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commercial broadcaster grade audio?
- Thread starter towerdog
- Start date
MotorMouthMaul Rx mod
http://www.motormouthmaul.com/linked/cobra 148 rx mod.pdf
http://www.motormouthmaul.com/linked/cobra 148 rx mod.pdf
good to know... I always figured that they did not have the bandwidth to make a huge difference
It looks like this mod mainly improves the response of the AF circuits. I actually found a recording on youtube that seems to show the difference:
CB RADIO COBRA 148 GTL AFTER AND BEFORE THE SRC WIDE RECEIVE MOD - YouTube
I think you're still limited a bit by the crystal filters though. Having a 6Khz AM filter bandwidth actually results in about 3Khz of actual audio bandwidth, since AM has two sidebands. With the MMM mod, you should be able to hear all the low end, but if you listen to someone with a really wide signal, they may have highs up around 5 to 6Khz which will be lost.
(Note that earlier I had asserted that these filters might limit TX response too, but that was a mistake on my part. Ham rigs do that; CBs don't. Hopefully I'm not wrong about the filters being a limiting factor for RX response though.
)
The Kenwood TS-850SAT that I have allows you to select the filter width at both IF stages from the front panel. There are options for 2.7Khz, 6Khz, 12Khz and 'bypass,' where filtering is disabled entirely. There is a noticeable difference on AM between 6Khz and 12Khz or bypass. HiFi audio sounds much crisper with the increased bandwidth.
-Bill
CB RADIO COBRA 148 GTL AFTER AND BEFORE THE SRC WIDE RECEIVE MOD - YouTube
I think you're still limited a bit by the crystal filters though. Having a 6Khz AM filter bandwidth actually results in about 3Khz of actual audio bandwidth, since AM has two sidebands. With the MMM mod, you should be able to hear all the low end, but if you listen to someone with a really wide signal, they may have highs up around 5 to 6Khz which will be lost.
(Note that earlier I had asserted that these filters might limit TX response too, but that was a mistake on my part. Ham rigs do that; CBs don't. Hopefully I'm not wrong about the filters being a limiting factor for RX response though.
)The Kenwood TS-850SAT that I have allows you to select the filter width at both IF stages from the front panel. There are options for 2.7Khz, 6Khz, 12Khz and 'bypass,' where filtering is disabled entirely. There is a noticeable difference on AM between 6Khz and 12Khz or bypass. HiFi audio sounds much crisper with the increased bandwidth.
-Bill
that's kinda what I was getting at, the other people that have nothing done to their receive most likely can't tell a huge difference because of the audio frequency roll off the filters cause
I had some time to putz around a bit this weekend, so I made a sample recording of my rig, illustrating what it sounds like when you try to cram HiFi audio through a 6Khz crystal filter.
http://people.freebsd.org/~wpaul/station/amtests.mp3
This recording is in AM mode (not ESSB). The transmitter is my Kenwood TS-950SDX. The receiver is the TS-850SAT. (Yeah, I know this is ham gear instead of CB gear, but the idea still applies.) The samples are:
- MC-43S hand mic through the front panel
- MC-60A desk mic through the front panel
- Behringer B1mic and audio gear through the rear panel ACC2 port
- Ditto, with the transmitter restricted to 3.1Khz of response
- Ditto, with the receiver set to use the 6Khz filters
- Ditto, with the receiver set to use the 12Khz filter (at the 455Khz IF)
- One more test with all the filters in the receiver bypassed again
Most of the tests are done with the 8.83Mhz and 455Khz IF filters bypassed. The audio circuitry of the receiver has not been modified. (There are a few caps you can change to widen the AF response out a little more, but I think it's pretty good as it is.) When the receiver is set so that the 6Khz filters are engaged, you can still hear the bassiness in the audio, but cutting out the highs makes it sound more muffled. Bypassing the filters yields the best results, but the 12Khz setting is pretty good too.
