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Rig Help

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OilyBob

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Feb 10, 2012
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Hi all

I have a Midland 77-099 and it is driving me mad. It was working fine if not a little short on range, then it stopped sending (still recived fine) so i replaced the mic all was good at close range but it is useless at anything over 2 mtrs. I have checked my grounds etc and they are fine, i have SWR'ed it and it reads 2.3 channel 1 and 2.7 channel 40.

First things first....

1. What aerial do you have? Tornado Stingger
2. What type of mount?Thunderpole right angled mirror mount 4 hole

3. Where specifically is it mounted (pic if possible)Its attached to my light bar with a ground running into the vehical and attaching to the roof inside (4mm cable)

4. What vehicle?Discovery 1 300TDi

5. Did you terminate the coax yourself or was it predone, are there any joins, how does it enter vehicle. i.e. is it compresssed by a door seal etc.I made the conections and soildered them, i have tested them and they are correct no shorts, it runs through the roof





Rob
 

mmckenna

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An SWR of 2.7:1 is likely too high for your radio to handle correctly. Could be that the physical length of the antenna is not correct. The SWR being better on the lower end (Ch. 1) suggest that the antenna could be too long. Some radios are designed to cut back the output power when the SWR gets too high. A combination of the low SWR and a non-resonate antenna will cause these issues. The fact that you are only getting very short distances out of the radio could also mean that the high SWR has damaged the final output transistor over time. The way I would check this on a radio would be to use a watt meter connected between the radio and a 50 ohm dummy load. Not sure what the rules are in the UK(?) but here in the states its 4 watts. Seeing anything less than 2 to 4 watts out of your radio (if 4 watts is normal) would suggest a final amp transistor failure. Likely if the final failed, you will only see a few milliwatts of output power.

Could be that your ground is too long. You need to keep the ground lead as short as possible. Continuity is good, but if the connection to the vehicle ground is too long, you could have an issue.

Could be that the ground connection is bad.

Could be that the coaxial cable is bad. Just because there isn't a short between the center conductor and the shield doesn't mean that the center conductor isn't broken somewhere.

A useful test would be to check continuity of the center conductor from the radio end all the way out to the antenna. Do the same for the outer conductor.
Inspect the antenna mount carefully, check for corrosion or other damage.

Another way to test would be to get a known good antenna to test your radio with, preferably on a separate vehicle. If the SWR is good on the other vehicle and your transmission range improves, it would point at an antenna or feed line problem. If it doesn't, it would suggest your radio is the culprit, with the antenna or feed line problem as a likely cause.
 
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