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Pointers for a homebrew 2-meter XCVR
I have looked at homebrewing an FM 2-meter XCVR and already got help from
this group. The goal is to spend time on something that others could duplicate and not work on a one of a kind. First, why homebrewing ? Two reasons: 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) It seems that the problem is the selection of components that can be sourced in relatively low volume and at a reasonable cost by amateurs (read: Digikey, Mouser and alike). Here is what I have found some far: 1) Transistors for RX front end: relatively easy to find if based on dual-gate MOSFET 2) RX band filters: I have decided to have a fixed capacitor and adjust the inductor.The availability of adjustable coils (Toko for example) has decreased in the last few years. Digikey only stocks a few of them but that should be OK in the near term. 3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be the only 2 frequencies stocked (most commercial boxes use between 35 and 70 MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have disappeared from Digikey (used to be there a few years ago). 4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part that is found in many commercial XCVR is the Toshiba TA31136. This part is not stocked by Toshiba's distributors in the US (12 weeks lead time if you want to order 2K of them). Good news is that the Rohm BA4116FV is a pin-to-pin compatible device and it is available at Digikey for $1.26. I don't know if this part works since I have not seen it used anywhere... 5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz IF.. 6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited availability. The exact type recommended by the IC vendor is hard to find.. 7) FM discriminator. I could not find a source for the ceramic discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the new P/N for the CDB450C24). I can understand the pain of the distributors since every FM IC requires a different discriminator. The discriminator coil that can be used instead is not easier to locate. 8) PLL: I am currently leaning towards National (LMX2306 or similar). They are cheap and available. NS has a nice PLL design tool online but the tool tries to convince me to switch to a better a part that I won't be able to handle (leadless package). It is clear that the new generations IC's are not designed for hand soldering at home... 9) Microprocessor and display: no problem here , plenty of choice. 10) TX chain transistors and PA Module: no problem with the regular vendors. www.rfparts.com seems to have a large selection of modules. 11) TX low pass filter: will need to be hand made. That's OK but who is selling tinned wire ? Some notes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! 2) Some hard to find parts are sometime available as spare for Ham or commercial radios but the prices are generally too high to be considered. 3) One way to go around the hard to find parts is to go with a more discrete solution (no IF/Mixer/DEMOD/SQUELCH IC) and hand wire all the inductors. This is not the way I am planning to go. 4) English is my 2nd language. Excuse the grammar mistakes and hard to understand sentences. |
"Bernard" ) writes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! But amateur radio has always been about scrounging. Once you know enough, you can make do in a lot of cases with what's available rather than what's specified. Indeed, over the decades many an article has been based on what the author had at hand (or in some cases what he thought would be readily available) rather than because there was something special about the parts. A beginner suffers from not knowing enough, and going down to the parts store with the list of parts and having no choice but to live with the prices, or if the parts aren't available. But once they have a more extensive understanding, they know that they can pull those bypass capacitors off that VCR, and use those generic transistors instead of the generic transistors specified in the article. $45 is kind of expensive. Take any older cordless phone, and one is bound to find a double conversion (10.7MHz and 455KHz) FM receiver, often using one of those Motorola ICs. You can get them cheap at garage sales over here, I've stopped bothering with them because they are still plentiful (though I suppose a later generation will be less useful, being more compact and maybe using different IF frequencies). Indeed, buy the handset and the base unit, and you get two IF strips. The ones I've taken apart have a ceramic 10.7MHz filter, of the type you'd find in an FM broadcast receiver, but that happens in a lot of stuff. (Note there are some exceptions, where the units are single converstion dropping from 49MHz to 455KHz, but the one I picked up like that did still use one of those Motorola ICs.) Before FRS took off, there were license free 49MHz superhet walkie talkies, that had dual conversion receivers with the better ones, and they could be adapted with a change of front end coils. These have faded away, so I don't know how available they are (I once bought a pair for twenty dollars at a garage sale), but they're is nothing forbidding their use. Baby monitors maybe, but I've never taken one apart and because of their use I have my suspcions that they may be single conversion, and perhaps even superregen. Old cellphones, the bigger