[1000mp] W8JI INRAD roofing filter measurements

[Garry Shapiro]

Lou:

Of course--but the quote specifically says "passive IMD in the filter", 
implying the nonlinearities are in the filter itself, rather than in the 
mixer preceding the filter. If there are nonlinearities in the amplifier 
section of the filter--and of course there will be to whatever 
extent--these are not "passive". I am trying to resolve whether this is 
semantics or an actual circuit phenomenon. Perhaps it did not translate 
exactly from the German.

Garry, NI6T



Lou wrote:
> I think you got it. As an example, diodes are passive non-linear devices
> exploited for mixing. Mixing is useful IMD.
>
> Lou W7HV
>
> -----Original Message-----
> From: 1000mp-bounces at mailman.qth.net [mailto:1000mp-bounces at mailman.qth.net]
> On Behalf Of Garry Shapiro
> Sent: Wednesday, April 25, 2007 2:38 PM
> To: All about Yaesu 1000mp
> Subject: Re: [1000mp] W8JI INRAD roofing filter measurements
>
> VA7OJ quotes "degradation...due to passive IMD in the filter." I am 
> unfamiliar with the term "passive IMD" but suppose it to mean IMD due to 
> nonlinearities in passive components in the filter.  Can anyone 
> knowledgeable in the subject contribute something here?
>
> Garry, NI6T
>
>
> Pete Smith wrote:
>   
>> Well, the very best close-in IMD figures from a stock radio in W8JI's 
>> tests are from the Orion, which has 6 and 1 kHz roofing filters as 
>> standard, and goes down to 200 Hz in the optional filters.  So it 
>> appears to me that what's happening in the 7800 must be something 
>> other than strictly roofing filter bandwidth.  I'm inclined to trust 
>> both my ears and W2VJN's engineering and believe that the Mk5 with 
>> roofing filter is a better receiver than without.
>>
>> 73, Pete N4ZR
>>
>> At 12:26 PM 4/25/2007, you wrote:
>>     
>>> Hi Pete,
>>>
>>> There is a fascinating article describing IMD tests on the IC-7800 by 
>>> DC4KU
>>> in CQ-DL, August 2005 (in German). In these tests, IP3 at 2 kHz offset
>>> degrades by an astounding 16 dB when switching from the 15 kHz to the 
>>> 6 kHz
>>> roofing filter. This degradation is due to passive IMD in the filter, 
>>> and
>>> possibly also to IMD in the filter driver amplifiers caused by 
>>> mismatch when
>>> the filter is excited outside its passband. I can send you an
>>> English-language summary of the relevant part privately, if you wish.
>>>
>>> It is highly significant that professional receivers manufactured by the
>>> likes of R&S, Rockwell-Collins, Racal and Harris have a single roofing
>>> filter. This filter is typically 12 to 16 kHz wide, to pass 
>>> multi-channel
>>> ISB, VFT (multiplexed teletype) and high-speed crypto, all of which have
>>> extremely stringent in-band IMD requirements. To quote a British 
>>> engineer
>>> who used to design shipboard HF receivers for the Royal Navy:
>>>
>>> The up-converting architecture, with a roofing filter at a first IF 
>>> above
>>> the highest RF frequency, allows the designer to limit the bandwidth
>>> presented to the first IF chain and second mixer. The bandwidth of this
>>> filter is a trade-off. Its 3 dB BW must be sufficient to pass the widest
>>> emission the receiver is required to handle, but not so narrow that 
>>> IMD and
>>> temperature-drift effects in the filter become a concern.
>>>
>>> Cheers for now, 73,
>>> Adam VA7OJ/AB4OJ
>>>
>>>
>>> -----Original Message-----
>>> From: 1000mp-bounces at mailman.qth.net 
>>> [mailto:1000mp-bounces at mailman.qth.net]
>>> On Behalf Of Pete Smith
>>> Sent: Wednesday, April 25, 2007 04:34
>>> To: All about Yaesu 1000mp
>>> Subject: Re: [1000mp] W8JI INRAD roofing filter measurements
>>>
>>> Put it in, Dave - takes 10 minutes and the difference in contest 
>>> conditions
>>> is remarkable.  I suspect that this will turn out to be some sort of
>>> measurement anomaly - why would inserting a 6 KHz filter in the first IF
>>> cause such marked deterioration in measurements with 2 KHz spacing?
>>>
>>> 73, Pete N4ZR
>>>
>>>
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