| Author |
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Anonymous
| | Posted on Thursday, June 14, 2001 - 2:37 pm: | 
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Have 2- 2950's, a Mirage and an RCI. Both old type. The Mirage's rx section seems noisier. Can the front end be tuned up (hate to use that word!)or do I have to live with it? All things equal, the Mirage is noisier, RCI rcvr. is better. I know they're the same boards- right????? |
307 (307)
| | Posted on Thursday, June 14, 2001 - 6:54 pm: |
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They are the same radios and YES they could be tuned up a little. There are some adjustments to enhance the ANL/NB. |
307 (307)
| | Posted on Thursday, June 14, 2001 - 6:57 pm: |
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The NB works like this , when a spike is detected it shuts down the front end so that it will not pass through the filter. It shuts it down so fast that you can not detect it. The ANL is actually a filter around the AM detecter that clips off anything above 3/10's of a volt. You can also clean up noise by putting a set of germanium diodes back to back across the AM detector to ground and this will help. |
WALTERB
| | Posted on Thursday, June 14, 2001 - 11:57 pm: |
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Have had a lot of these radios, sometimes all you have to do is back down L9 clockwise just a little and i mean a little but make sure you turn it clockwise, that will quite the reciever, scribe the pot before you start so you can move it back to where it was before you started if that is not to your lickings. 2950 have way more gain than needed and sometimes they set them a little Hot and you pick up a little more noise than is necessary. I think it was 307 that said that they don't check every radio and they can be a little off. |
Mr_Rf
| | Posted on Monday, December 24, 2001 - 10:39 pm: |
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Continuing this issue I am looking for an truely experienced tech's answer...
Seems a lot of the locals I talk to that have a Mirage 2950 experience more than the usual "hiss" from the speaker even with the antenna unhooked. I borrowed a 2950 from a friend for a few days and noticed the problem (pretty darned annoying). Before I dive into one of these with a little trial & error does anyone have the answers to the following:
1. Is there just too much front end/IF gain causing this problem to be common, or is either the mixer and/or VCO typicaly noisy?
2 If so, is there a certain transistor/FET in the mixer or vco that is usually the common cause, and a known better replacement for it?
3. I could also use a copy of the board layout and schematic for the RF sections. Can anyone help?
Thanks,
Mr_RF |
Inspector
| | Posted on Saturday, December 29, 2001 - 1:29 am: |
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The problem lies in the AM/AGC section. Replace diodes D1,d2,d34,& d35 with ECG583 or RCA SK9975 Shottky Barrier diodes. This improves noise blanking and AM detection. Next, replce transistor Q18 with a 2SC2026 low noise/ high gain transistor- quiets receive and improves reception. Next, paralel R233 with a 4.7uF electrolytic capacitor- crisp, more articulate audio. This should help bunches! |
Highlander
| | Posted on Monday, December 31, 2001 - 4:39 pm: |
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SS8541 did the mods Inspector is talking about on my Galaxy 2517 (except the capacitor part), and it really works well. |
Thunderbolt
| | Posted on Sunday, January 06, 2002 - 6:35 pm: |
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I have a 2950Dx and when I turn my heater fan on it comes through the radio like a wobble sound.I also loose alot of recieve also. the locals I am listening too sound weaker. I have it connected to the battery with #8 wire and 3 other radios I tried does not pick up the noise. I know the noise is produced most likely by tracking dust in the motor but the DX is the only one that picks it up and kills the recieve. What can I do? |
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