and clunkier the better, offer up narrow band FM IF filters, and even complete IF strips. The first IF will usually be in the 45MHz or higher range, but given that they do include the conversion crystal to 455KHz, it doesn't really matter. The older ones are cheap now, and the further back you go the more discrete components you'll see. They'll be through-hole ICs, and identifiable, rather than more recent ones that are surface mount and much higher density where you can only use the ICs for the intended purpose. One problem that has arisen is that construction articles in recent decades have become more about providing a kit to the builder. Expect the builder to copy it perfectly, buy the exact parts, and maybe even buy it as a kit from the author or a third party. Once that happens, the author focuses on using parts that are easy to come by, and the article is about "building it like this" instead of explaining the philosophy and possible alternatives to the parts. But it's only through understanding that people can look at a schematic and realize they can use that filter they have. The more they are spoon fed the more dependent they become. Michael VE2BVW |
"Bernard" wrote in message
news:5Wwie.9489$jj.5508@lakeread06... I have looked at homebrewing an FM 2-meter XCVR and already got help from this group. The goal is to spend time on something that others could duplicate and not work on a one of a kind. First, why homebrewing ? Two reasons: 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) It seems that the problem is the selection of components that can be sourced in relatively low volume and at a reasonable cost by amateurs (read: Digikey, Mouser and alike). Here is what I have found some far: 1) Transistors for RX front end: relatively easy to find if based on dual-gate MOSFET 2) RX band filters: I have decided to have a fixed capacitor and adjust the inductor.The availability of adjustable coils (Toko for example) has decreased in the last few years. Digikey only stocks a few of them but that should be OK in the near term. 3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be the only 2 frequencies stocked (most commercial boxes use between 35 and 70 MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have disappeared from Digikey (used to be there a few years ago). 4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part that is found in many commercial XCVR is the Toshiba TA31136. This part is not stocked by Toshiba's distributors in the US (12 weeks lead time if you want to order 2K of them). Good news is that the Rohm BA4116FV is a pin-to-pin compatible device and it is available at Digikey for $1.26. I don't know if this part works since I have not seen it used anywhere... 5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz IF.. 6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited availability. The exact type recommended by the IC vendor is hard to find.. 7) FM discriminator. I could not find a source for the ceramic discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the new P/N for the CDB450C24). I can understand the pain of the distributors since every FM IC requires a different discriminator. The discriminator coil that can be used instead is not easier to locate. 8) PLL: I am currently leaning towards National (LMX2306 or similar). They are cheap and available. NS has a nice PLL design tool online but the tool tries to convince me to switch to a better a part that I won't be able to handle (leadless package). It is clear that the new generations IC's are not designed for hand soldering at home... 9) Microprocessor and display: no problem here , plenty of choice. 10) TX chain transistors and PA Module: no problem with the regular vendors. www.rfparts.com seems to have a large selection of modules. 11) TX low pass filter: will need to be hand made. That's OK but who is selling tinned wire ? Some notes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! 2) Some hard to find parts are sometime available as spare for Ham or commercial radios but the prices are generally too high to be considered. 3) One way to go around the hard to find parts is to go with a more discrete solution (no IF/Mixer/DEMOD/SQUELCH IC) and hand wire all the inductors. This is not the way I am planning to go. 4) English is my 2nd language. Excuse the grammar mistakes and hard to understand sentences. I agree with Michael. A Radio/TV repair shop where they dispose of old circuit boards or equipment that cost more $$ to repair ... gold mine of parts (some discontinued -- just start desoldering) DSP-10 designed by Bob Larkin, W7PUA. Kits on sale at Dayton and through TAPR. For more information see http://www.proaxis.com/~boblark/dsp10.htm gb |
"Bernard" wrote in message
news:5Wwie.9489$jj.5508@lakeread06... I have looked at homebrewing an FM 2-meter XCVR and already got help from this group. The goal is to spend time on something that others could duplicate and not work on a one of a kind. First, why homebrewing ? Two reasons: 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) It seems that the problem is the selection of components that can be sourced in relatively low volume and at a reasonable cost by amateurs (read: Digikey, Mouser and alike). Also try Dan's Small Parts for a variety of home builder parts http://www.danssmallpartsandkits.net/ gb |
Bernard, Michael: Thanks for this wonderful question and great answer.
