I recently had a chance to look at one of these as a friend of mine needed the deadkey lowered in order to use it with his amp.
Upon first looks this radio holds true to the classic Uniden styling, which in my opinion is a good thing.
I'm not going to go over all the features of the radio, as all that info can be found elsewhere on the interwebs.
This radio was untouched and in "just left the factory" condition.
The deadkey out of the box was already only 2 watts. PEP swing was about 6 watts.
Upon opening up the radio, the first thing that hits you is the new SMT design of the board.
There are no adjustments to make for receiver sensitivity, and no adjustments for the noise blanker.
(a pic is included at the bottom of this post)
That being said, I found no need to adjust either of these. the receiver in this radio is quite sensitive, and hears down to about .3uv.
the noise blanker does its job well, and easily blanked out my homebrew relay noise source.
the few adjustments allowed are done by VR's. These trimmers are very small, very fragile, and DO NOT have detents for stopping its travel. in other words, they will spin round and round as you turn them.
you can adjust the S-meter, which in this radio did not need adjustment.
you can adjust the squelch range, and it did not seem to need adjustment either.
you can adjust the frequency of the radio, and this was off by 200hz (27.1852 on ch. 19) easily fixed with a slight adjustment.
lastly you can adjust the AMC, but we'll discuss that below when we talk about the transmitter.
Ok, now for the part everyone cares about- the transmitter adjustments.
To start with, this radio uses a 2SC2314 for the driver, and an IRF520 for the final.
I found the Gate of the IRF520 had about 5 volts on it, and with no way to adjust it, i have to assume that's where Uniden wants it.
There is an inductor to adjust for the final output, but there is not one for the driver output.
Yes, there are three metal cans near the driver, but following circuit traces is all but impossible with these new SMT boards, so i left them alone.
yes, these are probably the TX mixer cans, but even if i knew for certain that these were TX mixer cans, there's usually not much to be gained by adjusting them anyway.
I do not recommend turning these cans while looking at a wattmeter no matter how strong the urge.
I was able to adjust the final output inductor using a 1000hz tone, and was able to attain a 3.5 watt deadkey with about 10 watts of PEP swing.
now for the part everyone is going to try to adjust. the AMC trimmer.
i first just had the wattmeter attached and was able to adjust this control up to about a 25 watt swing!
IT'S A LIE!!!
i put the radio on the scope and the pattern looked TERRIBLE! i don't just mean some flat lines forming on your sinewave terrible, im talking about skewed squarewave kind of terrible.
this radio will unleash a barrage of harmonics and trash the likes of which you have rarely seen when this control is maxed with a wattmeter alone.
GUARANTEED!
backed the control down to a nice looking sinewave and ended up with 16 watts PEP.
now, here's the part where i try to convince the purchasers of this radio to either leave the AMC adjustment alone, or at least have a scope around when you adjust it.
I did not get any on air tests of how my voice sounded with the AMC wide open.
maybe some people will think this sound is appealing, maybe it's muffled and worthless, i don't know because i didnt bother to check it.
the reason you don't want to run your 78LTD with the AMC wide open is specifically because this is an SMT chassis.
These little tiny parts just cannot handle being driven to extremes like the old through hole components could.
when the AMC gets jacked up to full open, all these little parts get overloaded with harmonics that stress them out.
when these parts get stressed out they are either going to change in value, or blow, but it will happen eventually.
I fully believe that Uniden knows this, and also knows that many people will turn that AMC control up, and need a new radio in a year or so.
There's no fixing these guys! Uniden will not release any service info or schematics on these boards, so aside from replacing finals and reverse polarity diodes, there's not much that can be done to bring them back to life.
I would certainly never take on in for a repair without knowing for sure that it's one of the big easily replaceable parts at fault.
I also wanted to mention that big resistor near the final. those of you familiar with the cobra 29LTD swing mod might think that this resistor can be changed in value or have a cap paralleled with it in order to decrease the deadkey while keeping the swing high.
NOPE!
my best guess is that this resistor sets the bias level for the gate of the final. changing its value will not increase or decrease your output. I even tried putting a cap across it just to be able to tell those who might try it that it does not have the desired, or any noticeable effect on output.
the only way to lower the deadkey in these radios while maintaining a higher PEP wattage is by adding diodes in series with the diode that goes from the modulation transformer to the driver and final.
I added five diodes in series to achieve a 2 watt deadkey.
final output with a clean pattern on the scope was a 2 watt deadkey with about 10 watts of PEP swing.
yes, this is a bit above 100% modulation, but the pattern was still a nice sinewave that showed minimal signs of flat-topping occurring.
try to increase this PEP number to 12 watts or above, and the pattern just goes nuts.
all in all i found this to be a pretty nice radio that i would enjoy owning. It's well built and all the faceplate controls are connected by ribbon cable instead of the method cobra is now using where the horizontal boards solder directly to the vertical boards. (that method will definitely break with continued vibration)
as with any new radio, the case screws all needed a final tightening, and i use a bit of nail polish to keep them from vibrating loose.
In the pic below you will notice that i added an electrolytic to the power jacks for some additional filtering and headroom, and i also added a ferrite bead to the power wire.
I do not have enough experience with this chassis to know whether or not they are actually needed, but they certainly cannot hurt, and may keep the user from experiencing a problem or two in a certain installation.
hope this review was informative.
