[Calaveras]

There has been some discussion on this forum recently about 1 dB Gain Compression (P1dB) and Third Order Intercepts (IP3) relating to preamp performance. The term “Overload” is also tossed around quite a bit. What does any of this mean when it comes to selecting a preamp? What signal levels does it take for a preamp to be “overloaded?” I have not seen anyone try to quantify this.

Often "overload" is loosely used to mean the maximum signal a preamp can output. This is basically the definition of 1dB gain compression. This might be okay if there is only one strong signal present but it is not useful when two or more strong signals are present which is often the case. In this discussion I’m defining overload to mean the input level to a preamp of two signals that cause the Third Order Intermod products to be strong enough to interfere with the weakest signal that the can be decoded. This occurs at much lower signal levels than does gain compression.

In order to determine overload, IP3 and preamp gain needs to be known. Preamp noise figure is helpful too. Third order intermods increase in amplitude at 3 times the rate of the main signals. This leads to the fictitious number IP3 where the main signals (two equal input signals are needed to run the test) and the intermods are equal in amplitude. It is fictitious because IP3 is always higher than P1dB so the amplifier output can never reach IP3. If you know IP3 and the preamp signal outputs you can calculate the third order intermods quite easily.

Intermods = IP3-3x(IP3-Signal Output)

For example:

IP3 = +30 dBm
Signals = +10 dBm
Intermods = 30 – 3x(30-10) = -30 dBm

It’s time to see how preamp gain and noise figure affect what constitutes overload. I’ll use a 6 MHz bandwidth as a round number for a DTV signal. The noise in a 6 MHz bandwidth at room temperature is -106 dBm (another round number) at the antenna terminals. Let’s say the preamp has 20 dB of gain and a 3 dB noise figure. The noise level at the preamp output will be increased 20 dB + 3 dB or -83 dBm. Any intermod products that are greater than -83 dBm have the potential to interfere with reception of a weak station if they happen to fall in the bandwidth of that station.

Now let’s look at a real preamp and see what the maximum level of two input signals has to be to potentially cause a problem. I’m going to use the new Clearstream Juice preamp and the numbers posted by ADTech:

Gain = 19 dB
Noise Figure = 3 dB on UHF
IP3 = +37 dBm
P1dB = +23 dBm

The output noise level of this preamp is -106 dBm + 19 dB + 3 dB = -84 dBm.

Rearrange the formula above to solve for Signal Output:

Signal Output = IP3 – (IP3-Intermods)/3

Signal Output = 37 – (37 – (-84))/3 = -3.33 dBm

With a preamp gain of 19 dB the maximum input of two signals is -22.33 dBm.

Let’s say we used an antenna with 10 dB of gain. Now look at the NM and Signal Pwr columns in any TV Fool report. The Noise Margin – Signal Power is 90.8. (TV Fool uses -106 dBm as the noise level at the antenna terminals. Since 15.2 dB is minimum Signal-to-Noise to decode a DTV signal, -106 dBm + 15.2 equals the Noise Margin - Signal Pwr or 90.8.)

The maximum Noise Margin without causing preamp overload using a 10 dB gain antenna is:

NM = 90.8 - (10 – (-22.33)) = 58.47 dB.

Any pair of signals with a Noise Margin > 58.5 dB can potentially cause a reception problem on a very weak station using the above preamp and antenna. More strong signals mean even lower Noise Margins can cause a problem.

If you have just one strong signal and the rest are fairly weak (my situation) then you should be able to tolerate a much higher Noise Margin without overload. It all depends on how weak the other stations are.

Let’s take a look at a few more examples.

Tin Lee UHF preamp

Gain = 30 dB
Noise Figure = 2 dB
IP3 = +31 dBm
P1dB = 19 dBm

Output Noise Level =-106 dBm + 30 dB + 2 dB = -74 dBm

Signal Output = 31 – (31 – (-74))/3 = -4 dBm

With a preamp gain of 30 dB the maximum input of two signals is -34.0 dBm.

Using the TV Fool number of 90.8 and antenna gain of 10 dB:

NM = 90.8 - (10 – (-34)) = 46.8 dB (Maximum of any 2 signals)


Next let’s look at the RCA TVPRAMP1R. I measured this preamp but I don’t know IP3. Based on IP3 of the other preamps and P1dB I measured on UHF I’m going to estimate the low 20 dBms. I’ll use +22dBm.

