[Premium-Rx] Marconi LP Filter

[Bob Milne]

Hi Gary & All,

Has anyone actually listened to a rig with linear-phase filters and
come up with any observations? While I agree linear-phase filters
exhibit less ringing, I'm also of the opinion that amount of ringing
exhibited by conventional mechanical or crystal filters has a lot to
do with how hard they are hit by transients. Here, in my humble
opinion, is where the IF amplification, gain distribution, and AGC
loop characteristics differ greatly among receivers--Premium or
otherwise. I would suspect that a specific filter would exhibit
varying degrees of ringing depending on what particular receiver it's
installed in.

Now that's a design issue. And I'll bet quality of recovered audio is
not a major design consideration of most (maybe all?) Premium RXs.
They're designed to spec and the audio is what it is. It just happens
that the audio turns out better on some designs--but not necessarily
by intent.

I don't know this for a fact, but I suspect that Drake is one company
that does consider audio an important design consideration. Notice how
many reviewers have had nice things to say about the audio in the R8
series. And in the old days, Collins was legendary for the audio
quality produced by its transmitters and receivers.

Hmmm...are there actually DXers with Golden Ears (to borrow an
over-used Hi-Fi term)? From the comments on this list, it would seem
so.

Regards....
....Bob 

On Wed, 08 Oct 2003 07:33:30 +1000, you wrote:

>Interesting that no-one has mentioned the IF filter group delay or PHASE
>RESPONSE!
>
>I think you will find this is responsible for many of the effects described
>qualitatively by others here. For example, the amount of ringing exhibited
>by a filter is a function of its phase response. When a receiver is used for
>data reception, linear phase response (ie. flat group delay) is what it is
>all about.
>
>Comments anyone?
>
>Regards,
>George Georgevits
>Power and Digital Instruments Pty Ltd
>
>
>-----Original Message-----
>From: premium-rx-bounces at ml.skirrow.org
>[mailto:premium-rx-bounces at ml.skirrow.org]On Behalf Of Richard M. MC
>Clung
>Sent: Wednesday, 8 October 2003 3:11 AM
>To: Premium-RX LIST
>Subject: [Premium-Rx] Marconi LP Filter
>
>
>I just received a really nice 300KHz LP Filter. It is in a metal case
>that has spring loaded thumb screws to attach it to something else.
>
>It is passive with a BNC chassis connectorfor input and a short cable
>with BNC connector for output on the rear of the chassis and a switch
>to select or bypass the filter on the front panel.
>
>It is 10 inches long X 2 3/4 inches height X 1 5/8 inches wide.
>
>The chassis data is:
>
>MARCONI INSTRUMENTS LTD
>300 KHZ LOW PASS (B) FILTER
>TK 2095
>TYPE NO 52095-014P
>BATCH NO J 173311
>TO CCIR RECOMMENDATION NO 339/1
>
>The PCB data is:
>PM3
>44816-108
>300KHZ LP
>
>I put it on the spectrum analyzer and it is flat from 0 KHz to 300KHz
>with a 2dBm insertation loss is 36dBm down at 308KHz and 50dBm down at
>319KHz.
>
>I'd like to use it ahead of my VLF RCVR's and would like to get any
>documentation on it.
>
>I'd also like to retune it to 500KHz. It has adjustable inductors in
>it.
>
>Anyone ever see one of these or have any doucmentation on it?
>
>RICH  WA6KNW
>
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