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I am technically challenged and wonder what it would entail to have a Ubitx in AM mode
Art
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Here's a nice description of a simple AM detector:
? ??
I'd first try attaching the diode (1n34a, or perhaps a BAT54s) off of pin 2 of T5, where it drives the 12mhz crystal filter.
Source resistance there is around 200 ohms, so you'd get a bigger signal than at the 50 ohms of T5 pin 5.
T5 presents a DC path to ground, so no need for the RF choke shown in the above link.
The 45mhz filter at Y1 limits the bandwidth to something reasonable for AM, as Farhan has previously noted.
Might work better if you remove the load presented by X2 and X8 somehow.
Output of the diode detector would drive the preamp at Q70.
I'd remove C50 and drive the base of Q70 from the diode detector through a series 1uF cap.
The germanium 1n34a is ideal because it has a very low forward voltage drop, to receive low level signals.
A Schottky diode like one side of the BAT54s diodes used in the uBitx will work, but is not so sensitive.
The cheap 1n34a's out on ebay are Schottky diodes at best.
A good source for a real 1n34a is:? ?
Problem is, not enough gain in the front end of the uBitx to drive the simple diode detector
for anything but the strongest incoming AM signals.??
You could add another RF amp specifically to drive the diode detector, tap the signal from Q32 to drive this new amp.
Maybe just duplicate the Q30,Q31,Q32 amplifier.
I'd be tempted to try a cheap MMIC such as this:???
Or you could move on to the next page of that tutorial link above and think about implementing a synchronous detector.
You can sort of receive an AM signal with an SSB receiver by carefully tuning it in, but tuning is very tricky.
The BFO must sit right on top of that AM carrier or you will get a beat note, and no matter how close you are the phasing won't be ideal.
A synchronous AM detector makes your SSB receiver's BFO synchronize with the incoming carrier, so tuning locks in when you get close.?
Disclaimer:? I haven't built an AM receiver since messing with a chunk of galena and a cat-whisker
some 55 years ago.
Jerry, KE7ER
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On Thu, Dec 28, 2017 at 09:34 am, <k0kuk.vhf@...> wrote:
wonder what it would entail to have a Ubitx in AM mode
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This may not be ideal, there will be other mixer products present.
Perhaps precede the AM diode detector with a 12mhz LC bandpass filter?
Can't use the crystal filter, as it is too narrow for an AM signal.
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On Thu, Dec 28, 2017 at 10:20 am, Jerry Gaffke wrote:
I'd first try attaching the diode (1n34a, or perhaps a BAT54s) off of pin 2 of T5, where it drives the 12mhz crystal filter.
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While an interesting challenge, I'd be inclined to leave the uBitx alone and build a stand-alone AM transmitter/receiver.?
Or at least an AM transmitter that you can use with your uBitx. The uBitx as an SSB receiver will receive AM but you will need to zero beat stations. AM operators aren't necessarily on the same frequency so if there's a group on you may need to slightly adjust the tuning if trying to receive AM on an SSB receiver. Whereas with a dedicated AM receiver you don't have to.?
If you were to build an AM receiver I'd use something like an NE602 for the converter, an MK484/ZN414 as an IF amplifier and detector, some 455 kHz IF transformers (or ceramic filter) for IF selectivity and an LM386 for audio.?
As for an AM transmitter there are 7 MHz pirate radio designs of about 10w that can be adapted for amateur use.?
I discuss AM in more detail at?http://home.alphalink.com.au/~parkerp/gateway/am.htm
73, Peter VK3YE
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I have plenty of AM transmitters and receivers as well as transceivers that do AM but I thought it would just be interesting to incorporated into the ubitx....
On 28 Dec 2017 1:34 pm, "Peter Parker" < vk3ye@...> wrote: While an interesting challenge, I'd be inclined to leave the uBitx alone and build a stand-alone AM transmitter/receiver.?
Or at least an AM transmitter that you can use with your uBitx. The uBitx as an SSB receiver will receive AM but you will need to zero beat stations. AM operators aren't necessarily on the same frequency so if there's a group on you may need to slightly adjust the tuning if trying to receive AM on an SSB receiver. Whereas with a dedicated AM receiver you don't have to.?
If you were to build an AM receiver I'd use something like an NE602 for the converter, an MK484/ZN414 as an IF amplifier and detector, some 455 kHz IF transformers (or ceramic filter) for IF selectivity and an LM386 for audio.?
As for an AM transmitter there are 7 MHz pirate radio designs of about 10w that can be adapted for amateur use.?
I discuss AM in more detail at?
73, Peter VK3YE
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On Thu, Dec 28, 2017 at 11:34 am, Peter Parker wrote:
If anyone is interested in going the homebrew AM route, I built a 160m AM superhet receiver using the exact same stage and parts line-up Peter recommends:
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I added an AM/CW 30 watt transmitter:
??
The 160m AM receiver works well and alignment was a breeze.? The MK484 is a good AM detector.?
I recently tried a 40m version (same stages and parts). It needed more IF selectivity. I ordered a 455kHz ceramic 6khz filter from Minikits, just haven't soldered it in yet.? It should also work fine.? There's a bunch of AM guys on 7190kHz in VK east coast, so there are some active AM stations to listen to.
