[1000mp] W8JI INRAD roofing filter measurements

[Pete Smith]

Hi Lou - The big problem with the high first IF, as I understand it, is 
that it is very difficult to design a relatively narrow crystal filter at 
that frequency.  right after the Orion came out, I saw George at Dayton and 
asked him why Inrad couldn't offer a narrow first filter for the MP/Mk5 
series.  He said he'd been working on it, but had not yet found a 
manufacturer.  A couple of years later he did.

I can't explain the W8JI results, but wonder why the noise blanker mod 
would destructively interact with the roofing filter in the Mk5.  I do know 
that my radio, which does not have the NB mod, sounds much better.

73, Pete

  At 05:43 PM 4/25/2007, Lou wrote:
>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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