> Awe c'mon Scott, I'm not gonna let you get off without explaining where the > extra stage of multiplication is!
I was quite confused myself..... then I sat and did the math. Realize that 3x3=9.... Simple enough. But 2x3x3, 3x2x3, 3x3x2, 4x3, or 3x4 all equal 12, so it could have been any of these that made things work. Here is my theory using 222.400Mhz operating frequency: LO = 211.2 Mhz Crystal Freq. = ~23.466 X9 (tripler & tripler) 23.4667 x 3 = 70.400 x 3 = 211.2 Crystal Freq. = ~17.600 X12 (quadrupler & tripler) 17.6000 x 4 = 70.400 x 3 = 211.2 There you go! In one instance it is using the first stage as a tripler and in the other it is being used as a quadrupler. > So in your test you only changed the LO to do the comparisons? Are you > comfortable there were no other variables? I also investigated the mixer area after I played with the LO. I wasn't able to make any improvement in sensitivity, but I was able to change where the short was applied to make the cap tune more in the center of its range. > I traded emails with David VE7LTD and he made a note that the metering point > diode may not be perfect for the LO on 220, which I noticed. The values I'm > used to seeing were much lower but sensitivity was good. I concur. In the final mod, there was about the same meter 3 as with a VHF, but meter 4 was low in comparison. Limiter current - meter 1 - seemed to be way off. It took lots of signal to make it work properly. Scott Scott Zimmerman Amateur Radio Call N3XCC 612 Barnett Rd Boswell, PA 15531 ----- Original Message ----- From: Don To: 'Scott Zimmerman' Sent: Friday, March 23, 2007 1:23 PM Subject: RE: [Repeater-Builder] Re: 220 conversion Awe c'mon Scott, I'm not gonna let you get off without explaining where the extra stage of multiplication is! So in your test you only changed the LO to do the comparisons? Are you comfortable there were no other variables? End results are very helpful if the only variable is the LO. I traded emails with David VE7LTD and he made a note that the metering point diode may not be perfect for the LO on 220, which I noticed. The values I'm used to seeing were much lower but sensitivity was good. FYI 73 Don W5DK ------------------------------------------------------------------------------ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Zimmerman snip 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.) SNIP ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.446 / Virus Database: 268.18.17/730 - Release Date: 3/22/2007 7:44 AM