Yea, scrounging and making do with what is available is the way to go. There's a great book "First Light" by Richard Preston. It is about the Palomar Mountain telescope. There is a section on the technical team that builds the modern instruments used with the old 'scope. They got a lot of their best parts by "dumpster diving" in California. 73 Bill M0HBR, CU2JL, N2CQR http://planeta.clix.pt/n2cqr Michael Black wrote: "Bernard" ) writes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! But amateur radio has always been about scrounging. Once you know enough, you can make do in a lot of cases with what's available rather than what's specified. Indeed, over the decades many an article has been based on what the author had at hand (or in some cases what he thought would be readily available) rather than because there was something special about the parts. A beginner suffers from not knowing enough, and going down to the parts store with the list of parts and having no choice but to live with the prices, or if the parts aren't available. But once they have a more extensive understanding, they know that they can pull those bypass capacitors off that VCR, and use those generic transistors instead of the generic transistors specified in the article. $45 is kind of expensive. Take any older cordless phone, and one is bound to find a double conversion (10.7MHz and 455KHz) FM receiver, often using one of those Motorola ICs. You can get them cheap at garage sales over here, I've stopped bothering with them because they are still plentiful (though I suppose a later generation will be less useful, being more compact and maybe using different IF frequencies). Indeed, buy the handset and the base unit, and you get two IF strips. The ones I've taken apart have a ceramic 10.7MHz filter, of the type you'd find in an FM broadcast receiver, but that happens in a lot of stuff. (Note there are some exceptions, where the units are single converstion dropping from 49MHz to 455KHz, but the one I picked up like that did still use one of those Motorola ICs.) Before FRS took off, there were license free 49MHz superhet walkie talkies, that had dual conversion receivers with the better ones, and they could be adapted with a change of front end coils. These have faded away, so I don't know how available they are (I once bought a pair for twenty dollars at a garage sale), but they're is nothing forbidding their use. Baby monitors maybe, but I've never taken one apart and because of their use I have my suspcions that they may be single conversion, and perhaps even superregen. Old cellphones, the bigger and clunkier the better, offer up narrow band FM IF filters, and even complete IF strips. The first IF will usually be in the 45MHz or higher range, but given that they do include the conversion crystal to 455KHz, it doesn't really matter. The older ones are cheap now, and the further back you go the more discrete components you'll see. They'll be through-hole ICs, and identifiable, rather than more recent ones that are surface mount and much higher density where you can only use the ICs for the intended purpose. One problem that has arisen is that construction articles in recent decades have become more about providing a kit to the builder. Expect the builder to copy it perfectly, buy the exact parts, and maybe even buy it as a kit from the author or a third party. Once that happens, the author focuses on using parts that are easy to come by, and the article is about "building it like this" instead of explaining the philosophy and possible alternatives to the parts. But it's only through understanding that people can look at a schematic and realize they can use that filter they have. The more they are spoon fed the more dependent they become. Michael VE2BVW |
Bernard wrote:
I have looked at homebrewing an FM 2-meter XCVR and already got help from this group. The goal is to spend time on something that others could duplicate and not work on a one of a kind. First, why homebrewing ? Two reasons: 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) It seems that the problem is the selection of components that can be sourced in relatively low volume and at a reasonable cost by amateurs (read: Digikey, Mouser and alike). Here is what I have found some far: 1) Transistors for RX front end: relatively easy to find if based on dual-gate MOSFET Last time I looked Digi-Key had a good selection of NEC parts. 2-7, various RF part complaints) The world seems to be going to direct-conversion I-Q receivers with the baseband going to a DSP for processing. Reverse for TX. I think this would work fine for any mode on 2m, including FM if you're clever with your algorithms. 8) PLL: I am currently leaning towards National (LMX2306 or similar). They are cheap and available. NS has a nice PLL design tool online but the tool tries to convince me to switch to a better a part that I won't be able to handle (leadless package). It is clear that the new generations IC's are not designed for hand soldering at home... This is why God made Toaster Ovens. Do a web search on "toaster oven reflow". 9) Microprocessor and display: no problem here , plenty of choice. 10) TX chain transistors and PA Module: no problem with the regular vendors. www.rfparts.com seems to have a large selection of modules. 11) TX low pass filter: will need to be hand made. That's OK but who is selling tinned wire ? Some notes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! Not a bad way to go. 2) Some hard to find parts are sometime available as spare for Ham or commercial radios but the prices are generally too high to be considered. 3) One way to go around the hard to find parts is to go with a more discrete solution (no IF/Mixer/DEMOD/SQUELCH IC) and hand wire all the inductors. This is not the way I am planning to go. 4) English is my 2nd language. Excuse the grammar mistakes and hard to understand sentences. Your written English is most definitely up to par -- if you hadn't mentioned it I wouldn't be able to tell that you're not a native speaker. -- ------------------------------------------- Tim Wescott Wescott Design Services http://www.wescottdesign.com |
