Sorry I haven't responded to this is previous, but I did some research. I actually converted a GE Mastr II receiver to 220. (Several times actually!!)
As they say in the world of mathematics, "I ran through all the permutations". I used 2 5C compensated elements from Bomar on 222.400 for my testing. One was a x9 multiplier with a crystal frequency of 23.46666. The other was a x12 multiplier with a crystal frequency of 17.600. Both of these were used for low-side injection. These were obtained while researching the cross-talk phenomenon that happens between transmit harmonics and receiver sensitive spots. (More about that in different articles to come) Here is what I found: http://homepage.mac.com/pseabolt/mods/oscillat.htm The mods from W4UWH work OK. The best sensitivity I could get from tuning and re-tuning and trying different combinations of capacitor tuning positions, was about -106dB for 12dB SINAD. The most interesting thing was that either ICOM seem to work equally well! (I don't understand it either, but I was able to tune and make the same sensitivity with either crystal.) This mod worked, but it seemed to be a lot of hocus-pocus magic to get the LO to tune correctly. I DID NOT change the transistors as suggested in the article. I'm not sure if that would have helped the sensitivity or not. Frankly I was so dismayed at how difficult it was to tune that I simply didn't take the time to swap the transistors. Due to the lack of suggestion of a formula change and the fact that he changes all of the stages in the LO chain, I would agree with those that this modification is simply a "raise the frequency" type mod. It does not change the multiplier from a x9. http://www.jonadams.com/pages/amateur_radio/ge_mastr_2_220mhz_mods.htm These mods are very similar to the mods I settled on as my final recommendation. They change the multiplier from a x9 to a x12. This fact is spelled out in the conversion. The change is done in the last 2 stages of the LO. The first LO stage remains as-is. The second tripler is changed to a doubler and the third buffer stage is changed to a tripler. Everything seems to work ok until the last tripler stage. I'm not sure if it's an omission in the mods or what happened, but the author doesn't change anything in the final stage to make it a tripler! I couldn't get this mod to work at all. http://www.condor-connection.org/mods/mastr2.htm The condor connection's mods seemed to work the best. They are the same as the Jon Adams mods above, but they actually make a modification to the inductor in the last stage. This makes the stage tune correctly as a tripler. This mod seemed to have LOTS of injection level. With this mod, tuned per the book the first time, I was able to make 12dB SINAD at -115dB of signal. This is what I would have expected to see. This mod seems well suited to repeatability. It will need re-written with some descriptive pictures, but it works. The tuning of it impressed me especially. My plan is to take pictures of the "winning" mods exactly as I did them, make them into a bit better article, and post them for all to use. I should have this done later today. Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 ----- Original Message ----- From: "w5dk_don" <[EMAIL PROTECTED]> To: <Repeater-Builder@yahoogroups.com> Sent: Tuesday, March 20, 2007 2:25 PM Subject: [Repeater-Builder] Re: 220 conversion > Scott, > Thanks for your summary and also the previous note regarding > stabilty of xtals when using the rocks above 18 megs. My recieve > xtal is 23 something so your experience mentioned was noted here. > > But below you mentioned a rc xtal formula change from vhf but linked > to the W4UWH method, which I used recently. It uses the standard VHF > math. I think thats an error. > > Also on the IF/mixer, I made that one short on the bottom/non > component side from a through hole on the board to a ground trace. > It was easier than dealing with the resistor. Not sure if every > board has a hole under that coil right where ya need it. > > 73 > Don W5DK > > --- In Repeater-Builder@yahoogroups.com, "Scott Zimmerman" > <[EMAIL PROTECTED]> wrote: >> >> I went to the Condor site and notice that they don't give a > formula for the Rx crystal, is it the same as for the M2 mod? >> >> I'm not sure. Here at repeater builder we use the following for > 220 Mastr II's >> >> For the PLL exciter: (preferred) >> http://www.repeater-builder.com/ge/mastrII222pllexciter.html >> >> For a phase exciter: >> http://www.condor-connection.org/mods/mastr2.htm >> >> Helical assy: >> http://homepage.mac.com/pseabolt/mods/rf_assembly.htm >> >> PA assy: (we use our AMPBD for a circuit board) >> http://homepage.mac.com/pseabolt/mods/pa.htm >> http://www.repeater-builder.com/products/ampbd.html >> >> Osc. Mult: (I have not found it necessary to replace the > transistors as described) >> http://homepage.mac.com/pseabolt/mods/oscillat.htm >> >> Mixer board: >> http://homepage.mac.com/pseabolt/mods/mixer.htm >> >> In the above receive conversion, the crystal multiplication factor > has changed from x9 to x12. You can now use the formula: fc=(fo- > 11.2)/12. This should give you a crystal in the 17-18 MHz range. If > you are ordering from Bomar Crystal, you can specify part #19A129393 > \12. >> >> The above is for a Mastr II. I would think that the MVP and Exec > II would be similar. I have only done an MVP exciter, not the > complete radio, so I can't speak about how to convert the MVP > receiver. >> >> Good Luck. >> >> Scott >> >> Scott Zimmerman >> Amateur Radio Call N3XCC >> 612 Barnett Rd >> Boswell, PA 15531 >> >> ----- Original Message ----- >> From: James H Vernetti >> To: Repeater-Builder@yahoogroups.com >> Sent: Tuesday, March 20, 2007 12:19 PM >> Subject: Re: [Repeater-Builder] 220 conversion >> >> >> Scott thanks for the info I am just in the planning stage for > this project and trying to line all the ducks up in a row, I have > both M2 and MVP available to convert. I went to the Condor site and > notice that they don't give a formula for the Rx crystal, is it the > same as for the M2 mod? >> 73 >> Jim wd0ekr >> >> >> >> ------------------------------------------------------------------- > ----------- >> >> >> No virus found in this incoming message. >> Checked by AVG Free Edition. >> Version: 7.5.446 / Virus Database: 268.18.15/728 - Release Date: > 3/20/2007 8:07 AM >> > > > > > > > > Yahoo! Groups Links > > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.446 / Virus Database: 268.18.16/729 - Release Date: 3/21/2007 > 7:52 AM >
