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Post by ab5ni on Oct 14, 2014 5:22:23 GMT -5
Is it just me, or do you guys also think that the vast majority of transistorized rigs received audio sounds a bit "tinny" with few lows in their audio frequency response? I'm starting to think this might have something to do with the internal capacitance of the transistors rolling off the lows. Either that, or maybe the older tube radios are using audio transformers on their output and the transistor radios don't? I haven't actually looked into this, so I'm hoping that maybe some of you have. So, what do you say? I have yet to find a transistorized rig that has decent receive audio.
73,
Randy AB5NI
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Post by tecnicoloco2000 on Oct 14, 2014 15:03:24 GMT -5
Replace some capacitors in the rx chain to change the tone BTW is you have a Cobra 148GTL or a Cobra 2000GTL,you can make some changes that will sound pretty good on RX and TX  Plastic Audio |
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Sandbagger
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Post by Sandbagger on Oct 14, 2014 15:38:56 GMT -5
Is it just me, or do you guys also think that the vast majority of transistorized rigs received audio sounds a bit "tinny" with few lows in their audio frequency response? I'm starting to think this might have something to do with the internal capacitance of the transistors rolling off the lows. Either that, or maybe the older tube radios are using audio transformers on their output and the transistor radios don't? I haven't actually looked into this, so I'm hoping that maybe some of you have. So, what do you say? I have yet to find a transistorized rig that has decent receive audio. 73, Randy AB5NI There are several reasons why this is. The first, and most obvious is that tubes have a much "warmer" sound, which tends to revolve around he rich audio harmonics that accomplish this. Also the speakers on most tube rigs are a bit larger and usually of a better quality. Lastly, more modern solid state rigs employ a greater degree of audio bandwidth limiting which tends to roll off below 300hz and above 3 Khz. Tube rigs typically drop to 100 hz or lower. You can mod the receiver to widen the bandwidth, and that may help. Also using a better quality external speaker can do wonders. |
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Post by ab5ni on Oct 14, 2014 17:43:13 GMT -5
Replace some capacitors in the rx chain to change the tone BTW is you have a Cobra 148GTL or a Cobra 2000GTL,you can make some changes that will sound pretty good on RX and TX Plastic Audio As a matter of fact, I'm in need of a couple of 148GTL's for a project. Going to convert them over to 40 and 20 Mtrs. Trying to get two broken rigs on EBay and repair them, but I keep getting beat out on my bids. Guess I'm too damn cheap or something  . When I get them, I'll surely be looking at modifying the rigs in nearly all aspects. Thanks for the info! 73, Randy AB5NI |
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Post by ab5ni on Oct 14, 2014 17:53:10 GMT -5
Is it just me, or do you guys also think that the vast majority of transistorized rigs received audio sounds a bit "tinny" with few lows in their audio frequency response? I'm starting to think this might have something to do with the internal capacitance of the transistors rolling off the lows. Either that, or maybe the older tube radios are using audio transformers on their output and the transistor radios don't? I haven't actually looked into this, so I'm hoping that maybe some of you have. So, what do you say? I have yet to find a transistorized rig that has decent receive audio. 73, Randy AB5NI There are several reasons why this is. The first, and most obvious is that tubes have a much "warmer" sound, which tends to revolve around he rich audio harmonics that accomplish this. Also the speakers on most tube rigs are a bit larger and usually of a better quality. Lastly, more modern solid state rigs employ a greater degree of audio bandwidth limiting which tends to roll off below 300hz and above 3 Khz. Tube rigs typically drop to 100 hz or lower. You can mod the receiver to widen the bandwidth, and that may help. Also using a better quality external speaker can do wonders. Well, I'm on the search for decent quality audio on all my rigs, and I do use an external speaker, SB. I'm also aware of tubes sounding a bit better than transistors. The guys in the guitar world also enjoy the way tubes distort when compared to transistors. 2.7KHz is also the bandwidth used in the old POTS (Plain Old Telephone System) phones, btw. It's no wonder they sound tinny. I'm absolutely positive I'll require these mods . Thanks for the info! 73, Randy AB5NI |
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Sandbagger