Michael,
I did not intend to turn this thread into a philosophical debate (I had enough with the "no progress in decades" thread" !) but your are bringing a good point. I should have stated more clearly that my intend is what you describe as "providing a kit to the builder". We may debate (please don't !) on the value that this brings to the builder. On a 1 to 10 scale, buying a transceiver is a 0 and building it from raw silicon, carbon and copper is a 10+. Where does building a "kit" from an article stand on that scale ? I guess somewhere between 1 and 9. But I am going to firmly defend the fact that it is more than zero. I can find many projects that anybody can build with spares (like many "one transistor radio") but I also believe that to go beyond that you need a PCB and an orderable parts list... When this is done, some may chose a path that will teach them a lot. More than 25 years ago, I did many mods on the first 2-meter FM transceiver that I owned. It was fun but finding the spare Japanese IC's that I burned in the process was a nightmare ! I whish I had done these mods on a XCVR that I built, even if I had to buy the PCB and the key components. Good point on the 49 MHz intercom. I have a pair of them. And you are right, they have a wideband ceramic filter at 10.7 MHz. I guess they need to because they share the second conversion Xtal with the PLL (10.240 MHz) so the IF is really at 10.695 MHz (2nd if is at 455 KHz). This is confirmed by looking at the PLL datasheet. The bad news is that the PLL has a 60 MHz max input with preprogrammed channels. By the way, my intercom is not full-duplex but the phones are. May be somewhere someone is running a repeater with modified 49 MHz phone ! Thanks again ! Bernard "Michael Black" wrote in message ... "Bernard" ) writes: 1) I recently bought a dual conversion 72MHz RC receiver. For $45 (and 13 grams !), one can get one Toshiba TA31136FN, a ceramic discriminator, a 11.155 MHz (10.7 + .455) crystal, one 10.7 MHz crystal and one 455 kHz ceramic filters, one IF transformer, 3 adjustable inductors, one dual-gate mosfet (unidentified), a 3.3V regulator and more. I am not sure what to think except that this might be a non traditional way to source 1/2 of the RX section ! But amateur radio has always been about scrounging. Once you know enough, you can make do in a lot of cases with what's available rather than what's specified. Indeed, over the decades many an article has been based on what the author had at hand (or in some cases what he thought would be readily available) rather than because there was something special about the parts. A beginner suffers from not knowing enough, and going down to the parts store with the list of parts and having no choice but to live with the prices, or if the parts aren't available. But once they have a more extensive understanding, they know that they can pull those bypass capacitors off that VCR, and use those generic transistors instead of the generic transistors specified in the article. $45 is kind of expensive. Take any older cordless phone, and one is bound to find a double conversion (10.7MHz and 455KHz) FM receiver, often using one of those Motorola ICs. You can get them cheap at garage sales over here, I've stopped bothering with them because they are still plentiful (though I suppose a later generation will be less useful, being more compact and maybe using different IF frequencies). Indeed, buy the handset and the base unit, and you get two IF strips. The ones I've taken apart have a ceramic 10.7MHz filter, of the type you'd find in an FM broadcast receiver, but that happens in a lot of stuff. (Note there are some exceptions, where the units are single converstion dropping from 49MHz to 455KHz, but the one I picked up like that did still use one of those Motorola ICs.) Before FRS took off, there were license free 49MHz superhet walkie talkies, that had dual conversion receivers with the better ones, and they could be adapted with a change of front end coils. These have faded away, so I don't know how available they are (I once bought a pair for twenty dollars at a garage sale), but they're is nothing forbidding their use. Baby monitors maybe, but I've never taken one apart and because of their use I have my suspcions that they may be single conversion, and perhaps even superregen. Old cellphones, the bigger and clunkier the better, offer up narrow band FM IF filters, and even complete IF strips. The first IF will usually be in the 45MHz or higher range, but given that they do include the conversion crystal to 455KHz, it doesn't really matter. The older ones are cheap now, and the further back you go the more discrete components you'll see. They'll be through-hole ICs, and identifiable, rather than more recent ones that are surface mount and much higher density where you can only use the ICs for the intended purpose. One problem that has arisen is that construction articles in recent decades have become more about providing a kit to the builder. Expect the builder to copy it perfectly, buy the exact parts, and maybe even buy it as a kit from the author or a third party. Once that happens, the author focuses on using parts that are easy to come by, and the article is about "building it like this" instead of explaining the philosophy and possible alternatives to the parts. But it's only through understanding that people can look at a schematic and realize they can use that filter they have. The more they are spoon fed the more dependent they become. Michael VE2BVW |
"Tim Wescott" wrote in message
