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Old 14-Aug-2020, 11:47 PM   #10
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,738
Originally Posted by rsw1941 View Post
rabbit73, I see you're from S.E. Virginia. I grew up in Mechanicsville, just north of Richmond, back when we actually watched with rabbit ears. With a great deal of effort I managed to graduate from Virginia Tech in '63 after about 5.5 years and a switch from EE to Marketing.
Previously, I'm from NJ. I started at Rutgers to be an EE, my father died, had to leave school and joined the Army during the Korean war (radio operator in Germany). Was an AV Tech for the Government for 30 years. I've been a ham since the early '50s. I started doing antenna experiments when I was 8; I'm now 87 and still learning.

When I was a kid our family had a vacation in ME on Orr's Island. That's when I learned to love blueberry pie. After I was married, my wife and I went to EXPO '67 in Montreal. On the way back we stopped to see Cadillac Mountain in Acadia National Park; she loved it.

When you say, "The SNR is measured from the noise level to the top of the signal." do you mean from 0, or from the top of the noise level?
From the top of the adjacent noise level. This scan was made with an RST-SDR.COM V3 dongle and free open-source spectrum analyzer software from GitHub. The software is not available ready-to-use. It is necessary to assemble it in a folder. I found that difficult to do, but finally got it to work. The dB scale numbers are only relative, not absolute.

This is the screen shot that goes with that test. The SNR given by the tuner is actually MER based on the constellation diagram. It would be difficult to measure the noise level in a channel that's in use:

I'd hate to replace the antenna, but would consider doing so if there were one with a better VHF section. Can you suggest one? Might a gain of even 2 or 3dB on Channel 2 be significant? SNR of 17dB and better generally delivers a rock solid signal.
I find it difficult to suggest another antenna because of the lack of reliable references. I can't find data for the 3020 that I trust. Yes, I know that CM gives gain figures for the 3020. Even if you had a better antenna, your reception of channel 2 wouldn't be 100% reliable because it is a Tropo signal subject to the whims of propagation. Since channel 2 is your weakest desired channel, you might improve reliability from say 50% to 70%.

I found the net gain for the 2020; the channel 2 gain is poor. Since the 3020 has more elements in it's LPDA VHF section, I assume that it would do better on channel 2.

I see that CM has brought back the 3671 (Ultra-Hi Crossfire 100):

This is a gain chart for the Winegard HD8200U, note gain is in dBd, not dBi

Keep in mind that I removed the UHF section and attached the balun directly to the end of the connectors that reached from the VHF section thru the UHF section.
It's difficult to predict how much that mod might have changed the VHF gain. In the review of the 3020 by Tyler that I linked above, he said (at 1:03) that the location of the balun affected the performance of the antenna.

I should have posted a version of the map and table of data from TV Fool. The file is attached.

Thank you for the image of your report. My guess was pretty close. I prefer a link to the report, so that I can click on the callsign to see the terrain profile. I had hoped that you would have done a report, which would have been more accurate because the reports generated by TVFool use an outdated database.

Sometimes I ask a poster for his address and antenna coordinates in a PM for privacy. That allows me to look at the sat view of the location to see if there are any objects in the signal path like trees.
Attached Images
File Type: jpg Thor33-3Ant-8dBmVtoTV_SNRrev.jpg (135.6 KB, 934 views)
File Type: jpg ThorCH33to3Cant-8dBmV.jpg (129.5 KB, 966 views)
File Type: jpg CM 2020 Net Gain.jpg (157.2 KB, 913 views)
File Type: jpg rsw1941TVFhisReportImage2.jpg (141.7 KB, 968 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 15-Aug-2020 at 12:55 AM.
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