help choosing the right antenna

[Jspyderr]

Thanks for your help. I have read and searched as much as I can but I would appreciate if you could double check my results. Any help you give would be greatly appreciated.

http://www.tvfool.com/?option=com_wr...8e030825ea9173

The channels I want are (real) 10 (nm 3.1), 19 (nm 7.7), 28 (nm 3.0), 44 (nm5.5). Straight north of me. I am looking for the best antenna to pick up these channels......

channel master 4228HD

very good on UHF....
http://www.hdtvprimer.com/antennas/comparing.html
net gain channel 19 is 13.3 dbi
net gain channel 28 is 14.5 dbi
net gain channel 44 is 14.1 dbi

and supposed to be ok on some high vhf
net gain channel 10 is 4 dbi

or the winegard hd7698p
net gain channel 19 is 9.5 dbi
net gain channel 28 is 11.5 dbi
net gain channel 44 is 12.8 dbi
net gain channel 10 is 11 dbi

hmm.... after typing the above, channel 10 and 28 are the weakest, it looks like the hd7698p might be the best for me. Let me know what you think or if you know of any better ones, im happy to hear about those.

I will be feeding 4 TV's. do you think I will need a pre-amp? If so a strong one like cm7777 or a weaker one?

Also channel 26 is fairly close to me, will this mess me up with a pre-amp or are either of these antennas directional enough that it wont?

Thanks again, I appreciate all your expert advice!

[rabbit73]

Welcome to the forum, Jspyderr:

The channels I want are (real) 10 (nm 3.1), 19 (nm 7.7), 28 (nm 3.0), 44 (nm5.5). Straight north of me. I am looking for the best antenna to pick up these channels......

10 KOLR CBS, NM 3.1 dB
19 KSPR ABC, NM 7.7 dB
28 KOZL MyN, NM 3.0 dB
44 KYTV NBC, NM 5.5 dB

channel master 4228HD.....and supposed to be ok on some high vhf
net gain channel 10 is 4 dbi

That gain curve looks very bad; not to be trusted. The PCB balun isn't very good for VHF. The original 4228 did better on VHF.

it looks like the hd7698p might be the best for me.

I agree.

I will be feeding 4 TV's.

First you try it with one TV. Then you add a 4-way splitter. If you run out of signal, replace the passive splitter with a CM3414 distribution amp.

do you think I will need a pre-amp? If so a strong one like cm7777 or a weaker one?.....Also channel 26 is fairly close to me, will this mess me up with a pre-amp

You will need a preamp for your weak 2Edge signals, but a 7777 will be overloaded by 26.
7777 specs
Max input level 15 dBmV = -34 dBm
Max output level 40 dBmV
FM trap 88-108 MHz; >15dB

K26GS, -33.3 dBm Signal Pwr + antenna gain 14 dB = -19.3 dBm, OVERLOAD

7778 specs
Gain 16dB
Max input level 34 dBmV = -15 dBm
Max output level 50 dBmV

K26GS, -33.3 dBm Signal Pwr + antenna gain 14 dB = -19.3 dBm, OK

But -19.3 dBm + 16 dB preamp gain = -3.3 dBm, Tuner OVERLOAD

Looking at it by Noise Margin:

K26GS, Noise Margin 57.6 dB + 14 dB antenna gain = NM 71.6 dB, OVERLOAD



Interpreting Noise Margin in the TV Fool Reporthttp://www.aa6g.org/DTV/Reception/tvfool_nm.html

are either of these antennas directional enough that it wont?

The directional pattern will help attenuate 26 when the antenna is aimed North, but it might not be enough. CH 26 will be 74 degrees off-axis. Maybe down 15 to 20 dB.

If not, insert a Channel Plus NF-471 filter, and use KWBM for MyN.

NF-471: Notch Filter
Removes CATV channels 75-80 and UHF channels 24-29
Notch filter frequency 529.25 MHz to 559.25 MHz
24 530-536 MHz
25 536-542
26 542-548
27 548-554
28 554-560
29 560-566

http://www.markertek.com/product/cp-...FRKRfgodruUD5g

http://www.solidsignal.com/pview.asp...FZSFfgodGyIMLQ

http://www.amazon.com/Linear-NF-471-.../dp/B000J3AEYA

Pete Higgins using NF-471
http://forum.tvfool.com/showpost.php...2&postcount=40

I couldn't find a curve for the NF-471, but I did find one for the NF-469 which gives you the idea. Here is a case using the NF-469:

http://www.highdefforum.com/local-hd...ml#post1388901

Using your short coordinates, I did an FMFOOL report to see if there were any strong local FM signals that might interfere with TV reception. You have KCWD on 96.1 MHz with a signal power of -20.1 dBm. If the FM filter in the preamp doesn't take care of it, you will need to add an FM filter before the preamp input.

