[Repeater-Builder] Re: Question re: Crystal Ordering for UHF MICOR Receiver
Amen Larry, I know of a case first hand where the crap from a micor mobile cost the site owner more than $10k to deal with/fix. And the FCC was not the expense... cheers, s. --- In Repeater-Builder@yahoogroups.com, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > > That's for sure about the MICOR UHF transmitter - follow the instructions, including the special MICOR section notes on the Repeater-Builder web site. Lately, every UHF MICOR Repeater transmitter that I've converted to the 440-450 ham band has had a big, nasty spur about 30 MHz above the desired Transmit frequency. I've tuned the filters, circulator, etc. but one transmitter in particular gave me fits. > > I tried tuning the exciter filter repeatedly (which is actually a VHF exciter, 1/3 of the intended UHF transmit frequency) using a signal generator and spectrum analyzer. I tried different exciters, filters, IPAs, 75-watt PA decks, etc. but still had that big spur. I finally hit on the right combination of tweaks in the exciter filter by just using a VHF hand-held radio on the exciter's frequency and looking for maximum output at the filter output on a wattmeter/dummy load. Success, finally - everything was clean. > > A few weeks ago, I was "volunteered" to help another local Repeater group go through their 75-Watt UHF MICOR Repeater, since I had just done one for myself and everything was still fresh in my memory about the things to look out for. Sure enough, this one also had a big spur about 30 MHz above the 440 transmit frequency. We'd never have known except by looking at the spectrum analyzer, and by the excessive power loss through the duplexer since a bunch of the Power Output was not on the intended frequency. This time, I took their exciter filter out, tuned it for maximum power output with the VHF handheld and wattmeter/dummy load and then reinstalled it. Everything was clean and all the power output was on the desired 440 frequency. Lesson learned and verified a second time > > LJ
Re: [Repeater-Builder] Re: Question re: Crystal Ordering for UHF MICOR Receiver
That's for sure about the MICOR UHF transmitter - follow the instructions, including the special MICOR section notes on the Repeater-Builder web site. Lately, every UHF MICOR Repeater transmitter that I've converted to the 440-450 ham band has had a big, nasty spur about 30 MHz above the desired Transmit frequency. I've tuned the filters, circulator, etc. but one transmitter in particular gave me fits. I tried tuning the exciter filter repeatedly (which is actually a VHF exciter, 1/3 of the intended UHF transmit frequency) using a signal generator and spectrum analyzer. I tried different exciters, filters, IPAs, 75-watt PA decks, etc. but still had that big spur. I finally hit on the right combination of tweaks in the exciter filter by just using a VHF hand-held radio on the exciter's frequency and looking for maximum output at the filter output on a wattmeter/dummy load. Success, finally - everything was clean. A few weeks ago, I was "volunteered" to help another local Repeater group go through their 75-Watt UHF MICOR Repeater, since I had just done one for myself and everything was still fresh in my memory about the things to look out for. Sure enough, this one also had a big spur about 30 MHz above the 440 transmit frequency. We'd never have known except by looking at the spectrum analyzer, and by the excessive power loss through the duplexer since a bunch of the Power Output was not on the intended frequency. This time, I took their exciter filter out, tuned it for maximum power output with the VHF handheld and wattmeter/dummy load and then reinstalled it. Everything was clean and all the power output was on the desired 440 frequency. Lesson learned and verified a second time LJ -Original Message- >From: skipp025 <[EMAIL PROTECTED]> >Sent: Jan 2, 2007 9:51 AM >To: Repeater-Builder@yahoogroups.com >Subject: [Repeater-Builder] Re: Question re: Crystal Ordering for UHF MICOR >Receiver > >> On a UHF Micor, AFC is not an option, it's a standard feature. >> UNLESS you are going to disable the AFC functionality of your >> UHF Micor receiver, you'll need to flip the diode polarity > >I found it easier to disable the AFC. If you don't... with a poor >quality crytal in a not so stable (temp) room you'd often find your >repeater quite aways below F-center in the cool morning and quite >aways above F-center in the hot evenings. Being the owner of a >"VFO Repeater" was not something to be proud of. T'was one of my >first real cases of buying cheap crystals that became obvious >real fast. > >Since I never wanted the afc action in the repeater conversions... >I never bothered to change the diodes... I just disabled the AFC. > >> > [EMAIL PROTECTED] wrote: >> > OK thanks - I'm trusting then also that I can do the same on >> > UHF, order high-side injection crystals for my KXN1024A UHF >> > Receiver channel element and leave the discriminator diodes >> > as they are. > >Where I learned the gals at International Crystal know their stuff >very well. If you call and specify the UHF Micor Mobile Crystal for >a KXN-1024 with high side injection... they know what you want and >how to make it with out 100 extra questions. > >Once you get the channel element done right... you need to be sure >you follow the proper manual transmitter alignment instructions. A >shortcut in the tx alignment steps can result in a very nasty >transmitter. > >cheers, >skipp >
[Repeater-Builder] Re: Question re: Crystal Ordering for UHF MICOR Receiver
> On a UHF Micor, AFC is not an option, it's a standard feature. > UNLESS you are going to disable the AFC functionality of your > UHF Micor receiver, you'll need to flip the diode polarity I found it easier to disable the AFC. If you don't... with a poor quality crytal in a not so stable (temp) room you'd often find your repeater quite aways below F-center in the cool morning and quite aways above F-center in the hot evenings. Being the owner of a "VFO Repeater" was not something to be proud of. T'was one of my first real cases of buying cheap crystals that became obvious real fast. Since I never wanted the afc action in the repeater conversions... I never bothered to change the diodes... I just disabled the AFC. > > [EMAIL PROTECTED] wrote: > > OK thanks - I'm trusting then also that I can do the same on > > UHF, order high-side injection crystals for my KXN1024A UHF > > Receiver channel element and leave the discriminator diodes > > as they are. Where I learned the gals at International Crystal know their stuff very well. If you call and specify the UHF Micor Mobile Crystal for a KXN-1024 with high side injection... they know what you want and how to make it with out 100 extra questions. Once you get the channel element done right... you need to be sure you follow the proper manual transmitter alignment instructions. A shortcut in the tx alignment steps can result in a very nasty transmitter. cheers, skipp
