[Discuss-gnuradio] Tuning Hardware

[Alan Gray]

Hi all, just a quick update on my progress in finding a suitable tuning 
solution

As I have mentioned previously, we were supplied with a large number of 
Microtune 4702DT5 tuners free of charge (datasheet available at 
http://www.mrgray.net/sdr/4702DT5.pdf) These are similar to the 4937 3x7702 
modules being used currently but use only a single downconversion stage and 
output at an IF of 36MHz.

Although we had these units, we decided it was still preferable to get our 
hands on the 4937 units as this would mean less time would need to be spent 
designing hardware. Unfortunately, as has been previously noted, finding a 
supplier for these parts is exceedingly difficult. After contacting all the 
suppliers in the Asia-Pacific region with no luck, we contacted Microtune 
direct and were informed that they had ceased production of that line of 
products, and that they too were unable to supply us with any modules.

They were however very helpful in suggesting a possible solution to our 
problem. Apparently the 4937 is made from the same components as the 4702, 
with another device at the output stage to shift the output frequency down 
to 5.75 MHz.
The device they use is an IC from NEC Electronics; UPC2798GR (the data 
sheet can be found at http://www.mrgray.net/sdr/2798.pdf). Using this IC 
means that it should be possible to design the desired output frequency.

While the data sheets include a sample design and a sample PCB layout, I 
have little experience in this area of electronics, especially in 
oscillator design, so the without any good examples designing the hardware 
is looking kinda daunting at the moment. Basically it seems to me that I 
need to feed the output of the 4702 tuner into the 2798 module, as well as 
a constant local oscillator signal which would then be mixed to produce the 
desired output frequency. This output would then be low pass filtered and 
amplified to obtain a suitable output signal. If anyone can assist with 
some information on how I could easily design the local oscillator 
(Suggested references, application notes, anything really) it would be much 
appreciated.

With the Microtune apparently ceasing construction of the 4937, it seems 
that some other tuning solution must be obtained. As I indicated earlier, 
our source at Panasonic may be willing to donate a fairly large number 
(around 500) of the 4702DT5 tuners to the project if we can find an 
appropriate use for them, so it might be well worth the effort to come up 
with some sort of solution.

I will continue to work on a suitable design, but any assistance others can 
provide would be most welcome

Alan