[Exotics] Marconi LP Filter

[JaMi Smith]

Rich,

And the bad news is . . .

They were all parted out . . .

Yeah, I have seen them before, and I even used to have a bunch of them
for various different frequencies, But I don't have anything left but
possibly a few parts.

I have run across both the filters that the boxes that they plugged
into.

As I remember, some of the boxes were labeled "Transmitter" and the
others "Receiver", but I could never figure out what type of system they
were used in. It seemed very low frequency, what ever it was.

I bought them from C & H Surplus, here in Pasadena California, where I
live, very cheaply, simply to strip down for the attenuators and the
beautiful Marconi knobs and panel meters.

The boxes had some really nice rotary attenuators that I thought would
be useful for some of my T-Hunting apparatus, but as it turned out, they
were not 50 ohm, as I had thought, but rather 75 ohm, as was everything
else in the boxes, so I couldn't use them. If I remember correctly, all
of the filters were also 75 ohm.

I thought that I could possibly make some sense out of some of the
filters, originally thinking that they were possibly bandpass filters of
different bandwidths for a common IF, such as 455kc, or 10.7 or 21.4
MHz. I ultimately gave up on them, realizing they were for much lower
frequencies, and stripped off all of the neat looking inductors and a
few of the variable capacitors, all of which went into the old junk box,
and I haven't seen them in years. The remains of the boards were thrown
away.

As for the attenuators, If I remember correctly, I gave them to a friend
that had a Marconi Signal Generator with an attenuator with some broken
cams and switches, so he could use the ones I had to try and rebuild
his, which looked mechanically similar, if not identical, except for the
resistor values.

About the only thing that I can tell you about the boxes and the
filters, was that the inputs and outputs of the ones I had were all 75
ohms, and there were a bunch of 75 ohm cables running around inside all
of the boxes that I had.

Hopefully that is of some help.

I check out C & H on a somewhat regular basis, but haven't seen any
other similar Marconi stuff in years, but I keep all of my "exotics"
posts, so if I ever see any more, I will let you know.

JaMi Smith, KK6CU


----- Original Message -----
From: "Richard M. MC Clung" <wa6knw@sbcglobal.net>
To: "Exotics LIST" <exotics@mailman.qth.net>
Sent: Tuesday, October 07, 2003 12:41 PM
Subject: [Exotics] 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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