So yeah, tweaking the AF stages in a given rig will allow you to recover a lot of lost low end, and will gain you a little bit at the high end, but you'll still be limited at the RF level by the crystal filters. And the missing highs really do make a difference when listening to a wide AM signal.
So is it worth it to go to all the trouble to make your station sound that good on 11 meters when most people won't be able to appreciate it? I guess it depends on your perspective. Some people consider it a worthwhile area of experimentation. Some people just like to show off. (Not all of us are able to run a gazillion watts like the guys on the superbowl, so we need to find other ways to make ourselves stand out. )
Personally I keep hoping the SDR radio craze comes to 11 meters some day. With rigs like the Flex, the filtering is entirely controlled by software and can be as narrow or wide as you want it, without having to use crystal filters.
-Bill
http://people.freebsd.org/~wpaul/station/amtests.mp3
This recording is in AM mode (not ESSB). The transmitter is my Kenwood TS-950SDX. The receiver is the TS-850SAT. (Yeah, I know this is ham gear instead of CB gear, but the idea still applies.) The samples are:
- MC-43S hand mic through the front panel
- MC-60A desk mic through the front panel
- Behringer B1mic and audio gear through the rear panel ACC2 port
- Ditto, with the transmitter restricted to 3.1Khz of response
- Ditto, with the receiver set to use the 6Khz filters
- Ditto, with the receiver set to use the 12Khz filter (at the 455Khz IF)
- One more test with all the filters in the receiver bypassed again
Most of the tests are done with the 8.83Mhz and 455Khz IF filters bypassed. The audio circuitry of the receiver has not been modified. (There are a few caps you can change to widen the AF response out a little more, but I think it's pretty good as it is.) When the receiver is set so that the 6Khz filters are engaged, you can still hear the bassiness in the audio, but cutting out the highs makes it sound more muffled. Bypassing the filters yields the best results, but the 12Khz setting is pretty good too.
So yeah, tweaking the AF stages in a given rig will allow you to recover a lot of lost low end, and will gain you a little bit at the high end, but you'll still be limited at the RF level by the crystal filters. And the missing highs really do make a difference when listening to a wide AM signal.
So is it worth it to go to all the trouble to make your station sound that good on 11 meters when most people won't be able to appreciate it? I guess it depends on your perspective. Some people consider it a worthwhile area of experimentation. Some people just like to show off. (Not all of us are able to run a gazillion watts like the guys on the superbowl, so we need to find other ways to make ourselves stand out.
)Personally I keep hoping the SDR radio craze comes to 11 meters some day. With rigs like the Flex, the filtering is entirely controlled by software and can be as narrow or wide as you want it, without having to use crystal filters.
-Bill
It looks like this mod mainly improves the response of the AF circuits. I actually found a recording on youtube that seems to show the difference:
CB RADIO COBRA 148 GTL AFTER AND BEFORE THE SRC WIDE RECEIVE MOD - YouTube
I think you're still limited a bit by the crystal filters though. Having a 6Khz AM filter bandwidth actually results in about 3Khz of actual audio bandwidth, since AM has two sidebands. With the MMM mod, you should be able to hear all the low end, but if you listen to someone with a really wide signal, they may have highs up around 5 to 6Khz which will be lost.
(Note that earlier I had asserted that these filters might limit TX response too, but that was a mistake on my part. Ham rigs do that; CBs don't. Hopefully I'm not wrong about the filters being a limiting factor for RX response though.
The Kenwood TS-850SAT that I have allows you to select the filter width at both IF stages from the front panel. There are options for 2.7Khz, 6Khz, 12Khz and 'bypass,' where filtering is disabled entirely. There is a noticeable difference on AM between 6Khz and 12Khz or bypass. HiFi audio sounds much crisper with the increased bandwidth.
