Re: [Discuss-gnuradio] Microtune 4937 RF module discontinued ...

[Paul J. Zawada]

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


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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