RCA TVPRAMP1R

Gain = 25 dB
Noise Figure = 2 dB
IP3 = +22 dBm
P1dB = +10 dBm

Output Noise Level =-106 dBm + 25 dB + 2 dB = -79 dBm

Signal Output = 22 – (22 – (-79))/3 = -11.67 dBm

With a preamp gain of 25 dB the maximum input of two signals is -36.67 dBm.

Using the TV Fool number of 90.8 and antenna gain of 10 dB:

NM = 90.8 - (10 – (-36.67)) = 44.13 dB (Maximum of any 2 signals)


Finally let’s look at the discontinued Winegard HDP269 that was always at the top of overload resistant preamps. I measured this preamp but again I don’t know IP3. Based on IP3 of the other preamps and P1dB I measured on UHF I’m going to estimate the upper 20 dBms. I’ll use +27dBm.

Winegard HDP269

Gain = 12 dB
Noise Figure = 3 dB
IP3 = +27 dBm
P1dB = +15 dBm

Output Noise Level =-106 dBm + 12 dB + 3 dB = -91 dBm

Signal Output = 27 – (27 – (-91))/3 = -12.33 dBm

With a preamp gain of 12 dB the maximum input of two signals is -24.33 dBm.

Using the TV Fool number of 90.8 and antenna gain of 10 dB:

NM = 90.8 - (10 – (-24.33)) = 56.5 dB (Maximum of any 2 signals)


The bottom line is you want the highest IP3 you can get and no more gain than you need to minimize the possibility of interference from third order intermods to weak stations in a strong signal environment.

I think the advice to not use a preamp with a gain antenna mounted outside when Noise Margins are predicted to be >+50 dB is justified.

 

[tylerSC]

But sometimes you need a bit of amplification for the very weak distant stations, but the strong locals will cause overload or drown out the weak ones. Then that is where filters and attenuators come into play, I suppose. And sometimes I think it may be the TV tuner that is overloaded rather than the preamp.

 

[Calaveras]

I don't have a very good handle on what it takes to overload a tuner. The information I have says that a well designed tuner should be able to handle two signals at -2 dBm but I don't know what IP3 of a tuner is. That's a pretty big signal so I would think it would not be easy to overload a TV tuner. Maybe with a preamp and a distribution amp but not with an antenna alone.

My one extremely strong station has a measured NM of 69 dB. The output of the preamp for this one station is +13 dBm which is reduced to about -5 dBm by the time it gets to the TV. This does negatively impact the AGC. I used a notch filter after the preamp and that fixed the AGC issue. Right now though the filter is placed before the preamp and everything is fine.

A preamp only needs enough gain to overcome losses (including TV noise figure) between the antenna and the TV plus about 8 dB. Anything more than that just increases the probability of intermod problems. 19 dB gain is perfect for 100' of RG-6 and a typical TV.

 

[rabbit73]

Understanding Overload, SFDR, Intermod, and why Spurious Signals affect Weak Signals

.....The term “Overload” is also tossed around quite a bit. What does any of this mean when it comes to selecting a preamp? What signal levels does it take for a preamp to be “overloaded?” I have not seen anyone try to quantify this.

Good questions.

Often "overload" is loosely used to mean the maximum signal a preamp can output. This is basically the definition of 1dB gain compression. This might be okay if there is only one strong signal present but it is not useful when two or more strong signals are present which is often the case.

Forum member holl_ands has a preamp chart listing max input for two signals, with a footnote about derating for more than two signals.
http://imageevent.com/holl_ands/files/ota
Scroll down to file 16
Modified solidsignal Chart Comparing Preamps - RevB
http://imageevent.com/holl_ands/files/ota?p=15&n=1&m=-1&c=3&l=0&w=1&s=0&z=4

The Spurious Free Dynamic Range (SFDR) needed is the difference in strength between your strongest signal and your weakest desired signal, using the dBm Pwr scale on your tvfool report. This difference is expressed in terms of dB, not dBm, because the original units are the same. To this you must add 16 dB that is required for the SNR of the weakest desired signal. Another way to think of it is from the top of the strongest signal down to the bottom (noise floor) of the weakest desired signal. The top of the spurious signals must be at or below the noise floor if they are not to cause interference.

