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Post by Night Ranger on Aug 2, 2015 13:26:11 GMT -5
I wonder if this will get rid of my co-channeling? Twelve 455 kHz 7.5 kHz bandwitdh ceramic filters in series.   Night Ranger |
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Post by tecnicoloco2000 on Aug 2, 2015 13:50:07 GMT -5
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Sandbagger
Administrator/The Boss 
Posts: 6,247 
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Post by Sandbagger on Aug 2, 2015 15:35:39 GMT -5
I wonder if this will get rid of my co-channeling? Twelve 455 kHz 7.5 kHz bandwitdh ceramic filters in series. Night Ranger Nope. Not unless your bleedover is coming from a strong station one channel away that is running no more than 100% modulation. Of course the path loss of all those filters in series would probably kill a good bit of your sensitivity without a 12db pre-amp in front of them. |
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Post by Night Ranger on Aug 2, 2015 17:46:47 GMT -5
I wonder if this will get rid of my co-channeling? Twelve 455 kHz 7.5 kHz bandwitdh ceramic filters in series. Night Ranger Nope. Not unless your bleedover is coming from a strong station one channel away that is running no more than 100% modulation. Of course the path loss of all those filters in series would probably kill a good bit of your sensitivity without a 12db pre-amp in front of them. I'm joking of course. It won't stop the wide banded transmissions, but it should knock out strong clean signals. I'd probably have to put an IF amp after every two or three ceramic filters to equalize the signal loss, and with so many IF amps I'd probably raise the noise floor. The dual 455 kHz ceramic filters I installed on my Krazy Kraco made a noticeable improvement, and the 11.275 MHz crystal I installed in the 1st IF on my Midland 13-853 helped. That Midland 13-853 needs some additional amplification on the the AGC though. I purchased 20 LT455EW ceramic filters to help with selectivity on some of the radios in my collection. I'll probably just chain one after the built in stock 455 kHz ceramic filter on the radios that need it the most like the Cybernet AM chassis, Morse CB-2000 (pretty sorry on selectivity), and the 14 crystal synthesis rigs that do not have a fixed 1st IF frequency. Night Ranger |
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Sandbagger
Administrator/The Boss
Posts: 6,247
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Post by Sandbagger on Aug 2, 2015 18:19:56 GMT -5
Nope. Not unless your bleedover is coming from a strong station one channel away that is running no more than 100% modulation. Of course the path loss of all those filters in series would probably kill a good bit of your sensitivity without a 12db pre-amp in front of them. I'm joking of course. It won't stop the wide banded transmissions, but it should knock out strong clean signals. I'd probably have to put an IF amp after every two or three ceramic filters to equalize the signal loss, and with so many IF amps I'd probably raise the noise floor. The dual 455 kHz ceramic filters I installed on my Krazy Kraco made a noticeable improvement, and the 11.275 MHz crystal I installed in the 1st IF on my Midland 13-853 helped. That Midland 13-853 needs some additional amplification on the the AGC though. I purchased 20 LT455EW ceramic filters to help with selectivity on some of the radios in my collection. I'll probably just chain one after the built in stock 455 kHz ceramic filter on the radios that need it the most like the Cybernet AM chassis, Morse CB-2000 (pretty sorry on selectivity), and the 14 crystal synthesis rigs that do not have a fixed 1st IF frequency. Night Ranger I've thought about doing something similar to a couple of my radios (Like the SBE Trinidad) which have no filters at all and simply rely on the "Q" of the tuned IF cans to supply selectivity (which isn't all that great). When there was a decent bit of activity on channel 14, I usually had to switch to one of my more selective radios like the Browning, Tram or the Hy-Gain 623. But when most of the "splash" was caused by overmodulation splatter, even the radios with good sharp filtering did not make much difference. So I reverted back to my original thinking that I wanted to keep the radios as close to stock as possible, just so flaws like this could be experienced, as they were in the 70's, and the differences in design could be compared. Back in the 70's when bleedover was a daily fact of life, I didn't have the luxury of having 3 high end premium radios to switch to, and I often wondered how the various makes of radios stacked up against each other in the all-important channel rejection area. Now I can sort of do that comparison, although the level of signals I see now is nothing like what they were then. |
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