Well a lot of people are under the impression that Mosfet=poor audio and rf distortion. It is even worse on SSB.
Some people are going on and on about the mosfets injecting rf into the audio blah blah blah.....
First the above thoughts and logic leading to both are wrong. The reason for the perceived issue is also wrong!
The circuits being used have been used for a long time nothing new to the circuits so if RF is being injected into the audio inappropriately it would have been the same before as it is now. The circuit is not new. The mosfets still work with the same needed in puts and outputs transitors can take many form but all of them have some for of base collector and emitter and all have voltage going in and out and need specific bias and voltages etc.
The problem is on the tune side of things. Everyone wants to get as much power as they can out of their gear and people are used to being able to get a lot more power out then the OEM recomends. So if an OEM was using 2 x 2879's and listed the output at 200 watts people would get out the golden screw driver adn push it to 350-500 watts and all was good. Well we have seen cheap durable great sounding high power 12Volt bipolar transistors vanish almost over night.
Fastward now we have mosfets replacing bipolar devices. They are even cheaper then bipolars but the cheapest ones have to have 8 of them used to do watt 2 Mitsubishi 2SC2879 did. Every dime you combine output devices you get more power dissipation you tend to lose efficiency and gain drops. So now when all these people go taking the golden screw driver to their 8 final radio sure they can get 400++ watts out but it is suffering some serious gain issues at that level of output and the intermod numbers while not being measured by anyone shows up as crap audio and a nasty nasty pattern on the scope. Flip the radio to SSB and it get's even worse and looks even worse.
The solution would be to go to more expensive transistors most of them in the 48V range and use less of them. It would not matter if they mosfet or LDMOS or bipolar at the end of the day. You need a good circuit design then you need to stay with in the limits of that circuit and the chosen transitors.
The reason the mosfets are not the issue is that if they where then single final CB's that use mosfets as the final would suffer the same degraded audio performance as the. Likewise dual final mosfet CB and export radios would also suffer. Even worse would be the radios that where not designed or modified by the OEM to use mosfets that had been modified years later for the use of mosfets for the finals.
people are pushing the gear beyond it's limitations and just because they can get the watts out of the linear they think they out to sound great. By linear I am talking about traditional single or dual final radios that have separate linear amps built into them usualy slapped on the bottom by their OEM's to sell a high power grossly illegal export radio with 100-500 watt's of output.
If the radio has an RF power control you can tune it to within an inch of it's life then turn it down especially on side band to say the 12 o'clock position and sound great even on SSB.
So the problem is unrealistic expectations from customers, cheap OEM not wanting to redesign for more expensive transistors, and technicians that pandor(sp) to poorly educated customer base that want to be louder then their neighbor at any cost! I can see it now one guy lets call him Joe has a nicely set up RCI2970N2 that had it's power turned down from the overly biased non-swinging stock RCI factory tune of 200 watts carrier swinging 300 out of the box to something like 50 watts swinging 200 and sounds great and his gear will likely last 10-20 years no issues running 24/7. Joe finds out at his local hunting club another guy lets call him Bill just a got a RCI2970N2 and his tech set up so it keys 200 and swings to 450 watts. So now Joe takes his unit to Bills tech and he sets it up just like Bills. Now Joe has all the power but no one he normally talks too on SSB can understand him he sounds terrible. Since Bill also has the same unit and sounds equally bad it must be RCI radios or it must be mosfet transistors that sound terrible.
Because most butcher shops I mean CB communication stores have unskilled less then knowledgeable people butcher radios for sale we see this repeated. Because the RCI has the best performance per dollar on the market and the rest of the RCI lineup under the thinly vield disguise of Galaxy/Connex/etc...have a lot of the similar circuits and components this get's repeated over and over and over again.
I just did this with a radio. I took a good sounding single final 40 channel FCC type accepted SSB radio from the 1980's. I put a RFX-150 on the radio and set it up so it would only swing up to 100 watts max on AM. It sounded great. I sent it out to a friend with a scope and told him I wanted him to make sure it looked good on the scope on SSB and told him he could adjust the wattage as he saw fit so long as the looked good and sounded good. Obviously I had him check AM as well but he said it was fine as it was. It turned out I had the SSB at around 200 watts and it was a little ugly but I adjusted it just by ear. He had to turn it down to around 150 watts.
I do 90% of my talking on SSB not AM. I still like to be load and proud on AM but only if I sound clean. Watts on a meter are kind of meaningless if they do not do anything for you and even worse if they hurt you.
I know my sample size of 1 is not significant. I plan on doing this same exercise on 2 other radio's. I am going to put a RFX-150 on a Realistic TRC453 SSB radio that is similar tot he Uniden PC122. If I get the same resutls it will be telling. Then maybe I will repeat with a 3rd radio tune it like most palces do and get 200+ watts out of that little RFX-150 unit and see what we see.
I think we will likely already know what the end result will be. Now imagine I was taking 2-4 of those RFX-150 units and coupling them together with each one tuned to it's max!!!
