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post #121 of 127 Old 10-30-2018, 10:56 PM
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Quote:
Originally Posted by rabbit73 View Post
Thank you for the current measurement. It's much lower than mine.

I measured my RCA TVPRAMP1R Preamp again. I got different readings than when it as new, and used two meters as a double check. I don't trust it now.
oh that's strange i guess there must be something wrong with most of the power supplys that they shipped with the amplifiers

does your amp seem to be working though?



RCA did email me back and the guy asked for my address & said he will see if there is anything he can do for me but he said he can't make any promises
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post #122 of 127 Old 11-02-2018, 03:52 PM
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TWO Defective RCA TVPRAMP1 Preamps

Quote:
Originally Posted by jmm83 View Post
oh that's strange i guess there must be something wrong with most of the power supplys that they shipped with the amplifiers

does your amp seem to be working though?
Ah, no.

My first RCA TVPRAMP1Z preamp had these measurements:
Voltage out of power inserter without preamp: 19.5 VDC
Voltage with preamp connected: 9.5 VDC
Load current: 70 mADC
Gain 23 db

I thought it was strange that the voltage out with no load was so high because the power inserter contains a voltage regulator, but it worked.




Recent measurements of first TVPRAMP1Z:
No load voltage: 13.5 VDC
Voltage under load: 7.37 VDC
Load current: 18 mADC
Gain: 0 dB; Uh-Oh! Then, when I checked again, there is gain. Intermittent from a cold solder joint?

Second (new) TVPRAMP1E measurements (note the "E" instead of "Z" or "R" at the end of the model number, supposedly for a change in packaging. You see a simulated American flag with only 5 stars and IN THE USA on the box and think that it is Made in America. If you look again, you see Designed and Engineered IN THE USA on the front panel and MADE IN CHINA on the end panel.):
No load voltage: 9.11 VDC
Voltage to preamp under load: 9.11 VDC
Load current: 75 mADC

well, that looked good so far, but
Gain: 5 dB; not so good

I thought there was something wrong with my signal level meter, so I substituted a CM7777HD at low gain:
Gain: 17 dB; right where it should be.

My meter is OK, the RCA preamp isn't OK.

Nice box. Too bad the quality control for the preamp isn't up to the same standard.
The seals on both boxes were intact when received, indicating they were new, not returns

I can not recommend the RCA TVPRAMP1 preamp.
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If you can not measure it, you can not improve it.
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Last edited by rabbit73; 11-03-2018 at 04:10 PM.
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post #123 of 127 Old 11-08-2018, 12:41 AM
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Oh that's not Good

I'll let you know what mine is when i get it
what kind signal level meter do you use? and how do you hook it to the booster?
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post #124 of 127 Old 11-08-2018, 07:13 PM
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Quote:
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Oh that's not Good

I'll let you know what mine is when i get it
what kind signal level meter do you use? and how do you hook it to the booster?
I use a Sadelco 719E and a Sadelco DisplayMax 800. The 719E is designed for measuring analog TV signals, but can be used for measuring digital TV signals with a correction factor, and the 800 is designed for measuring analog and digital TV signals.



I pick a fairly strong stable LOS signal and measure it without the preamp:

Antenna > coax > F-81 adapter > short coax > signal level meter

I then substitute the preamp for the F-81:

Antenna > coax > preamp > short coax > power inserter > short coax > signal level meter

The difference between the two meter readings is the preamp gain.

OTA signals constantly vary in strength, so I have to do it a few times to get consistent readings.

As a test, I used a Channel Master 7777HD preamp at the low gain setting of 17 dB. It's a nice amp for indoor tests, but I don't like the housing design for outdoor use. The connectors need to be on the bottom of an enclosure for weather protection, and a mast clamp would have been better than plastic zip ties.



