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 Post subject: Re: Getting There
PostPosted: Fri Feb 08, 2013 10:22 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Jim,
I installed a new SI570 and now have 1.3V RMS coming out of it! After the R39 R40 voltage divider I get about 260mv RMS on Pin 8 of the mixer. Now Keying the transmitter in CW I get a beautiful 10.7 MHz 390mv RMS sine wave going into L10 but a horrible looking waveform of about 115mv RMS coming out and going to pins 3 & 4 of the mixer. I can't even get a frequency measurement on this waveform as it is so bad. So now I am thinking the mixer is bad. I do get a 120mv RMS signal coming out on pin 1 that is the correct frequency (same as the dial freq) but it certainly isn't pretty. Do you think L10 might be the problem and not the mixer that is responsible for the terrible signal going into the mixer IF pins? All other voltages/signals seem reasonable to me but I am still loosing so much signal thru the filters after the mixer there is little or nothing to amplify. As I was writing this and playing with the band settings I just noticed I get a decent signal on C45 when the rig is on 50MHz! By decent I am seeing a little over 30mv RMS on C45. I would think that when the rig is on 50MHz, this would be the only time there wouldn't be any signal going thru C45. I guess I better check the operation of SW1- SW3. I need to figure out how these are supposed to work because something sure seems strange here. Any ideas gladly excepted. :) Thanks, Eric


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 Post subject: Re: Getting There
PostPosted: Mon Feb 11, 2013 7:31 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Right out of the filter (L10) you should have a very mice sine wave. It's hard to think that the filter could mess it up, It might have too high attenuation or incorrect filtering characteristics but it doesn't seem possible for it to introduce time varying distortion. Seems like the mixer has to be doing that.

Maybe you could remove the mixer, put a 50ish ohm resister to ground on pin 3 or 4 and looking at the waveform to see if it's if it is the problem is definitely the mixer.

Jim


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 Post subject: Re: Getting There
PostPosted: Mon Feb 11, 2013 4:54 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Jim,
It looks like my mixer died as I have a very nice 10.7MHz sine wave on pins 3 & 4 of the mixer when I have it removed and pin 3 grounded through a 47 ohm resistor. It is about 85mv RMS and 250mv pk-pk. I'll get one on order. Thanks again for your support, Eric


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 Post subject: Re: Getting There
PostPosted: Sun Feb 24, 2013 12:20 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
The new mixer and the change of components for the 10/12 meter filter has cured the problems on 10 and 12 meters. I made my 1st contact today on 12 meters with OP2A in Belgium. He gave me a 5 and 2 report and made comment on how nice clean and crisp my audio was. I was using my GAP Titan vertical for an antenna and it doesn't have the best match on this frequency so I am very pleased with the performance. I still need to figure out why my output is only about 1 watt on 6M and I am getting about 15 watts out on 10 and 12. I still have a problem with crashing the radio at times tuning and I am using a CUI C14 N16N-A3 optical encoder. This encoder only has 16 pulses/revolution but thought it would work OK and it does except for crashing the radio and putting garbage in the display from time to time. Can you recommend an encoder that will work better or do you think this is the problem? Thanks for your help and I am getting close to having this working as it should. Eric


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 Post subject: Re: Getting There
PostPosted: Sun Feb 24, 2013 10:44 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
Eric:

Have you installed debouncing capacitors on your mechanical encoder? That will mostly solve the crashing problem.

Now, I'm using a Clarostat 600 series optical encoder with 128 increments per revolution. (I bought it from Newark for about $35.) It is very smooth; and it never crashes the system.

--Marc


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 Post subject: Re: Getting There
PostPosted: Mon Feb 25, 2013 6:45 am 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Hi Marc,
Yes I the caps installed on both encoders actually and am pretty sure that it has to be the optical encoder that I am using as that is the only time the system crashed. Especially when I am moving it very slowly. I may follow your lead and use the one you are using. Thanks for the advice and information.
73's,
Eric


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 Post subject: Re: Getting There
PostPosted: Wed Feb 27, 2013 7:17 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Marc,
I installed the encoder you suggested and it works beautifully. I have played with the radio for about 20 min and it has yet to crash. :D Now if I could only figure out why I have so little output on 6M I could button this up and call it done. I am sure I will find that problem eventually and I really appreciate your suggestion for this encoder. The other optical encoder was better then the original encoder listed in the BOM but not nearly as nice as this one. It sure doesn't take long to tune across the band with 128 pulses per revolution! I think I would have preferred one with a little less counts per revolution but this one doesn't crash the radio and that is HUGE! Maybe this will be fine to tune with but the band is dead at the moment and I haven't had a chance to see how it tunes a station. Thanks again for the recommendation of this replacement, Eric


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