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Cobra 25 Ltd Classic Recieve Mod Questions

izzyd73

New Member
Aug 10, 2014
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I have a 25 ltd classic I picked up at a thrift shop for 6 bucks and thought what the hell let's have some fun. I picked up a rfx75 and installed it then took it to the local cb shop to have it fine tuned and afterwards was told it's putting out 100 watts and everything is good to go. The wattage I'm not as concerned with as much as I am with the recieve. I looked around the Internet and at one point found an article about changing a few resistors and increasing the amount of receiving the radio will do. My biggest concern is that I'm TX more than I can RX and I want to balance that out. The setup I'm running is cobra to swr meter then to a k30 mag mount on a f350 diesel van with swr about 1.6 to 1.8, I know the antenna makes a huge difference and I do have plans on either a k40 or wilson 1000. but with my current antenna I'm already experiencing talking farther than I hear. I'm in hopes that someone here has an idea of the recieve mod I'm talking about and can help
 

Look in to an antenna preamp & run an extra ground strap to the antenna mount to lower the SWRs 2CTO93 & I'm backout
 
Please don't for the love of god use a pre-amp unless the S meter is on zero on receive without it turned on. All you'll do is amplify the crap and make the signal to noise ratio worse actually making weaker signals harder to hear and increase bleedover from strong stations on nearby channels.

A ground strap will do nothing and changing to a fixed mount from a magmount will make the thing work better.
 
Run a Sirio 5000 Performer; that can help increase receive and transmit somewhat better.
Didn't the shop align the receiver part when it was in there?

BTW, you might want to add a cooling fan to the RFX since you are pushing it too hard @100w . . .
 
Run a Sirio 5000 Performer; that can help increase receive and transmit somewhat better.
Didn't the shop align the receiver part when it was in there?
Yes it was all aligned and its on frequency and not over mod on TX after doing a little more research I think I'm expecting too much from this radio and stop comparing it to an old 29 ltd classic I had that was all done up lol
 
It's usually the other way around you can hear three times further than you can talk.
With the truck off and parked do you have the same swr on channel 1 and 40? if so then your matched.
Did the shop tune the receive ?
What are you making your basis on as far as you can receive, are you in contact with another radio?
Receive condition vary as far as skip, your location, etc.
There is a mod where you can change a transistor and a few diodes to help improve receive, but the radio has to be tuned to receive after the mod is done.
Most of the time the problem is in the antenna system, can you swap out the antenna or try the radio in another vehicle?
 
The setup I'm running is cobra to swr meter then to a k30 mag mount on a f350 diesel van with swr about 1.6 to 1.8, I know the antenna makes a huge difference and I do have plans on either a k40 or wilson 1000.
Skipping the magnet mount and going to a hard mount will definitely improve your receive.
 
It's usually the other way around you can hear three times further than you can talk.
With the truck off and parked do you have the same swr on channel 1 and 40? if so then your matched.
Did the shop tune the receive ?
What are you making your basis on as far as you can receive, are you in contact with another radio?
Receive condition vary as far as skip, your location, etc.
There is a mod where you can change a transistor and a few diodes to help improve receive, but the radio has to be tuned to receive after the mod is done.
Most of the time the problem is in the antenna system, can you swap out the antenna or try the radio in another vehicle?
Yes I was in contact with another radio when it happened. The difference between 1 and 40 is about .2 swr and I haven't tried it on my car yet but I am thinking a different antenna would help
 
with the watts you are putting out you will have to talk to another radio putting out the same watts to get a better receive. like others have said to raise your receive all you will do is raise the floor noise levels. the nradio on the other end has to put out more watts to raise your actual voice receive
 
Antenna, get a new antenna, the k30 is not going to cut it. Height is might and closer to 108" total length will definitely help with rx and tx capability. The sirio performer 5000 or a megawatt 4000 mag mount or hard mount both would be better than the current antenna. I too had a k30 and k40 and they were okay and worked but are at about bottom of the barrel when it comes to performance IMO. Went from the k40 to a sirio 5000 performer with a pl145 mag mount and it was night and day difference. Big difference in height and quality of the antenna as well helped a bunch. IMO I would ditch the k30 and get a better antenna setup before modding the radio any further. I know there are several good antennas out there, what I posted is just my own experience with antennas I have used. Hop this helps and have a great one. God bless.
 

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