-Bill
So you can tx and rx 12khz wide with your kw....man it must sound awesome.
robb,
you have two methods to widen your receiver, first IF in most cb's is a 300kc or so ceramic filter unless its a modern rig with 7 or 8kc first IF crystal filter,
part of the bandwidth is set by the 455khz second IF filter as stated above often a cfw455ht 6kc and partly by the caps/resistors in the audio chain after the detector,
caps to ground reduce treble, higher value less treble,
caps in series effect bass, higher value more bass,
imagine the resistors and capacitors acting together as a frequency variable divider network.
you can improve the fidelity to hear what the wide boys are transmitting if you are willing to sacrifice selectivity by changing the 455ht to something like a
cfw455G ( 9KC )
cfw455F (12KC)
cfw455E (15kc),
other filters such as LF-H8S work ok too, try to find a filter with similar impedance and insertion loss, the wide boys sound much better with a wider filter,
a switched if bandwidth board would be a cool mod, a socket to plug n play filters would be better than nothing,
on the tx side the same cap rule applies from the mic socket to the mic preamp and beyond, after the mic preamp the signal splits,
one line towards the balanced modulator for ssb tx,
another line goes to the AM reg/mod circuit, and one to the fm reactance modulator,
if you want full AM tx bandwidth its easy to directly drive the modulator bypassing the radio's own audio tailoring and amc circuit like i did with my 4lb globe king "ar144"
when using direct drive you need some form of limiter in your off-board gear,
ssb tx bandwidth is largely determined by the ssb filter but the caps/resistors in the tx audio chain play their part as they do in the am/fm tx audio,
on single conversion sets like washington /144 ect the ssb filter is used for AM, i swapped the stock 4kc for a 15kc, it gave me wide AM and carrier suppression issues.
you have two methods to widen your receiver, first IF in most cb's is a 300kc or so ceramic filter unless its a modern rig with 7 or 8kc first IF crystal filter,
part of the bandwidth is set by the 455khz second IF filter as stated above often a cfw455ht 6kc and partly by the caps/resistors in the audio chain after the detector,
caps to ground reduce treble, higher value less treble,
caps in series effect bass, higher value more bass,
imagine the resistors and capacitors acting together as a frequency variable divider network.
you can improve the fidelity to hear what the wide boys are transmitting if you are willing to sacrifice selectivity by changing the 455ht to something like a
cfw455G ( 9KC )
cfw455F (12KC)
cfw455E (15kc),
other filters such as LF-H8S work ok too, try to find a filter with similar impedance and insertion loss, the wide boys sound much better with a wider filter,
a switched if bandwidth board would be a cool mod, a socket to plug n play filters would be better than nothing,
on the tx side the same cap rule applies from the mic socket to the mic preamp and beyond, after the mic preamp the signal splits,
one line towards the balanced modulator for ssb tx,
another line goes to the AM reg/mod circuit, and one to the fm reactance modulator,
if you want full AM tx bandwidth its easy to directly drive the modulator bypassing the radio's own audio tailoring and amc circuit like i did with my 4lb globe king "ar144"
when using direct drive you need some form of limiter in your off-board gear,
ssb tx bandwidth is largely determined by the ssb filter but the caps/resistors in the tx audio chain play their part as they do in the am/fm tx audio,
on single conversion sets like washington /144 ect the ssb filter is used for AM, i swapped the stock 4kc for a 15kc, it gave me wide AM and carrier suppression issues.
Well, again, the 12Khz here is for the RF signal filtering, and with AM, you have two sidebands (basically the same audio is transmitted twice). So the resulting audio response is actually half that. If you have a 6Khz filter with AM, you'll hear about 3Khz of audio (maybe a little more since the skirts on the filter are not completely sharp). If you have a 12Khz filter, you'll get about 6Khz of audio, and so on.
With SSB, the filter width directly corresponds to the audio bandwidth since there's just the one sideband. And the TS-850 does let you bypass the filters in transmit too, and that will increase your TX audio response. But Kenwood designed the rig such that the filters are used to suppress the alternate sideband when operating in SSB mode, so turning the filters off is a bad idea for SSB: you'll end up transmitting on both USB and LSB at the same time.