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Post by Sandbagger on Oct 14, 2014 19:11:49 GMT -5
There are several reasons why this is. The first, and most obvious is that tubes have a much "warmer" sound, which tends to revolve around he rich audio harmonics that accomplish this. Also the speakers on most tube rigs are a bit larger and usually of a better quality. Lastly, more modern solid state rigs employ a greater degree of audio bandwidth limiting which tends to roll off below 300hz and above 3 Khz. Tube rigs typically drop to 100 hz or lower. You can mod the receiver to widen the bandwidth, and that may help. Also using a better quality external speaker can do wonders. Well, I'm on the search for decent quality audio on all my rigs, and I do use an external speaker, SB. I'm also aware of tubes sounding a bit better than transistors. The guys in the guitar world also enjoy the way tubes distort when compared to transistors. 2.7KHz is also the bandwidth used in the old POTS (Plain Old Telephone System) phones, btw. It's no wonder they sound tinny. I'm absolutely positive I'll require these mods . Thanks for the info! If you have some decent test equipment, like a variable audio generator driving an RF signal generator, and a scope (or audio spectrum analyzer), you can poke around in the receiver until you get the response that you like. It should be very easy to expand the low frequencies for some fuller sounding audio. The high end will be limited by the filter bandwidth in the IF, as well as the LP filtering in the audio section. And this will vary in implementation depending on which chassis manufacturer. The stricter bandwidth specs came into play when the 40 channel radios came into the picture in 1977, as part of the FCC's tighter technical specs. Older 23 channel radios may be a bit looser, which probably explains when they tend to sound better as well. I have an SBE Trinidad that has not only fairly full sounding transmit, but also on receive. Not bad for a solid state rig. |
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Sandbagger
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Post by Sandbagger on Oct 14, 2014 19:19:51 GMT -5
Replace some capacitors in the rx chain to change the tone BTW is you have a Cobra 148GTL or a Cobra 2000GTL,you can make some changes that will sound pretty good on RX and TX Plastic Audio As a matter of fact, I'm in need of a couple of 148GTL's for a project. Going to convert them over to 40 and 20 Mtrs. Trying to get two broken rigs on EBay and repair them, but I keep getting beat out on my bids. Guess I'm too damn cheap or something . When I get them, I'll surely be looking at modifying the rigs in nearly all aspects. Thanks for the info! The chassis in those Cobras are pretty much the standard by which most modern CB and "export" rigs are based off of. The Cobra 148 has been around in one form or another for over 30 years. They should pretty much be a dime a dozen. But there are guys out there looking for the older versions of the radio as they were made with better quality parts, and were generally more reliable. There are also a ton of published mods for them. Everything from channel expansions to audio mods. It should give you a jumping off point to get a good idea of what and were to play, although I'm sure you'll find a more effective mod on your own, in much the same way as I did when I expanded the TX audio bandwidth on my Cobra 2000. Keep trying E-Bay. It's feast or famine there. One week you won't be able to give away a particular model radio. And the next week one will go for crazy money. It's all in the timing. |
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Post by ab5ni on Oct 15, 2014 14:46:41 GMT -5
Well, I'm on the search for decent quality audio on all my rigs, and I do use an external speaker, SB. I'm also aware of tubes sounding a bit better than transistors. The guys in the guitar world also enjoy the way tubes distort when compared to transistors. 2.7KHz is also the bandwidth used in the old POTS (Plain Old Telephone System) phones, btw. It's no wonder they sound tinny. I'm absolutely positive I'll require these mods . Thanks for the info! If you have some decent test equipment, like a variable audio generator driving an RF signal generator, and a scope (or audio spectrum analyzer), you can poke around in the receiver until you get the response that you like. It should be very easy to expand the low frequencies for some fuller sounding audio. The high end will be limited by the filter bandwidth in the IF, as well as the LP filtering in the audio section. And this will vary in implementation depending on which chassis manufacturer. The stricter bandwidth specs came into play when the 40 channel radios came into the picture in 1977, as part of the FCC's tighter technical specs. Older 23 