Anything more than 40 watts PEP is asking for trouble. The carrier should never be set at more than 25% of the maximum PEP output. It's not the resistors or the common caps people replace that are the weak link. The trouble is in many areas from the size of the DC choke feeding the final, the series pass modulator handling the extra current and the risk of blowing up the receiver because it's always connected to the antenna terminal even in TX.
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
irf520 mod on cobra 148 nwst?
- Thread starter pimphand442
- Start date
Shockwave do not waste your time. I learned when I was 19 and I am 43 soon to be 44 that trying to use logic and common sense in the CB world is a waste of time! If anything you should encourage them since this has the net result of emptying peoples pockets faster which is like a self regulator! Just look at how they are burning through expensive BJT's that should last 20+ years only last them 6 months and they need more.
Never mind going from the power potential of a 2SC1969 to the output of a IRF520 is functionally meaningless in the real world. It is even more useless once you exceed the 4:1 rule on AM.
No matter how many time you tell them that a clean high gain 4:1 signal that is cool running and well filtered is the way go it is wasted. For what ever reason the idea of having a radio that keys 2 watt's swinging 8 rms going into an external amplifier. The higher the hfe of the driver and final and the BJT's in the amp the better!
No one seems to stop and think about hfe and imd at the voltage and drive levels concerned or the freq. range and preference of the transistors. Always about watt's on a cheap meter. SSB is easier to play with power wise but imd matter's much more than on am. Often a transistor will sound decent on AM but you try it on SSB and yo find it sounds terrible.
In terms of chasing watt's we see it again in the Cobra 25,29 and like radio's. People always want to take out the lower power much higher gain driver and finals to replace them with 2SC1969's and than volt them and do NPC etc....In many of these smaller non SSB radio's the final might be a 5-10 watt final per the white paper but you see if you look they always have a minimum hfe of 60-100 compared to the minimum hfe of 20 for the 2SC1969. You almost need to do NPC mod just to break even in a way because the hfe can be so low on the 2SC1969 compared to the orignal final.
I do not talk to Dosey Meter's or to Bird Meter's I talk to people. Likewise I do not transmit into a dummy load with perfect SWR I transmit into coax that terminates into a real world less than perfect antenna.
Gain does not show up on a Bird meter! LOL If you have two amps one has 400 watts of rms output power and a gain of 11 the other amp has an rms output of 350 watts rms but has a gain of 90 while the amp with 400 watt's is going to have the most carrier and it's signal will be the dominate signal on air likely you will hear the 350 watt system's audio loud and clear over the more powerful station if distance, antenna etc... are otherwise identical.
When you hear a station that has no carrier signal on your RX meter but their audio is loud and clear what do you think is getting the job done? It is not the carrier is it?
In fact because CB'er's go by watt meter's you can use low gain MRF428(?) low beta MRF455's(cheap) and still put out big numbers on a meter which keeps cost down and sells amps!
Most people do not understand the significance of gain compared to just watt's alone. It reminds me of horse power versus torque in a way. You have to have a pretty expensive spectrum analyzer to see the difference and even then you have to know what you are actually looking for.
The same can be said for imd no one talks about it but it does matter.
I have said it before and I will say it again. The only reason to put a mosfet in a radio that came with bjt's for it's driver and final is to maximize profits and take advantage of customers. I can buy 10-20 popular mosfet's to use as finals for the price on 1 2SC1969. Most people have no idea how S-Units, db's and sinad works so for them more is always better. They have no idea that you have to radically increase power to make a significant change in real world performance.
On top of that I do not like the way mosfets drive amplifiers or how they wildly they swing. Mosfets driver's produce more peak watt's in an amp but fewer rms watt's which is the opposite of what I want to do. Second I hate how no matter how low you turn the deadkey a lot of these radio's with mosfets will swing to insanely high pep number's. What is the point of turning down the rf power on a radio if it only turns the deadkey down???
Never mind going from the power potential of a 2SC1969 to the output of a IRF520 is functionally meaningless in the real world. It is even more useless once you exceed the 4:1 rule on AM.
No matter how many time you tell them that a clean high gain 4:1 signal that is cool running and well filtered is the way go it is wasted. For what ever reason the idea of having a radio that keys 2 watt's swinging 8 rms going into an external amplifier. The higher the hfe of the driver and final and the BJT's in the amp the better!
No one seems to stop and think about hfe and imd at the voltage and drive levels concerned or the freq. range and preference of the transistors. Always about watt's on a cheap meter. SSB is easier to play with power wise but imd matter's much more than on am. Often a transistor will sound decent on AM but you try it on SSB and yo find it sounds terrible.
In terms of chasing watt's we see it again in the Cobra 25,29 and like radio's. People always want to take out the lower power much higher gain driver and finals to replace them with 2SC1969's and than volt them and do NPC etc....In many of these smaller non SSB radio's the final might be a 5-10 watt final per the white paper but you see if you look they always have a minimum hfe of 60-100 compared to the minimum hfe of 20 for the 2SC1969. You almost need to do NPC mod just to break even in a way because the hfe can be so low on the 2SC1969 compared to the orignal final.
I do not talk to Dosey Meter's or to Bird Meter's I talk to people. Likewise I do not transmit into a dummy load with perfect SWR I transmit into coax that terminates into a real world less than perfect antenna.
Gain does not show up on a Bird meter! LOL If you have two amps one has 400 watts of rms output power and a gain of 11 the other amp has an rms output of 350 watts rms but has a gain of 90 while the amp with 400 watt's is going to have the most carrier and it's signal will be the dominate signal on air likely you will hear the 350 watt system's audio loud and clear over the more powerful station if distance, antenna etc... are otherwise identical.
When you hear a station that has no carrier signal on your RX meter but their audio is loud and clear what do you think is getting the job done? It is not the carrier is it?
In fact because CB'er's go by watt meter's you can use low gain MRF428(?) low beta MRF455's(cheap) and still put out big numbers on a meter which keeps cost down and sells amps!
Most people do not understand the significance of gain compared to just watt's alone. It reminds me of horse power versus torque in a way. You have to have a pretty expensive spectrum analyzer to see the difference and even then you have to know what you are actually looking for.
The same can be said for imd no one talks about it but it does matter.
I have said it before and I will say it again. The only reason to put a mosfet in a radio that came with bjt's for it's driver and final is to maximize profits and take advantage of customers. I can buy 10-20 popular mosfet's to use as finals for the price on 1 2SC1969. Most people have no idea how S-Units, db's and sinad works so for them more is always better. They have no idea that you have to radically increase power to make a significant change in real world performance.
On top of that I do not like the way mosfets drive amplifiers or how they wildly they swing. Mosfets driver's produce more peak watt's in an amp but fewer rms watt's which is the opposite of what I want to do. Second I hate how no matter how low you turn the deadkey a lot of these radio's with mosfets will swing to insanely high pep number's. What is the point of turning down the rf power on a radio if it only turns the deadkey down???
So by this logic a tetrode amplifier running the same carrier as a triode will out perform it because the tetrode has more gain? That almost sounds like the guys that say 1446 transistors are "audio pills."