You can also use the NM scale for your calculations, but I prefer to use the Pwr scale because most tuners drop out around -85 dBm.

ATSC Recommended Practice:
Receiver Performance Guidelines
Document A/74:2010, 7 April 2010
http://www.atsc.org/cms/standards/a_74-2010.pdf

5 RECEIVER PERFORMANCE GUIDELINES

5.1 Sensitivity
Quote:
A DTV receiver should achieve a bit error rate in the transport stream of no worse than 3x10E-6 (i.e., the FCC Advisory Committee on Advanced Television Service, ACATS, Threshold of Visibility, TOV) for input RF signal levels directly to the tuner from –83 dBm to –5 dBm for both the VHF and UHF bands.
End quote.

The intermodulation distortion (IMD) creates new spurious signals within the preamp itself that can interfere with the reception of your weakest desired signals if the spurious signals are stronger than the noise floor of the weakest desired signals. The spurious signals are caused by the interaction between two or more of your strongest signals.

As holl_ands has mentioned, if you attenuate all your signals by one dB before the preamp, the IMD is reduced by 3 dB, which lowers the noise floor. However, since you have also reduced the strength of your weakest desired signal, the net SNR gain of the weakest desired signal is not 3 dB, but 2 dB. Still, not a bad deal if you use a 3 dB attenuator to improve the SNR of your weakest desired signal by 6 dB.

IMD is not the only distortion that can be created within the preamp; you can also have distortion caused by signals so strong that the top of the strong signals are clipped, which causes compression of the signals. This can be seen if you increase the input to the preamp by, for example, 10 dB and the output increases by less than 10 dB.

When I did my tests of preamp overload, I noticed that my original CM7777 exhibited compression sooner than my CM3410 with increasing signal strength; the CM3410 showed IMD first because it is more resistant to overload.

The final test is here:
http://www.digitalhome.ca/forum/showpost.php?p=1597002&postcount=3490

This is the image in that post that summarizes the concept to optimize the SFDR for any particular location:

Some forum members take exception to my method of simulating preamp overload, but I stand by my conclusions, and feedback from other forum members who have successfully used attenuation before a preamp validate the concept.

When a large SFDR is needed, you might be able to pull it off using a preamp that is resistant to overload with an attenuator at its input, the value determined by trial-and-error. The goal is to use just enough attenuation to reduce the spurious signals without making your desired signal too weak.

If you can't find a preamp that has sufficient SFDR for your location, and you are not able to optimize your preamp with an input attenuator for your signals, then you must resort to more exotic (expensive) measures to receive your weak signals without interference from your very strong local signals.

One solution would be to have a separate antenna, a single channel bandpass filter from Tin Lee, and a preamp for your most needed weak signal. Another approach, as tylerSC mentioned, and as you mentioned with your CH18 notch filter, is to use a filter to attenuate your strongest signal. However, if you have many strong signals, it gets expensive to buy a $100 single channel bandstop filter to attenuate each one, not to mention the sum of the insertion losses in the passbands.
http://www.tinlee.com/Matv_filters.php

Take a look at this tvfool report:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=f1f0d54ffeaa4f

That poster has many strong local signals, with the strongest one being WUTV-DT, real CH14, with a NM of 68.3 dB, and a signal power of -22.5 dBm.

His goal is reliable CN tower reception of CFTO RF9, CICA RF19, CBLT RF20 and CBLFT RF25 ( CIII RF41 if possible) from his location (some are listed as pending). As you can see, they are very weak with small or negative NMs. Furthermore, they are 2Edge signals that vary in signal strength much more than LOS signals.

So far, he is finding it very difficult reaching his goal.
http://www.digitalhome.ca/forum/showpost.php?p=2442721&postcount=4046

Your definition of preamp overload is similar to, but not exactly the same as, what I call type one overload:

THREE TYPES OF OVERLOAD

There are three types of preamp or tuner overload, in order of increasing signal strength:

1. The strong signals almost cause enough IM distortion to interfere with the reception of weak desired signals, but the spurious signals are at or below the noise floor. This is the point that holl_ands uses in his preamp charts to obtain max SFDR (Spurious Free Dynamic Range). No damage will happen.

As the strongest signals continue to increase in strength, more of the weaker signals are damaged until you reach:

2. The strong signals cause overload to the preamp or tuner that makes it impossible to receive any signals. No damage will happen. The strongest signals are still there, but they can't be decoded because the IMD products have damaged them so that they contain more errors (high BER....bit error ratio/rate) than can be corrected by the FEC (forward error correction).

