Don, Do you have a manual? The 5 helical resonators together are the front end and the three together are the tuning for the injection to the mixer. Really easy radio to work on. Are the 461.XXX crystals EF Johnson or another make. A 461 receiver really should come down to 440 OK. It still sounds like you need to add some to the helicals.
Paul -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] Behalf Of donlspivey Sent: Tuesday, February 28, 2006 12:58 PM To: [email protected] Subject: [Repeater-Builder] Re: Help With EF Johnson CR-1000 Repeater Thanks for the help Paul: Originally it was on 461.375, which appears to be from the factory. Both the exiter and receiver look to be a cast mobile radio chassis remounted for rack use with unnecesscary circuitry not installed. All looks original and non modified. It's very clean. The receiver has a row of 5 helicals then three more used in other ways, mixer..etc. The exciter chassis does not have the holes where the helicals screws would have gone threaded, so it's not a mobile converted to repeater service. Unless there's another issue as to why I the sensitivity isn't there, it looks to be in great shape. No repairs are apparant, nobody has butchered it. I mentioned that I went through the factory tune up procedure step by step and each time the voltage I found was below the range given in the service docs. I also mentioned after changing the helical screws/slugs the sensitivity increased a lot and those voltages did get a lot closer to the bottom end of the range it gives. I mentioned I changed the JFET in the mixer although a generic sub within the correct frequency range and voltages. With the exception of needing to change the compensating cap for the new crystal, I had the exciter tuned up in about 5 minutes. I believe it was putting out 15 watts with the original crystal and I had exactly the same after retuning it. Sure looks like it's still an issue with the helicals. Much like I've encountered with Micor receivers. However, this is my first EFJ repeater so any hints or tips would be greatly appreciated, the boys down here with ARES are appreciative too. Thanks again for your help...Don --- In [email protected], "Paul Finch" <[EMAIL PROTECTED]> wrote: > > Don, > > Do you know what band the radio was on when in service? If it was a 480 MHz > radio it would tune to 460 but have major problems tuning to 440. If this > was the case you need to lengthen the helical resonators about 1/2 turn to > start with, that is if my memory serves me right. > > That is a very good receiver, what does it look like, they had a couple > different versions. Both had the same basic electronics but different > housings. > > Does the exciter tune up? > > Paul > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] Behalf Of donlspivey > Sent: Monday, February 27, 2006 9:48 AM > To: [email protected] > Subject: [Repeater-Builder] Help With EF Johnson CR-1000 Repeater > > > Ok you Johnson ghuru's out there, please read this. > > I was asked by an area ARES group to lend a hand and convert an > EF Johnson CR-1000 series UHF repeater to amateur use. This is, of > course, free gratis on my part, I'll even chip in the ID'er since it's > for a good cause. > > I cannot get the receive sensitivity where it should be. Initially > when I received it, the JFET located inside the preselector was blown. > I replaced it with a generic JFET but not an exact match. > > At first I couldn't get the sensitity any lower than about 50uv and > several tuning screws were bottomed out in the row of helicals > suggesting the new frequency is beyond the range of the preselector. I > replaced the screws with a similar brass screw but about 3/8 in longer > and I was able to get the sensitivity down into the 10-15uv range, > obvioiusly a big improvement, but still way off. No screws were > bottoming out at this point. > > I first retuned the receiver as per the factory manual. I did, > however, note the suggested minimum voltage reading I should see were > always lower. I've really never particularly paid strict attention to > these "should be about" readings, but all increased after the machine > screw changeout suggesting they could possibly increase more once the > proper sensitivity is reached. > > Does anyone have experience with this repeater or the mobile chassis > it's patterned after? I can assume the helicals will need > modification, but that's why I asking the experts!!!! > > The group that will own/manage this repeater are buidling their shack > this week and hanging hardline, so it looks like I may be the "holdup" > here. Please point me in the right direction...Thanks...de N5MZQ > > > > > > > > > > > Yahoo! Groups Links > Yahoo! Groups Links 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/