I give this radio a solid thumbs up!
LC
Upon first looks this radio holds true to the classic Uniden styling, which in my opinion is a good thing.
I'm not going to go over all the features of the radio, as all that info can be found elsewhere on the interwebs.
This radio was untouched and in "just left the factory" condition.
The deadkey out of the box was already only 2 watts. PEP swing was about 6 watts.
Upon opening up the radio, the first thing that hits you is the new SMT design of the board.
There are no adjustments to make for receiver sensitivity, and no adjustments for the noise blanker.
(a pic is included at the bottom of this post)
That being said, I found no need to adjust either of these. the receiver in this radio is quite sensitive, and hears down to about .3uv.
the noise blanker does its job well, and easily blanked out my homebrew relay noise source.
the few adjustments allowed are done by VR's. These trimmers are very small, very fragile, and DO NOT have detents for stopping its travel. in other words, they will spin round and round as you turn them.
you can adjust the S-meter, which in this radio did not need adjustment.
you can adjust the squelch range, and it did not seem to need adjustment either.
you can adjust the frequency of the radio, and this was off by 200hz (27.1852 on ch. 19) easily fixed with a slight adjustment.
lastly you can adjust the AMC, but we'll discuss that below when we talk about the transmitter.
Ok, now for the part everyone cares about- the transmitter adjustments.
To start with, this radio uses a 2SC2314 for the driver, and an IRF520 for the final.
I found the Gate of the IRF520 had about 5 volts on it, and with no way to adjust it, i have to assume that's where Uniden wants it.
There is an inductor to adjust for the final output, but there is not one for the driver output.
Yes, there are three metal cans near the driver, but following circuit traces is all but impossible with these new SMT boards, so i left them alone.
yes, these are probably the TX mixer cans, but even if i knew for certain that these were TX mixer cans, there's usually not much to be gained by adjusting them anyway.
I do not recommend turning these cans while looking at a wattmeter no matter how strong the urge.
I was able to adjust the final output inductor using a 1000hz tone, and was able to attain a 3.5 watt deadkey with about 10 watts of PEP swing.
now for the part everyone is going to try to adjust. the AMC trimmer.
i first just had the wattmeter attached and was able to adjust this control up to about a 25 watt swing!
IT'S A LIE!!!
i put the radio on the scope and the pattern looked TERRIBLE! i don't just mean some flat lines forming on your sinewave terrible, im talking about skewed squarewave kind of terrible.
this radio will unleash a barrage of harmonics and trash the likes of which you have rarely seen when this control is maxed with a wattmeter alone.
GUARANTEED!
backed the control down to a nice looking sinewave and ended up with 16 watts PEP.
now, here's the part where i try to convince the purchasers of this radio to either leave the AMC adjustment alone, or at least have a scope around when you adjust it.
I did not get any on air tests of how my voice sounded with the AMC wide open.
maybe some people will think this sound is appealing, maybe it's muffled and worthless, i don't know because i didnt bother to check it.
the reason you don't want to run your 78LTD with the AMC wide open is specifically because this is an SMT chassis.
These little tiny parts just cannot handle being driven to extremes like the old through hole components could.
when the AMC gets jacked up to full open, all these little parts get overloaded with harmonics that stress them out.
when these parts get stressed out they are either going to change in value, or blow, but it will happen eventually.
I fully believe that Uniden knows this, and also knows that many people will turn that AMC control up, and need a new radio in a year or so.
There's no fixing these guys! Uniden will not release any service info or schematics on these boards, so aside from replacing finals and reverse polarity diodes, there's not much that can be done to bring them back to life.
I would certainly never take on in for a repair without knowing for sure that it's one of the big easily replaceable parts at fault.
I also wanted to mention that big resistor near the final. those of you familiar with the cobra 29LTD swing mod might think that this resistor can be changed in value or have a cap paralleled with it in order to decrease the deadkey while keeping the swing high.
NOPE!
my best guess is that this resistor sets the bias level for the gate of the final. changing its value will not increase or decrease your output. I even tried putting a cap across it just to be able to tell those who might try it that it does not have the desired, or any noticeable effect on output.
the only way to lower the deadkey in these radios while maintaining a higher PEP wattage is by adding diodes in series with the diode that goes from the modulation transformer to the driver and final.
I added five diodes in series to achieve a 2 watt deadkey.
final output with a clean pattern on the scope was a 2 watt deadkey with about 10 watts of PEP swing.
yes, this is a bit above 100% modulation, but the pattern was still a nice sinewave that showed minimal signs of flat-topping occurring.
try to increase this PEP number to 12 watts or above, and the pattern just goes nuts.
all in all i found this to be a pretty nice radio that i would enjoy owning. It's well built and all the faceplate controls are connected by ribbon cable instead of the method cobra is now using where the horizontal boards solder directly to the vertical boards. (that method will definitely break with continued vibration)
as with any new radio, the case screws all needed a final tightening, and i use a bit of nail polish to keep them from vibrating loose.
In the pic below you will notice that i added an electrolytic to the power jacks for some additional filtering and headroom, and i also added a ferrite bead to the power wire.
I do not have enough experience with this chassis to know whether or not they are actually needed, but they certainly cannot hurt, and may keep the user from experiencing a problem or two in a certain installation.
hope this review was informative.
I give this radio a solid thumbs up!
LC