3. The signals are so strong that the input transistor is toast. You are not likely to encounter OTA signals that strong, unless you live next door to a high power transmitter and you have your high gain antenna aimed at the transmitter's antenna.

As a general rule, tuners can tolerate stronger signals than preamps before overload. The difference in strength is approx. equal to the preamp gain.

5.2 Multi-Signal Overload
Quote:
The DTV receiver should accommodate more than one undesired, high-level, NSTC or DTV signal at its input, received from transmission facilities that are in close proximity to one another. For purposes of this guideline, it should be assumed that multiple signals, each approaching –8 dBm, will exist at the input of the receiver.
End quote.

 

[Calaveras]

Good questions.
Forum member holl_ands has a preamp chart listing max input for two signals, with a footnote about derating for more than two signals.
http://imageevent.com/holl_ands/files/ota
Scroll down to file 16
Modified solidsignal Chart Comparing Preamps - RevB
http://imageevent.com/holl_ands/files/ota?p=15&n=1&m=-1&c=3&l=0&w=1&s=0&z=4

I don't see any huge disagreements between us. I have no idea how holl_ands calculated the maximum signal inputs for his table. There's no IP3 listed for any of the preamps which is required to calculate 3rd order IMD. I wanted to stay away from a table like that because every preamp in the table is now discontinued. The only preamp we have in common is the HDP269 and our results don't agree.

The Spurious Free Dynamic Range (SFDR) needed is the difference in strength between your strongest signal and your weakest desired signal, using the dBm Pwr scale on your tvfool report.

We have a little different definition of SFDR. Yours is centered around what you need in your particular situation and mine is on the device.

As holl_ands has mentioned, if you attenuate all your signals by one dB before the preamp, the IMD is reduced by 3 dB, which lowers the noise floor. However, since you have also reduced the strength of your weakest desired signal, the net SNR gain of the weakest desired signal is not 3 dB, but 2 dB. Still, not a bad deal if you use a 3 dB attenuator to improve the SNR of your weakest desired signal by 6 dB.

This only works if your weakest signal has enough noise margin. If you need more than a couple dB attenuation then you're just as well off not using any preamp.

When I did my tests of preamp overload, I noticed that my original CM7777 exhibited compression sooner than my CM3410 with increasing signal strength; the CM3410 showed IMD first because it is more resistant to overload.

Every amplifier will have measurable IMD before the output reaches the 1 dB gain compression point (overload).

Take a look at this tvfool report:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=f1f0d54ffeaa4f

That poster has many strong local signals, with the strongest one being WUTV-DT, real CH14, with a NM of 68.3 dB, and a signal power of -22.5 dBm.

His goal is reliable CN tower reception of CFTO RF9, CICA RF19, CBLT RF20 and CBLFT RF25 ( CIII RF41 if possible) from his location (some are listed as pending). As you can see, they are very weak with small or negative NMs. Furthermore, they are 2Edge signals that vary in signal strength much more than LOS signals.

So far, he is finding it very difficult reaching his goal.
http://www.digitalhome.ca/forum/showpost.php?p=2442721&postcount=4046

There are some situations that are impossible and some situations where a preamp isn't realistic. The worst situation is a weak station adjacent to a strong station. I have the 70 dB noise margin KUVS (heading 237 degrees) next to the weak KOFY (heading 253 degrees). The only way I've been able to receive KOFY was to adjust the spacing of my 91XGs so that KUVS is in a deep null when pointed at KOFY. The problem with even that is the null is

 

[rabbit73]

Thanks for your comments on my post.

I don't see any huge disagreements between us.

Right; I just wanted to add a different way of looking at the problem to help others understand.

I have no idea how holl_ands calculated the maximum signal inputs for his table.

This is his method:
http://imageevent.com/holl_ands/files/ota?p=7&n=1&m=-1&c=3&l=0&w=1&s=0&z=4

We have a little different definition of SFDR. Yours is centered around what you need in your particular situation and mine is on the device.

I was looking for a different way to approach the problem for people who have difficulty understanding Gain Compression (P1dB) and Third Order Intercepts (IP3) relating to preamp performance.

This only works if your weakest signal has enough noise margin.