AM is another matter. The best way to get HiFi out of the TS-850 is to mod the radio to bypass the mic pre-amp circuits and feed the balanced modulator direct from your audio rack, and then turn off all the crystal filters. It's still low-level modulated, but the fidelity is excellent.
The TS-950SDX on the other hand uses a digital signal processor for modulation in AM and SSB modes. Normally it limits you to 3.1Khz on both SSB and AM, but there's a trick to max it out, which which yields about 6.7Khz audio response in both modes. For AM, that means your signal is 13Khz wide. I *think* the TS-850 modded for HiFi AM can achieve better response, but the TS-950SDX has the advantage of being capable of HiFi on both AM and SSB with the same mic setup. (I think the only thing that really beats the SDX all around in terms of fidelity is the Flex 5000.)
You can listen to the clip I posted earlier to hear what it sounds like for yourself. (It's the TS-950SDX transmitting and the TS-850 receiving.) I've got the SDX dialed in pretty well now, but I'm still experimenting. (Too many knobs and switches, damnit. Can't resist the urge to fiddle.) BTW, I mostly credit the Behringer DEQ2496 with actually making me sound halfway decent in that recording. I don't know how I got along without that thing before.
-Bill
Thanks for explaining that...I appreciate it.....and the TS-850 sounds like a awesome radio.
Hello Bob:
PHP:
on single conversion sets like washington /144 ect the ssb filter is used for AM, i swapped the stock 4kc for a 15kcThe stock filters on the single conversion units are a little bit wider than the ones used on double conversion,I swapped the filter from a 142 into a 148 have a very minor issue with carrier suppression but sounds pretty good in SSB also swapped the 455 filter with a wider one for AM
On my old favorite TS-530 I swapped the 2.4Khz for a 4khz filter and a few caps and sounds pretty good too.
Good seeing you still coming around trowing good ideas and opinions amigo
73 de Andy/Tecnicoloco
I had some time to putz around a bit this weekend, so I made a sample recording of my rig, illustrating what it sounds like when you try to cram HiFi audio through a 6Khz crystal filter.
http://people.freebsd.org/~wpaul/station/amtests.mp3
This recording is in AM mode (not ESSB). The transmitter is my Kenwood TS-950SDX. The receiver is the TS-850SAT. (Yeah, I know this is ham gear instead of CB gear, but the idea still applies.) The samples are:
- MC-43S hand mic through the front panel
- MC-60A desk mic through the front panel
- Behringer B1mic and audio gear through the rear panel ACC2 port
- Ditto, with the transmitter restricted to 3.1Khz of response
- Ditto, with the receiver set to use the 6Khz filters
- Ditto, with the receiver set to use the 12Khz filter (at the 455Khz IF)
- One more test with all the filters in the receiver bypassed again
Most of the tests are done with the 8.83Mhz and 455Khz IF filters bypassed. The audio circuitry of the receiver has not been modified. (There are a few caps you can change to widen the AF response out a little more, but I think it's pretty good as it is.) When the receiver is set so that the 6Khz filters are engaged, you can still hear the bassiness in the audio, but cutting out the highs makes it sound more muffled. Bypassing the filters yields the best results, but the 12Khz setting is pretty good too.
So yeah, tweaking the AF stages in a given rig will allow you to recover a lot of lost low end, and will gain you a little bit at the high end, but you'll still be limited at the RF level by the crystal filters. And the missing highs really do make a difference when listening to a wide AM signal.
So is it worth it to go to all the trouble to make your station sound that good on 11 meters when most people won't be able to appreciate it? I guess it depends on your perspective. Some people consider it a worthwhile area of experimentation. Some people just like to show off. (Not all of us are able to run a gazillion watts like the guys on the superbowl, so we need to find other ways to make ourselves stand out.
Personally I keep hoping the SDR radio craze comes to 11 meters some day. With rigs like the Flex, the filtering is entirely controlled by software and can be as narrow or wide as you want it, without having to use crystal filters.
-Bill
The Behringer mic sounded by far the best.
What radios have adjustable bandwidth like that?