Pre-Amplifiers, Usage & Reviews

SWHouston

Moderator
Staff member
#1
If this thread becomes Sticky then fine, but if not, this IS a subject which many Users are very interested in, and is definitely a needed topic of discussion.

I apologize if someone thinks I'm "stealing their thunder" on this, but frequently topics are suggested, and never followed up on. and I really think this is a viable issue. I'll go another step here, and recommend that when a situation is under discussion, that "whoever" gives a link to a Chart (TVFool would be nice) where we can see some actual dB's and distances that related to the recommendation made.

So, just to get things started, here's goes...

I had an opportunity to discuss Antenna Choices with illuvatar81 and jlhugh who both live in Wichita Falls, here's the general TVF Chart for them...

Wichita Falls TX 10/2009

Now, given the numbers you can see in the Chart, would you recommend a Pre-Amp for them, and if so, which one? I'm mainly looking at their ABC and FOX stations, being rather low on signal strength.

Have a good Day ! :dancing:
S.W.
 

IDRick

DTVUSA Member
#2
What is the antenna aim, 328 degrees AZ or something closer to 267 degrees? NBC and CBS are too strong for *any* pre-amp. Assuming the situation allows for good reception, the user can probably feed 2 to 3 tvs with a roof mounted antenna and moderate cable length. A distribution amp may be needed if there will be many splits and long cable runs in the distribution system.


I like to use Holland's calculations and his pre-amp table. See the table and a brief discussion of calculations here: Digital Forum - View Single Post - Signal Amplifiers (Amps, Preamps, Distro Amps) - See Chart in Post #1 The calculations are briefly discussed at the bottom of the downloaded page.
 

IDRick

DTVUSA Member
#3
How about this situation: TV Fool Which amplifier, if any, would you recommend?

This is my home and I've done extensive testing on the roof. I'm using a DIY 4-bay with a wide beam. It receives both high vhf and uhf. Approximate antenna gain is 12 dBd on UHF and 4 dBd on VHF. Antenna aim is 235 degrees (azimuth). Based on several tests, I know that I will lose 4 to 5 dB on each channel by aiming 35 degrees off axis. I have used pad attentuators, a converter box, 25 ft cable, and a tv to determine margin to dropout (ie amount of attenuation required to lose the signal). Margin to dropout values for each station are as follows (235 degree aim):

ch 8 KIFI 44 dB
ch 17 KISU 39 dB
ch 36 KIDK 37 dB
ch 23 KPVI 38 dB
ch 15 KPIF 34 dB
ch 31 KFXP 30 dB
ch 47 3ABN 15 dB

**Add ~10 dB to obtain the received signal at the antenna, before balun loss.

The distribution system includes ~160ft of rg-6 cable and 3 two way splitters. System losses exceed the margin to dropout for ch 47.
 
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Don_M

DTVUSA Member
#4
Rick's aim is dead on: KFDX and KAUZ are so strong there that a bent paper clip in the RF In connector would probably pull them in. Stations that strong will usually overwhelm any amplifier.

The ABC and Fox affiliates may be well down the list, but aren't really weak signals. They're still well within the "green" area of the report, meaning both could still be received by a carefully-placed UHF indoor antenna. Their position helps illustrate just how strong the NBC and CBS stations are!

Perhaps we've been a bit too diplomatic on this topic, so I'll say it more plainly: Amplifiers are a last resort. The physics of DTV signals are such that every other signal-maximizing strategy needs to be tried first. There's only a narrow range of circumstances in which an amp helps with receiving "weak" signals. It's safe to say that the location described in this TVFool report doesn't fall within that range.
 

SWHouston

Moderator
Staff member
#5
IDRick,
A DB8 (100° Beamwidth/15.8 db) was mentioned, and set to aim/center in the range between the two farms (256/322°) he didn't want to use a Rotator.

Now, I hope you don't take this wrong, cause I'm not trying to argue here, but, I think an Amp can be used, but, I need to explain that first.

TVFool rates the strongest (NBC Station) at a 75.8 NMdB

Though TVF is very generous in saying what you can and can't receive, I personally know that one is going to have problems when the Sig Strength drops below 50 NMdB, with Pixs and Sound dropouts, and that going over 100 NMDb is well within the capability of most Tuners without overloading.

