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Author Topic: AM/FM DSP Noise Filter  (Read 2897 times)
AF6D
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« on: June 11, 2017, 01:29:38 PM »

I know that noise is vertically polarized and normally AM in its qualities. As an experiment I took a West Mountain Radio Clear Speech DSP and ran it between the audio output jack of my rig and an external speaker. Using it's four position control I could take a variety of signals and remove a lot of the noise from signals that had dropped below -100 dDm. I know that in theory they are not meant for FM but I know that it worked. Has anyone else tried putting a DSP filter in line between the discriminator audio and the controller and then using the dip switch to set it for a fixed value? I noticed that I could clearly hear scratchy signals with noticeably less scratch on them then without. I didn't pull out the spectrum analyzer and did the testing by ear. I got the idea from my Yaesu ft - 847 that has DSP that works in the FM mode also. Not as effective but it works. I know that it defies the nature of a FM signal through the receiver. An increase in the limit or current etc etc. All I know is it worked.
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N8EKT
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« Reply #1 on: June 14, 2017, 07:08:00 PM »

Normally, preemphasis and deemphasis takes care of noise

If the DSP rolls off the higher frequencies in a similar fashion, it may work
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AF6D
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« Reply #2 on: June 14, 2017, 07:21:44 PM »

Thank you for your reply.

I use  commercial Kenwood's and Vertex. Decent radios. As for the repeater, it is a Motorola MSF 5000. Considering the results my experiment I wondered if it might be beneficial to put a DSP in it in the audio line from the receiver to the Arcom controller. I's set it at level 2 and a strong signal would cause no effect. It's just a thought and I wondered if anyone else had noticed that a DSP designed for AM/SSB/CW worked well on FM.

I won't waste my time if the consensus is that it is a waste of time.  Grin
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K4JJL
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« Reply #3 on: June 15, 2017, 01:36:24 PM »

the Arcom controller.

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