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Mrfishdude 19-Mar-2017 3:26 PM

Mrfishdude's Challenge
I have a place on the Gasconade river near Dixon MO, and am trying to pick up a couple of OTA UHF Channels.
link to my report:

Mrfishdude 19-Mar-2017 3:38 PM

More Info from Mrfishdude
My first attempt was a 50 foot tower, 8 bay bowtie, CM brand Pre-amp, 100 foot run of RG-6 quad and an old TV Guide brand DVR - Tuner. I have removed the 8bay and looking to replace with 91 element yaggi.
I have another 10 foot of tower and 20 foot of 2 inch aluminum pipe for a mast. also have access to either RG-11 or 500 hardline.
Round one I could pick up channels from Springfield Mo:
These were intermittent Tropo signal.(time of day, time of year)
Please let me know what you gents think about my weak links or place to nab that extra .5Db.
My budget for this round 2 is closer to $100 not $1000.

Thanks for your time.

ADTech 19-Mar-2017 4:59 PM


From having grown up not too far from your area (southern Gasconade County), I can tell you that a large portion of south-central Missouri simply doesn't offer the option for reliable OTA reception. The distances are often too great, the terrain can be wicked, and sporadic reception is about as good as it's ever going to get.

Let's get a few more details so we can understand what's happened, perhaps that will provide insight going forward.

Can you specifically identify which UHF 8-bay and which CM preamp you have been using?

Are you now or are you able in the future willing to use a rotor? That might offer improved odds of Fox out of Lebanon or PBS out of Sedalia, for example.

Do you have a more modern TV set with a presumably improved tuner? Older tuners often offer poor performance when compared to those of recent vintage.

Does your tower location offer a tree-free signal path in the required directions? Weak UHF signals and trees usually means frustration, especially when the trees leaf out.

Do you have some wiggle room in that budget?

I would recommend waiting 2-4 weeks before committing to any purchases, we'll know then what the new post-repack channel assignments will be and there's no sense in installing a system that might end up needing tweaking to accommodate changes that might occur.

The RG11 or the hardline aren't necessary if the preamp is installed in the proper location in the system, RG6 or QS is fine.

I'd stay away from all of the UHF Yagis and the off-brand 8-Bays as all of them are tuned to peak up in the cellular bands. Plus, with the looming spectrum repack, all of those existing old designs are going to be even poorer choices once stations currently above channel 36 relocate to lower frequencies over the next 3+ years.

rabbit73 19-Mar-2017 8:32 PM

4 Attachment(s)
Hello, Mrfishdude

That is a difficult location for TV reception.

The first four channels are off the air according to rabbit, so the next channel is PBS. The curvature of the earth blocks the direct signal:

And, if my estimate of your location is correct, you are down the hill near the river.

rabbit73 19-Mar-2017 9:34 PM

I have three suggestions to improve your odds.

1. Select an antenna that has more gain than most for CH 15. As implied by ADTech, they can vary a lot at the low end of UHF.

2. Tilt the front of the antenna up to catch the signal coming down from the ridge.

3. Switch to a preamp with a very low noise figure.

I will expand on these ideas when I have the time.

Billiam 19-Mar-2017 10:01 PM

One of the Kitztech pre amps may help. I tried the 500 model which makes the claim that it won't overload in strong signal areas. I did find it did that. But it did have good gain on the weakest signals where I tested it. But the strong local signals made it useless there.

ADTech 20-Mar-2017 12:50 AM

FWIW, I tested the KT500 in my lab a while back. My conclusion was that it was a significant disappointment in that the dual-stage design caused a severe loss of performance if the gain control was even touched to reduce total gain. If it was left alone, the amp overloaded very easily.

There are better options.

I did test a KT200 for gain and noise figure about 5 years ago before I had overload test capability. It was very quiet (around 1 dB), as I recall, although not quite as quiet as advertised. Precise measurement of such low noise figures is extraordinarily difficult with tiny errors of several tenths of a dB almost impossible to avoid.