... Bernard wrote: I have looked at homebrewing an FM 2-meter XCVR and already got help from this group. The goal is to spend time on something that others could duplicate and not work on a one of a kind. First, why homebrewing ? Two reasons: 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) 8) PLL: I am currently leaning towards National (LMX2306 or similar). They are cheap and available. NS has a nice PLL design tool online but the tool tries to convince me to switch to a better a part that I won't be able to handle (leadless package). It is clear that the new generations IC's are not designed for hand soldering at home... This is why God made Toaster Ovens. Do a web search on "toaster oven reflow". ------------------------------------------- Tim Wescott Seattle Robotics is the group that uses the toaster oven for reflow. It actually works very well ! 'Have you seen my new soldering Iron? by Kenneth Maxon http://www.seattlerobotics.org/encod...6/oven_art.htm g. beat w9gb |
The world seems to be going to direct-conversion I-Q receivers with the
baseband going to a DSP for processing. Reverse for TX. I think this would work fine for any mode on 2m, including FM if you're clever with your algorithms. You are right, for example most of the 802.11 or Bluetooth solutions are zero-IF, but I don't think that this is ideal for Ham Radio (the main issue is re-injection of the LO into the RX). A better option (for us) is the low IF option (like in the DSP10). The DSP10 has an IF at 19.665 MHz and one at 15 KHz. The concept is excellent but slightly overdesigned for what I want to achieve. The drawback (when compared to zero-IF) is that the low-IF receivers still requires dual conversion and IF filters to achieve any level of performance. |
You are right, for example most of the 802.11 or Bluetooth solutions are
zero-IF, but I don't think that this is ideal for Ham Radio (the main issue is re-injection of the LO into the RX). Bernard, If your goal is to make a kit that uses simple, commonly available components and exploits a 'powerful microprocessor' for flexibility, then DSP is definitely the way to go. If properly done, it virtually eliminates the need for all of the old ham-favorite special function chips. With respect to 're-injection of the LO into the RX', I'm not quite sure what you mean. There is the potential for LO leakage out of the antenna port because the LO is on the receive frequency, but this is pretty easily managed with careful electrical and electro-mechanical design. Joe W3JDR "Bernard" wrote in message news:FeBie.17870$ye1.3226@okepread06... The world seems to be going to direct-conversion I-Q receivers with the baseband going to a DSP for processing. Reverse for TX. I think this would work fine for any mode on 2m, including FM if you're clever with your algorithms. You are right, for example most of the 802.11 or Bluetooth solutions are zero-IF, but I don't think that this is ideal for Ham Radio (the main issue is re-injection of the LO into the RX). A better option (for us) is the low IF option (like in the DSP10). The DSP10 has an IF at 19.665 MHz and one at 15 KHz. The concept is excellent but slightly overdesigned for what I want to achieve. The drawback (when compared to zero-IF) is that the low-IF receivers still requires dual conversion and IF filters to achieve any level of performance. |
"Bernard" wrote in message
news:5Wwie.9489$jj.5508@lakeread06... 1) It is homebrewed 2) There is room for a "powerful" microprocessor that will do other things (APRS is one of them) Nice goals, but your target market will be kind of limited. Whatever you come up with is going to cost 2-4x commercial. I can't really see the point of APRS. A nice, compact, inexpensive APRS box would be nice, but a homebrew VHF rig isn't going to get there. Now, maybe a little box with a TNC and GPS built in that would plug into an HT might come close, but that's not what you are focusing on here. 2) RX band filters: I have decided to have a fixed capacitor and adjust the inductor. That does make for harder parts selection. Why that choice? 5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz IF.. 10.7 is a pretty low first IF. You might consider using a higher IF and winding the transformers on toroids. 8) PLL: I am currently leaning towards National (LMX2306 or similar). They Think about DDS. There are some really nice DDS choices from Analog Devices and TI. TI has some really nice, cheap synthesizers. DDS is way less of a pain than PLL. TI's 440 MHz part can easily work down to 2 meters. Yes, they are pretty much all TSSOP but that is manageable to hand solder on a PCB. Messy to prototype but then that will be a problem at VHF anyway. ... |
On Wed, 18 May 2005 10:41:19 GMT, W3JDR wrote:
Bernard, If your goal is to make a kit that uses simple, commonly available components and exploits a 'powerful microprocessor' for flexibility, then DSP is definitely the way to go. If properly done, it virtually eliminates the need for all of the old ham-favorite special function chips. With respect to 're-injection of the LO into the RX', I'm not quite sure what you mean. There is the potential for LO leakage out of the antenna port because the LO is on the receive frequency, but this is pretty easily managed with careful electrical and electro-mechanical design. Joe W3JDR If I remember rightly, there's a description of a DSP-based 2m transceiver in 'Experimental Methods in RF Design...' 73 John, G4GOY |
"Tim Wescott" wrote in message
... This is why God made Toaster Ovens. Do a web search on "toaster oven reflow". Most of the DDS and PLL chips are available in TSSOP. You don't need a toaster oven for that, your typical soldering iron works just fine. Now, if you had to resort to a BGA that would be a different story. I would encourage Bernard to consider mostly SMT parts. SMT resistors and caps are a lot more convenient than leaded, and a lot smaller. Eliminates any issues with lead inductance, too. Maybe a little more expensive, though. Your written English is most definitely up to par -- if you hadn't mentioned it I wouldn't be able to tell that you're not a native speaker. I agree ... |
1) Transistors for RX front end: relatively easy to find if based on
