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72642Re: Followup to FInally Done & Filter Question

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  • warrenallgyer
    Mar 7, 2013
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      The filters are documented in Robby's page at http://www.wb5rvz.org/

      Remember, you do not need a filter for every band. The external filter is only required for the lowest band in your particular build configuration. The 40/30/20 build, for example, will meet the -40 dB spec on 30 and 20 with the internal filters. Only on 40 meters will the second harmonic normally be higher than the limit.

      I would not assume that the filters incorporated in an amplifier will be adequate. They may be.... but an amplifier manufacturer could rightfully assume that the exciter providing the signal is already compliant and, therefore, may not provide filtering for high incoming harmonics.

      Warren Allgyer - W8TOD

      --- In softrock40@yahoogroups.com, "davidlopez2@..." <brewgod23@...> wrote:
      >
      > Is there a link to the schematics for these external filter assemblies with parts list? I would like to build these filters for my unit. Is there a discussion on a filter box that includes all the filters for 160M to 6M all in one box, switchable?
      >
      > Also, if you buy an external power amp with filtering internal to the amp, this filtering will not be required, correct?
      >
      > --- In softrock40@yahoogroups.com, "warrenallgyer" <allgyer@> wrote:
      > >
      > > Hi Rick
      > >
      > > The additional filters are to be used only for the lowest band in the group covered by your particular build. In your case you would put the filter in line for 40 meters but take it out for 30 and 20. It goes on the output, between the antenna and the RXTX.
      > >
      > > The reason for this is, in order for the radio to cover multiple bands, the on board low pass filters do not begin to "bite" until a few MHz above the highest band. For the 40/30/20 the filter 3 db point is in the neighborhood of 16-17 MHz. On 40 meters your second harmonic falls in the 14 MHz range and is passed undeterred by the onboard filter. Hence the need for something external.
      > >
      > > There are a number of ways to construct the filters.. the easiest would be on a small piece of copper clad. The sexiest (if I say so myself!!!) is in some photos that I have posted in the Photos section of this board where I separated two SMA connectors with spacers, then wired the toroids and caps in between the spacers, and covered the whole assembly with heat shrink.
      > >
      > > OK.. now that I have hurt my arm patting myself on the back.. maybe NOT the sexiest... but they are cute. You could do the same idea with a chassis mount BNC or even UHF if you want. They are very stable mechanically and easy to build.
      > >
      > > Warren Allgyer - W8TOD
      > >
      > > --- In softrock40@yahoogroups.com, "richard.lawn@" <rjlawn@> wrote:
      > > >
      > > > As I understand the instructions, parts are provided to build an external filter based on the band combination built, in my case 40/30/20. Is this correct as it seems odd not include this necessary filter on the main board. If I'm understanding this correctly and this filter goes between the antenna and RF input on the main board, I'd appreciate suggestions on how users have built this external filter - perf board or what?
      > > >
      > > > Rick
      > > > W2JAZ
      > > >
      > >
      >
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