[Elecraft] low pass filters

[W2xj]

OTA TV is growing rapidly which is why cable companies are hurting. I’ve been exclusively OTA for over 10 years. Also, with the repack a number of stations are being moved back to VHF. 

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On Feb 18, 2019, at 11:41 PM, K9MA <k9ma at sdellington.us> wrote:

>> On Sun, Feb 17, 2019 at 4:26 PM Don Wilhelm<donwilh at embarqmail.com>  wrote:
>> 
>> 
>> Low pass filters come from a past era when the FCC requirements were not
>> as stringent and TVs responded to those higher order harmonics from
>> amateur transmitters.  That is no longer the case.
> 
> Here, Don is talking about external low pass filters intended to suppress VHF harmonics. If you live in an area where TV signals are weak, they may still be necessary. Of course, hardly anyone receives their TV service that way any more, and most TV stations have moved to the UHF bands, anyway.
> 
> The low pass filters in solid state radios and amplifiers are necessary because their outputs are untuned, and the nonlinearity of transistors generates lots of harmonics, including low order ones. In the days of vacuum tubes, the pi network served as an effective filter. The popular pi-L was even better.
> 
> It might be interesting, during a major contest, to listen on the second harmonic, say around 14.120 when there's a lot of activity on 40. Many are using solid state amplifiers now, and even 43 dB down may be audible.  I've never positively identified one, but a lot of stations don't come back to me for other reasons, so it would be hard to tell.
> 
> 
> 73,
> 
> Scott K9MA
> 
> -- 
> Scott  K9MA
> 
> k9ma at sdellington.us
> 
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