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Old 11-Sep-2013, 11:54 PM   #6
Pete Higgins
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Join Date: Apr 2013
Location: California, 58 miles @112 degrees from Mt. Wilson
Posts: 83
Re: Lna-200

tripelo,

Thanks for your input.

I downloaded the data sheet for Q2, the Avago ATF-54143 and sure enough their data sheet says the 4F I read is the device code for that part. The date code character must have been too small for either my wife or I to read. You probably are also right about Q3’s function as well since their data sheet shows a schematic for an example active biasing ckt. and says “Active biasing provides a means of keeping the quiescent bias point constant over temperature and constant over lot to lot variations in device dc performance.”, both of which would be essential in a production design intended for outdoor use.

I thought at first Winegard might be advertising the UHF amplifying device NF instead of the overall amplifiers NF but the ATF-54143 data sheet lists a 0.5 dB overall noise figure for the device and depending on drain-to-source voltage and current less than half that across the UHF TV band, so that’s not it. Also, in his less than pristine environment, ADTech found a 2.8 dB average NF on UHF for the LNA-200 which is slightly worse than the 2.6 dB he found for the RCA TVPRAMP1R he tested. Do you think his environment could be contributing a noise floor or NF threshold?

Avago’s data sheet also says that “The device can handle +20 dBm RF Input Power provided IGS is limited to 2 mA”. I’m not quite sure how to interpolate that number in terms of Winegards advertised “Maximum Total Input (microvolts)” of “2,024,789” which in a 75 ohm system, I calculated to be a signal level of about +17.38 dBm unless they are being a little conservative with this rating (~˝ the power ?). And, given both of those numbers, I don’t understand why I was seeing what appeared to be overload. I assumed that overload was creating spurious responses that raised the noise floor above my channel 31 (5.1-.3) MDS signal level. That was definitely a characteristic of the LNA-200 when hooked to two different antennas because in both cases when I replaced it with one of the RCA’s I got the channel back. I don’t think it was the gain differential because when I was using the +15 dB PCT MA2-M’s I always got channel 31.

About the only thing I think I do understand is getting my local TV station with the antenna pointed to San Diego. The RCA’s are shielded and the Winegards are not.
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