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post #16771 of 16779 Old 09-28-2017, 01:52 PM
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Don't know how well it works, but it is much cheaper in Walmart stores.
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post #16772 of 16779 Old 10-17-2017, 12:50 PM
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Kitztech KT-501 Preamp Tests

I purchased and tested a KT-501. There was a report that Kitztech claimed IP3 as +36 dBm. If true that would be a good number for handling of strong signals. Unfortunately I was not able to confirm that number. It appears to me KT-501 is just a lower gain version of the KT-500.

I've attached a series of spectrum analyzer images showing tests results for gain, noise figure and IP3 for VHF and UHF for the KT-501. The images are as follows:

1) VHF Gain
2) UHF Gain
3) VHF NF
4) UHF NF
5) VHF IP3
6) UHF IP3

Here's a summary of the test results for the KT-501 and KT-500. All tests are done with gain set to maximum.

KT-501 / KT-500

VHF Gain - 16 dB / 35.5 dB
UHF Gain - 16.8 dB / 33.5 dB
VHF NF - 1.8 dB / 1.3 dB
UHF NF - 1.9 dB / 1.3 dB
VHF IP3 - +26.2 dBm / +21.6 dBm
UHF IP3 - +26.3 dBm / +21.3 dBm

Those numbers for UHF IP3 on both preamps are some of the lowest I've measured. I can't recommend either of these preamps. The KT-200 is a much better preamp. I measured its IP3 at +30 dBm and the NF is a bit lower.

The best commercial preamp I've measured for IP3 is a 30 dB gain Tinlee MA-25U-77A at +37.5 dBm. The next best is the Clearstream Juice at 35.5 dBm. Both of those numbers are excellent.

The Juice preamp NF is about 1 dB higher than the 500/501 but I think that's a very small price to pay for the much superior strong signal handling. If you have a station that's so weak that 1 dB actually makes any difference then the station won't be anywhere near 100% reception.
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post #16773 of 16779 Old 10-18-2017, 04:31 PM
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Since you're talking about various pre-amps, have you ever found one that would work for me, 3/4 mile from Sutro Tower? I sure could use some gain for the Walnut Grove stations, but all preamps I've tried are overloaded by the strong Sutro signals, so I haven't been able to use one.

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post #16774 of 16779 Old 10-18-2017, 05:14 PM
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Using a High SFDR Preamp in a Strong Signal Location

Quote:
Originally Posted by Larry Kenney View Post
Since you're talking about various pre-amps, have you ever found one that would work for me, 3/4 mile from Sutro Tower?


Larry:

Calaveras did a comparison chart of preamps. What you want is a preamp with a high max input in dBm and a high SFDR (Spurious-Free Dynamic Range).



The Spurious-Free Dynamic range is the difference between the strongest signal and the weakest desired signal plus the minimum SNR of 16 dB for the weakest signal. IOW, from the top of the strongest signal to the bottom of the weakest desired signal.



As a first approximation you can use the dBm figures on your tvfool signal report. For a more accurate calculation, you would need to measure the signals from your antenna with a signal level meter because the strong signals from a close tower are above your location.

If the calculated SFDR for your signals is equal to or less than the listed SFDR for the preamp, you have a chance. If your calculated SFDR is greater than any listed SFDR, you would need to attenuate your strongest signals.

As you can see from Chuck's chart, the medium gain preamps have the best SFDR. The Tin Lee preamp is an excellent preamp. It has a low NF and a lot of gain which is what Chuck needed for his long coax run, but not the best SFDR. It was the ideal preamp for his location.

But, you're not done yet because you have to match your signals to fit the possible SFDR of your preamp.

If your signals are strong (too hot), the strongest signals will start to cause partial overload of a preamp or tuner, and they will create spurious signals from IMD (Intermodulation Distortion) that will raise the noise floor and reduce the SNR of your weakest signals. The weakest signals will be strong enough, but they will be damaged. IOW, the strongest signals are bumping out the top of the SFDR window.

OTOH, if all your signals are a little too weak, the strong signals will not create spurs from IMD, but the weakest signals will be too weak to decode. IOW, they have fallen out the bottom of the SFRD window.

Your task is to match your signals to the SFDR window. You do this by starting with the signals a little too hot and add attenuation to the signals from the antenna.

It might seem counterintuitive to make the weak signals even weaker, but this will improve the SNR of the weak signals because the spurious signals drop three times as fast as the weak signals when you add attenuation. For every one dB of attenuation, the IMD will go down 3 dB, giving you a potential SNR gain of 2 dB.