channel radios may be a bit looser, which probably explains when they tend to sound better as well. I have an SBE Trinidad that has not only fairly full sounding transmit, but also on receive. Not bad for a solid state rig. I'm fine on the test gear, except I don't have a spectrum analyzer. I'd really love to have one, but I'm just too damn frugal to spend many thousands of dollars on something that works. If I can get one at a hamfest at the right price, I'd probably pick one up, though. My friends swear by them, and I've used theirs' before, so I do know what I'm missing out on by not having one. One guy I know says he'd be completely "RF blind" without his spectrum analyzer. Those are good points you bring up about the FCC tightening up their specs. Fortunately, when I convert these rigs over to the ham bands, I won't have to worry about such nonsense. You are right about it being simple to open one of these things up on receive. I can't see it being anything more then changing a couple of cap values and done. 73, Randy AB5NI |
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Post by ab5ni on Oct 15, 2014 14:49:42 GMT -5
As a matter of fact, I'm in need of a couple of 148GTL's for a project. Going to convert them over to 40 and 20 Mtrs. Trying to get two broken rigs on EBay and repair them, but I keep getting beat out on my bids. Guess I'm too damn cheap or something . When I get them, I'll surely be looking at modifying the rigs in nearly all aspects. Thanks for the info! The chassis in those Cobras are pretty much the standard by which most modern CB and "export" rigs are based off of. The Cobra 148 has been around in one form or another for over 30 years. They should pretty much be a dime a dozen. But there are guys out there looking for the older versions of the radio as they were made with better quality parts, and were generally more reliable. There are also a ton of published mods for them. Everything from channel expansions to audio mods. It should give you a jumping off point to get a good idea of what and were to play, although I'm sure you'll find a more effective mod on your own, in much the same way as I did when I expanded the TX audio bandwidth on my Cobra 2000. Keep trying E-Bay. It's feast or famine there. One week you won't be able to give away a particular model radio. And the next week one will go for crazy money. It's all in the timing. Thanks again for the advice, SB! I'll make sure I take that all into consideration when doing the conversions. I actually have a good set of bookmarks I've set that will help me in doing all of this stuff. 73, Randy AB5NI |
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Sandbagger
Administrator/The Boss
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Post by Sandbagger on Oct 15, 2014 16:18:21 GMT -5
If you have some decent test equipment, like a variable audio generator driving an RF signal generator, and a scope (or audio spectrum analyzer), you can poke around in the receiver until you get the response that you like. It should be very easy to expand the low frequencies for some fuller sounding audio. The high end will be limited by the filter bandwidth in the IF, as well as the LP filtering in the audio section. And this will vary in implementation depending on which chassis manufacturer. The stricter bandwidth specs came into play when the 40 channel radios came into the picture in 1977, as part of the FCC's tighter technical specs. Older 23 channel radios may be a bit looser, which probably explains when they tend to sound better as well. I have an SBE Trinidad that has not only fairly full sounding transmit, but also on receive. Not bad for a solid state rig. I'm fine on the test gear, except I don't have a spectrum analyzer. I'd really love to have one, but I'm just too damn frugal to spend many thousands of dollars on something that works. If I can get one at a hamfest at the right price, I'd probably pick one up, though. My friends swear by them, and I've used theirs' before, so I do know what I'm missing out on by not having one. One guy I know says he'd be completely "RF blind" without his spectrum analyzer. Those are good points you bring up about the FCC tightening up their specs. Fortunately, when I convert these rigs over to the ham bands, I won't have to worry about such nonsense. You are right about it being simple to open one of these things up on receive. I can't see it being anything more then changing a couple of cap values and done. You can add one more guy to the list of who's "RF Blind" without a spectrum analyzer. I've gotten so used to having one, I'm almost hesitant to align a transmitter without it. I won't put a transmitter on the air that doesn't have a spurious output that's greater than -45dbc. As for audio spectrum analyzers, you can get software versions that run on a laptop. Great for plotting audio response. |
