How Truthful Is A Scan?

Posters report channel problems (e.g. pixilation) even though their Tablo shows 100% reception (all those green dots).

The problem with the scan is that it is NOT entirely truthful. For example, my Tablo shows 100% for the Get channel (34.3). Do I buy this? Nope! Several of my other devices, such as my Hauppauge PC tuner card, show NUMERICALLY the exact signal strength. It varies between 21.7 to 24.6 during the day - i.e. between 70 and 80%. So depending upon the hour, the signal strength for GetTV can fluctuate between 70 and 80%. That is an ongoing ten percent variation.

RF propagation also varies by season. My signal strengths shoot up by 20% in the fall and winter and drop during the summer. Morning and evenings vary as well. Heat, cold, clouds, wind, etc. influence reception.

A one shot scan DOES NOT report the true antenna performance during a 24 hour period or even seasonally. The tropo effect can make signals appear to be 100% for a day or so and then the signal slides down to 60%.

Multipath is another variable in signal reportage. Signals bouncing off objects, if arriving out of sync will degrade the signal. However if they arrive simultaneously, they enhance the signal. One can see on a meter in a multipath situation, signals fluctuating widely. One moment the signal is at 100%, the next at 5%. That really is a composite set of signals compounding each other in a negative or positive way.

So a one shot scan is not entirely truthful or fully comprehensive of one’s reception patterns. One moment the Tablo gets the channel perfectly, the next day it doesn’t. A user reboots the Tablo and it’s on track again. The reboot may have occurred as the signal propagation changed positively. A few days later the reception pattern may change making the Tablo appear flakey.

RF signal propagation and reception is not like the electricity that stably flows into one’s house from the power utility. RF is continuously changing.

The scan ‘circles’ show an approximate overview of the signal strength at the time of the scan. They are not updated dynamically.

Tip: whenever I have an option between recording the same show during the day and at night, I always choose the night edition. My reception is best and most stable between 9 PM and 3 AM. PBS Create for instance runs the same shows three times in a 24 hour period. I always record the third showing - in the midnight hours.

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And that is why on a Wednesday, reception may be problematic even if the scan showed perfect reception on a Monday.

It appears that the Tablo considers the 80 to 100% signal strength of my Hauppauge to be five green circles. That is a range of 20%. Which is acceptable since 80% signal strength and upwards is ideal. My LG TV, which is my best tuner, also thinks the same way - 80% and up is “excellent.”

One thing I have noticed is that I either have 1, 3, or 5 circles. Never 2 or 4. And if it is 3 or less, the channel is not watchable.

My guess is that these five levels are about 20% ranges each. So if a five is 80-100, a four is 60-80, then a three is 40-60. Below 50% it’s a crapshoot if the tuner will lock onto a channel. And the three falls into that range.

Here’s the tricky thing about ranges. If one gets 5 green circles for an 80% signal strength in winter, then in summer that 80 may fall to a 60 (seasonal variation can be 20-30%), those five green circles in summer are really then four.

I had the opposite happen. I lost a channel and its’ subs once the leaves started to fall. I rotated the antenna with no luck. So it looks like it might be an elevation issue now. I plan to add another antenna (higher or lower) to get lost channel back along with some other off the beaten path channels.

The same thing happened to me a few years ago! We had a tree in front of my house and it was in the way of the antenna. My wife didn’t like the tree anyway so she suggested I cut it down. I was only too happy to do so since it was right in front of the antenna (maybe three feet away). I was happily cutting the tree down thinking, whoopee my signal strength will go up.

Darn, my signal strength went DOWN! What the hell? That’s when I started disbelieving that all trees were evil for antennas. Perhaps the tree concentrated or directed the signal somehow towards the antenna! Problem was I couldn’t prop the tree up again. One can’t uncut a tree :evergreen_tree:

Where do you live? My GetTV and Escape are the two that I lose when it is raining. They are in Killeen and I’m in Austin. They are on VHF digital RF. I understand RF. When it is heavy fog I get extra channelsif I scan.

Atlanta, Georgia. GetTV is 34.3 (real channel 48 or hi UHF). Some 30 miles away. TVFool tells me that it’s in the mid-range of receivable channels (not easily getable but not hard).

GetTV has the best Christmas programming thus far. Been doing a lot of recording of Christmas classics on GetTV this week and last.

I’m curious about your antenna system. What kind of antenna are you using and what is the distance to transmission towers?
I went through a slew of so called high performance “HD” indoor leaf type antennas before finally deciding to bite the bullet and install a compact outdoor antenna. The difference was dramatic. Although some of the indoors could capture many channels none of them were reliable. Signal strength would vary from anywhere between 20% (no pic) to 90%. The variations could occur from day to day or minute to minute. Totally unpredictable. With this kind of signal instability channel scans are useless as any particular session can produce widely different results sometimes failing to capture even generally available channels entirely. Totally in agreement with your assessment.
Since installing new antenna I’m getting SOLID 98% readings on most available channels, the weakest being a solid 88%. Signal is fed thru 35 ft of triple shielded coax to a two way splitter. One output to Tablo the other directly to TV input. Switching inputs makes for instant channel selection preview via TV (luv it).
In conclusion, unless you happen to be ideally located in terms of distance and geographic landscape, I regard anything other than a decent outdoor antenna system as virtually worthless especially for purposes of recording. Marginal signal strength is easily affected by all kinds of atmospheric disturbances both man made and natural. Planes, winds, even your neighbors dog passing gas (yes kidding - or maybe not?).

Sounds like yor signal is marginal for your locale. Only cure for inconsistency on weaker channels as I’m sure you know is a more efficient antenna system. I’d rather lose a channel altogether than wonder if it’s recording properly.

Ot’s the distance between Killeen and Austin. If I got an outdoor antenna, it would help but I live in an apartment an the Winegard FL5500A is good enough.

You should have heeded the old adage - don’t f… with mother nature.

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I’m in a very difficult reception area - a valley surrounded by forests and slopes of trees 32 miles from the broadcast towers. I tried a variety of indoor and outdoor antennas over the past decade. None met my needs completely. Finally I decided to build my own customized for my particular situation.

The antenna system I built is featured here:

I was inspired to go the DIY route by this website:

The designs I considered are discussed here:

This website is an encyclopaedia of antenna architecture that has guided my thinking:

I get 50 stations. The signal strength on most of them is between 80 to 100% according to the Hauppauge meter. The Tablo shows five green circles for all of them.

One cannot get a more powerful antenna than the FF6x2 (check out its performance in DBi terms on the first link above). The only antenna to rival it is the Gray-Hoverman which I was tempted to build and is also a great antenna.

The cost per FF6 was about eight dollars built with material from Home Depot.

The antenna has a Kitztech 500 preamp:

It has 36 db gain with less than 1 db noise. From the preamp I have a Channel Master 3414 four port distribution amp:

There is a four way split with one coax going to the Tablo. The others go to several TVs and PCs. One of those drops is further subdivided with a three way splitter. In all there are seven drops from the antenna. The Tablo was the last component added to the system that I started building two years ago.

P.S. I’ve also built an FM antenna for HD Radio reception.


Wow, that’s some extensive system you’ve got going. I admire your determination. Thanks for the very comprehensive input.

One of the reasons I wrote this up was if anyone wanted to go that route (DIY), there are sources of knowledge available (designs, plans, details, etc.). All too often I hear people advising others that it is impossible to get good OTA reception because of this or that. Nothing is impossible.