I agree with VK3YE, I wouldn't bother modding the uBitx for AM. Although f's suggestion of a NE602 synchronous AM detector does sound intriguing.? But it all adds parts and complexity.??
Paul VK3HN.?
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This might be the NE602 synchronous AM detector Farhan mentioned:
? ??
Looks rather complex, perhaps there are better chips for this now.
Am curious if anyone knows of better ways to do this.
Jerry, KE7ER
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On Thu, Dec 28, 2017 at 04:55 pm, VK3HN wrote:
Although f's suggestion of a NE602 synchronous AM detector does sound intriguing.?
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I wonder if the si4730 chip could be used at say 12MHz for AM reception? This frequency is inside the si4730 working parameters.? The modules are very cheap to buy ex China and can be configured over an i2c port on the arduino.? Input would be taken before the uBitx crystal filter and analogue output taken to the volume control input.? It may be able to be made to nicely integrate with the ubitx?? What do you think?
Mike ZL1AXG
On Fri, 29 Dec 2017 at 5:04 PM, Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote: This might be the NE602 synchronous AM detector Farhan mentioned:
? ??
Looks rather complex, perhaps there are better chips for this now.
Am curious if anyone knows of better ways to do this.
Jerry, KE7ER
On Thu, Dec 28, 2017 at 04:55 pm, VK3HN wrote:
Although f's suggestion of a NE602 synchronous AM detector does sound intriguing.?
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Interesting thought.
The Si4730 is darn near a complete radio already.
Though having signals go through the uBitx's 45mhz first IF would avoid trouble from strong adjacent QRM.
And would be fun to show onlookers how well the uBitx does at receiving broadcast FM stations.
SiLabs does have some SW receivers suitable for receiving 12mhz, I don't think the Si4730 is one of them.
Could move the uBitx second local oscillator to 45mhz+1.7mhz such that the Si4730 sees 1.7mhz.
Jerry
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On Thu, Dec 28, 2017 at 08:43 pm, Mike Woods wrote:
I wonder if the si4730 chip could be used at say 12MHz for AM reception? This frequency is inside the si4730 working parameters.? The modules are very cheap to buy ex China and can be configured over an i2c port on the arduino.? Input would be taken before the uBitx crystal filter and analogue output taken to the volume control input.? It may be able to be made to nicely integrate with the ubitx?? What do you think?
?
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You are right - the IF would need to shift to the broadcast band ... but that shouldn¡¯t be a problem for the raduino. ? The si4374 or 75 are capable of receiving shortwave, but there are no prebuilt modules available for these chips.? Still, worth a bit of experimentation perhaps.? I may order a couple of modules to play around with.? A few other projects are lined up for now, that is, after we get back from summer holidays!
Mike ZL1AXG
On Fri, 29 Dec 2017 at 6:20 PM, Jerry Gaffke via Groups.Io <jgaffke= [email protected]> wrote: Interesting thought.
The Si4730 is darn near a complete radio already.
Though having signals go through the uBitx's 45mhz first IF would avoid trouble from strong adjacent QRM.
And would be fun to show onlookers how well the uBitx does at receiving broadcast FM stations.
SiLabs does have some SW receivers suitable for receiving 12mhz, I don't think the Si4730 is one of them.
Could move the uBitx second local oscillator to 45mhz+1.7mhz such that the Si4730 sees 1.7mhz.
Jerry
?
On Thu, Dec 28, 2017 at 08:43 pm, Mike Woods wrote:
I wonder if the si4730 chip could be used at say 12MHz for AM reception? This frequency is inside the si4730 working parameters.? The modules are very cheap to buy ex China and can be configured over an i2c port on the arduino.? Input would be taken before the uBitx crystal filter and analogue output taken to the volume control input.? It may be able to be made to nicely integrate with the ubitx?? What do you think?
?
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Hi Guys
Jerry wrote
"Looks rather complex, perhaps there are better chips for this now.Am curious if anyone knows of better ways to do this. (?synchronous AM)"
Try looking for designs using TBA120, or SO42P, the latter is the Telefunken equivalent but some articles are in German so easier to find using that part number.? I think that you may also be able to us MC1330, but that's going from a very old (rusty) memory.
I'm waiting for my UBitX,, in a bag somewhere maybe in the UK, but on its way.
Regards David G8DJM
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Hi Guys
Further to the AM topic, I came across this discussion on the UK Vintage forum on?quasi-synchronous, it relates mailly to Video detection but it still amplitude modulation.
My Ubitx has still not turned up, it was ordered on the 9 Dec, shipped in the 14 Dec went into a bag at the airport a couple of days later, Hmmm
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Regards David S? G8DJM
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Mines in the same batch, according to hfsigs.... its on its way.
The wait continues.
Phil - G7BZD
On Fri, Jan 5, 2018 at 11:35 PM, David S via Groups.Io <dcsuk10@...> wrote: Hi Guys
Further to the AM topic, I came across this discussion on the UK Vintage forum on?quasi-synchronous, it relates mailly to Video detection but it still amplitude modulation.
My Ubitx has still not turned up, it was ordered on the 9 Dec, shipped in the 14 Dec went into a bag at the airport a couple of days later, Hmmm
?
Regards David S? G8DJM
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Art Howard
Peter Parker
VK3HN
Raj vu2zap