dual-gate MOSFET OK, but you can get better noise figure from a GaAs part. 2) RX band filters: I have decided to have a fixed capacitor and adjust the inductor.The availability of adjustable coils (Toko for example) has decreased in the last few years. Digikey only stocks a few of them but that should be OK in the near term. Mouser stocks a VERY nice line of low cost VHF shielded inductors. Google "xicon" and "tunable coil" on the Mouser website. 3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be the only 2 frequencies stocked (most commercial boxes use between 35 and 70 MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have disappeared from Digikey (used to be there a few years ago). Again, Mouser is your friend -- google "xicon" and "transformer". If I were doing it, I'd do a 70 MHz. first IF and then 10.7 MHz. second IF. Forget dropping down to 455 unless you have to. 4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part that is found in many commercial XCVR is the Toshiba TA31136. This part is not stocked by Toshiba's distributors in the US (12 weeks lead time if you want to order 2K of them). Good news is that the Rohm BA4116FV is a pin-to-pin compatible device and it is available at Digikey for $1.26. I don't know if this part works since I have not seen it used anywhere... Phillips makes (made??) a nice line of FM ICs. You might give them a try. 5) 2nd mixer crystal. The 10.245 MHz crystals are easily available but not the 21.4 +/- .455. This seems to remove the option of using a 21.4 MHz IF.. 6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited availability. The exact type recommended by the IC vendor is hard to find.. Why crystals? You are going to have a synthesizer for the front end anyway, why not use the synthesizer crystal as your timebase and synthesize the mixer oscillator? You said you wanted some stuff for the microprocessor to do anyway; controlling a synthesizer is one of them. Or, you could get a parallel input synthesizer and hardwire it to a fixed frequency. 7) FM discriminator. I could not find a source for the ceramic discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the new P/N for the CDB450C24). I can understand the pain of the distributors since every FM IC requires a different discriminator. The discriminator coil that can be used instead is not easier to locate. A discriminator (or ratio detector) is nothing more than a couple of transformers coupled bottom to top. You can make a two-coil ratio detector as easy as buying one. 11) TX low pass filter: will need to be hand made. That's OK but who is selling tinned wire ? Why would you need tinned wire? Plain old magnet wire is easy to come by. Jim |
Thanks for all the comments. Here is some feedback:
The Palomar telescope: quite an interesting story. My answer: would it be better if many could build their own with parts from Sears and Home Depot or is it better as a one of a kind made from Southern California trash ? DSP10: definitely a very good design but with a different goal. I think that adding a DSP substantially increases the barrier to entry but I take note that this was suggested a few times (even if it will end up just replacing a $1.26 demodulator). In the TX chain the DSP implementation is actually more complicated because it would require an additional mixer (assuming that the only goal is FM) instead of directly modulating the VCO. Taking parts from Radio and TV: this is how I got started in electronic 30 years ago. I would not suggest it to someone who is starting in the hobby. One reason is Murphy. This TV might be in the dumpster just because the one part you need failed ! Dan's Small Parts (http://www.danssmallpartsandkits.net/): very good, thanks for the link. I would sometimes want more information about some parts but I guess this is why there is a phone number to call. Toaster reflow: I will look into this but this getting border line for me ! I decided a few years a go to stop making my own PCB's and order them online (APC circuit or alike). I may do the same for soldering ! Market for APRS + XCVR: I am not looking at it in term of market but rather combining 2 interests (RF and µP) on one platform. Zero-IF: I don't know if this has been done in a decent 2-meter receiver. If anyone has a pointer I would be interested Experimental Methods in RF Design: it is on my list of book to buy now (if you own this book, check the errata. They are online). Mouser: I will have a better look at their line of inductors (by the way, I prefer adjusting the inductor due to some old memories of melting adjustable capacitors !) Philips: yes I looked at them. The only part they have left is the SA615. This market is more or less gone. The big professional users are moving to digital voice... TI: they have fast D/A (400 MHZ) out of which a motivated hobbiest could build a DDS but I did not see synthesizers or DDS parts. I will double check and have a second look at ADI's DDS I will update the group after I make up my mind... Bernard |
Bernard wrote:
Thanks for all the comments. Here is some feedback: The Palomar telescope: quite an interesting story. My answer: would it be better if many could build their own with parts from Sears and Home Depot or is it better as a one of a kind made from Southern California trash ? DSP10: definitely a very good design but with a different goal. I think that adding a DSP substantially increases the barrier to entry but I take note that this was suggested a few times (even if it will end up just replacing a $1.26 demodulator). In the TX chain the DSP implementation is actually more complicated because it would require an additional mixer (assuming that the only goal is FM) instead of directly modulating the VCO. Taking parts from Radio and TV: this is how I got started in electronic 30 years ago. I would not suggest it to someone who is starting in the hobby. One reason is Murphy. This TV might be in the dumpster just because the one part you need failed ! Dan's Small Parts (http://www.danssmallpartsandkits.net/): very good, thanks for the link. I would sometimes want more information about some parts but I guess this is why there is a phone