[Elecraft] Down-conversion

[Eric Swartz - WA6HHQ, Elecraft]

That is why we built special test fixtures for us and INRAD to test 
strong signal IMD handling on all of our K3 filters.

73, Eric


On 11/18/2010 4:49 AM, Geoffrey Mackenzie-Kennedy wrote:
> Bruce,
>
> I believe that your suspicion is correct. The sticking point in the design
> of a high performance up-conversion receiver at this time is the first LO,
> whose phase noise must be suitably "low" and whose cost is acceptable. There
> can be problems with VHF "Roofing" filters, but there are ways to overcome
> these.
>
> Regarding the use of very narrow roofing filters (crystal) in a
> down-conversion receiver, there is an underlying filter generated IMD
> problem which might or might not affect the IMD performance of the overall
> receiver - depending upon the "IMD performance" of those parts of the
> receiver ahead of and behind the filter. The problem is that for any given
> quality of quartz used in the crystals, the IMD performance of a crystal
> filter can be shown to worsen as the filter's bandwidth narrows. I suspect
> that the 6 kHz roofing filter used in Kenwood's TS-590S ahead of the IF
> crystal filters is there to give some protection to the narrower IF filters.
>
> 73,
> Geoff
> GM4ESD
>
>
> Bruce McLaughlin wrote on Wednesday, November 17, 2010, at 11:02 PM:
>
>
>> I suspect it is going to become the standard for many if not most of the
>> new
>> radios.  As soon as it became apparent that effective roofing filters can
>> really improve the close in IMD performance, it seems as if a low first IF
>> frequency has become almost mandatory.  I note that the Orion and the new
>> Yaesu FT 5000 both use down conversion for the first IF and, therefore,
>> have
>> effective narrow roofing filters.  I wonder when, or if, ICOM and the
>> others
>> will follow suit.
> <snip>
>
>
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