Right, if you run out of signal before the spurious signals drop below the noise floor, it doesn't work. The saving grace is that when you add attenuation before the preamp, the noise floor falls faster than the signal strength of the weak signal, increasing the SNR.

If you don't have enough signal strength for your weak signal without a preamp, and your strongest signals create IMD in a preamp that wipes out your weakest signal, the attenuator before the preamp allows you to match the SFDR of the preamp to your signals.

I remember a poster who had overload with his preamp at the antenna, but his reception was OK with his preamp at the bottom of his 50 ft coax downlead. This bothered him because he thought his preamp must be near the antenna. He had stumbled on the attenuator technique which gave him about 3 dB of attenuation for UHF. He could have used an antenna or preamp with less gain, but we told him to leave it alone because his setup worked and was cost-effective.

If you need more than a couple dB attenuation then you're just as well off not using any preamp.

You are forgetting what you told us previously: A preamp can improve the System NF.
http://imageevent.com/holl_ands/files/ota?p=9&w=1&n=1&c=3&m=-1&s=0&y=2&z=4&l=0

http://www.digitalhome.ca/forum/showpost.php?p=877838&postcount=604

http://www.digitalhome.ca/forum/showpost.php?p=375668&postcount=1
click on link in above post after
Another excellent tool is majortom's Cascaded Noise Figure Spreadsheet:

The only way I've been able to receive KOFY was to adjust the spacing of my 91XGs so that KUVS is in a deep null when pointed at KOFY.

Interesting creative fix.

There are some situations that are impossible and some situations where a preamp isn't realistic.

Right.

 

[Calaveras]

This is his method:
http://imageevent.com/holl_ands/files/ota?p=7&n=1&m=-1&c=3&l=0&w=1&s=0&z=4

That page is about analog TV which is why there are those peak to average derating values.

If I calculate IP3 for the HDP269 using the signal input of -14.6 dBm (-2.6 dBm output) from his table, IP3 is about +42 dBm. That's impossible. I don't know what's wrong. If I use the Winegard number of 350,000uV input, then IP3 is about +22 dBm. I estimated +27 dBm. Not right but better than +42. If the Winegard spec is for 5 signals as suggested, then IP is +28 dBm.

I need another signal generator to measure IP3.

You are forgetting what you told us previously: A preamp can improve the System NF.
Right.

Okay. There is a gap between a preamp with no attenuation and no preamp at all. You could really fine tune the system if you wanted to with 1 dB attenuation steps. Usually I recommend a preamp with no more gain than necessary. Mid way is no preamp but instead use a distribution amp and letting your 100' of RG-6 be the attenuator. Finally if the signals are really strong then no amp of any kind.

 

[rabbit73]

That's impossible. I don't know what's wrong.

I find it difficult to understand his method.

That page is about analog TV which is why there are those peak to average derating values.

The DTV signal is an analog signal (8VSB.....SSSC) that contains digital information. When you use a SLM designed to measure analog TV signals, you add a correction factor of 6.8 dB when measuring DTV signals.

The Sadelco tech told me that when the DisplayMax800 measures a DTV signal in the single channel scanning mode, it takes multiple readings across the channel, takes the average of those readings, and adds 6.8 dB.

When measuring an analog TV signal, it measures the peaks of the video and sound carriers.

I don't know the characteristics of detector used.

There is more power in the 6 MHz DTV channel, than in an analog channel. Unlike the analog signal, it nearly fills the whole channel.

Okay. There is a gap between a preamp with no attenuation and no preamp at all. You could really fine tune the system if you wanted to with 1 dB attenuation steps.

Thank you. You understand the concept better than most other people.

 

[Calaveras]

I find it difficult to understand his method.
The DTV signal is an analog signal (8VSB.....SSSC) that contains digital information. When you use a SLM designed to measure analog TV signals, you add a correction factor of 6.8 dB when measuring DTV signals.

The Sadelco tech told me that when the DisplayMax800 measures a DTV signal in the single channel scanning mode, it takes multiple readings across the channel, takes the average of those readings, and adds 6.8 dB.

When measuring an analog TV signal, it measures the peaks of the video and sound carriers.

I don't know the characteristics of detector used.

There is more power in the 6 MHz DTV channel, than in an analog channel. Unlike the analog signal, it nearly fills the whole channel.
Thank you. You understand the concept better than most other people.

