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Old 7-Sep-2020, 2:41 PM   #31
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,747
Quote:
Originally Posted by verder
Unfortunately, I do not own an HDHomeRun yet so I don't have access to that additional signal information.
Sorry, I got a little ahead of you. I like my HDHR4-2US (the gray one); I avoided the 4-tuner models.

The signal quality reading from your MediaSonic tuner should help. At what percent reading does dropout happen? That point should be similar to the 50% signal quality point of the HDHR.
Quote:
I had an old ViewSonics amplifier lying around (VSAV10-1000-2WZ w/a 10dB forward gain) and used that with the Gray-Hoverman antenna I built. I had the antenna in the same location as Mclapp that I played around with yesterday. Unfortunately, the reception today was worse than yesterday with the Mclapp. I need to go back to the Mclapp build and try it with the amplifier and see if that improves anything. The amplifier is pretty old (~2001) and has been sitting in the garage as a leftover from the previous owners. I'll look at running that experiment tomorrow. If I pick up a new amplifier, do you have any recommendations about what I should buy? I see box stores with amplifiers that range from 4dB to 20dB gains. Not sure how to correctly gauge what I should be looking for.


That is a cable drop amp. If it's working OK, it should be helpful. It should be placed close to the antenna to compensate for the coax and splitter loss. The 7 dB noise figure is a little high. I use a CM 3410 or a CM7777HD Amplify for that kind of indoor testing. For outside close to the antenna I would use a regular preamp like an Antennas Direct Juice or a CM 7778 V3. Avoid the RCA TVPRAMP1R; the quality control is poor. I bought two new ones in sealed boxes; both failed.

It's important to have a preamp close to the antenna for the best system noise figure. The first device in a system primarily determines the system noise figure as shown by the Friis Formula:
https://en.wikipedia.org/wiki/Friis_formulas_for_noise

Do I understand you correctly; you have your test antenna inside?

That would mean you have
tree loss,
building loss,
cable loss,
and splitter loss
before the signals get to your tuner.

That's not too different than mine; I have an indoor antenna behind a tree and cable loss (25 ft), but my antenna looks out a window to reduce building loss. My signal report is similar, except there is just one direction:

https://www.rabbitears.info/searchma...tudy_id=145947

Quote:
Today's experiments consisted of some simple bench top testing and some garage rafter testing. The bench top testing was literally bench top. I've got a workbench in my garage and just placed the Gray-Hoverman build facing due south. I did that to perform some sanity checking with the Airspy R2 on my build. Turns out that I've apparently got some issues with the R2 where I see spikes every 8MHz no matter what center frequency I'm at. These appear at a mid-gain setting. This happens with no antenna, with antenna, USB cable swapped, computer swapped, within SDR# and within SpectrumSpy. I've got a support request in to Airspy US to see what may be the problem... could be between the chair and the keyboard (ha!), but I don't think I'm doing anything different from before and the behavior is certainly different.
Quote:
Regarding the Airspy issues: if I go to "Free" mode in SDR# and adjust the LNA Gain between a value of around 6-16 or so, I see the 'ghost' signal appear. Values outside of that range do not cause it to turn up. Jacking with the IF and Mixer gains don't cause any problems. Is it possible that the TV signals I was measuring the other day with SpectrumSpy did something to the LNA?
The signal would have to be extremely strong to damage your Airspy SDR. That's unfortunate that you are having trouble with your Airspy R2; they are expensive.

I don't completely understand your problem. Can you show us a photo?

Does your Airspy receive FM signals OK?

Have you tried a new download of SDR#?

Are you using an SMA to F adapter or an SMA to F adapter cable on the R2? I leave an adapter cable on all 3 of my SDRs to protect their SMA input connectors. If I just used a small metal SMA to F adapter for the RG6 to connect to the SDR it might weaken the SMA connector.
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Last edited by rabbit73; 7-Sep-2020 at 10:43 PM.
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