I have a 148GTL that receives low on AM only. SSB reads fine. When I inject a S-9 signal into the antenna jack the radio's s-meter reads 9 s-units on SSB. When it is injected on the AM side it reads about 1.5 s-units. All the cans in the rx chain seem to peak ok and none of the slugs are bottomed out or near the rim. Any ideas why sensitivity would be low on AM only and fine on both sidebands?