Maximum total input voltage for preamplifiers

[cho232]

What effect does the maximum total input voltage specification have on a preamplifier?

[winegard]

The maximum total input voltage is the maximum amount of signal in microvolt’s the amplifier can handle without overloading. It is like saying the maximum amount of gas your fuel tank can handle is 30 gallons. If you overload the amplifier with too much signal your pictures will be distorted, have channels on top of channels, or not even see a channel if the overload is severe enough on analog signals.

With digital signals overload will cause the digital tuners to search for signal and you will not receive any kind of picture.

[Skyhooker]

OK but can we get a little more specific?

If I have your highest gain Yagi (9032) and your very finest UHF preamp, mounted on my roof, 40 miles southwest from Philadelphia with no edges in-between (i.e. LOS) what are the chances that your preamp will or could go into overload from time to time?

I have in the past had to point away from the Philly antenna farm - slightly broadside to the source if that's a hint.

An extreme example is having the Yagi totally broadside to a near-megawatt DTV station @50-miles-out in York, PA. Pointing at the tower or anywhere close got me nothing. It's been times like that when I wanted to bypass the preamp but can't. Or, remotely change the front-end sensitivity (i.e. attenuate the antenna => preamp path) but can't.

RG6 cable length is ~100 feet and no spitter - direct connection to my STB receiver.

I think I may know what you might say: Select the preamp gain for the RF cable and accessory dB losses and nothing more. I only say that IF the overload tolerance of a lower-gain preamp INCREASES vs. stays the same. Is that generally TRUE? Considering the DTV transition with increased power and/or higher antenna position, and I'm only compensating for cable loss then I should learn that a lower-gain preamp, which should have a better noise-floor figure, won't overload easily - is the overall better choice. Yes?

Lots of question marks here so please try and address.

Skyhooker

[KNP 2516]

Hello,

Maybe I can help.

First off, hooking a television directly to the antenna is never a good idea. You should always have a ground block outside of the house in case of lightning. Right there would probably be a loss of about 3 db, which if you think that you have too much signal - would help you to shed off some of it..

The wire you use, could be at fault, there is good RG 6 coax and not so good RG 6 coax.

The best stuff to use would be a Quad Shield wire such as the Belden 1829 AC, you want to have a wire with as low a loss as possible and a good shield - so you can resist noise interference.

Again, there are good amplifiers and not so good amplifiers.

A amplifier is used to increase gain. A amplifier is not selective - it not only increases the level of signal present at the antenna, it also amplifies all the noise present at the amplifier. You could have interference from some other sort of transmitter in your area and not even know it until the digital revolution came along and changed all your frequencies.

What is to you a super station - is not really all that great at 40 miles. Yes you will get a 100% signal, but if there is other signals around the signal that you are trying to receive - you are still going to have problems.

The FCC is very careful how and where they put a television stations frequency in relationship with other frequency's in the same area.

I'm sure that if you have a great signal, that you have already disconnected the pre amplifier and tried the antenna without it. If the signal is good enough that you still have 100% of the signal, then you don't need that particular amplifier.

Your very finest UHF pre amp does not tell us which model pre amp you have.
Now we are getting into generalizations.

If by your finest Pre amp you mean - a Winegard AP 8275, then yes it is a good performer.

How ever - if you look at your TV fool report and see that you do not need that amount of amplifier, then might I suggest that you step down a couple of notches and buy something with less gain such as a Winegard AP 8700

Just as you have asked, there is times when you can get too much gain. In 40 miles, I don't believe that it is happening that way. Your best bet is to install a antenna rotor and check your reception with different positions of the antenna and not rely on any one position to get r done for you.

Digital TV = and a highly directional antenna, like the one you have requires a antenna rotor for best reception.

By turning off the center of the signal - you can reject part of the signal and loose some gain - if that is what you are trying to do.

Unfortunately some people on the internet gave advice as to what antenna was the best and people ran right out and bought it before they did any detective work as to what kind of a signal they had in their area and then they are stuck with too little or too much antenna or amplifier.

[winegard]

Yes you correct in that as you increase the gain of the preamplifier you give up input capability which means the amplifier is more prone to overload. You are correct in that all you can expect an amplifier to do is overcome your equipment loss. Amplifier can not pull in signal or extend the receiving range of an antenna.

[Skyhooker]

Thank you so much for responding. Short history: In 2004 when I bought the TV and Samsung SR-T165 STB I also bought a complete antenna package from Tweeter (RIP). CM3671 combo antenna, CM Titan 7778, CM9521 rotor kit w/remote, and (just checked) white coax labeled "LWC RG6/U Quad Shield 18Ga". The antenna was a turn-key deal, stem-to-stern installation and, guaranteed to work. Well it didn't. I went back to them after getting some advice to "get the biggest darn Yagi and the hottest/best UHF-only preamp" and Tweeter agreed that I buy the new antenna and pre, they'd refund me my costs and send the guy out again to make the swap. I can not find the receipt for the Winegard pre but it would have been the highest gain/lowest noise model at that time. If the AP 8275 fits that bill then that was probably it. I think it claimed 26dB gain.

Yes, they installed a new ground rod and a shield-grounding block and the rod is of course in a different place than my AC ground rod. The cable used is as per above but I'll take note of the Belden #.

BTW, shedding dBs "after" the preamp does nothing good IF the signal is already distorted due to preamp input overload. I have also tried attenuation right at my STB to check the possibility that the signal was clean but the STB was unhappy. No luck.

I live in a semi-rural area. The Philly farm is 40 mi @64 degrees; the York, PA stations are 50+ @309 degrees; the Baltimore candlelabra tower is 60 mi at least @252 degrees; there are radio stations in Wilmington, DE but neither the antenna or preamp is "cut" for those.