Billiam 20-Mar-2017 2:00 AM

Wish I had tried the KT200 instead. Overload was so bad with the 500 that most of my channels were unwatchable. Definitely best suited to areas where all signals are weak.

rabbit73 20-Mar-2017 2:35 AM

3 Attachment(s)
The Antennas Direct 91XG was not rescaled for the 14-51 UHF band, but the DB8E was rescaled to improve the gain at the low end.

The 91XG and the HDB91X yagis have a tilt feature built in, but the DB8E does not; it would be a custom mod. I have received several reports from people who were located behind a hill and have used the tilt feature; they were able to receive channels that were impossible before tilting the antenna.

The only way you can do better with an antenna is with a custom designed yagi for channel 15.

It is impossible to receive signals weaker than NM -15 dB because they are buried in the Thermal Noise Floor below -106 dBm. If you are able to receive channels listed below -15 dB NM, either the tvfool report is wrong or the signal has been enhanced by Tropospheric Propagation.

Here is the System Noise Figure calculation for the above diagram:

You can do a little better if you use a preamp with a lower noise figure and a lower loss balun:

Yes, the KT-200 would also be my choice. Keep in mind that the ultra low noise preamps are more sensitive to static damage; that's the trade-off. The Antennas Direct PA-18 might be a good compromise design for your location, but you haven't told us which CM preamp you are using.

I second the suggestion to use the best tuner you can find; they do vary in sensitivity.

Mrfishdude 20-Mar-2017 6:12 AM

I thought newer tuner might help to decode data from noise. Same train of thought with narrow beam antenna so as to not amp unwanted noise for better signal to noise ratio.
I hope to be there this weekend and get some model numbers for you. Also to get a better GPS number. I am on a hill not on the riverbank. Just not the TALLEST hill!
Any research on quality of TV tuners out there for DX? Manufacturer X vs Y?

rabbit73 20-Mar-2017 12:48 PM


Also to get a better GPS number.
Thank you. If you send me the coordinates for your antenna by Private Message, I will redo my analysis.

You can use the tvfool interactive map. When you move the cursor by drag-and-drop, the coordinates below the map will change.

ADTech 20-Mar-2017 1:31 PM


Originally Posted by Billiam (Post 57629)
Wish I had tried the KT200 instead. Overload was so bad with the 500 that most of my channels were unwatchable. Definitely best suited to areas where all signals are weak.

I couldn't think of a single case where I'd recommend the KT500 based on it's performance, it really was that big of an expensive disappointment. My analysis was not alone. Forum poster Calaveras (on AVS) also analyzed it independently and reached a similar conclusion.

rabbit73 20-Mar-2017 3:15 PM

2 Attachment(s)

Any research on quality of TV tuners out there for DX? Manufacturer X vs Y?
Unfortunately, there are no published comparisons of tuner performance.

When the converter boxes came out, they had the best tuners because they had to meet performance specs to qualify for the coupon program. Later, the tuners in the TVs were improved to the same level.

Lately, some of the tuners aren't as good for OTA because the manufacturers now think only in terms of cable use and streaming. Some "TVs" are even being sold without tuners and are called displays, what we used to call monitors.

I have found that Sony TVs have good tuners for OTA and they also have a diagnostics screen that gives relative signal strength, SNR, and uncorrected errors; very helpful for antenna work.

Here is the diagnostics screen for my KDL22L5000:

Bad signal with picture freeze, SNR below 15 dB, and uncorrected errors:

Good Signal:

Lately, I have been doing experiments with indoor antennas, which are the only option for some people. This is the diagnostics screen for my KDL32R400A. I have added notes and a picture of the antenna.

In order to test for tuner sensitivity, I hook up two tuners with a splitter and a variable attenuator. I then increase the attenuation to see which tuner drops out last, making it the winner. The test can be made with or without a preamp, as long as the attenuator is after the power inserter if a preamp is being used.

