[1000mp] W8JI INRAD roofing filter measurements

[Lou]

Hi Pete,

I too greatly respect W2JVN's engineering. So far, all lab tests and
listening reports agree.  The MkV is substantially better with the INRAD
roofing filter. There is no question.

However, having done the W8JI NB mod, which also makes a substantial
improvement, should I now add the INRAD roofing filter?  W8JI's data
suggests no.  By doing so I would be undoing some of the NB mod improvement
even though it would still be as better than a stock radio.

Of course, the above conclusion is based one datum point, that being the one
on the W8JI website. I also don't know of any rationale explaining an
interaction between the two mods that would account for the effect.

BTW, George has a nice write-up on the INRAD site discussing roofing
filters.  He points out that the main difference between rigs like the Orion
and K2, and rigs from the other major manufactures is that the first IF is
in the HF region (typically 10-11 MHz)for the former and VHF region for the
latter. 

Lou W7HV


-----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 1:31 PM
To: farson at shaw.ca; All about Yaesu 1000mp
Subject: RE: [1000mp] W8JI INRAD roofing filter measurements

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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