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Re: [Discuss-gnuradio] Microtune 4937 RF module discontinued ...
From: |
Paul J. Zawada |
Subject: |
Re: [Discuss-gnuradio] Microtune 4937 RF module discontinued ... |
Date: |
Tue, 22 Jul 2003 08:27:37 -0500 |
At 5:28 PM +1000 7/22/03, Alan Gray wrote:
I've had the same problems finding the 4937 tuner, and am currently
in the process of adapting the hardware design to use a 4702 tuner
module with an IF output at 36MHz. When we contacted Microtune they
suggested using a tuner such as the 4702 and an additional
downconversion stage (they suggested the NEC Electronics UPC2798GR
which is apparently what they use in the 4937 tuners anyway)
I've ordered a few of the NEC IC's but they're taking a long time to
arrive. In the mean time I'm going to attempt to put together some
hardware to use a 4702 module as is. I'm hoping that I should be
able to sample the bandlimited signal without any downconversion
(it's theoretically possible) and thus avoid the need for any more
components.
I've been shying away from Microtune since they and their
manufacturers rep for my area have been so difficult to work with.
They sent me a sample of the 4937 and swore up and down they still
had them in stock (in the Philippines) but for the life of me I could
not get them to send me an official quote. I was all set to buy
$1000 of tuners (their minimum order) and told them the PO would be
cut as soon as I got a quote, but they don't seem to be interested in
my business. (I tried for weeks to get a quote.) Given this
experience, I am reluctant to jump to another Microtune product. If
you're willing to do an external downconversion from 36-44 MHz, it
seems to me that there are a lot of tuners available to consider...
I've been looking at the Zarlink chips... Anyone else have any good
candidates?
Further to this, I've got just a quick question about the schematic design:
What is the purpose of the op-amp circuitry connected to the IF
outputs of the 4937? It looks to be acting as a buffer and changing
the output impedance of the system, however I'd like to be sure.
I'll be dealing with a higher frequency output, and while the OPA691
appears to be able to operate at even higher frequencies I'm
anticipating having to change that part of the circuit around a
little, just need to know exactly what it does.
In addition to being a convenient way to match the impedance, the op
amp also converts the balanced (differential) output of the Microtune
tuner to an unbalanced (single-ended) output...
--zawada
--
Paul J. Zawada, PE | Principal Network Research Engineer
address@hidden | National Center for Supercomputing Applications
+1 217 649 2233 | University of Illinois at Urbana-Champaign