If your SWR is good barefoot and over a 2.5 with 300 watts into a Wilson, you can be sure the amplifier is the issue. Those ERF7530 transistors are the bottom of the line for RF amps at this frequency and power level. Lets be clear, you can't buy a lower quality part for this application. No other manufacturer has ever tried to market a 75 watt, 30 MHz. transistor RF transistor in a audio or switching transistor package like this before because they knew the only market that would even consider going this low would be CB.
The builders of these amps don't believe a single thing they tell their buyer either. The proof that they are well aware they're selling you junk is specifying the use of an abnormally long patch cord between the oscillator (amp) and your radio. Good RF design always places the exciter as closer to the power amp as possible. The long coax introduces reactance to cover up the fact their amp is almost completely unstable while attempting to tame the self oscillations cheap transistors so easily generate at this frequency.
If we keep buying this junk and accepting the fact that we can't get a good SWR without knowing why, the process will continue. They get to charge you the same price for a "300 watt" amp but the transistors cost 10 times less then good ones designed for the job. To me these MOSFET amps are just as bad as the guys that tried to sell linears with the 2SC1307 CB final in them back in the 1980's. It makes no sense to build an amp with a transistor that can really only provide you with about 6 db of useable gain. They claim 10 db but 100 watts in with 300 out is under 6.
An ERF7530 is only rated at 20 watts carrier and can't even modulate that to 100% without going over it's rated specs. You have to run four of them on AM at 75 watts carrier and 300 watts peak just to stay in specs that are beyond the capabilities of the package they stuff it in anyhow. Some people have luck with these amps while many have oscillation problems that disguise themselves as antenna SWR problems.
The people selling the defective amps will always say the SWR problem is your antenna or coax when it almost never is. Those that have a variable power with a wide range can usually prove this to themselves. For example, if you can set your radio to make a 20 watt carrier and have a good SWR, then turn the amp on and reset the variable for the same 20 watts out of the amp with a bad SWR, no one can tell you it's the extra power and you'll know the amp is the problem using no expensive test equipment.
It doesn't bring me pleasure to have to reveal the inferior quality here. I'd much rather be able to tell you this is a reliable cost effective option but to say they are temperamental would be putting it mildly. There is no headroom here because the manufacturer has already used it all in their specs to make the sale. Good for less than 20 watts average on AM is the bottom line or in this case the top of the line you can expect. Whenever you have the choice, ALWAYS avoid CB MOSFET's. Buy RF transistors made by a company that manufacturers thousands of transistors. Not a company that manufacturers a few rubber stamps to use on someone else's transistors when they find 2 or 3 that work in another application.
The builders of these amps don't believe a single thing they tell their buyer either. The proof that they are well aware they're selling you junk is specifying the use of an abnormally long patch cord between the oscillator (amp) and your radio. Good RF design always places the exciter as closer to the power amp as possible. The long coax introduces reactance to cover up the fact their amp is almost completely unstable while attempting to tame the self oscillations cheap transistors so easily generate at this frequency.
If we keep buying this junk and accepting the fact that we can't get a good SWR without knowing why, the process will continue. They get to charge you the same price for a "300 watt" amp but the transistors cost 10 times less then good ones designed for the job. To me these MOSFET amps are just as bad as the guys that tried to sell linears with the 2SC1307 CB final in them back in the 1980's. It makes no sense to build an amp with a transistor that can really only provide you with about 6 db of useable gain. They claim 10 db but 100 watts in with 300 out is under 6.
An ERF7530 is only rated at 20 watts carrier and can't even modulate that to 100% without going over it's rated specs. You have to run four of them on AM at 75 watts carrier and 300 watts peak just to stay in specs that are beyond the capabilities of the package they stuff it in anyhow. Some people have luck with these amps while many have oscillation problems that disguise themselves as antenna SWR problems.
The people selling the defective amps will always say the SWR problem is your antenna or coax when it almost never is. Those that have a variable power with a wide range can usually prove this to themselves. For example, if you can set your radio to make a 20 watt carrier and have a good SWR, then turn the amp on and reset the variable for the same 20 watts out of the amp with a bad SWR, no one can tell you it's the extra power and you'll know the amp is the problem using no expensive test equipment.
It doesn't bring me pleasure to have to reveal the inferior quality here. I'd much rather be able to tell you this is a reliable cost effective option but to say they are temperamental would be putting it mildly. There is no headroom here because the manufacturer has already used it all in their specs to make the sale. Good for less than 20 watts average on AM is the bottom line or in this case the top of the line you can expect. Whenever you have the choice, ALWAYS avoid CB MOSFET's. Buy RF transistors made by a company that manufacturers thousands of transistors. Not a company that manufacturers a few rubber stamps to use on someone else's transistors when they find 2 or 3 that work in another application.