Channel 31

719E without preamp: -5 dBmV
719E with preamp: +11.5 dBmV
Difference: 16.5 dB

800 without preamp: -3.5 dBmV
800 with preamp: +13.3 dBmV
Difference: 16.8 dB

Used Sadelco meters can be found on eBay. The last 719E I found (used for above test) was in good condition and cost $75 including shipping. I don't bid any more than I am willing to lose if returns aren't allowed.

For a more accurate measurement of preamp gain, I use the video carrier from an analog modulator as a signal source for a stable signal.

Blonder Tongue HAVM Modulator with fixed attenuator on output set for analog channel 32:

Modulator without preamp: 9.9 dBmV
Modulator and preamp: 26.9 dBmV
Difference: 17 dB

It is possible to measure preamp gain without a signal level meter. The technique uses the dropout point of a TV tuner, which is about -84 dBm. All you need is a variable attenuator and a few inexpensive fixed attenuators. Calaveras has described a similar technique that uses the dropout point to determine SNR; see this post by him:
http://01966633.com/forum/25-hd...l#post24727115
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Last edited by rabbit73; 11-11-2018 at 09:37 AM.
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post #125 of 127 Old 11-09-2018, 09:17 AM
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Measuring Preamp Gain Without a Signal Level Meter Using Tuner Dropout



The gain of a preamp can be measured without a signal level meter if a few precautions are observed.
The preamp must be close to the tuner. If it is up near the antenna, you will be able to measure a difference between with and without, but it probably will not be the preamp gain.

As above, use a fairly strong stable LOS signal. Weak 2Edge signals will give misleading results. The tuner noise figure can be ignored because it will be the same for both measurements. The preamp noise figure can be ignored because it is well below the test signal, and it will be attenuated when the signal is attenuated.

Antenna > coax > F-81 > short coax > variable attenuator > short coax > tuner

Channel 31

Attenuation required for dropout without preamp: 28 dB
consisting of 20 dB fixed plus 2-1/8 counter clockwise turns of ATT-1 attenuator (8 dB)

This also means that if the signal is 28 dB above dropout, its strength at the tuner input before attenuation is
-84 dBm + 28 dB = -56 dBm



Antenna > coax > preamp > short coax > power inserter > short coax > variable attenuator > short coax > tuner

Attenuation required for dropout with preamp: 45 dB
consisting of 40 dB (two 20s) fixed plus 1-1/2 counter clockwise turns of ATT-1 attenuator (5 dB)

Preamp gain = 45 - 28 = 17 dB

The CM 7777HD preamp that I used has the preamp and power inserter combined when fed power into the DC connector on the preamp housing. I like the CM 7777HD for use as an instrumentation amp, but I don't like the housing for outdoor use. The connectors need to be on the bottom of an enclosure for weather protection.

Although it wasn't necessary for the test, I split the signal after the power inserter to feed a signal level meter and the tuner to see the dropout point:

-18.1 dBmV - 17 dB meter amp - 49 dB convert = -84.1 dBm

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www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 11-11-2018 at 08:30 AM.
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post #126 of 127 Old 11-10-2018, 02:17 PM
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I'm Getting 9.04 With no Load and 8.98 With a Load on it & 62.8 MA

It Did not seem to make any difference in reception or in signal strength
I Guess Most of these amps Must have a problem with them

i will be sending it back
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post #127 of 127 Old 11-10-2018, 03:48 PM
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Thank you for the report.

Quote:
Originally Posted by jmm83 View Post
I'm Getting 9.04 With no Load and 8.98 With a Load on it & 62.8 MA
That seems within normal limits.
Quote:
It Did not seem to make any difference in reception
Once the signal is strong enough for good reception, you probably will not notice any difference in reception with an even stronger signal.
Quote:
or in signal strength
That would require an accurate measurement.
Quote:
I Guess Most of these amps Must have a problem with them

i will be sending it back
I understand your feeling. Some users like their RCA preamp, but I certainly don't have confidence in the RCA TVPRAMP1 now.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
www.megalithia.com/elect/aerialsite/dttpoorman.html

Last edited by rabbit73; 11-11-2018 at 08:04 AM.
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