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preamps--mast mount vs. in shack



Question for the list---

Assume I put a preamp with the following specs in the shack vs. on the mast 
(at the antenna).

Frequency 		144-148 MHz
Noise factor(dB)	0.5
Gain(dB)		24
1 dB Compression (dBm)	+12
1 dB Bandwidth (MHz)	7.0


Assume the coax is 75' of 9913, which claims 1.6 dB attenuation in a 100' 
length at 150 MHz.

How do I calculate the benefit of having the preamp at the antenna, rather 
than in the shack?  I've browsed the web a good bit, but not found the 
right place yet (and a Handbook on CD is on my Xmas list!)

I guess the 75' length has 75/100 x 1.6 = 1.2 dB loss.  So, I can get that 
far, if I did that math right.  It has something to do with signal to noise 
ratio...but not sure how to calculate it.  I understand the 1.2 dB loss, 
but I think there is more to it than just that loss...

Any pointers to a site that discusses this?

Thanks in advance,

Mark L. Hammond  [N8MH]

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