Using three different OTA STBs I have NEVER seen the on-screen signal strength/quality meter pegged. Always two or three bars down from max, at best.

Yes, I have a rotor otherwise I'd be in the dark most of the time. I literally have to tweak it nearly every night. And yes, I believe I'm having to "off-point" the Yagi to cripple it a bit and in that extreme case I mentioned, had to go broadside one year for the Super Bowl on Fox in York PA because I can not get Philly Fox 29.1, UHF 42. What I get when I tune to 42 is 22.1 PBS, also 42 UHF, which is in Annapolis, MD, directly behind the Yagi, 50-60 miles away - backwards. TV fool gives me a co-channel warning for that case but I'm not using an omnidirectional antenna!

No, I have not bypassed the preamp. Like I wrote, I wish I could do that remotely. What DO people do when they have one close-in farm and another that's fringe, or deep fringe?

Does the lower gain Winegard AP 8700 also have lower noise and higher input voltage tolerance?

One thing I did not mention that may cause you to go "Aha!". I am surrounded by Tulip Poplar trees. Their leaves are probably like small RF mirrors. The tree-line is about 100 or so feet from the antenna. Otherwise I'm on relatively high ground (several hundred feet) and the antenna is another 35 feet up.

SAT-TV is not an option due to the low angle and tall trees.

For now, I'm looking at the largest, deepest fringe, combos available b/c I don't know what else to do other than to back-off on the preamp gain, replace the coax, and hope for the best. Or, actually find someone with an 8VSB meter who knows what they are doing.

Jim

[KNP 2516]

The stories out of Philadelphia are that they are having problems with their signals.

The television stations knows that they have problems and the only alternative is for them to move back to VHF

Your YAGI antenna is set up for UHF only as is your 7778 pre amplifier.

A station too close to you or on the same frequency is always going to give you problems.

Getting a more powerful antenna isn't going to help over modulation.

I would hold off a little longer on any antenna until you find out what they are going to do, or else you might find out that they moved the stations back to VHF and then you will have to buy another antenna.

Without a exact address, there is no way for me to generate a report for you as to what signals you have and what antenna you need.

Do not concern yourself as much with distance as what you should be concerned with what is between you and the transmitter.

Anything blocking the signal - and that is it!

No amplifier is going to make a signal when none is present.

[Skyhooker]

KNP 216

My address:

17 N. Rosemont Circle
"Glen Farms"
Elkton, MD 21921

I did not know that the Philly farm was having transition problems -just seemed to be true from what I saw. 10 is messed up (fine at 62 now at 34), 3 was very good @26 and they didn't change but not the same now, 6 and 12 are now VHF so a done-deal no-show with my current set-up. Philly has a 9 now. Don't know what that is all about - thought 10 would be a shoe-in at their original VHF slot but now can't due to adjacent channel issues with the new 9.

I have run the TVfool locater tool but please do the same. Yey don't know about my tulip poplars.

Thanks again,

Jim

[Skyhooker]

First a correction: I mentioned previously that my OTA DTV life started in 2004. It was late 2002 actually.

Seems like I killed my chances for additional advice with the comment about being ringed by layers of tulip poplar trees. For those unfamiliar, imagine a cluster things as straight as but twice the height of a "telephone pole" with branches and leaves.

Re-cap:
- Yes, I've always had a rotor.
- I have the 9032 Yagi strapped to my chimney and understand that it's UHF only.
- Yes, let's say I have the AP-8275 preamp
- From the printing on my RG-6U coax cable it is of the quad-shield type.
- I know full well I have to change antennas b/c DTV channels-of-interest have fallen back into the VHF band. That's a no-brainer.
- The 9032 has no interest in Fox 29.1 but loves PBS 22.1 off its stern (i.e. both use UHF 42)
- I've had to sometimes turn the 9032 away from and even broadside to the transmission source.
- Why doesn't somebody make a preamp that will bypass itself when you remove its DC power?

New stuff:
-There is no DTV UHF 52-69 anymore so why are UHF amd combo antennas still cut for channel 69? Designing a Yagi or the Yagi portion of a combo for channel 51 betters the perfomance for the frequencies below. Isn't that Yagi 101 as in, design for only the highest frequency of interest? Gain above that freq degrades quickly to the benefit of freqs below. We don't want gain for whomever the FCC sold 52 to 69 to.
- My 100' of RG-6U coax will eat about 6db at 700MHz (i.e. the approx upper limit of OTA DTV, chan 51) so I have no need for a 25 - 30dB preamp. Add some misc downstream losses so yes KNP 2516, it seems like the AP-8700 would be more than enough gain and nearly quadruples the input overload figure. It is curious that the inherent noise figures are the same between the 8275 and the 8700. Hmmmm...
- All my stuff on the roof is 7 years old. KNP 2516 wrote elsewhere that stuff gets tired after exposure to the elements so I just wonder what that meant exactly. What is it that degrades vs. quits, etc?
- In any case, I find myself looking at Winegard's largest combo antennas and backing off of the preamp gain.
- KNP 2516 seems to know that Philly DTV is messed up. Any details on that ? How do I find out?

[winegard]

Good morning Skyhooker -

-There is no DTV UHF 52-69 anymore so why are UHF amd combo antennas still cut for channel 69? Designing a Yagi or the Yagi portion of a combo for channel 51 betters the perfomance for the frequencies below. Isn't that Yagi 101 as in, design for only the highest frequency of interest? Gain above that freq degrades quickly to the benefit of freqs below. We don't want gain for whomever the FCC sold 52 to 69 to.

While I cannot go into exact details of new products being released before they are officially announced, Winegard Company will continue to produce the highest quality antenna possible.



I've sent your other questions over to technical services.