Now...
If you take Winegard's opinion, they would recommend a...
Winegard HDP269 (3 dB Noise)
But they would do that on Mileage, not that I disagree with the choice given the 12 dB gain, but I just never understood how they could just come up with an arbitrary distance, for a recommendation, without considering Signal Strength.

That 12 dB plus Antenna Gain would bring the total up to 103.8 NMdB, which would be ok for the Tuner before any system loses, and, I think you could even use a...
Antennas Direct PA-18 (2.8 dB Noise)

Either of these would at least give him some help on his ABC and FOX..
Your/or others thoughts on this ?

S.W.
 
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#6
I have similar signal strenghts at my location. Both the HDP-269 & CM 3414 distribution amp do overload the system somewhat even with a low gain antenna. If I had to choose, I'd go with the CM 3414 over the Winegard for distribution purposes. It seems a bit more tolerant, and iIMO is a much better choice when feeding multiple tuners.
TV Fool
 

IDRick

DTVUSA Member
#7
Hi SW,

Did you have a chance to look at Holl_ands spreadsheet? Holl_ands is a well respected communications engineer. According to Holl_ands, the max input for two strong UHF channels is -14.5 dBm for the HDP 269. So what is the max input? We can calculate that number from tvfool data and from a few assumptions.

Average power of NBC and CBS is -15.4 dBm
Reduce by 7 dB to convert to peak, power is now -7.4 dBm
Add in antenna gain (assume 10 dB), power is now, +2.6 dBm
Subtract balun loss, 1.5 dB, and our max input is +1.1 dBm

NBC and CBS would clearly overload the HDP269 (+1.1 dBm is > -14.5 dBm)

You will reduce the power some by aiming the antenna away from the NBC and CBS towers. How much depends on the antenna. With a CM 4221, you would reduce the signal by about 4 to 5 dB. This attenuation is not enough to prevent pre-amp overload.

What should he do? First, I do not believe the AD specs on the DB-8. It does not have a 100 degree beamwidth. Compare the wide beamwidth on the C-2 antenna (ClearStream2 from AntennasDirect.com) versus the DB-8 (DB-8 from AntennasDirect) I can offer three solutions. First, you can build a DIY 4-bay like I have. My antenna receives high VHF + UHF channels and has a wide beam width (similar to the CM 4221). Alternatively, you could look at EV's Kosmic antenna (same design as mine but fully assembled). Finally, you could consider two antennas (use a CM 4221 aimed at 297 degrees azimuth and an Y5-7-13 aimed at 328 degrees). The Y5 will pick up your ABC channel and the CM4221 will pick up the UHF channels. Use a UVSJ to join the VHF and UHF signals into a single downlead. Put the UHF antenna on top the mast and Y5 about 3 to 5 feet below. His situation is very similar to mine and I'm confident that my solutions are reasonable based on the available data.

At these distances and signals strengths, one should be able to receive sufficient signal with an appropriate antenna(s) and no pre-amp is needed.

HTH and all the best,

Rick
 
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Piggie

Super Moderator
#8
I apologize if someone thinks I'm "stealing their thunder" on this, but frequently topics are suggested, and never followed up on.
S.W.
I was going to at one time and started an article on amps, but essentially if you use Hollands chart and understand TVFool reports then it's simple.

Yeap, I said was going to do it. There is no way in heck I have the time any more.

I guess someone could just ban or delete me.
 

SWHouston

Moderator
Staff member
#9
Don_M

Sorry, I missed your post when replying previously, another Grey Hair day for me yesterday. :gramps:
Diplomacy !, I have a tendency to set such protocol aside when in discussion like this. In my life experience (that's a LOT now) and I've come up with a couple of "sayings".
"Some of my most avid opponents across a Conference Table, have become my best friends across a Dinner Table", and
"The only "stupid" question, is one that goes unasked".

You imply what I know as the KISS principal, it works every time, and an extra buck spent on good quality components in distribution, is well spent given the life of them.

As I told Rick, I'm not experiencing the same results as you indicate as far as the Stations listed in the "Green" section of a TVF Chart. Are you then saying that one need not consider an Amp for any station listed in Green?
I, and others I've talked to, have problems with any listing with a value of less than 50 NMdB.