number to call. Toaster reflow: I will look into this but this getting border line for me ! I decided a few years a go to stop making my own PCB's and order them online (APC circuit or alike). I may do the same for soldering ! Market for APRS + XCVR: I am not looking at it in term of market but rather combining 2 interests (RF and µP) on one platform. Zero-IF: I don't know if this has been done in a decent 2-meter receiver. If anyone has a pointer I would be interested Experimental Methods in RF Design: it is on my list of book to buy now (if you own this book, check the errata. They are online). Mouser: I will have a better look at their line of inductors (by the way, I prefer adjusting the inductor due to some old memories of melting adjustable capacitors !) Philips: yes I looked at them. The only part they have left is the SA615. This market is more or less gone. The big professional users are moving to digital voice... TI: they have fast D/A (400 MHZ) out of which a motivated hobbiest could build a DDS but I did not see synthesizers or DDS parts. I will double check and have a second look at ADI's DDS I will update the group after I make up my mind... Bernard I can see this will be a difficult project for you....maybe not technically, but emotionally. If I may say so... I find homebrewing 'any something' falls into one of two broad categories. One is to play around with the mind of experimentation, not to spend too much money at the outset, to learn from the failures, and have the project on the shelf eternally awaiting modifications for better performance.... and typically at several times the cost of a commercial ready-made equivalent. Two - would be trying actually build something state-of-the-art and trouble-free with the anticipation of actually using it on a daily basis....and typically at several times the cost of a commercial ready-made equivalent :-) Neither is bad but they are entirely different disciplines to the hobby of rolling your own and this has to be determined early on as you plan the project. Most of us wind up somewhere between the two extremes. "It works great, but..." Over-thinking the project often results in never getting started. -Bill |
In article ,
says... 8) PLL: I am currently leaning towards National (LMX2306 or similar). They Think about DDS. There are some really nice DDS choices from Analog Devices and TI. TI has some really nice, cheap synthesizers. DDS is way less of a pain than PLL. TI's 440 MHz part can easily work down to 2 meters. Maybe use an image from a plain old AD9850 or AD9851... no need for a fast clock if you only want to cover a 4 MHz chunk of spectrum. The National and Analog PLL chips are great, but not needed here. -- jm ------------------------------------------------------ http://www.qsl.net/ke5fx Note: My E-mail address has been altered to avoid spam ------------------------------------------------------ |
On Wed, 18 May 2005 08:54:23 -0700, "RST Engineering"
wrote: 1) Transistors for RX front end: relatively easy to find if based on dual-gate MOSFET OK, but you can get better noise figure from a GaAs part. True, however most uses for 2m a good transistor or fet will be adaquate and likely easier to use. GaAs fets are harder to use and can easily take off at microwave and harder to find. For real fast lashups I've used MAR or ERA (MiniCircuits) MIMICS and they are the easiest way to get good stable and predictable gain at VHF through microwave and a kit of 30pieces was around 49$ (ERA 1,2, and 3types). Parts can be had for under 2$US in singles. Compared to transistors, FETs and GaAs devices they are noiser but for a lot of things a MAR6 at 3db and 20DB gain to 1000mhz is not shabby. 2) RX band filters: I have decided to have a fixed capacitor and adjust the inductor.The availability of adjustable coils (Toko for example) has decreased in the last few years. Digikey only stocks a few of them but that should be OK in the near term. Mouser stocks a VERY nice line of low cost VHF shielded inductors. Google "xicon" and "tunable coil" on the Mouser website. There are many suppliers. For 2m use it's possible to design with a bandpass frontend easily and then tuning is less an issue. I just wind coils and bend them as needed to tune. Programs to calculate a coild for that are easy to find on the 'net. 3) First IF filters: not much choice since 10.7MHz and 21.4 MHz seem to be the only 2 frequencies stocked (most commercial boxes use between 35 and 70 MHz). The IF inductors/transformers at 10.7 MHz and 455 KHz have disappeared from Digikey (used to be there a few years ago). However for those who care to it's possibel to roll your own. Ladder filters using very common 20 or 24 mhz clock crystals are do able. Again, Mouser is your friend -- google "xicon" and "transformer". If I were doing it, I'd do a 70 MHz. first IF and then 10.7 MHz. second IF. Forget dropping down to 455 unless you have to. Dual conversion using Murata and other 455khz filters is easy. Motorola (3357 and friends) and other have a complete dual conversion IF (everthing after first mixer) in a DIP and all you need is 10.7, CFU455 filters and 455 if can for the quadarture dectector and 10.245 mixer crystal. These are easily ripped from: Baby monitors, (flea markets and garage sales) 49mhz hts (non supperregen) (flea markets and garage sales) Old scanners (flea markets and garage sales) Other older radios that have been 4d (4d diseased, dying, dead or decaying). (flea markets and garage sales) 4) 2nd IF + FM demodulator. The Motorola parts (MC33xx) are gone. The part that is found in many commercial XCVR is the Toshiba TA31136. This part is not stocked by Toshiba's distributors in the US (12 weeks lead time if you want to order 2K of them). Good news is that the Rohm BA4116FV is a pin-to-pin compatible device and it is available at Digikey for $1.26. I don't know if this part works since I have not seen it used anywhere... There are suppliers selling NOS motorola parts: http://www.danssmallpartsandkits.net/ has them sometimes