HowD
Member
I have a BC250D and a PRO-2006. The PRO seems better at rejecting intermod.
I just put up an outdoor antenna. Excellent results! However, there was some really severe intermod. I was able to track down the two main culprits, and I have almost 100% eliminated the interference.
Here's how I got rid of one FM broadcast station:
NOTE: The information here is in the public domain and may appear elsewhere. It's all about helping our peers...
REMINDER: BE CAREFUL with the antenna jack on your scanner. You will need to ensure that there is not a lot of weight pulling on the scanner's antenna jack.
First, I put my incoming antenna lead to a bunch of adapters so I could place a Radio Shack "FM Trap" (part number 15-577C) inline. Yes, the adapters may cause signal loss, but the results were immediate removal of the FM station's intermod. I couldn't believe how clearly the airport towers (yes, I can hear 2 of them) came in. Yes, the FM trap is 75 Ohms and everything else is 50 Ohms....however, it's doing a great job here.
There was, however, still some pretty nasty interference on the Military UHF band, coming from a local TV station. I made a "stub" filter. It is extremely easy to do:
REMINDER: BE CAREFUL with the antenna jack on your scanner. You will need to ensure that there is not a lot of weight pulling on the scanner's antenna jack.
1. Determine the frequency of the station that is interfering.
2. Divide 75 by that frequency (75/f)
3. Take the answer to #2 and multiply it by 0.67
4. You now know how long (in centimeters) to make the stub filter.
5. Obtain a length of coaxial cable somewhat longer than the number of mm in #4.
6. Solder a connector on the end (or buy a small, pre-made cable assembly--note that you will be cutting one end of it and leaving that end without any connector.)
7. Carefully measure from the tip of the connector along the length of the cable the number of cm in #4.
8. Cut the cable. If you want to be extra careful, cut the cable a little bit long and then you can trim it to fine-tune it.
9. Attach the antenna cable to one side of a "T" connector. Attach the stub (that's right, the other end of the stub is OPEN) to the other side of the "T" and then connect the "T" to your scanner's antenna input.
10. You should notice a dramatic reduction in the interference for that particular offending frequency.
In my case, I have both the FM Trap and the stub filter connected.
Your results may vary.
Please let me know if this helps!
NOTES
Part #s:
T-Adapter: 278-198 (you may need different connectors, but this part number is a start...)
FM Trap: 15-577C
The offending TV station was Channel 12.
The audio for TV channel 12 is 209.75Mhz.
75 divided by 209.75 = 0.358
0.358 times 0.67 = 0.2395cm
0.2395 * 100 = 23.95cm
Thus, the stub is 23.95 cm long.
QUESTION: What if there are even more stations causing interference? I'm not quite sure. Can the stubs be combined by using more "T" connectors?
I just put up an outdoor antenna. Excellent results! However, there was some really severe intermod. I was able to track down the two main culprits, and I have almost 100% eliminated the interference.
Here's how I got rid of one FM broadcast station:
NOTE: The information here is in the public domain and may appear elsewhere. It's all about helping our peers...
REMINDER: BE CAREFUL with the antenna jack on your scanner. You will need to ensure that there is not a lot of weight pulling on the scanner's antenna jack.
First, I put my incoming antenna lead to a bunch of adapters so I could place a Radio Shack "FM Trap" (part number 15-577C) inline. Yes, the adapters may cause signal loss, but the results were immediate removal of the FM station's intermod. I couldn't believe how clearly the airport towers (yes, I can hear 2 of them) came in. Yes, the FM trap is 75 Ohms and everything else is 50 Ohms....however, it's doing a great job here.
There was, however, still some pretty nasty interference on the Military UHF band, coming from a local TV station. I made a "stub" filter. It is extremely easy to do:
REMINDER: BE CAREFUL with the antenna jack on your scanner. You will need to ensure that there is not a lot of weight pulling on the scanner's antenna jack.
1. Determine the frequency of the station that is interfering.
2. Divide 75 by that frequency (75/f)
3. Take the answer to #2 and multiply it by 0.67
4. You now know how long (in centimeters) to make the stub filter.
5. Obtain a length of coaxial cable somewhat longer than the number of mm in #4.
6. Solder a connector on the end (or buy a small, pre-made cable assembly--note that you will be cutting one end of it and leaving that end without any connector.)
7. Carefully measure from the tip of the connector along the length of the cable the number of cm in #4.
8. Cut the cable. If you want to be extra careful, cut the cable a little bit long and then you can trim it to fine-tune it.
9. Attach the antenna cable to one side of a "T" connector. Attach the stub (that's right, the other end of the stub is OPEN) to the other side of the "T" and then connect the "T" to your scanner's antenna input.
10. You should notice a dramatic reduction in the interference for that particular offending frequency.
In my case, I have both the FM Trap and the stub filter connected.
Your results may vary.
Please let me know if this helps!
NOTES
Part #s:
T-Adapter: 278-198 (you may need different connectors, but this part number is a start...)
FM Trap: 15-577C
The offending TV station was Channel 12.
The audio for TV channel 12 is 209.75Mhz.
75 divided by 209.75 = 0.358
0.358 times 0.67 = 0.2395cm
0.2395 * 100 = 23.95cm
Thus, the stub is 23.95 cm long.
QUESTION: What if there are even more stations causing interference? I'm not quite sure. Can the stubs be combined by using more "T" connectors?
