| Author |
Message |
    
Icepick
| | Posted on Tuesday, November 19, 2002 - 7:19 pm: | 
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My Magnum 257 has a less than clear signal on FM mode. I use this a lot with my wife, and it's very hard to hear on my other radios. Very "Anoying"! Could you please tell me where the VR ajustments are for the FM,TX and RX? Much much thanks!!!! Ice Pick...... |
307
| | Posted on Tuesday, November 19, 2002 - 9:30 pm: |
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I wish I could help however , I never even seen the 257 let alone any mods or information on them..
Anyone help this guy?
307 |
2600
| | Posted on Wednesday, November 20, 2002 - 12:30 am: |
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Is the FM garbled on receive, or transmit, or both? If the modulation limiter got "clipped" incorrectly, FM will sound so bad you can't believe it. The clue here is to see if backing away from the mike clears it up completely. I have seen taxicab FM radios that you couldn't understand unless the driver held the mike at arm's length and spoke quietly. If the limiter on the other radio got "clipped" the same way, your receiver may have nothing to do with it.
All these small "ham" radios but a couple have one slug-tuned coil that controls the FM receive modulation ONLY. Someone who just turns each slug, then moves on to the next one watching for meter peaks will probably not put it back where it had been set. This one is not peaked on any meter, but gets set for MINIMUM DISTORTION on FM receive. If it gets turned either way from that spot, even a clean-modulated radio on the other end will sound nasty.
I vaguely remember a rumor that this thing resembled an "Eagle" brand radio of some model on the inside. I still haven't found anything online but an "owner's manual" for the thing, no diagrams. With a schematic, I can tell you which one of all those slugs is that one, anyway.
73 |
Tech671
| | Posted on Wednesday, November 20, 2002 - 6:07 am: |
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These radios when run on FM need the variable power set at 11-12:00. Over that and it over-taxes the regulator and can cause distortion. If someone has cranked the FM deviation too much, it can distort, try working with the mike gain a bit. |
Icepick
| | Posted on Wednesday, November 20, 2002 - 8:14 pm: |
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Many thanks 671,2600,and 307......
I will try all of the above. As far as I can tell, there are only two vr's that can not be accounted for. One has no vr number, and the other is covered in wax. Will also try to contact Magnum again. Again, thank you fellas!!!
Icepick 222 |
Ss8541
| | Posted on Wednesday, November 20, 2002 - 11:45 pm: |
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this should help;
if you have access to a comm analyzer it is best to set max deviation to no more than +/-2.5khz(covers a bandwidth of 11khz) to minimize adjacent ch bleedover. of cours this is after the 'limiter' has been replaced if missing. setting deviation to the older business/lmr band level of +/-5khz(covers a bandwidth of 16khz) will cause severe bleedover to the adjacent channels in the 11 meter band. a comm analyzer or rf gen with fm capabilities will also help you adjust the fm rx properly if it is out of whack. lastly if this was all caused by a 'tech', you may want to look into finding another tech. |
Icepick
| | Posted on Saturday, November 30, 2002 - 8:59 pm: |
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Thanks for all your input guys! All it took was turning the RF gian and variable power down.... Many thanks!!!!!! I love this forum!!!!
73's Icepick |
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