Looking for 8.8125 MHz xtal
Hello all,
I'm slowly working through my backlog of projects, and I found the MMDS LNB that I'd planned to use for AO-40. I'm hopeful that we'll eventually have another 13cm transponder and I'd like to find the requisite 8.8125 MHz crystal for the LO conversion.
ICM did respond to my inquiry, so they're not totally out of business yet, but they don't have it anymore.
Does anyone have a spare crystal they'd care to part with for a nominal price?
Specs from one of the webpages:
Crystal Update Information
The original crystal has been analyzed by International Crystal. A
+replacement crystal should have the following characteristics:
The crystal is in a HC-49U holder 33 pF load capacitance Accuracy of 10ppm at room temp and 10ppm -30 to 60 celsius. Frequency = 8.8125 MHz for a 145 MHz IF output The specification number at Internaltional Crystal Mfg. isEX49AF320119. Their catalog number is #525345, 8.8125 MHz
Thanks,
--- Zach N0ZGO
Hi Zach,
Whoa, your message raised a bunch of mental dust... Is this for the infamous Drake 2880 downconverter?
Perhaps as an alternative, the approach I took with mine was to not force the IF to be in the 2m ham band, but rather to center it in the Drake's original 200-400mhz passband. I would then use my ICOM IC-R7000 all mode scanning receiver for the remainder of the RF chain. A local oscillator frequency of 2100mhz put AO-40's 2401 mhz downlink at 301 mhz (easy math). It ended up working reasonably well.
Putting the IF outside the ham band gave me the flexibility to use either (any) ham band for the uplink, without worrying about interference. If you are looking to a future as-yet unknown bird, that might be a good idea. If they use 2m for the uplink, using that for the IF as well is going to be a problem. It also left (and used) the Drake's original passband filtering unmodified, improving the unit's performance. In place of the ICOM receiver, I would now use an SDR Dongle, something not yet available back in the day.
The crystal I ordered was 8.203125 mhz. It was from ICM, but perhaps they might have that value (or something close to it)? Their part number was EX45AF15.
Good luck!
Greg KO6TH
Zach Metzinger wrote:
Hello all,
I'm slowly working through my backlog of projects, and I found the MMDS LNB that I'd planned to use for AO-40. I'm hopeful that we'll eventually have another 13cm transponder and I'd like to find the requisite 8.8125 MHz crystal for the LO conversion.
ICM did respond to my inquiry, so they're not totally out of business yet, but they don't have it anymore.
Does anyone have a spare crystal they'd care to part with for a nominal price?
Specs from one of the webpages:
Crystal Update Information
The original crystal has been analyzed by International Crystal. A+replacement crystal should have the following characteristics:
The crystal is in a HC-49U holder 33 pF load capacitance Accuracy of 10ppm at room temp and 10ppm -30 to 60 celsius. Frequency = 8.8125 MHz for a 145 MHz IF output The specification number at Internaltional Crystal Mfg. isEX49AF320119. Their catalog number is #525345, 8.8125 MHz
Thanks,
--- Zach N0ZGO _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
On Thu, Jun 01, 2017 at 10:31:39AM -0700, Greg D wrote:
Hi Zach,
Whoa, your message raised a bunch of mental dust... Is this for the infamous Drake 2880 downconverter?
Perhaps as an alternative, the approach I took with mine was to not force the IF to be in the 2m ham band, but rather to center it in the Drake's original 200-400mhz passband. I would then use my ICOM IC-R7000 all mode scanning receiver for the remainder of the RF chain. A local oscillator frequency of 2100mhz put AO-40's 2401 mhz downlink at 301 mhz (easy math). It ended up working reasonably well.
Putting the IF outside the ham band gave me the flexibility to use either (any) ham band for the uplink, without worrying about interference. If you are looking to a future as-yet unknown bird, that might be a good idea. If they use 2m for the uplink, using that for the IF as well is going to be a problem. It also left (and used) the Drake's original passband filtering unmodified, improving the unit's performance. In place of the ICOM receiver, I would now use an SDR Dongle, something not yet available back in the day.
Hello Greg,
Good guess, but not quite! This is a California Amplifier LNB that I picked up when AO-40 started having problems, so I tossed it in a box and forgot about it. Recent work has me digging back into those boxes and going down rabbit holes long since forgotten about. :-)
Using an SDR or a general-coverage receiver is a good idea for fixed-base work, but I don't have anything mobile that is general coverage. I do appreciate the ideas!
--- Zach N0ZGO
Hi Zach,
Oh, ok. No direct experience here for the CA LNB, but I seem to remember people modifying it in similar ways to the Drake. If so, the same technique could work. The idea is to give yourself the maximum flexibility for whatever bands and modes might be used in the future.
