What is the right way to test rx filters in the P1225/GP300 portable Radio's.
Do you generate a tone of 455 khz into them and see if it passes or what is the professional way..
regards,
john
R2600 Analyzer question
Moderator: Queue Moderator
-
johnny1225
- Posts: 229
- Joined: Thu Jul 22, 2004 8:27 am
My two bits worth:
In general, testing the IF band pass filters is accomplished with the RF
demod probe, and the Sweep generator function.
Monitor the IF amp after the filter so you do not detune the circuit under test.
You may generate either the IF frequency, or the receive freq.
Usuially, a defective IF filter will show up as distorted audio, improper squelch action, poor 12db SINAD.
Another way to do a quick test is to manually tune seceral kc above and below the receive frequency with a 3kc tone, see if the distortion improves.
Consult the manual for recomended tests for your particular radio.
In general, testing the IF band pass filters is accomplished with the RF
demod probe, and the Sweep generator function.
Monitor the IF amp after the filter so you do not detune the circuit under test.
You may generate either the IF frequency, or the receive freq.
Usuially, a defective IF filter will show up as distorted audio, improper squelch action, poor 12db SINAD.
Another way to do a quick test is to manually tune seceral kc above and below the receive frequency with a 3kc tone, see if the distortion improves.
Consult the manual for recomended tests for your particular radio.
Aloha, Bernie
-
psapengineer
- Posts: 175
- Joined: Thu Oct 07, 2004 10:00 am
Another Way
Assuming it's a wide band version of the radio:
Generate a 1KHz tone with plenty of carrier into the radio.
Start off at about 1KHz of deviation and increase it to 7KHz. It should get louder and not distort significantly. The "modulation acceptance" spec is about 7.5 KHz on wide band equipment. This allows the "other" radio you're listening to to drift some in carrier frequency.
Then, like Bernie suggests, generate about 3KHz of deviation and "rock" the carrier frequency up and down about 7KHz each side of center. The points at which the audio distorts should be symmetrical about the center carrier frequency.
Like "Bernie" comments, if the audio gets better skewed from center you've got a problem. It's either the crystal filters or the injection frequency. I'm not sure how injection is accomplished on the GP300.
Good luck, Bob
Generate a 1KHz tone with plenty of carrier into the radio.
Start off at about 1KHz of deviation and increase it to 7KHz. It should get louder and not distort significantly. The "modulation acceptance" spec is about 7.5 KHz on wide band equipment. This allows the "other" radio you're listening to to drift some in carrier frequency.
Then, like Bernie suggests, generate about 3KHz of deviation and "rock" the carrier frequency up and down about 7KHz each side of center. The points at which the audio distorts should be symmetrical about the center carrier frequency.
Like "Bernie" comments, if the audio gets better skewed from center you've got a problem. It's either the crystal filters or the injection frequency. I'm not sure how injection is accomplished on the GP300.
Good luck, Bob