rather than trying to cut microscopic traces and soldering jumpers on the DDS module. Either way, you have to add one transistor and a few passive components.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Mon 14, 2017 9:34 pm 
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I looked at N3ZI's VFO. He sells it as a kit for almost $90. It has way more bells and whistles than I need for a Part 15 transmitter. Bob's design with the PIC chip is another way to go with it. The advantage with a PIC IC is that you have a lot more control over the PCB design(s). It's a bit more involved in programming them but the learning curve is about the same as an Arduino. I'm going to try the 9850 modification to modulate the transmitter first. I have several of these modules so I can afford to trash one if it doesn't work out that well. I do know that the 9850 modules have problems when powered with 5V. That may be why Bob had linearity problems modulating it. They're known to get freaky above 4 Volts. The Arduino has a 3.3 v output and that's what I'm using to power the 9850 module. I'll see what happens when I hook up the modulating circuit and view it on my scope.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Tue 15, 2017 1:32 am 
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Cool.


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 Post subject: Re: LM386N MK-XI BCB Transmitter
PostPosted: Aug Tue 15, 2017 4:17 am 
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I hadn't heard about the 5 volt supply being a problem with the DDS chip, but I'm operating it on a 3.3 volt supply. So it shouldn't be an issue.

FYI, the modification that I'm referring to is the one given on this page:
http://www.nomad.ee/micros/rfgenerator/

The amplitude modulation modification uses the RSET pin which was originally intended to set the DDS output to a fixed level by connecting a fixed resistance between RSET and ground. I don't think the mfgr. ever really intended this to be used for modulation, though it may have been an afterthought*. Connecting a MOSFET from RSET to ground is not going to give linear modulation (especially when the original 3.9k resistor is still connected), because it fails to account for the fact that the RSET input needs to see a linearly varying sink current. It wouldn't be hard to make a voltage controlled current sink to do this: one BJT and a resistor. I'd considered doing this, but I don't think it would have worked well with just a single 5 V supply. Plus there was still the nuisance of having to cut traces and solder jumpers on the DDS module. So, I decided that since we're dealing with low level signals at the output anyway, it would be just as easy to apply the modulation there.

* Appnote AN-423 appears to be the original source of the 2N7000 MOSFET modulation scheme, but it's short on numbers and suspiciously devoid of any kinds of specs on linearity.


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