Inrad 2.0k SSB Filter for Yaesu FT-817 857 897

Discussion in 'General Technical Questions and Answers' started by MM6LMP, Jun 17, 2011.

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  1. MM6LMP

    MM6LMP Ham Member QRZ Page

    I sort of understand what this filter will do on RX but not too sure what it's supposed to do on TX. Anyone care to explain with as little jargon as possible. Does it narrow or broaden bandwidth for example?
  2. KB3LIX

    KB3LIX Ham Member QRZ Page

    The filter will limit the transmit bandwidth to the passband of the filter.
    I use a 2.3 KC Collins Machanical filter in my FT-897D and route
    the transmit signal thru the filter. Seems to work fine.
  3. M3KXZ

    M3KXZ Ham Member QRZ Page

    If you want to make your TX audio more crisp and clear, then first of all look at adjusting the USB and LSB TX carrier offsets to suit your voice better. My voice is pretty bassy which doesn't really work well fro cutting through the noise. Altering the TX carrier offset helps make better use of the mid voice frequencies rather than the low ones.
  4. MM6LMP

    MM6LMP Ham Member QRZ Page

    Would this filter narrow the TX bandwidth to 2.0kc? If so why? Why would anyone deliberately make their audio so telephonic? Maybe I'm missing the point hope someone can enlighten me.
  5. K9STH

    K9STH Ham Member QRZ Page

    It will narrow the transmitted audio to 6 dB down at the 2.0 kHz bandwidth. How fast it goes down from there is dependent on the "skirts" of the filter.

    A bandwidth of 2.1 kHz is very common, especially with the older SSB equipment. All of my Collins S-Line equipment and all of my Heath SB-Line equipment have 2.1 kHz wide filters and they have some pretty good "skirts". I often get unsolicited comments on how good the audio is from all of this equipment. The equipment is set up so that the actual audio passed is between 300 Hz and 2400 Hz. This is plenty "wide" for excellent quality voice communications. All that going to a wider bandwidth does is to increase the high frequency component which generally lends nothing to the actual communications.

    On receive, a wider filter allows more adjacent frequency interference, etc. What you really need is a balance between "fidelity" and problems due to having a filter too wide. Filters that are 2.4 kHz to 2.7 kHz wide are cheaper to make than narrower filters and that is one reason that so many manufacturers use them. Also, many amateur radio operators are of the opinion that a wider filter "sounds" better because it does pass higher frequency audio. Unfortunately, having a wider filter definitely increases noise, adjacent frequency "splatter", and so forth.

    Glen, K9STH
  6. MM6LMP

    MM6LMP Ham Member QRZ Page

    Great stuff starting to make some sense of this now.
  7. M3KXZ

    M3KXZ Ham Member QRZ Page

    Another reason to make the audio more "telephonic" is that it makes more efficient use of the power available. No point spreading a limited amount of power over a wider bandwidth.
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