Rick,

(on your second post)
I would say no on the Pre-Amp up front, again using the KISS principal, give a simple system it a try. It's usually not all that much trouble to install an Amp once one gets things set up, and the need is clear.
However, at one point, I might have said that an amp may be needed, but now, I'm really having second thoughts about that, given that the criteria I've used, seemingly is questionable.
But to answer your question directly, IF i were to think of an Amp to apply here, it might be the...
Winegard AP-8700

(on your other post)
I downloaded the Spreadsheet, but haven't had a chance to "play" with it. I'm not sure if I understand which entry goes where, but as I said, I haven't had a chance to look at it closely.

WOW, I had not seen the Polar Graphs on the DB8, that's definitely a surprise to me. Again, I as many have taken the Mfg general statement on trust, I'll be checking that site out for more information.
From experience and other's statements, reception of HiVHF has always been a little sketchy on the "Bow" Type antenna, though the Mfg imply they do it.
Again, another "conditional" statement, which they want you to think applies generally to their product.
HTH=?

Piggie,

I had no idea you have considered such a thread as this. However, I'm glad to get a Topic started on this information, though the more posts I read here, leads me to think of your Signature as an Axiom.

Delete you !, how can one delete something that's indelible. :D

Have a good Day ! :)
S.W.
 
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#10
But to answer your question directly, IF i were to think of an Amp to apply here, it might be the...
Winegard AP-8700
Have a good Day ! :)
S.W.
There is no pre-amp out there that is recommended with these kind of signal strenghts as it will only make things worse. :flame:If you do desire some of the weaker stations, you will need to rely on proper antenna selection for any chance of reliable reception. (Been there/done that more than once).

If you do find a need for additional gain to feed multiple splits, a distribution amp is a much better choice in this situation. You should be able to feed at least 4 splits without one.
 

IDRick

DTVUSA Member
#11
Rick,

(on your second post)
I would say no on the Pre-Amp up front, again using the KISS principal, give a simple system it a try. It's usually not all that much trouble to install an Amp once one gets things set up, and the need is clear.
However, at one point, I might have said that an amp may be needed, but now, I'm really having second thoughts about that, given that the criteria I've used, seemingly is questionable.
But to answer your question directly, IF i were to think of an Amp to apply here, it might be the...
Winegard AP-8700
Bingo! :)

My goal is to receive all my locals with a single antenna and *no* rotor. I've worked hard to get to this point where I have a workable solution for all but Ch 47. I can receive it just fine but lose it due to high distribution losses. Using Holl_ands calculations, I can add an AP-8700 without overloading the pre-amp or overloading the tv tuners. Ch47 would be retained since the 8700 would cover the distribution losses. Alternatively, one could use a distribution amp and achieve the same result. My situation is a classical case where amplification is needed in a high signal strength area.

Best,

Rick
 

IDRick

DTVUSA Member
#12
There is no pre-amp out there that is recommended with these kind of signal strenghts as it will only make things worse. :flame:If you do desire some of the weaker stations, you will need to rely on proper antenna selection for any chance of reliable reception. (Been there/done that more than once).

If you do find a need for additional gain to feed multiple splits, a distribution amp is a much better choice in this situation. You should be able to feed at least 4 splits without one.
You bring up excellent points No Static At All. An amplifier should not be the first tool grabbed from the toolbox but it can be good choice to resolve issue(s). There are higher gain antennas for ch 47 such as the XG-91 than my DIY antenna. However, XG-91 has a narrow beamwidth and would require the use of a rotor. Since we desire to record OTA with dvr's, using a rotor is problematic for meeting our interests.

You bring up the excellent point that is possible to overload the amplifier and/or the tv tuner if too large an amp is used in a high signal strength area. I have followed the advice of respected engineer and done the calculations for tuner/pre-amp overload. A mid range pre-amp or distribution amp can be used without overloading the tuner or amp.

The top five locals all have 30 dB or higher margins to dropout. If they were all I wanted, then there would be no need for an amplifier. I could still have over 10 dB margin to dropout on these channels after accounting for distribution losses.

Best,

Rick
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#15
Well, I wouldnt recommend an amplifier for the OPs if using one TV, however if using multiple TVs then amplification further down the coax line can help (classic distribution amp).

Ive also encountered situations where when using one TV, an amplifier in front of the TV(down the coax line) helps. The ultra low noise amplifiers like the KitzTech, especially. (or Verstärker, ReseachComm)

The best amp I have is a Motorola BDA S1 GASFet bi-directional cable modem capable job, spec'd 2 dB noise figure.
 