Don't forget, an SDR dongle can work very well mobile, as laptops do well in that environment, and could set you up for some of the digital modes that could be employed. I even plugged mine into my Android tablet with SDRTouch. Lots of options for these versatile gems. Many use them for the current crop of satellites, but be sure to get one with good front-end filtering (or add it externally) or you could get a strong desense.
One of your challenges is going to be knowing exactly what the conversion equation is, i.e. where exactly your LO ended up. Given the frequencies and multipliers involved, a very small offset in the LO crystal can result in a large offset in actual receive, making it difficult to find the satellite the first time. I think mine was off by something like 50 mhz on AO-40, even after tweaking the LO with a frequency counter. Very touchy.
For testing, and given that there's not much ham-related stuff on that band, you might scan the horizon and count microwave ovens (2450 mhz -ish), though they are not very frequency-stable. Best is around dinner time :) I also had good results listening for the 17th harmonic from a 2m transceiver fed to a diode as the load (144*17 = 2448). You might even try that with the 18th or 19th harmonic (2592 or 2736 mhz) on an unmodified unit, to be sure it's still working.
Good luck,
Greg KO6TH
Zach Metzinger wrote:
Hello Greg,
Good guess, but not quite! This is a California Amplifier LNB that I picked up when AO-40 started having problems, so I tossed it in a box and forgot about it. Recent work has me digging back into those boxes and going down rabbit holes long since forgotten about. :-)
Using an SDR or a general-coverage receiver is a good idea for fixed-base work, but I don't have anything mobile that is general coverage. I do appreciate the ideas!
--- Zach N0ZGO
On Thu, Jun 01, 2017 at 01:29:10PM -0700, Greg D wrote:
One of your challenges is going to be knowing exactly what the conversion equation is, i.e. where exactly your LO ended up. Given the frequencies and multipliers involved, a very small offset in the LO crystal can result in a large offset in actual receive, making it difficult to find the satellite the first time. I think mine was off by something like 50 mhz on AO-40, even after tweaking the LO with a frequency counter. Very touchy.
For testing, and given that there's not much ham-related stuff on that band, you might scan the horizon and count microwave ovens (2450 mhz -ish), though they are not very frequency-stable. Best is around dinner time :) I also had good results listening for the 17th harmonic from a 2m transceiver fed to a diode as the load (144*17 = 2448). You might even try that with the 18th or 19th harmonic (2592 or 2736 mhz) on an unmodified unit, to be sure it's still working.
Greg,
That's a great idea on the 2m rig as an exciter for a diode comb generator. I'll have to try that out tonight on my unmodified unit! I assume that you attached the diode on the other side of a 20 dB pad to give some sort of reasonable return loss for the rig?
Many thanks go to Alan wa4sca@gmail.com for providing the requisite crystal. My alternate plan was to replace the LO generation in the unit with a custom PLL board. That might be interesting to do and then compare the xtal modification with the custom PLL for phase noise and overall performance.
--- Zach N0ZGO
Looking back in my notes, the diode-based generator idea was from K5OE, where he put a 1N4005 diode in parallel with five 47K 1/2 watt resistors (so, all 6 in parallel), driven at 29.999 mhz directly from his HF rig. I did the same from my 2M HT, and it seemed to work. Also a lot more portable. No clue what sort of return loss it presented, but the HT survived just fine.
http://home.wavecable.com/~ko6th/Dsc00067.jpg
I also tried using a 50mhz crystal oscillator module connected directly to a small 13cm ground plane antenna. That worked too, though the signal was much quieter (48th harmonic).
Greg KO6TH
Zach Metzinger wrote:
That's a great idea on the 2m rig as an exciter for a diode comb generator. I'll have to try that out tonight on my unmodified unit! I assume that you attached the diode on the other side of a 20 dB pad to give some sort of reasonable return loss for the rig?
On Thu, Jun 01, 2017 at 03:31:49PM -0700, Greg D wrote:
Looking back in my notes, the diode-based generator idea was from K5OE, where he put a 1N4005 diode in parallel with five 47K 1/2 watt resistors (so, all 6 in parallel), driven at 29.999 mhz directly from his HF rig. I did the same from my 2M HT, and it seemed to work. Also a lot more portable. No clue what sort of return loss it presented, but the HT survived just fine.
http://home.wavecable.com/~ko6th/Dsc00067.jpg
I also tried using a 50mhz crystal oscillator module connected directly to a small 13cm ground plane antenna. That worked too, though the signal was much quieter (48th harmonic).
Well, since it worked for your DJ-580T, I bet it will work on mine, too.
Not sure I have that exact rubber band, however. :-)
--- Zach N0ZGO
participants (2)
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Greg D -
Zach Metzinger