Yes, I know 8VSB is analog. Nothing over the air is actually digital.

His example uses a station with 1320KW ERP so that has to be an analog station.

It sounds to me as though the meter has an IF bandwidth less than one channel wide so you have to apply a correction factor to obtain the total signal power.

 

[ADTech]

Yes, you have to have two RF signal generators to do IM measurements.

The following are some selected test results from measurements I've made.

Here's a handy calculator: http://www.changpuak.ch/electronics/calc_19.php All you do is plug in the following numbers: Amplitude of fundamental tones, amplitude of IM3 products, Gain at test frequency, Noise figure, bandwidth. This will compute an idealized (SNR=0) SFDR and maximum two-tone input signal power for spurious-free operation under test laboratory conditions.

For a test Juice
at 500 MHz, P1=+7.7 dBm, P2=-52 dBm, Gain=17.6, NF=2.6, BW=6,000. OIP3=37.55 dBm, max 2-tone input is -21.24 dBm, SFDR=82.38 dB

As a comparison, here are the results for a Boost XT (LNA200):
at 500 MHz, P1=-0.4 dBm, P2=-59 dBm, Gain=18.5, NF=2, BW=6,000. OIP3=28.9 dBm, max 2-tone input is -27.81 dBm, SFDR=76.41dB

And for a recent RCA TVPRAMP1R:
at 500 MHz, P1=-10 dBm, P2=-70 dBm, Gain=24.5, NF=2.6, BW=6,000. OIP3=20 dBm, max 2-tone input is -37.5 dBm, SFDR=66.08dB

I tested the HDP269 about two years ago, but those measurements were made with a spectrum analyzer that read 10 dB off due to a problem with one of the internal attenuators. I *think* I've correctly compensated for it in the following numbers. I don't have the amp any more so I cannot re-test it unless I get my hands on another one. As it happened that day, I was testing with a constant -10 dBm tone pair input instead of shooting for a -60 dBc IM3 product as I usually do now.

at 500 MHz, P1=0 dBm, P2=-50 dBm, Gain=10, NF=5.0, BW=6,000. OIP3=25 dBm, max 2-tone input is -23.74 dBm, SFDR=77.48 dB

Several of those amps have separate VHF paths available and they can have markedly different VHF performance from their UHF numbers. I've only include a single frequency for brevity.

 

[rabbit73]

The April 2015 QST Magazine has an interesting article on this topic:

Microwavelengths Column

Dynamic Range
Gauging your receiver's weak-signal sensitivity in a strong-signal environment.

Several sections of interest are:
Amplifiers and Distortion
Spurious-Free Dynamic Range

Article begins on page 62

 

[tylerSC]

Because IP3 and P1db figures are reportedly very good, I have purchased a Clearstream Juice amp to test with a very weak signal surrounded by very strong signals. Supposedly this amp is overload resistant and will help handle a mix of strong and weak signals. The Kitztech 100 will work sometimes, but still suffers drop outs from the weak channel, despite the low noise figure. The Juice noise figure is stated at 2db, but perhaps the good P1db figure will help. I will also use an AD or MCM FM trap, and possibly an attenuator before the preamp. This is not a scientific test or review, just a personal experiment. It has already been stated the Juice is a good amp in the proper application.

 

[tylerSC]

Because IP3 and P1db figures are reportedly very good, I have purchased a Clearstream Juice amp to test with a very weak signal surrounded by very strong signals. Supposedly this amp is overload resistant and will help handle a mix of strong and weak signals. The Kitztech 100 will work sometimes, but still suffers drop outs from the weak channel, despite the low noise figure. The Juice noise figure is stated at 2db, but perhaps the good P1db figure will help. I will also use an AD or MCM FM trap, and possibly an attenuator before the preamp. This is not a scientific test or review, just a personal experiment. It has already been stated the Juice is a good amp in the proper application.

Preliminary report, the Juice amp is very good. Basically the same or better readings as the Kitztech, although still issues with the weak signal dropping out during the day. Added an FM trap, but will work some more with some attenuators in the coming days. The weak translator signal used to be more stable during the day, but a local UHF nearby increased power, and several low power FM signals have signed on also nearby. So the noise floor may now be just a bit too high for the weak TV signal. Not a scientific evaluation, but very good results with the Juice amp which appears to be a solid performer.