First let me start out by saying that I currently have an SCR1000 in service on 2 meters but the Mastr II is cooking on the bench and will replace the Spectrum as soon as I finish the box to move the CAT-1000 into.
At 08:43 PM 11/26/2003, ac0y5 wrote: >It seems a lot of the complaints are from oscillator drift and >tuning drift. I have a few questions Does anyone know if the main >problem resides in the exciter, or the power amp? I have replaced the PA in this SCR1000 because the old one failed. This is a 75 watt model which has the power control board (which gives you high/low power switching). The manual tells you that you MUST re-align the exciter to make it work properly on the reduced voltage. I always found it to be a bit unstable so it always stayed on high power. If you tune the PA, you'll find some instability there also. I don't know the answer to the question of bad components or bad design. I'd rather stick with what I've got personal experience with. As for oscillator drift, the SCR1000 was available with a crystal oven but mine didn't come that way. It's lived its entire life in the house where there have been no extremes of heat and cold. Yet, it would still move around some. I did place a small light bulb (in series with a resistor) right in the oscillator portion of the exciter board and it seemed to become more stable. >My plan would >eliminate all problems related to the oscillator because the Tx and >Rx will be generated from a pair of Numerically Controlled >Oscillators well filtered. I have already designed the entire >circuit. Now, if Anyone knows where the problem may lay then I will >be able to take care of the problem an external PA that I have or an >exciter that I can buy cheaply. The power supply should be okay I had problems with the power supply. In the 75 watt model the power resistors which are mounted on terminal strips between the transformer and the large heat sink on the back get so hot that they will melt their leads right out of the solder. That compounds the problem and led to erosion of a resistor lead and supply failure. The entire supply is horribly inefficient, generating more heat than the entire unit consumed in its electronics. I finally removed the transformer, the resistors and the large heat sink with the pass transistors and powered the unit externally. >and >it has been stated that the receiver is quite sensitive. If >necessary I can add a 5 or 7 pole helical resonator to the front end. It's sensitive if you can get it tuned without desensitization. That's the biggest problem with the receiver. It isn't as sharp as commercial receivers like the Mastr II or Micor so don't expect that kind of performance. From your many other posts it would appear you have considerable repeater experience which makes me wonder why you would want to take this on. It's not a joy to work on. The controller is junk (I replaced it with a CAT1000 over a decade ago). It's just old technology that doesn't come close to the old technology you find built by GE and Motorola. If you must redesign the oscillators, replace the exciter and PA, redesign/modify the receiver, come up with a controller, perhaps replace the power supply, hope the switches aren't intermittent (like some of mine), replace the meters (the originals were useless), toss the local microphone and get something better, what's left? It WAS a pretty box. I just spent the evening drilling a front panel for my new VHF controller box which will contain the CAT1000, some interface stuff, a TS64, 4-LEDs, a volume control, a squelch control, enable/disable and simulate switches for COR, CTCSS and PTT, a speaker, a fuse, and on/off switch, and two test jacks to access the speaker leads from the front. It will look and function almost identically to the controller (containing a CAT250) that I use with the UHF Mastr II. The Spectrum is going away... finally. Good luck with your project. I'd be interested to know how it all works out for you. 73 and Happy Thanksgiving everyone! Tony W4ZT Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