My local signals are not strong enough to cause IMD, but I have run attenuator simulations at two locations by adding amplification to my local signals. I'm convinced that the method works.

1st example:



2nd example:

Ant > 7777HD #2 > variable attenuator > CM3410 > 7777HD #1 > splitter > TV and signal level meter

The low gain (green LED) setting was used for both CM7777HD/Amplify preamps. The 7777HD #2 preamp made the local signals stronger. The CM3410 handles strong signals with low distortion, so it was used to feed the signals to CM7777HD #1, which was the device under test.






A setting of 8 dB on the attenuator gave the strongest signal with a good SNR. Note that the noise floor dropped 20 dB for a 10 dB change in the attenuator. The noise floor was high from electrical interference, and the sum of the NFs from the preamps in series for the simulation. The strength of the signal varied because the antenna was indoors and the signal had to pass through trees and buildings. Oh, and the weather was bad because of a storm coming up the coast from the south. Not ideal, but the test is still valid; it was the best that I could do at my present location.

The point is, the SFDR of the preamp is fixed at certain maximum and minimum dBm values. You must adjust the dynamic range of your signals to match those values to make full use of the preamp SFDR.
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Last edited by rabbit73; Yesterday at 07:24 AM.
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post #16775 of 16779 Old 10-18-2017, 05:54 PM
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Quote:
Originally Posted by Calaveras View Post
Kitztech KT-501 Preamp Tests

I purchased and tested a KT-501. There was a report that Kitztech claimed IP3 as +36 dBm. If true that would be a good number for handling of strong signals. Unfortunately I was not able to confirm that number. It appears to me KT-501 is just a lower gain version of the KT-500.

I've attached a series of spectrum analyzer images showing tests results for gain, noise figure and IP3 for VHF and UHF for the KT-501. The images are as follows:

1) VHF Gain
2) UHF Gain
3) VHF NF
4) UHF NF
5) VHF IP3
6) UHF IP3

Here's a summary of the test results for the KT-501 and KT-500. All tests are done with gain set to maximum.

KT-501 / KT-500

VHF Gain - 16 dB / 35.5 dB
UHF Gain - 16.8 dB / 33.5 dB
VHF NF - 1.8 dB / 1.3 dB
UHF NF - 1.9 dB / 1.3 dB
VHF IP3 - +26.2 dBm / +21.6 dBm
UHF IP3 - +26.3 dBm / +21.3 dBm

Those numbers for UHF IP3 on both preamps are some of the lowest I've measured. I can't recommend either of these preamps. The KT-200 is a much better preamp. I measured its IP3 at +30 dBm and the NF is a bit lower.

The best commercial preamp I've measured for IP3 is a 30 dB gain Tinlee MA-25U-77A at +37.5 dBm. The next best is the Clearstream Juice at 35.5 dBm. Both of those numbers are excellent.

The Juice preamp NF is about 1 dB higher than the 500/501 but I think that's a very small price to pay for the much superior strong signal handling. If you have a station that's so weak that 1 dB actually makes any difference then the station won't be anywhere near 100% reception.
So the IP3 is the critical factor influencing overload protection from strong signals. The Juice has been reported as one of the best preamps for dealing with strong signals and overload concerns and you seem to confirm those reports. I am going to switch to the Juice amp at a problematic attic installation I am currently dealing with, zip code 29615. I will replace the new CM-Amplify that seems to work well but there appears to be some overload issues, despite the dual gain adjustments. Have you had a chance to test or review the Amplify from Channel Master?
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post #16776 of 16779 Old 10-19-2017, 12:26 AM
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Quote:
Originally Posted by rabbit73 View Post
Larry

Calaveras did a comparison chart of preamps. What you want is a preamp with a high max input in dBm and a great SFDR.
The Spurious Free Dynamic range is the difference between the strongest signal and the weakest desired signal plus the minimum SNR of 16 dB for the weakest signal. IOW, from the top of the strongest signal to the bottom of the weakest desired signal.
I'm going to have to study all of that information and try to make sense out of it to see if there's anything that will work for me.

Thanks for all of the information, Rabbit!

Larry

My complete SF Bay Area DTV Station Lists: http://www.choisser.com/sfonair.html
Lots of Broadcasting links and information: http://www.choisser.com/broadcast.html
Live reception scans from my HD Home Run receivers: http://www.larrykenney.com/hdhr/
Photos and info on my antennas: http://www.larrykenney.com/tvantennas.html
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post #16777 of 16779 Old 10-19-2017, 03:26 AM
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Quote:
Originally Posted by Calaveras View Post
Kitztech KT-501 Preamp Tests

I purchased and tested a KT-501. There was a report that Kitztech claimed IP3 as +36 dBm. If true that would be a good number for handling of strong signals. Unfortunately I was not able to confirm that number. It appears to me KT-501 is just a lower gain version of the KT-500.
<snip>
Here's a summary of the test results for the KT-501 and KT-500. All tests are done with gain set to maximum.

