Originally Posted by jmm83
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.
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: