Ok I've got a strange problem here. Hopefully this isn't a dumb question. But upon connecting the coax to the radio with just the center conductor of the coax plugged in radio picks up static, as soon as the barrel or "ground" is touched to the so239 threads receive goes away. What is my problem here? Diode? Resistor gone bad? What? Help much appreciated!
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Cobra 29 Chrome looses receive.
- Thread starter Collin Barnett
- Start date
I'm sure others will have better suggestions, but have you checked with an ohmmeter to make sure the coax isn't shorted? Can you connect this coax to another radio to see if it does the same thing? Can you connect the suspected bad radio to another antenna/coax setup to see if behaves the same way there?
Idea is to make sure the problem is the radio before trying to troubleshoot the radio. If you've already done any of these things, you're already ahead of the game.
Idea is to make sure the problem is the radio before trying to troubleshoot the radio. If you've already done any of these things, you're already ahead of the game.
sounds like an antenna issue.
with just the center pin connected, the coax itself is acting like an antenna of sorts, so you hear the increase in static.
as soon as you screw in the connector, the shield is attached and the coax now acts like a piece of coax, not an antenna.
if you have no receive when you connect your antenna, then you have no antenna.
check the antenna.
did i say antenna enough LOL?
LC
with just the center pin connected, the coax itself is acting like an antenna of sorts, so you hear the increase in static.
as soon as you screw in the connector, the shield is attached and the coax now acts like a piece of coax, not an antenna.
if you have no receive when you connect your antenna, then you have no antenna.
check the antenna.
did i say antenna enough LOL?
LC
Shadetree Mechanic
Delaware Base Station 808
It's not the coax
It's not the coax or antenna. Already checked with a couple other radios.
It's not the coax or antenna. Already checked with a couple other radios.
May indicate another problem.
Does the radio have a "static suppressor" resistor R55 by the antenna connector?
Between the SWR bridge and Heat sink Panel
If it's been removed, put a 1/.2 watt 2.2K on up to 4.7K resistor or see if the resistor in there, is still good.
Check it's location - it has an open lead and if not cared for...can potentially short out to the case ground thru the heat sink panel it sits right next to.
But is it good?
Best & easiest way to check is to put a DVM test leads onto the center and threaded section of the SO-239 - measure ohmic readings between 200 to 20K for this test. It - should be more than 1K - BOTH WAYS (leads reversed to prove resistance. Not a polarized current draining out the back of the radio). But not infinite.
Then do the same with a VOLTAGE check - if you get a voltage, you have a leaky cap problem or poor soldering causing the "dip" in receive. The rise in voltage can indicate several issues but main one being poor soldering or loose SO-239 and case screw bonding points - tighten down the hardware if you can.
Many times ,the coax tip is "unbalanced" when the SHIELD is not making contact - so it is more of an inherited antenna noise pickup than a good receiver - because the COAX SHIELD isolates the signal to within the coax itself so once the "return" from the antenna is established ,the currents in the coax are properly terminated into the back of the radio using the PI-filter and 52MHz trap in there.
Does the radio have a "static suppressor" resistor R55 by the antenna connector?
Between the SWR bridge and Heat sink Panel
If it's been removed, put a 1/.2 watt 2.2K on up to 4.7K resistor or see if the resistor in there, is still good.
Check it's location - it has an open lead and if not cared for...can potentially short out to the case ground thru the heat sink panel it sits right next to.
But is it good?
Best & easiest way to check is to put a DVM test leads onto the center and threaded section of the SO-239 - measure ohmic readings between 200 to 20K for this test. It - should be more than 1K - BOTH WAYS (leads reversed to prove resistance. Not a polarized current draining out the back of the radio). But not infinite.
Then do the same with a VOLTAGE check - if you get a voltage, you have a leaky cap problem or poor soldering causing the "dip" in receive. The rise in voltage can indicate several issues but main one being poor soldering or loose SO-239 and case screw bonding points - tighten down the hardware if you can.
Many times ,the coax tip is "unbalanced" when the SHIELD is not making contact - so it is more of an inherited antenna noise pickup than a good receiver - because the COAX SHIELD isolates the signal to within the coax itself so once the "return" from the antenna is established ,the currents in the coax are properly terminated into the back of the radio using the PI-filter and 52MHz trap in there.
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Thanks so much for the info! I'll take a look and do these checks as soon as I get a chance and reply back with my findings here.