Is there anything that can be done to improve the receive on a 148 gtl?It does ok now but but i would like it to be a little stronger. :roll:
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Poor receive/cobra 148 gtl
- Thread starter King Mudduck
- Start date
Wow KM, reminds me of the folks who ask "How much more wattage can you get out of a (fill in the blank) radio?"
No hint as to how much he's getting now. I'll tell him that anybody who answers without asking that question first may not be trustworthy. Gotta know what it's already delivering to tell if it will deliver more than that.
But you're asking about the receive side.
I'll guess that you don't have a RF signal generator. That's the standard tool for measuring the sensitivity of a receiver. That would reveal whether or not it can be improved, or if it's already doing everything that it can. Kinda like a wattmeter, but for the receive side.
The other question that nobody ever answers before I ask, is "Has it always been like this since you got it? Or did the receiver fall off after you used it for a while?"
That little bit of history info can reveal a lot, especially if it's a radio that you just got, and it's always been like this.
A radio that "changed", used to hear better than it does now, probably has a different kind of problem than a "it's always been like this" radio.
Without a signal generator, the next best tool to judge the sensitivity of the receiver is the noise level. If you turn off the ANL/NB, and turn down the squelch you should be able to hear a noise level.
Unplug the coax from the antenna socket, and see if you can hear the difference when you plug it back in.
If you can hear the noise level, and see it on the S-meter, there's not much improvement to be had. You can't hear anything weaker than the noise level. Making the noise louder won't improve your receiving range.
If you CAN'T detect the noise level, the receiver's sensitivity may not be up to snuff.
Carry one into a shop with that problem, and the first thing they'll do is see if all the receiver's adjustment coils are peaked for max sensitivity. If someone was fooling around inside, watching the wattmeter, some of these could be turned randomly, and no longer be set to a proper "peak" position. Generic term for this procedure is "alignment". It's a sufficiently common problem, most shops will check this first, and then see how sensitive the receiver is, and how much increased sensitivity the radio will now deliver, if any of the adjustment slugs were NOT already set to the proper peak.
Not a simple thing to try at home with no tools.
If noise is the problem, and you have a high S-meter reading on noise alone, flip the ANL/NB switch all the way up, and see if it makes the meter reading fall.
The noise blanker in that radio is pretty effective, but has two tuning slugs that have to be peaked for best blanking action. If the meter's noise level doesn't fall when the blanker is turned on, it will limit who you can hear.
Have you considered a preamp? They are only useful if your local noise level is too low to kick the S-meter. If you have a noise level higher than 1 or 2 S-units, the preamp will only make the noise louder, most of the time. Better yet, if you know somebody who has a preamp sitting on the shelf, borrow it to try. See if it gives you any improvement. And if it just makes the noise level larger, you didn't waste real money to find out. And you'll know why HE had it on the shelf, and NOT in line with the radio.
More than once, I have seen a big improvement in the receiver by raising the antenna. If you are using it as a base, this can make a large difference.
If you're using it mobile, odds are that what you can hear is already limited by the noise level.
73
No hint as to how much he's getting now. I'll tell him that anybody who answers without asking that question first may not be trustworthy. Gotta know what it's already delivering to tell if it will deliver more than that.
But you're asking about the receive side.
I'll guess that you don't have a RF signal generator. That's the standard tool for measuring the sensitivity of a receiver. That would reveal whether or not it can be improved, or if it's already doing everything that it can. Kinda like a wattmeter, but for the receive side.
The other question that nobody ever answers before I ask, is "Has it always been like this since you got it? Or did the receiver fall off after you used it for a while?"
That little bit of history info can reveal a lot, especially if it's a radio that you just got, and it's always been like this.
A radio that "changed", used to hear better than it does now, probably has a different kind of problem than a "it's always been like this" radio.
Without a signal generator, the next best tool to judge the sensitivity of the receiver is the noise level. If you turn off the ANL/NB, and turn down the squelch you should be able to hear a noise level.
Unplug the coax from the antenna socket, and see if you can hear the difference when you plug it back in.
If you can hear the noise level, and see it on the S-meter, there's not much improvement to be had. You can't hear anything weaker than the noise level. Making the noise louder won't improve your receiving range.
If you CAN'T detect the noise level, the receiver's sensitivity may not be up to snuff.
Carry one into a shop with that problem, and the first thing they'll do is see if all the receiver's adjustment coils are peaked for max sensitivity. If someone was fooling around inside, watching the wattmeter, some of these could be turned randomly, and no longer be set to a proper "peak" position. Generic term for this procedure is "alignment". It's a sufficiently common problem, most shops will check this first, and then see how sensitive the receiver is, and how much increased sensitivity the radio will now deliver, if any of the adjustment slugs were NOT already set to the proper peak.
Not a simple thing to try at home with no tools.
If noise is the problem, and you have a high S-meter reading on noise alone, flip the ANL/NB switch all the way up, and see if it makes the meter reading fall.
The noise blanker in that radio is pretty effective, but has two tuning slugs that have to be peaked for best blanking action. If the meter's noise level doesn't fall when the blanker is turned on, it will limit who you can hear.
Have you considered a preamp? They are only useful if your local noise level is too low to kick the S-meter. If you have a noise level higher than 1 or 2 S-units, the preamp will only make the noise louder, most of the time. Better yet, if you know somebody who has a preamp sitting on the shelf, borrow it to try. See if it gives you any improvement. And if it just makes the noise level larger, you didn't waste real money to find out. And you'll know why HE had it on the shelf, and NOT in line with the radio.