Ant > coax > variable attenuator > fixed attenuator > splitter > tuners

The value of the fixed attenuator depends upon the strength of the signal. I use a fairly strong stable signal for testing. Sometimes a 20 dB fixed, sometimes a fixed 10 dB, and sometimes both.

Attenuation values 1, 3, 6, 8, 10, 12, 16, 20dB (FAM)
click on 1 dB for other values; the up and down arrows are faint

The most recent tuner sensitivity test that I have done was to compare the CM7003 STB tuner with my Sony KDL32R400A that I had calibrated for signal strength with my signal level meter (SLM). But, you can make the test without knowing the absolute values for signal strength.

The ATT-1 knob has 3-3/4 turns, so I put a mark on the knob with an ultra fine point Sharpie to count the turns. Clockwise rotation increases the signal; minimum attenuation at full clockwise rotation. I started there, and rotated the knob counterclockwise to increase the attenuation for the test.

I used the WTKR CBS, RF 40, virtual 3.1 signal for the test. It wasn't as stable as an LOS signal that I usually use because of trees, but it was what was available for the test.

These are the readings:

Dropout was at about -85 dBm, where you would expect it to be.

Thermal Noise Floor -106 dBm + 15 dB SNR = -91 dBm
and then adding tuner Noise Figure:
-91 dBm + 6 dB Tuner NF = -85 dBm

The CM7003 tuner is about as sensitive as the Sony, which is good, but the 7003 remote control isn't very responsive. The aim is critical and sometimes it is necessary to push a button more than once. I bought a Sony RM-VLZ620 Learning Remote and taught it some of the basic buttons on the CM-7003 remote. The box is much more responsive to the Sony remote.

Original post for test:

rickbb 20-Mar-2017 5:53 PM


Originally Posted by rabbit73 (Post 57637)
Unfortunately, there are no published comparisons of tuner performance.

Even if there were published results they would be obsolete in months.

We buy a lot of large format TV's to put into custom built cabinets for placement in retail stores as a POS displays. Every order we place we get the "that model has been discontinued" and wind up having to redesign our kiosks, again.

Manufactures no long do a yearly model, the model run is only as large as the parts they ordered at the time. Next model is so changed it won't look or work anything like the last one.

Billiam 22-Mar-2017 12:15 AM

Insignia TV Tuners seem to be good. Quite sensitive. I have a 19 inch Insignia that is now around 5 years old and the tuner in that TV is better than my 7 year old 32 inch Samsung. Had a new Insignia 32 inch TV and that was also better than the Samsung. Broke it by accident. Will look to buy a replacement for it this year.

I can attest to Rabbit73's claim that Sony also makes a good TV tuner. I bought a 32 inch at the same time I bought the Sony and found the sensitivity in that was excellent. I was able to lock onto signals with a SNR of 14 vs. 15.5 with the Samsung. Gave that to my brother though since he needed a TV.

Mrfishdude 22-Mar-2017 1:47 AM

Any thoughts on adding tower height? I assume since I have another section and a friend crazy enough to help me install it( he has experience on tower work). it cant hurt the cause. Would it make sense to maybe look for still another 10 foot section?
Thank you all for your help, it is greatly appreciated.

rabbit73 22-Mar-2017 3:04 AM

It might help, but without knowing the exact coordinates of your antenna, it is hard to say.

You can use the interactive map and enter different heights below the map.

Keep in mind that the wave front of 2Edge signals is not uniform because of scattering. IOW, there can be hot and cold spots as you change height.

jrgagne99 24-Mar-2017 7:08 PM


Originally Posted by rabbit73 (Post 57631)
The Antennas Direct 91XG was not rescaled for the 14-51 UHF band, but the DB8E was rescaled to improve the gain at the low end.

Hey Rabbit, thanks for putting that comparison together. It gives me even more hope that the DB8e i picked up a couple weeks ago might give me a better chance of picking up the low-end of UHF compared to my HDB91X yagi(s). Now if only the snow up on the roof would melt I could try it out...

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