Some people are going on and on about the mosfets injecting rf into the audio blah blah blah.....
First the above thoughts and logic leading to both are wrong. The reason for the perceived issue is also wrong!
The circuits being used have been used for a long time nothing new to the circuits so if RF is being injected into the audio inappropriately it would have been the same before as it is now. The circuit is not new. The mosfets still work with the same needed in puts and outputs transitors can take many form but all of them have some for of base collector and emitter and all have voltage going in and out and need specific bias and voltages etc.
The problem is on the tune side of things. Everyone wants to get as much power as they can out of their gear and people are used to being able to get a lot more power out then the OEM recomends. So if an OEM was using 2 x 2879's and listed the output at 200 watts people would get out the golden screw driver adn push it to 350-500 watts and all was good. Well we have seen cheap durable great sounding high power 12Volt bipolar transistors vanish almost over night.
Fastward now we have mosfets replacing bipolar devices. They are even cheaper then bipolars but the cheapest ones have to have 8 of them used to do watt 2 Mitsubishi 2SC2879 did. Every dime you combine output devices you get more power dissipation you tend to lose efficiency and gain drops. So now when all these people go taking the golden screw driver to their 8 final radio sure they can get 400++ watts out but it is suffering some serious gain issues at that level of output and the intermod numbers while not being measured by anyone shows up as crap audio and a nasty nasty pattern on the scope. Flip the radio to SSB and it get's even worse and looks even worse.
The solution would be to go to more expensive transistors most of them in the 48V range and use less of them. It would not matter if they mosfet or LDMOS or bipolar at the end of the day. You need a good circuit design then you need to stay with in the limits of that circuit and the chosen transitors.
The reason the mosfets are not the issue is that if they where then single final CB's that use mosfets as the final would suffer the same degraded audio performance as the. Likewise dual final mosfet CB and export radios would also suffer. Even worse would be the radios that where not designed or modified by the OEM to use mosfets that had been modified years later for the use of mosfets for the finals.
people are pushing the gear beyond it's limitations and just because they can get the watts out of the linear they think they out to sound great. By linear I am talking about traditional single or dual final radios that have separate linear amps built into them usualy slapped on the bottom by their OEM's to sell a high power grossly illegal export radio with 100-500 watt's of output.
If the radio has an RF power control you can tune it to within an inch of it's life then turn it down especially on side band to say the 12 o'clock position and sound great even on SSB.
So the problem is unrealistic expectations from customers, cheap OEM not wanting to redesign for more expensive transistors, and technicians that pandor(sp) to poorly educated customer base that want to be louder then their neighbor at any cost! I can see it now one guy lets call him Joe has a nicely set up RCI2970N2 that had it's power turned down from the overly biased non-swinging stock RCI factory tune of 200 watts carrier swinging 300 out of the box to something like 50 watts swinging 200 and sounds great and his gear will likely last 10-20 years no issues running 24/7. Joe finds out at his local hunting club another guy lets call him Bill just a got a RCI2970N2 and his tech set up so it keys 200 and swings to 450 watts. So now Joe takes his unit to Bills tech and he sets it up just like Bills. Now Joe has all the power but no one he normally talks too on SSB can understand him he sounds terrible. Since Bill also has the same unit and sounds equally bad it must be RCI radios or it must be mosfet transistors that sound terrible.
Because most butcher shops I mean CB communication stores have unskilled less then knowledgeable people butcher radios for sale we see this repeated. Because the RCI has the best performance per dollar on the market and the rest of the RCI lineup under the thinly vield disguise of Galaxy/Connex/etc...have a lot of the similar circuits and components this get's repeated over and over and over again.
I just did this with a radio. I took a good sounding single final 40 channel FCC type accepted SSB radio from the 1980's. I put a RFX-150 on the radio and set it up so it would only swing up to 100 watts max on AM. It sounded great. I sent it out to a friend with a scope and told him I wanted him to make sure it looked good on the scope on SSB and told him he could adjust the wattage as he saw fit so long as the looked good and sounded good. Obviously I had him check AM as well but he said it was fine as it was. It turned out I had the SSB at around 200 watts and it was a little ugly but I adjusted it just by ear. He had to turn it down to around 150 watts.
I do 90% of my talking on SSB not AM. I still like to be load and proud on AM but only if I sound clean. Watts on a meter are kind of meaningless if they do not do anything for you and even worse if they hurt you.
I know my sample size of 1 is not significant. I plan on doing this same exercise on 2 other radio's. I am going to put a RFX-150 on a Realistic TRC453 SSB radio that is similar tot he Uniden PC122. If I get the same resutls it will be telling. Then maybe I will repeat with a 3rd radio tune it like most palces do and get 200+ watts out of that little RFX-150 unit and see what we see.
I think we will likely already know what the end result will be. Now imagine I was taking 2-4 of those RFX-150 units and coupling them together with each one tuned to it's max!!!
