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#1
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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 |
#2
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"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 |
#3
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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. |
#4
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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. |
#5
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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 |
#6
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"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 ... |
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