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Post by ab5ni on Oct 15, 2014 17:39:45 GMT -5
Replace some capacitors in the rx chain to change the tone BTW is you have a Cobra 148GTL or a Cobra 2000GTL,you can make some changes that will sound pretty good on RX and TX Plastic Audio Hi loco tech dude, and thanks for the reply . Yeah, that's what I was thinking. Some cap is rolling off the lower frequencies. About as simple as it gets, for sure. 73, Randy AB5NI |
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Post by ab5ni on Oct 15, 2014 18:02:57 GMT -5
I'm fine on the test gear, except I don't have a spectrum analyzer. I'd really love to have one, but I'm just too damn frugal to spend many thousands of dollars on something that works. If I can get one at a hamfest at the right price, I'd probably pick one up, though. My friends swear by them, and I've used theirs' before, so I do know what I'm missing out on by not having one. One guy I know says he'd be completely "RF blind" without his spectrum analyzer. Those are good points you bring up about the FCC tightening up their specs. Fortunately, when I convert these rigs over to the ham bands, I won't have to worry about such nonsense. You are right about it being simple to open one of these things up on receive. I can't see it being anything more then changing a couple of cap values and done. You can add one more guy to the list of who's "RF Blind" without a spectrum analyzer. I've gotten so used to having one, I'm almost hesitant to align a transmitter without it. I won't put a transmitter on the air that doesn't have a spurious output that's greater than -45dbc. As for audio spectrum analyzers, you can get software versions that run on a laptop. Great for plotting audio response. There has to be some secret when it comes to purchasing spectrum analyzers, and I don't know it yet! I read an article where one guy purchased a brand new analyzer for $1,500.00, sold his old analyzer, thinking that current technology must have caught up with his old one by now, but he goes on to say that he was sadly mistaken and totally disappointed. Said he could get some use out of the thing, but just barely. It wasn't his old analyzer by a long shot. I can only imagine that it's great to have an analyzer, being able to tune down spurs, adjust bandpass and lowpass filters, see both sides of your AM signal, adjust FM deviation, look at filter skirts, and proving to the FCC that your homebrew rig IS -70dbc when they stop by for a visit . One of these days, I'll get one, I hope... I really need to download one of those DSP-based audio analyzers. Do you guys know if there is a specific one I should use? 73, Randy AB5NI |
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Sandbagger
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Post by Sandbagger on Oct 15, 2014 18:35:05 GMT -5
You can add one more guy to the list of who's "RF Blind" without a spectrum analyzer. I've gotten so used to having one, I'm almost hesitant to align a transmitter without it. I won't put a transmitter on the air that doesn't have a spurious output that's greater than -45dbc. As for audio spectrum analyzers, you can get software versions that run on a laptop. Great for plotting audio response. There has to be some secret when it comes to purchasing spectrum analyzers, and I don't know it yet! I read an article where one guy purchased a brand new analyzer for $1,500.00, sold his old analyzer, thinking that current technology must have caught up with his old one by now, but he goes on to say that he was sadly mistaken and totally disappointed. Said he could get some use out of the thing, but just barely. It wasn't his old analyzer by a long shot. I can only imagine that it's great to have an analyzer, being able to tune down spurs, adjust bandpass and lowpass filters, see both sides of your AM signal, adjust FM deviation, look at filter skirts, and proving to the FCC that your homebrew rig IS -70dbc when they stop by for a visit . One of these days, I'll get one, I hope... I really need to download one of those DSP-based audio analyzers. Do you guys know if there is a specific one I should use? I use one called "Spectrum". I've had it for several years now. It has both the spectrum functions and a built-in audio generator. Another fellow hi-fi audio enthusiast passed it on to me. I don't use it all that much (It's actually easier to use my scope). But it does do the job. |
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Post by tecnicoloco2000 on Oct 15, 2014 22:43:51 GMT -5
SpectraPlus has a 30 days demo for a Audio Spectrum Analyzer link |
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Post by ab5ni on Oct 16, 2014 1:01:32 GMT -5
Sounds good, loco and SB. I'll make sure I give both of those a shot for sure.
