[Repeater-Builder] Re: Hamtronics PLL exciter
Was the original final transistor heat sink only anchored to the transistor case by a pressure fit? Did you try to firmly anchor the original heat sink with some type of insulated mounting hardware? skipp Bryan Fields [EMAIL PROTECTED] wrote: As we have had many issues with our 220 PLL exciter with microphonics and other noise, most of this was traced down to the final amp stage. This stage uses a Phillips to-38 style transistor which has the collector commen to the case, and Hamtronics puts a big heatsink on the case! Needless to say this creates a bunch of noise on the final signal due to RF being on the heatsink. We have been able to get about 3.0W out of it starting out ice cold, but after it heats up, it goes as low as 900mW. I replaced it with a NTE341 (MRF237 equiv), which has the emitter commen to the case and is designed to have the case soldered to the ground plane of the board for heatsinking. To make it fit it needs to be mounted backwards so i had to drill a hole for the base pin to go through an remove the green solder mask on the ground plane. I did not do any math on the circuits so my matching is probably not optimal, the only thing done was to change out the input and out put matching cap's with variable units that we had on hand. After this was done, I was able to get 2.30W out (@13.8V)of the exciter with no drop off due to heat, and 95% of all microphonics were eliminated! The output was checked after 1 hour and it was still at 2.28 watts output, so it looks like it was a success. I would think we could get more output if the matching networks were redone, but I did not feel like screwing with the coils for the backup repeater. I may do that in the future, and also try the real Motorola mrf237 in the circuit and see how it compairs to the NTE part. -- Bryan Fields, KB9MCI 22:58:17 up 15 min, 1 user, load average: 1.31, 0.93, 0.73 You will be surprised by a loud noise. Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Hamtronics PLL exciter
--- In Repeater-Builder@yahoogroups.com, skipp025 [EMAIL PROTECTED] wrote: Was the original final transistor heat sink only anchored to the transistor case by a pressure fit? Did you try to firmly anchor the original heat sink with some type of insulated mounting hardware? You'd still get significant capacitive coupling to the heat sink. The emitter-case transistor is a much better solution. Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Re: Hamtronics PLL exciter
Well, yes and no... you are right to think along the lines of the isolated or emitter-case (the emitter lead grounded) transistor being a better solution. One could use a Delrin, Teflon, G4 or G10 material to firmly secure the original heat sink. The added capacitance should be minimal if you were carefull. Also note the original transistor had more output, so one would have to also take that into consideration. There's always a better mouse trap... cheers, skipp Dave VanHorn [EMAIL PROTECTED] wrote: You'd still get significant capacitive coupling to the heat sink. The emitter-case transistor is a much better solution. skipp025 [EMAIL PROTECTED] wrote: Was the original final transistor heat sink only anchored to the transistor case by a pressure fit? Did you try to firmly anchor the original heat sink with some type of insulated mounting hardware? Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Re: Hamtronics PLL exciter
On Monday 30 January 2006 04:21 pm, skipp025 wrote: Also note the original transistor had more output, so one would have to also take that into consideration No, it would drop off to just under a watt after 10 min. The replacement does 2.3 watts after 1 one hour, so it's got more output as far as I see. -- Bryan Fields, KB9MCI 17:38:52 up 44 min, 2 users, load average: 0.36, 0.43, 0.36 When you live in a sick society, just about everything you do is wrong. Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
