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Old 10-Dec-2016, 8:03 PM   #3
Junior Member
Join Date: Dec 2016
Posts: 10
Signal analysis: I'm missing something jere

Thanks so much for your reply.

Originally Posted by Tower Guy View Post
In order to determine the advantage of stacked antennas you should add 2.5 db to the gain of a single antenna. But even then the spacing must be optimum, which can't be true on all channels at once. Next you SUBTRACT the 3 db noise figure of the 7777 preamp. The gain of the preamp can overcome the loss of the coax and splitters, but never add to the NM.
Well, I do have a Kitz preamp that advertises a lower noise figure and nominally higher gain...but the CM actually pulls in more stations when I do an A/B comparison.

Is NM the only determinant of "viewability", or is the dBm equally important? Is NM stated in terms of a dipole reference? In that case, stacked Yagis should give you something better than10 dB extra martin, right? (Sorry for the newbie questions, but NM is a new term for me in this context.)

Originally Posted by Tower Guy View Post
As for the low power stations, most of them are on low band VHF. Perhaps your stacked yagis are not intended to receive channels 2-6.
Nominally, they are full-VHF band...but none of the elements is longer than 40 cm so it's not going to have a bunch of gain down at 80 or even 60 MHz...but it won't have zero gain. With the NM of the repeaters (and a couple of them are LOS) I'm not understanding why I don't see their signal. Of course, I don't have a spectrum analyzer so I only have the TV to go by...

[/QUOTE]Next, verify your location using the online maps scheme.[/QUOTE]
Did that, the system places me correctly in the terrain. But the signal analysis indicates I should be "seeing through hills" that have me in the shadows for sure.

In particular, channel 3 (second item on the report) has a huge NM and PWR it should be screaming thru, right? Yes, there's an overlap of a weaker signal (sixth one down in the list), it's 30 degrees off in azimuth so nicely attenuated in the antenna's side-lobes. Similar story with channel 6, third one on the list.
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