KT-501 / KT-500

VHF Gain - 16 dB / 35.5 dB
UHF Gain - 16.8 dB / 33.5 dB
VHF NF - 1.8 dB / 1.3 dB
UHF NF - 1.9 dB / 1.3 dB
VHF IP3 - +26.2 dBm / +21.6 dBm
UHF IP3 - +26.3 dBm / +21.3 dBm

Those numbers for UHF IP3 on both preamps are some of the lowest I've measured. I can't recommend either of these preamps. The KT-200 is a much better preamp. I measured its IP3 at +30 dBm and the NF is a bit lower.

The best commercial preamp I've measured for IP3 is a 30 dB gain Tinlee MA-25U-77A at +37.5 dBm. The next best is the Clearstream Juice at 35.5 dBm. Both of those numbers are excellent.

The Juice preamp NF is about 1 dB higher than the 500/501 but I think that's a very small price to pay for the much superior strong signal handling. If you have a station that's so weak that 1 dB actually makes any difference then the station won't be anywhere near 100% reception.
Thanks for all the work in testing this out!!! It certainly helps me out in some of my decision-making...especially with the planning of my new antenna system installation at my house...I've got a challenge ahead of me to pull out a 2-edge station.

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post #16778 of 16779 Old 10-19-2017, 07:02 AM
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Quote:
Originally Posted by tylerSC View Post
So the IP3 is the critical factor influencing overload protection from strong signals. The Juice has been reported as one of the best preamps for dealing with strong signals and overload concerns and you seem to confirm those reports. I am going to switch to the Juice amp at a problematic attic installation I am currently dealing with, zip code 29615. I will replace the new CM-Amplify that seems to work well but there appears to be some overload issues, despite the dual gain adjustments. Have you had a chance to test or review the Amplify from Channel Master?
IP3 is number you can compare for each preamp. Gain also is a factor because the higher the gain the easier it is to overload. A high gain preamp needs to have a high IP3 unless all your signals (including out of band signals) are weak. A preamp with high IP3 and low gain like the Juice will be hardest to overload.

I forgot to mention the that CM3410 distribution amp is also an excellent amp with IP3= +34dBm on UHF and 15 dB gain. A CM3410 used as a preamp and a CM3414 distribution amp with up to 100' of coax would be about as overload tolerant as you can get with a good noise figure.

I have not tested the Amplify. Would you like me to test yours when you swap it out? PM me to make arrangements if you do. I purchased the Kitztech amps to run these tests and was disappointed with the results.
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post #16779 of 16779 Old Yesterday, 03:44 PM
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The KEY to receiving a Very Weak Station among a flood of Extremely Strong Stations is to use a Single Channel FILTER [or Inserter plus Single Channel Filter if TWO Weak Channels] (Tin-Lee, Jan Jenca or obsolete C-M JoinTenna) on a High Gain Antenna pointed towards the Desired Weak Station(s) PRIOR to going through a Preamp used ONLY for THAT Weak Single Channel Antenna. [STRONG Signals do NOT go thru Preamp or Distro Amp.] This severely attenuates ALL Channels except the one you want prior to going through the Preamp. [You can also use multiple Single Channel Inserters or a wider bandwidth Adjacent Channel Inserter if that is needed]. You MIGHT also need to ATTENUATE the signal levels from the Antenna receiving the REST of the Channels prior to RF Combiner [SAT type with DC PASS on Port to Preamp]....and furthermore, if you NEED additional help, you might want to ALSO add a SINGLE CHANNEL REJECT FILTER tuned to the Desired Weak Channel on the Full-Band Antenna to further reduce Intermod Noise getting into the Tuner:
Jan Jenca Channel Inserter (Combiner)
http://www.tinlee.com/MATV_headend.p...ILTERSANDTRAPS [Tin-Lee CF7 Single Channel Filter if only ONE Freq]

IF you want MULTIPLE Weak Channels, it's more complicated....and you'll also need one of these for the Second Weak Channel...both PRIOR to Preamp...and Preamp OUTPUT is connected to one port of RF Combiner:
http://www.tinlee.com/MATV_headend.p...IGNALINJECTORS [Tin-Lee AC7 Single Channel Injector]

Last edited by holl_ands; Yesterday at 04:02 PM.
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