Thanks and 73,
Randy AB5NI
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Sandbagger
Administrator/The Boss
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Post by Sandbagger on Oct 16, 2014 7:13:33 GMT -5
SpectraPlus has a 30 days demo for a Audio Spectrum Analyzer link That's the one I have, and I have the unlock key to make it permanent. |
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Post by ab5ni on Oct 16, 2014 8:35:30 GMT -5
SpectraPlus has a 30 days demo for a Audio Spectrum Analyzer link That's the one I have, and I have the unlock key to make it permanent. Man, those packages are a bit pricey, to say the least. 73, Randy AB5NI |
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Post by tecnicoloco2000 on Oct 19, 2014 23:48:01 GMT -5
SpectraPlus has a 30 days demo for a Audio Spectrum Analyzer link That's the one I have, and I have the unlock key to make it permanent. A 0% interest plastic card with a 50% cash reward ?  |
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Post by BBB on Oct 25, 2014 16:18:54 GMT -5
Wavetek and JDSU 4040D or 5000D portable spectrum analyzers are found on the bay for less than $200. Typically the refresh rate is about 1 second but with the peak hold feature you can get a great idea of what you signal "looks" like spectrally. There are also two markers and a bunch of stuff I'll never use. These were developed for cable TV techs to determine and test many variables in the field. They even make a rack mount version that typically goes for $300 and up. Just pop on a scanner antenna and you're good to go. Here's one that went for $165. Oh wait, too late, oh snap... that one ended up on my bench. See, gotta act faster www.ebay.com/itm/321555932302?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D321555932302%26_rdc%3D1 |
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Post by ab5ni on Oct 25, 2014 16:44:28 GMT -5
Wavetek and JDSU 4040D or 5000D portable spectrum analyzers are found on the bay for less than $200. Typically the refresh rate is about 1 second but with the peak hold feature you can get a great idea of what you signal "looks" like spectrally. There are also two markers and a bunch of stuff I'll never use. These were developed for cable TV techs to determine and test many variables in the field. They even make a rack mount version that typically goes for $300 and up. Just pop on a scanner antenna and you're good to go. Here's one that went for $165. Oh wait, too late, oh snap... that one ended up on my bench. See, gotta act faster www.ebay.com/itm/321555932302?ru=http%3A%2F%2Fwww.ebay.com%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D321555932302%26_rdc%3D1I've seen our cable guy use one of those while tracking down a problem we were having with our Internet connection. Wound up being a damn squirrel chewing through my cable and letting water inside the jacket, attenuating my signal. Anyway, I've seen one in use, following the cable guy talking tech crap and out of curiosity. I told him, "Ah, a spectrum analyzer -- nice!" He said, "Yeah, they have sample and hold capability, and they work decently, but they're not an HP or Techtronix analyzer by a long shot." I told him I understood and that they were a compromise, but I guess having one of those beats the hell out of not having one at all! Thanks for the info, BBB! 73, Randy AB5NI |
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Post by BBB on Oct 25, 2014 19:02:18 GMT -5
Due to the vintage, most of these Wavetek and JDSU Analyzer's NiMH batteries are finito. But don't fret, they can be exchanged for re-furb'd ones on the bay. You'll need the factory charger with it's PS/2 connector to charge the battery. To power it up with out a battery and even cheaper yet, I use any 3 amp (or larger) 12 VDC power supply wired to the bottom barrel connector port on the chassis. Use a 90 degree plug. Anything below 3 amps doesn't cut the mustard. Wall-wart bad Juju...bad, wall-wart, bad  Cons: these are 75 ohm devices, not that it matters much for just checking for spurs, ect. I picked up a Wavetek 75>50 ohm adapter for a few bucks. no provision for direct 120 VAC operation. refresh rate compared to laboratory units. Pros: their relatively small footprint on the desk. portability, with a battery or 12 volt source. the green back-lit LCD. built in AM-FM modulator with a speaker. bunch of stuff I probably don't understand yet like some of this stuff: www.jdsu.com/ProductLiterature/SDA-4040_AE_DS_print.pdf |
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Post by ab5ni on Oct 25, 2014 20:32:16 GMT -5
Due to the vintage, most of these Wavetek and JDSU Analyzer's NiMH batteries are finito. But don't fret, they can be exchanged for re-furb'd ones on the bay. You'll need the factory charger with it's PS/2 connector to charge the battery. To power it up with out a battery and even cheaper yet, I use any 3 amp (or larger) 12 VDC power supply wired to the bottom barrel connector port on the chassis. Use a 90 degree plug. Anything below 3 amps doesn't cut the mustard. Wall-wart bad Juju...bad, wall-wart, bad Cons: these are 75 ohm devices, not that it matters much for just checking for spurs, ect. I picked up a Wavetek 75>50 ohm adapter for a few bucks. no provision for direct 120 VAC operation. refresh rate compared to laboratory units. Pros: their relatively small footprint on the desk. portability, with a battery or 12 volt source. the green back-lit LCD. built in AM-FM modulator with a speaker. bunch of stuff I probably don't understand yet like some of this stuff: www.jdsu.com/ProductLiterature/SDA-4040_AE_DS_print.pdf A lot of great info here, BBB. I'm going to get in touch with a couple of friends who own local telecommunications companies that cater to the oil biz. They do a lot of VSAT installs and such, so I might be able to pick something up on the cheap . Should that fail, I'll bid on EBay and see what turns up. Again, thanks for the great info! 73, Randy AB5NI |
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. When I get them, I'll surely be looking at modifying the rigs in nearly all aspects. Thanks for the info!