You can do a more accurate FM report here:
http://www.fmfool.com/index.php?opti...pper&Itemid=29

[Jspyderr]

Excellent rabbit73, exactly the info I needed! I really appreciate it.

But I messed up. I grew up about 20 miles north of my current location and I remember our neighbor on top of a hill getting fox on channel 27, it was fuzzy and weak but they got it. I wrongly thought real channel 28 kozl-tv (virt 27.1)was it. When you mentioned an alternative to 28 as 31 myn, I realized my error. I really want fox but looking at my signal analysis it doesn't look good.

Any chance of me getting fox? It looks like channel 49 krbk is the strongest at -24 and tropo.

The winegard hd7698P gain at channel 49 is 14dbi.

So is the math: -24 + 14 = -10 which is below zero, so this is impossible?

Thanks for the welcome, I very much enjoy the knowledge I have found on here!

[rabbit73]

Any chance of me getting fox? It looks like channel 49 krbk is the strongest at -24 and tropo.

KRBK on 49 is very weak and Tropo; it will never be reliable. It is also 79.4 miles away and the curvature of the earth will block the signal.

So is the math: -24 + 14 = -10 which is below zero, so this is impossible?

The math is a little more optimistic:
-24 + 14 = -10 NM
-10 + 16 preamp gain -2 dB preamp NF = +4 NM
on a good day and if K26GS has been attenuated

BUT

KWBM 31 carries Fox as a subchannel simulcast of KRBK if rabbitears is right and the tvfool report is wrong when it says MyN

http://www.rabbitears.info/market.ph...&callsign=kwbm
https://en.wikipedia.org/wiki/KWBM
http://www.rabbitears.info/search.ph...pe=dBm&height=

[ADTech]

KWBM 31 carries Fox as a subchannel simulcast of KRBK if rabbitears is right and the tvfool report is wrong when it says MyN

rabbitears.info is correct. KRBK made a deal with KWBM to provide coverage for the area south of Springfield including Branson and points south towards Harrison since their 5 transmitter DTS system didn't cover much to the south.

-10 + 16 preamp gain -2 dB preamp NF = +4 NM

A reminder that antenna gain is the ONLY thing that improves the noise margin. Amplification actually reduces NM by the amount of the amp's noise figure as the amplifier also increases the noise floor by the amount of amplification (plus the NF) resulting in a net decrease of NM. There's a note to this effect in the signal analysis FAQs.

Therefore, the equation should read:
-10 -2 dB preamp NF = -12 NM
Signal power was increased by the amount of amplification as was the noise floor.

[rabbit73]

Signal power was increased by the amount of amplification as was the noise floor.

True, antenna gain will improve the NM; preamp NF will make it worse. But the use of the preamp will improve the System Noise Figure, so I think I am justified in adding the preamp gain as long as I subtract the preamp NF. If you subtract the preamp NF you must also add the preamp gain when considering the whole system, and not just the head end. My original 7777 certainly helped with my crappy signals, with a DB4e, a folded dipole for VHF-High, 50 feet of RG6, and my antenna at 5 feet AGL.



COMPARE System Noise Figures
With and Without Preamps

http://imageevent.com/holl_ands/file...=0&w=1&s=0&z=4

Why do you think it is proper to subtract the harm to the NM that is done by the preamp NF without adding the benefit to the System NF by the preamp gain, its superior NF, and placement at the head of the chain as proved by the Friss Cascaded Noise Figure Equation?

There's a note to this effect in the signal analysis FAQs.

Andy Lee also states that in a post:
http://www.avsforum.com/forum/25-hdt...l#post15700679

Everyone should note that the antenna is the ONLY element in the system that helps you GAIN Noise Margin.

A pre-amp does not change the intrinsic gain of the antenna. Amps boost the signal and noise floor simultaneously, so a crappy signal going into an amp will yield a strong, but even crappier signal (because of the amp's Noise Figure) at its output.

