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Re: Downconverter noise



On Tue, 2003-05-27 at 06:27, Jon Ogden wrote:
> On Tuesday, May 27, 2003, at 01:53 America/Chicago, Howard Long wrote:
> 

> Well, then I guess I stand corrected.  But it just doesn't make sense.  
> If the d/c is at S5 with no antenna and no signal, then you are already 
> at least 10 to 15 dB above the noise floor of your radio.  Does the 
> noise actually go DOWN once the antenna is mounted on the dish and put 
> in place?

If the full instruction sheet is read, it does make sense, these AIDC
converters were originally created to drive multiple tv's through
splitters over long distances (100' of rg-59).  So the IF conversion
gain on them is at around 37 dB.  So of course on 2m, the noise level is
going to be extremely high.  K5GNA recommends using at least 50' of
rg-59 and a 6 dB pad to get the s meter down to s0, or s1.  

On my FT-847, with the internal preamp on, the noise is usually s5-s7,
beacon would be about 20 over, even though that's not really the case
(bbq grill).

The mode I run it in most often is with the preamp off, (no 6 dB pad
inline due to the fact that mine fell apart).  This registers about s3
of noise, beacon around s6, s7

If I'm having trouble with a station I'll kick on the internal 10 dB
attenuator on the 847, this takes the noise down to s0, and the beacon
to about s3.  Even though I rarely get s meter movement from stations in
this case, it does decrease the noise and its sometimes easier to copy
them.

I'd suspect maybe the if amplifier in the aidc is degraded or junk if
he's able to hear slight noise rises when pointing, but no major noise
floor rise when powering it on.

> 
> I can tell you that form my experience you do hear an increase in noise 
> with the d/c on, but it certainly isn't enough to move the s-meter more 
> than a unit or less.  It's certainly not 5 units.
> 
> I'm confused..
> 
> 73,
> 
> Jon
> NA9D
> 


Ryan Butler, KB0JQO


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