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Wideband receiver architectures
Just curious... does anyone know what sort of architecture you find in your
typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? ---Joel |
#2
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Wideband receiver architectures
Joel Koltner kirjoitti:
Just curious... does anyone know what sort of architecture you find in your typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? ---Joel Solution for LO maybe is DDS. The practical solution of DDS is is extremely simple and cheap. Please google word "DDS" -- postipoika |
#3
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Wideband receiver architectures
Joel Koltner wrote:
Just curious... does anyone know what sort of architecture you find in your typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? ---Joel I suspect that they first upconvert to somewhat higher than the 1.3GHz upper frequency limit, then use a roofing filter with however many itty bitty IFs it takes to get back down to a reasonable bandpass filter. I also suspect that the receiver receives everything kinda well, not superlatively. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html |
#4
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Wideband receiver architectures
"Postipoika" wrote in message
... Solution for LO maybe is DDS. That's a big "maybe" -- even the fastest DDSes aren't much better than 1GSps or thereabouts, giving a realistic tuning range of 0-400MHz... and those parts are quite power hungry and not at all cheap (e.g., Analog Devices' AD9858 is several watts and nearly $50 even in quantities of 1000!). On the other hand, one of the much lower frequency DDSes in conjunction with a mixer would probably work well -- although it just shifts the problem to how to get nice and pure, very wide range fixed frequencies to mix with. (E.g., DDS does 0-200MHz, so now you need just, say, a 200MHz+/-IF, 400MHz+/-IF, 600MHz+/-IF, etc. oscillators to mix with...) Of course with the very fine-grained frequency resolution of a DDS, multiplying the output up would seem to be an obvious approach, but I'm told this isn't typically used due to the relatively high spur levels of the DDS itself. ---Joel |
#5
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Wideband receiver architectures
Joel Koltner wrote:
Just curious... does anyone know what sort of architecture you find in your typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? The HT-class wideband receivers typically will have a first IF in the 45 or 70 MHz range, and use a number of different PLL's one for each different band. Each PLL is literally less than a square cm on the PCB, and there's a lot of them. At least one Sony from the mid 90's had a 10.7MHz second IF, and if the frequency you wanted was anywhere near the first IF of 70MHz, then they skipped the first IF and went straight to the second IF. For FM the 10.7MHz IF is the ending point... for non-WBFM modes there was a third IF of 455kc with some ceramic filters. Some of the HT's have 5kHz channel spacing on the HF band with no finer tuning available (OK for SWLing but nothing else), but the slightly better ones have finer tuning in the HF range thanks to a the 2nd or 3rd LO being a PLL too. Image rejection is nearly completely nonexistent. Tim. |
#6
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Wideband receiver architectures
In article ,
Joel Koltner wrote: one of the much lower frequency DDSes in conjunction with a mixer would probably work well -- although it just shifts the problem to how to get nice and pure, very wide range fixed frequencies to mix with. (E.g., DDS does 0-200MHz, so now you need just, say, a 200MHz+/-IF, 400MHz+/-IF, 600MHz+/-IF, etc. oscillators to mix with...) From reading the occasional data sheet and appnote, I have the impression that (as Tim Wescott says) they upconvert to a high IF, like 3 GHz, and then convert down from there. In that case they might have an LO that tunes from 1.7-3 GHz, which is a much smaller range, proportionally, than 100kHz-1.3GHz. -- Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1 |
#7
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Wideband receiver architectures
On 16 Jun, 22:22, Postipoika
wrote: Joel Koltner kirjoitti: Just curious... does anyone know what sort of architecture you find in your typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? *I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. *So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? ---Joel Solution for LO maybe is DDS. The practical solution of DDS is is extremely simple and cheap. Please google word "DDS" -- postipoika My Yaesu FT-857D and FT-817ND transceivers use a PLL and DDS. The PLL cleans up the DDS output and the DDS gives the fine tuning. The 857 receives up to 450 MHz, and uses a 68.33 MHz first IF. Leon |
#8
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Wideband receiver architectures
Andy writes:
Look in the tech manual for a spectrum analyzer that covers a few Khz to 1.3 Ghz and you will see exactly how it's done. Typically, the LO runs above 1.3 Ghz and all signals are converted UP to a high IF where the first filter is a wideband SAW. A SAW can have several Mhz bandwidth way up there. Then the signal is downconverted to an IF that is compatible with the SAW bandwidth to achieve image rejection. The IF filter here is usually something like a crystal or ceramic filter, unless the requirements for instantaneous bandwidth forces a better group delay response. The hardest part is keeping the signal linear ( intermod, crossmod) in the presence of multiple simultaneous signals until the SAW and next IF filters are reached. Lots of tradeoffs have to be made. These tradeoffs have already been made in spectrum analyzers, so if you get a few different block diagrams of different units, you will see what specific frequency plans the designers have decided to use. The frequency plan of the cheapest spectrum analyzer would probably fit your purpose.... Coming up with a good frequency plan in view of the nonlinearities of the mixers used and the bandpass characteristics of the filters one employs is a real challenge sometimes. Andy in Eureka, Texas |
#9
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Wideband receiver architectures
Thanks Andy, that was most helpful.
---Joel |
#10
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Wideband receiver architectures
On Jun 16, 5:05 pm, "Joel Koltner"
wrote: Just curious... does anyone know what sort of architecture you find in your typical HT or mobile "receives everything from 100kHz - 1.3GHz!" radio to generate such a vast range of frequencies while still keeping the prices so low (plenty are available for $200, and I can't expect the LO makes up a particularly large percentage of that total price)? I would tend to lean towards something PLL-based given the typically channelized nature of available frequencies, but a single PLL would still need a VCO with a huge tuning range. So... perhaps a pair of mixed PLLs, with one doing the fine tuning and another the coarse tuning (having been multiplied up from a low frequency)? I attempted to decipher the schematic included with my Yaesu FTM-10R, but everything is so tiny it was rather hopeless! I don't suppose any of the reviews ever go through and sweep the LOs while watching for the worst case spur conditions, do they? ---Joel The one I had used triple conversion superhet. Mircoprocessor controlled. The first IF was like 336Mhz to 10.7Mhz to 455Khz. There was no front end. just direct conversion to the IF. So all the micro had to do was control the oscillator from 336Mhz to 900Mhz using up conversion on the low bands and down conversion on the higher bands. Cell phone band was locked out. Guess what you can pick cell phone band on the image frequency back in the day. 73 N8ZU |
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