Do not be fooled by lousy antennas that include a built-in amp and claim to be high-gain antennas. The amp's gain does NOT count toward the gain of the antenna itself.

But if you look at his second image in that post his analysis takes into consideration the harm done to the NM by the preamp NF AND the benefit provided by the preamp gain to turn a negative NM into a positive NM. See my attachment 2.

To put it another way, note that Andy adds the preamp gain at the same time that he adds the preamp NF to the Noise Floor. Why can't I do the same thing?

[Jspyderr]

Thanks guys. I will be very interested to hear if the signal strength with an amp would be positive or negative (in my sitituation).

As for 31.2 doing a simulcast of fox. I asked a neighbor with a small, cheap, indoor antenna facing Harrison, which is 13 miles away and she does not get it. I did see the info indicating its there but perhaps it is no longer or the info is wrong. It checked krbk 49.1 web sight to see if they mention it and I didn't find anything. But they do show they use six towers in various locations. The tower in Forsyth, mo would be 36 miles away, so I should be able to get that I hope.

http://www.fox5krbk.com/help/

Anyway I'm optimistic enough that I can receive abc, nbc, fox, and cbs that I think I should order the antenna and then we can actually talk about real results. Thanks again for your time and help. I have learned a lot.

[ADTech]

Keep in mind that the concept of the Noise Margin (NM) is a construct to help understand the probabilities of reception, it's a very useful tool in analyzing the possibilities for reception. It is not the definitive answer as to whether reception is possible or not due to its theoretical nature and the various assumptions that have gone into the calculation. Only installing a real antenna system will provide that definitive result.

I always recommend an appropriate pre-amp when very weak signals are involved, unless there are excluding circumstances, simply because it does indeed improve the system noise figure and, consequently, the "fade margin".

The tower listed for Forsyth is the KWBM tower. According to data on rabbitears.info recorded on 10/27/15, it was broadcasting KRBK's primary programming as one of its only sub-channel with Daystar as its primary feed. It does not broadcast the two additional subs carried on KRBK's own DTS system.

I did notice an incorrect assumption in post #2:

K26GS, -33.3 dBm Signal Pwr + antenna gain 14 dB = -19.3 dBm, OVERLOAD

It is necessary to use the gain (in dBd) at the reception angle, not the straight ahead peak gain. Assuming the UHF antenna is aimed due north, the amount of realized gain at ~75° off to the side is the correct number to use in that equation.

[rabbit73]

It is necessary to use the gain (in dBd) at the reception angle, not the straight ahead peak gain. Assuming the UHF antenna is aimed due north, the amount of realized gain at ~75° off to the side is the correct number to use in that equation.

That is correct. I was using worst case to be conservative so as not to promise more than what would be delivered (like what we have learned to do with trees). I was also trying to demonstrate the need to attenuate 26 to make it possible to receive weaker signals.

I did allow for it later when I was talking about the pattern, which is why I went to the trouble to find it and display it; I thought the CH32 pattern would be close enough.

Originally Posted by rabbit73

The directional pattern will help attenuate 26 when the antenna is aimed North, but it might not be enough. CH 26 will be 74 degrees off-axis. Maybe down 15 to 20 dB.

[rabbit73]

I added some notes to Andy Lee's Noise Margin Diagram to help me understand it better. FYI, Andy created the TV Fool website. His original NM diagrams can be found here in post #397:
http://www.avsforum.com/forum/25-hdt...l#post15700679

The dB values match his original scale; 3 dB for an average preamp NF, 6 dB for the ATSC estimate of the tuner NF, 12 dB gain for a 4-bay UHF antenna, and 24 dB gain for a preamp like the original CM 7777.

[rabbit73]

Here is a more compact revision of Andy Lee's Noise Margin Diagram that is 878 x 738 pixels without reducing the lettering size, so I'm showing the image in this post. The previous version is 1024 x 743 pixels, Andy's original size.

[rabbit73]

If you want to learn more about Noise Margin and preamps, here is a good tutorial by Chuck AA6G:

Signal Strength, Signal-to-Noise Ratio and Other Related Issues in DTV
http://www.aa6g.org/DTV/Noise/noise.html

This is a Noise Margin Diagram that I did to help me understand the concept: