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Old 13-Apr-2019, 4:03 PM   #13
Retired A/V Tech
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,738
Originally Posted by bobsgarage View Post
It would also be great to see your updated testing of the LNA 200.

So, how do you test those? Will you be testing for overload and Noise?
Measuring the noise figure of a preamp is not easily done; I don't have the proper equipment to do it accurately. It requires an expensive calibrated noise source. I depend upon the measurements done by Calaveras. The attachment is the result of his preamp measurements.

I can get a rough idea by monitoring the SNR of a weak signal. The preamp that gives the higher SNR of a weak signal should have the lowest NF.

You may have seen my posts about the pc-based Spectrum analyzer that Pete Higgins introduced to these groups. I'm wondering if I can use it to compare the LNA 200 to the KT 200?
A spectrum analyzer can be used to make an overload test by measuring IP3, Third order intercept point, which is what Calaveras does.

The way I make a preamp overload test is to increase the signal input to the preamp until the SNR of a weak signal starts to fall. This is the point when the IMD products from the stronger signals create spurious signals that raise the noise floor to reduce the SNR of the weak signal.
It doesn't surprise me that Winegard overstated the overload and noise figures. Isn't that the same company who came out with their 7 through 69 series of antennas right after we went to 51 channels? Sorry I couldn't resist that!
An antenna manufacturer isn't going redesign an antenna unless they can make a profit doing it.
When I bought my LNA 200 I wasn't a member of this forum yet, otherwise I probably wouldn't have purchased it. I had seen it on Amazon and Solid signal but my local electronics store had one on the shelf for a surprisingly lower price, I think I paid $30 for it. Impulse Buy!
It's an OK preamp, but it isn't as good as their marketing description says it is.
So, staying on topic, if the KT 200 has .4 DB of noise and LNA-200 is somewhere around 2 to 3 DB of noise, wouldn't that help a little?
A preamp with a lower NF should make a marginal weak signal a little more reliable. The tests by Calaveras say:
Kitztech KT-200 NF
VHF 0.6 dB
UHF 1.2 dB
Winegard LNA200 NF
VHF 5.7 dB
UHF 3.0 dB
Attached Images
File Type: jpg Preamp_Summary3S.jpg (362.3 KB, 1015 views)
If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 13-Apr-2019 at 4:06 PM.
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