More than once, I have seen a big improvement in the receiver by raising the antenna. If you are using it as a base, this can make a large difference.
If you're using it mobile, odds are that what you can hear is already limited by the noise level.
73
Thank you for your reply!I have had this radio for over a year now and the receive has never really been that strong,not even close to my cobra 29 or 25.It has been checked more than once by a tech that i have always taken my radios to and he says that its(receive)is as good as it can be.I have often heard that the 148 gtl has suffered from poor receive performance in the past so i thought that maybe someone would know of a trick that could be done to the radio to improve it.The overal performance of the radio is outstanding its just that i would like the rec,to be as strong as it is in my other radios.
Well, your tech may be right on the money, but I'll say this about "marginal" radio problems. They're the toughest kind to troubleshoot.
A radio that just WON'T transmit is usually a pretty straightforward problem to track down. A radio that will only swing half or two-thirds of full power is a lot tougher to explain, and fix.
Same rule applies to receivers. If it's "Dead, Jim", all you have to track down is where the process inside has stopped.
If the radio should be hearing a quarter of a microVolt, and it takes one whole microVolt, that's not nearly as clear-cut a failure. The clues I look for first are tuning slugs that don't behave quite like normal. Every radio will have some adjustments that "peak" very sharply when you turn the adjustment a few degrees either side of a peak. Others will be more broad, taking a quarter or half-turn to drop from the peak. A tuning slug that doesn't behave "normally" for that model is a clue that something in that section of the radio is not quite right.
Another thing to watch for is a tuning slug that appears to peak with the slug exactly flush with the rim of the hole in the metal can. It doesn't happen a lot, but the most common "marginal" sensitivity problem in solid-state radios that get to be 20 years old or more is for the built-in capacitor inside the metal 'can' to go bad. When that happens, it changes the adjustment of the slug, so that it no longer will turn "far enough" to reach a real peak. Trouble is, that the "flush" position of the slug is usually the effective end of its travel. Sure it will keep turning, as the slug protrudes up out of the housing. Makes that "end of travel" point SEEM to be a true peak, when it really isn't. Sometimes the most effective fix is to tack a disc capacitor onto the circuit board foils across the two pins of that IF/RF transformer/coil where the (failed) internal capacitor is hooked inside. Just replacing the bad coil/transformer is a more reliable solution, but more expensive. If you don't have a new replacement coil/transformer on hand, it's a quicker fix, too.
Like I said, this doesn't happen a lot, but if a receiver is ALMOST sensitive enough this is one of the first things I look for, especially if it's getting near or past that 20-year mark.
Remember one other thing. Nearly every "mod" that serves to increase receiver sensitivity will also REDUCE bleedover rejection, especially from one or two channels away. You can always turn down the RF gain, I suppose. Substituting parts to "goose" a receiver's sensitivity usually raises the noise level
AND the bleedover level.
This is not a "chronic" or "built-in" problem with that model. Or should I say "models". The 148 has been built by more subcontractors than I can keep track of. It's really a whole FAMILY of radios, not just ONE.
73
A radio that just WON'T transmit is usually a pretty straightforward problem to track down. A radio that will only swing half or two-thirds of full power is a lot tougher to explain, and fix.
Same rule applies to receivers. If it's "Dead, Jim", all you have to track down is where the process inside has stopped.
If the radio should be hearing a quarter of a microVolt, and it takes one whole microVolt, that's not nearly as clear-cut a failure. The clues I look for first are tuning slugs that don't behave quite like normal. Every radio will have some adjustments that "peak" very sharply when you turn the adjustment a few degrees either side of a peak. Others will be more broad, taking a quarter or half-turn to drop from the peak. A tuning slug that doesn't behave "normally" for that model is a clue that something in that section of the radio is not quite right.
Another thing to watch for is a tuning slug that appears to peak with the slug exactly flush with the rim of the hole in the metal can. It doesn't happen a lot, but the most common "marginal" sensitivity problem in solid-state radios that get to be 20 years old or more is for the built-in capacitor inside the metal 'can' to go bad. When that happens, it changes the adjustment of the slug, so that it no longer will turn "far enough" to reach a real peak. Trouble is, that the "flush" position of the slug is usually the effective end of its travel. Sure it will keep turning, as the slug protrudes up out of the housing. Makes that "end of travel" point SEEM to be a true peak, when it really isn't. Sometimes the most effective fix is to tack a disc capacitor onto the circuit board foils across the two pins of that IF/RF transformer/coil where the (failed) internal capacitor is hooked inside. Just replacing the bad coil/transformer is a more reliable solution, but more expensive. If you don't have a new replacement coil/transformer on hand, it's a quicker fix, too.
Like I said, this doesn't happen a lot, but if a receiver is ALMOST sensitive enough this is one of the first things I look for, especially if it's getting near or past that 20-year mark.
Remember one other thing. Nearly every "mod" that serves to increase receiver sensitivity will also REDUCE bleedover rejection, especially from one or two channels away. You can always turn down the RF gain, I suppose. Substituting parts to "goose" a receiver's sensitivity usually raises the noise level
AND the bleedover level.
This is not a "chronic" or "built-in" problem with that model. Or should I say "models". The 148 has been built by more subcontractors than I can keep track of. It's really a whole FAMILY of radios, not just ONE.
73
...runna pile-up on 6m SSB