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RE: 3733 vs DB6NT MKU-232A



As just some more data points, I have modified two 3733's and tested them on an HP NF meter and my results are almost exactly the same as Howard's.  Both my units have the stub cut and the Murata filter installed per K5GNA's instructions.  The one with the crystal replaced and a preamp-power mod installed shows 1.15 NF, 32 dB gain at 145 MHz.  The one with the stock crystal shows 1.10 NF, 33 dB gain at 123 MHz.  This latter unit is planned as part of my mobile/FD AO-40 setup using an FT-100--can't transmit at 123 MHz :-)  
73,
Jerry, K5OE

In a message dated Thu, 18 Oct 2001 10:28:31 AM Eastern Daylight Time, "Howard Long" <howard@howardlong.com> writes:

> Hello Art
> 
> > Does anyone have any experience comparing the modified 3733
> > (with stub cut and ceramic filter added) against a DB6NT
> > MKU-232A downconverter?
> 
> Using the same feed I've done a 1:1 test with a a TSI AIDC3733 I modified as
> per the K5GNA speicications having a measured NF of 1.14dB, and the DB6NT
> MKU24 downconverter with an NF of 0.65dB.
> 
> The MKU-232A is a dual stage preamp without downconverter, but more on that
> in a moment.
> 
> I couldn't tell the difference audibly between the two either on AO-40 or on
> UO-11, but the theory says I should suffer.
> 
> In truth I've found it's the antenna that makes by far the biggest
> defference.
> 
> One other point of note which applies to the DB6NT MKU-232A and MKU24
> downconverter is that it's really important to observe the maximum 1mW of RF
> appearing at the RF in of these units. I've fried the NE32584C on both these
> units with a 70cm uplink antenna close by. In comparison, the 3733 is
> unphased.
> 
> I've therefore invested in a reel of hot standby FET replacements for the
> DB6NT stuff.
> 
> I really like the DB6NT stuff, even though in Europe it's 'reassuringly
> expensive'. But it pays to abide by the instructions.
> 
> 73 Howard G6LVB
> 
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