http://partsandkits.com/parts.asp has the 3362 at 2 for 4$ (good source for toroids, NE602 and other bits). Phillips makes (made??) a nice line of FM ICs. You might give them a try. The 604 can be hard to find. 6) 2nd IF filter. The 455 KHz ceramic filters seem to have a very limited availability. The exact type recommended by the IC vendor is hard to find.. Often thats easy to substitute and wider (15kc) ones are easy to find. Why crystals? You are going to have a synthesizer for the front end anyway, why not use the synthesizer crystal as your timebase and synthesize the mixer oscillator? You said you wanted some stuff for the microprocessor to do anyway; controlling a synthesizer is one of them. Or, you could get a parallel input synthesizer and hardwire it to a fixed frequency. The only way to go unless you doing a repeater or other fixed frequency application. One caveat, it's far easier to create a clean crystal LO chain and for super low noise frontends the LO must also have narrow noise sidebands. 7) FM discriminator. I could not find a source for the ceramic discriminator recommended by Toshiba/Rohm (CDLBLA455KCAY24-B0 which is the new P/N for the CDB450C24). I can understand the pain of the distributors since every FM IC requires a different discriminator. The discriminator coil that can be used instead is not easier to locate. A discriminator (or ratio detector) is nothing more than a couple of transformers coupled bottom to top. You can make a two-coil ratio detector as easy as buying one. True, the ratshlock PRO4, Pro12, series and the Pro7 series scanners used a trnsistor 455khs IF and two common IF cans for a discriminator with excellent results. The transistors were of the 2n2222/2n3904 equivelent class easily gotten form JDR at 4-6 cents each. You can do a quadrature detector using a single IF can and a NE602 mixer. 11) TX low pass filter: will need to be hand made. That's OK but who is selling tinned wire ? Why would you need tinned wire? Plain old magnet wire is easy to come by. Yep! tinned is not a requirement. Besides of you do it right you not going to need much. I've used MAR6 mimic (cheap from Minicircuits) as RF with a TUF1 DBM feeding a MPF102 fet with it's output running into a textbook 3357 if chain for both 2m and similar for 440 and it's clean, easy and plenty of gain (sub .12 uv for 10db quieting FM). The Moto 3357 came from a 49mhz HT along with the 10.245 crystal, 10.7 filters and 455filter. I used a moto 145170 pll for the LO. Since the 3367 also does metering and squelch all it needed was audio (LM386-N). The front end was low loss (1db) bandpass before the MAR6 and image stripping (Higher loss bandpass) after the MAR6. the DBM can be one of a dozen different parts had cheap or even hand made (1n914s work ok at 2m). The post DBM fet was not optimized for gain only to buffer the DBM from the Crytal filter (10.7mhz). Of course of you want something as a kit Ramsy has a FM rx for (FR146C is 2m, they have 10m, 6m and 220) that can be used for that range and has fair rx performance but needs either crystal control (NE602 VFO is not adaquately stable) or PLL either of which is usable with that. (it's cheap too! 44.95$US). They do about .7 uV for decent quieting and they do also sell a RF preamp thats decent. I've built both and they work as expected using the VFO and better with crystal control. For experimentors its possible to do it. Parts even old ones are often found from small suppliers at resonable prices. Like someone said earlier learning where and what to look for is a big part of home made radio systems. It also helps to learn how to strip and use "old" parts. Allison KB1GMX |
On Thu, 19 May 2005 00:57:24 -0400, -exray- wrote:
Experimental Methods in RF Design: it is on my list of book to buy now (if you own this book, check the errata. They are online). Must have as well as a Radio Amatuers Handbooks of differing years! I can see this will be a difficult project for you....maybe not technically, but emotionally. If I may say so... I find homebrewing 'any something' falls into one of two broad categories. One is to play around with the mind of experimentation, not to spend too much money at the outset, to learn from the failures, and have the project on the shelf eternally awaiting modifications for better performance.... and typically at several times the cost of a commercial ready-made equivalent. Two - would be trying actually build something state-of-the-art and trouble-free with the anticipation of actually using it on a daily basis....and typically at several times the cost of a commercial ready-made equivalent :-) Then there are people like me. I build in the middle. I often want something that may not be state of the art (but still works excellent) and is specifically not feature laden yet still require stable and robust operation. I've done 6m transceivers that easily hear better than the best and TX with a clean high quality signal that are not state of the art. Please never equate the lack of state of the art with well executed design as the latter can be as good or better due to fewer compromizes that a production design might suffer. Shielding is one matter where the homebrewer can easily exceed commerial. Another area is designs where labor counts. Often my time is cheap but using a commercial coil or crystal filter is not. So making my own may factor $s for time. Neither is bad but they are entirely different disciplines to the hobby of rolling your own and this has to be determined early on as you plan the project. Most of us wind up somewhere between the two extremes. "It works great, but..." Over-thinking the project often results in never getting started. -Bill That kills most projects! Sometimes it's "better" to plunge in and have a few bits that fail or just done meet expectations. If the midset is right you just redesign it, replace it and keep building. Sometimes along the way you can also make a discovery that will enlighten. Allison KB!GMX |
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