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SWHouston

Moderator
Staff member
#16
Rick,

Give me a while longer on that Spreadsheet, I will have some questions if you don't mind, but in the meantime...

Back to your second post on your setup...
Did you/might you have considered the...
Winegard AP-4700
in stead of the 8700 ?

Have a good Day ! :)
S.W.
 

IDRick

DTVUSA Member
#17
Rick,

Give me a while longer on that Spreadsheet, I will have some questions if you don't mind, but in the meantime...

Back to your second post on your setup...
Did you/might you have considered the...
Winegard AP-4700
in stead of the 8700 ?

Have a good Day ! :)
S.W.
Hi SW,

Yes, the 4700 (UHF only pre-amp) is also a possibility versus the 8700 (UHF & VHF pre-amp). It is possible to overload a preamp on either or both UHF and VHF. Using the spreadsheet calcs, I am below the maximum input for both VHF and UHF. Since I have high distribution losses, it makes sense to me to use a combo pre-amp.

Feel free to post your questions on Holl_ands spreadsheet here in this thread or via PM.

Best,

Rick
 
#18
..... First, I do not believe the AD specs on the DB-8. It does not have a 100 degree beamwidth. ....
Rick
Rick,

A little OT for the thread at hand....

This subject just came up on one of the other forums.

I've looked all over AD's website and nowhere do they claim such a beam width for the DB8. So far, I can't find ANY claim of a beam width on their site for the DB8, either now or in the last several years (searched via archive.org). Other than online resellers erroneously claiming such a beam width, I can't find such a reference.

Based on polar plots they sent me a while back, it appears to have a BW of around 20-35 deg depending on frequency.

Just trying to figure out where that 100 degree number came from.

From experience and other's statements, reception of HiVHF has always been a little sketchy on the "Bow" Type antenna, though the Mfg imply they do it.
Ironically, I was playing with a DB8 at my sister's farm out in the middle of nowhere, Missouri today. I had the DB8 pointed at St Louis and was pleasantly surprised to receive KRCG-13 (VHF-12) from Jefferson City with the antenna either pointed at St Louis (about 60 miles) or at Jeff City on my Artec T18AR USB tuner. My Sencore's reading showed that the "real" gain on VHF-12 was about -10 dBd but, even at 41.7 miles (TVF NM of 17.5), that little T18AR still picked it up without errors. KOMU-8 (56 miles, NM -2.3) was completely absent on the DB8 but was easily caught by pointing a C5 at Columbia instead of the DB8.

TVFool plot for that location: http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=8adf782ae24e24

Sencore's BAR scan of the DB8 pointing at St Louis:
[/IMG]

Sorry about the legibility - the well-used meter's screen is tough to read in bright sunlight and harder to photograph clearly.

Ref level (top line) -18.7 dBmV
From left to right, the bars represent the signal strength of the channels in the current channel plan. Levels near or below the bold horizontal bar (-51.0 dBmV) are unused or are representing noise.

RF Channels
12, 14, 24, 26, 31, 35, 39, 43, 47, 55

All of these channels (except 55 of course), tuned right in with the little Artec on my laptop.
 
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IDRick

DTVUSA Member
#19
Rick,

A little OT for the thread at hand....

This subject just came up on one of the other forums.

I've looked all over AD's website and nowhere do they claim such a beam width for the DB8. So far, I can't find ANY claim of a beam width on their site for the DB8, either now or in the last several years (searched via archive.org). Other than online resellers erroneously claiming such a beam width, I can't find such a reference.

Based on polar plots they sent me a while back, it appears to have a BW of around 20-35 deg depending on frequency.

Just trying to figure out where that 100 degree number came from.
Solid Signal currently lists the DB8 beamwidth as 100 degrees. Others have sited solid signal when quoting beamwidth. Not sure whether the error occured in developing of marketing materials at Antennas Direct or during web page entry at solid signal. AD should really ask SS (and any other retailer that advertises the DB8) to correct their webpage.
 
#20
Solid Signal currently lists the DB8 beamwidth as 100 degrees. Others have sited solid signal when quoting beamwidth. Not sure whether the error occured in developing of marketing materials at Antennas Direct or during web page entry at solid signal. AD should really ask SS (and any other retailer that advertises the DB8) to correct their webpage.

So it's not the manufacturer misstating the performance as was suggested..

Is there anything wrong with an educated consumer pointing out to SS (or any other reseller) that they have an error on THEIR website?
 
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