Reception Mysteries

[ADTech]

Note that the noise floor (sensitivity) of the DigiAir Pro is only in the -75 to -80 dBm range which severely limits its usefulness in weak signal analysis unless you use a preamp (judiciously selected) to extend the noise floor. You'd still need to observe precautions related to its dynamic range.

[rabbit73]

I also have to add an amp before my SLM when making tuner sensitivity tests. Since it is only before the meter and not before the tuner, the added NF of the amp doesn't matter because I'm only measuring the top of the signal. I use a 4-way splitter when I'm comparing two tuners at dropout.

                                                   tuner
                               variable            /      
ANT > CM7777 > coax > power > attenuator > splitter 
                     inserter                      \
                                                   CM3410 > SLM

If I were using the Solid Signal DIGIAIR-PRO-ATSC meter, the NF of the 3410 amp would affect the signal quality readings (SNR, BER, and MER) of that meter.

[rabbit73]

Originally Posted by richardrosa

I just picked up this device:

http://rfexplorer.com/

It's a nice, portable (and relatively inexpensive) spectrum Analyser.

Works like a champ! I can actually see the ENTIRE UHF spectrum in one screen, or zoom in on a single channel.

Thanx to this device, I was able to adjust the UHF antenna direction a bit more precisely. Much better than the Analogue meter.

I can also see WHY channel 10 is gone. Pilot is nice and strong, but the rest of the signal is down in the dumps. Still don't know why this changed from this summer, but at least I now have a visual!

Rich

Thanks for the report. It sounds like it has been helpful for you. Which model did you get, the 3G Combo?

I did a terrain profile for WTNH:



That is a difficult path for the signal. It depends upon atmospheric refraction and diffraction at the mountain peak to get to you.

This is the tvfool version of the profile:

http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d7

Originally Posted by richardrosa

The VHF antenna I have also has a 'tilt' adjuster. I didn't bother with it, as I figured it might cause polarization issues, but maybe I'll give that a shot (next spring). BTW, I DID try adding an extra FM Trap in-line with the VHF antenna, but didn't seem to make any difference for Ch 10 reception.

I think it would be worth the trouble to tilt the front end of the 30-2475 up, or even replace it with the 30-2476. The polarization of the signal is already messed up because of the diffraction at the mountain peak.

[richardrosa]

Originally Posted by rabbit73

Thanks for the report. It sounds like it has been helpful for you. Which model did you get, the 3G Combo?

Yup. Got the 3G. Wish something like this was available YEARS ago.

I WILL give the antenna tilt a try. Now that I can see what is happening, it should instantly be obvious if that makes things better or worse. A new location may also be in order. All this to do in Spring (warmer weather).

BTW, What software did you use to generate those topography graphs?

Rich

[rabbit73]

BTW, What software did you use to generate those topography graphs?

I used this:
http://www.heywhatsthat.com/profiler.html

There isn't much in the way of instructions there; I had to figure it out by trial and error. If you have a problem with it, I can walk you through it step by step.