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--- lora:868filters [2026/03/07 20:51] – g5rkt
+++ lora:868filters [2026/03/07 22:08] (current) – [£62 868MHz helical cavity filter] g5rkt
@@ Line 1: / Line 1: @@
 ====== Messing about with filters for 868MHz ======
-Meshcore has been coming along leaps and bounds and, until recently, our local area had a dearth of repeaters so we lashed up "Soton WEST HBI Omni" (674cd415480a0de0aec84145eeedcae44c746d3ffaf1e16123babff712b2ab52) on 869.618MHz at one of our radio sites. Great location, covers everywhere but my oh MY, those LoRA boards do not like strong adjacent signals!
+Meshcore has been coming along leaps and bounds and, until recently, Southampton proper had a dearth of repeaters so we lashed up "Soton WEST HBI Omni" (674cd415480a0de0aec84145eeedcae44c746d3ffaf1e16123babff712b2ab52) on 869.618MHz at one of our radio sites. Great location, covers everywhere but my oh MY, those LoRA boards do not like strong adjacent signals!
 With a dummy load attached the RAK4631 board we are using has a reported noise floor of -118dBm. With the 11.5dBi Paradar antenna attached the noise floor jumped to -96dBm and inbound signals that should be strong-ish were reported to be around -10dB SNR, so Something Must Be Done!
 {{:lora:lora:hbi-nofilter.jpg?600|}}\\
-And strong adjacent signals we have, plenty of them. Television, 4G, and of course plenty of IR-2030 86xMHz traffic.
+And strong adjacent signals we have, plenty of them. Television, 4G, and unfortunately some very loud IR-2030 86xMHz traffic.
 Of course, Aliexpress to the rescue - plenty of things to try for comparatively little money.
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 {{:lora:acasom-cavity.jpg?600|}}\\
-They seem nicely put together, and the screws aren't painted down to the point of impossibility. We have purchased a few of these by this point, and they have turned up in a variety of conditions - one had clearly been adjusted with a pair of pliers! Oh well. Let's see what they look like.
+They seem nicely put together and the screws aren't painted down to the point of impossibility. We have purchased a few of these by this point and they have turned up in a variety of conditions - one had clearly been adjusted with a pair of pliers! Oh well. Let's see what they look like.
 {{:lora:cavity-before.jpg?600|}}\\
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 {{:lora:cavity-s21.jpg?600|}}\\
-Markers 1-4 are the four frequencies which we would like to reject, pulled down to -15dB to -35dB. Not too shabby! S11 is -33dB, S21 is -2.4dB so we have a filter which we can compare directly to the SAW filter currently on site.
+After some very careful fine-tuning markers 1-4, the frequencies which we would like to reject, were down to -15dB to -35dB. Not too shabby! S11 is -33dB, S21 is -2.4dB so we have a filter which we can compare directly to the SAW filter currently on site.
+{{:lora:finished_cavity.jpeg?600|}}\\
+Who said you can't put lipstick on a pig...
 To be continued!!