So here is cheap fix I stumbled across for a common problem .
The symptom is a Galaxy-type (RCI-made) SSB radio with off-frequency AM receive. You align all the SSB stuff and AM transmit dead on the money, only to find the AM receiver is centered 1.5 kHz or so above the channel frequency. A lot of 2950-type radios do this, but today we'll stick to the EPT3600 radio. This time it's a Galaxy DX99V from Y2K. A radio old enough to have its own driver's license. The owner got a chuckle when I revealed that to him.
And the reason the AM receiver is a kHz or 1.5 high is that the black plastic "CFW455H" 455kHz ceramic IF filter FL1 is off frequency by that much. It's an epidemic with RCI-made radios.
What was really wrong with this particular radio was that it was nearly one channel below the channel selected. Turns out the 10.240 crystal X1 was way off frequency, over 3 kHz high.
A new crystal was much closer, but the receiver still had that slightly-off frequency problem with the ceramic filter.
The dodge is to goose the frequency of X1 downwards. It was around 10.241.2 with the new crystal. There is a ceramic-disc capacitor in series with X1. It's C83 placed flat alongside X1 on the inboard-facing side of X1. Schematic shows 30 pf. Had a 24 pf part in it. Makes it seem the factory will select an exact value to match a particular batch of 10.24 crystals.
Long story short, replacing C83 with a jumper wire brought X1 down to about 10.238.3 MHz. This put the AM receiver dead on frequency when the internal and my external counter indicate channel center.
A jumper wire is both cheaper and easier than changing the 5-legged ceramic filter, and did the job. This might not appeal to a SSB operator, but for Joe Driver who only uses AM, it got him a result for half the price of changing out FL1. Besides, if the new ceramic filter is not any closer than the old one, you just wasted the time to find out.
And if you just don't have a new CFW455 on hand, this trick might make somebody's day.
Cheap.
Or is that "cheaply" ?
73
The symptom is a Galaxy-type (RCI-made) SSB radio with off-frequency AM receive. You align all the SSB stuff and AM transmit dead on the money, only to find the AM receiver is centered 1.5 kHz or so above the channel frequency. A lot of 2950-type radios do this, but today we'll stick to the EPT3600 radio. This time it's a Galaxy DX99V from Y2K. A radio old enough to have its own driver's license. The owner got a chuckle when I revealed that to him.
And the reason the AM receiver is a kHz or 1.5 high is that the black plastic "CFW455H" 455kHz ceramic IF filter FL1 is off frequency by that much. It's an epidemic with RCI-made radios.
What was really wrong with this particular radio was that it was nearly one channel below the channel selected. Turns out the 10.240 crystal X1 was way off frequency, over 3 kHz high.
A new crystal was much closer, but the receiver still had that slightly-off frequency problem with the ceramic filter.
The dodge is to goose the frequency of X1 downwards. It was around 10.241.2 with the new crystal. There is a ceramic-disc capacitor in series with X1. It's C83 placed flat alongside X1 on the inboard-facing side of X1. Schematic shows 30 pf. Had a 24 pf part in it. Makes it seem the factory will select an exact value to match a particular batch of 10.24 crystals.
Long story short, replacing C83 with a jumper wire brought X1 down to about 10.238.3 MHz. This put the AM receiver dead on frequency when the internal and my external counter indicate channel center.
A jumper wire is both cheaper and easier than changing the 5-legged ceramic filter, and did the job. This might not appeal to a SSB operator, but for Joe Driver who only uses AM, it got him a result for half the price of changing out FL1. Besides, if the new ceramic filter is not any closer than the old one, you just wasted the time to find out.
And if you just don't have a new CFW455 on hand, this trick might make somebody's day.
Cheap.
Or is that "cheaply" ?
73
