Re: Tuners and spurious responses

Posted by K9MA on Dec 23, 2018; 3:32am
URL: http://elecraft.85.s1.nabble.com/Tuners-and-spurious-responses-tp7647292p7647340.html

I haven't analyzed them thoroughly, but I can see how a link coupled
tuner could provide more far out rejection both above and below the
operating frequency than an L, T, or Pi.

Link coupled tuners can also, of course, be inherently balanced. I've
never been a fan of using baluns with single-ended tuners to feed
unmatched balanced antennas, because it's just about impossible to build
a practical balun that can cover the whole range of possible impedances.
Open wire can operate with a 10:1 SWR with modest losses, but the
impedance at the tuner could be anywhere from 45 to 4500 Ohms. The
problem with link coupled tuners is that tapped coils are cumbersome and
somewhat dangerous. The differential capacitor in the Johnson Matchbox
was a way around that, but it was expensive and limited the range of the
tuner.

73,
Scott K9MA

On 12/22/2018 21:20, Al Lorona wrote:

> No, not a null, but a rolloff. When I quoted -40 dB I didn't mean a
> notch at one frequency, but the stopband level reached by the time you
> get well into the broadcast band. So that would be -40 dB on all AM
> stations below a certain frequency.
>
> The K3 is a good receiver, but every receiver has its limits and
> certainly the K3 will suffer once an interfering signal gets above a
> certain level.
>
> A trap or stub would work, but my point was that it would be
> unnecessary if using a link-coupled tuner. Attenuating a 50 kW station
> by 40 dB makes it  sound like a 5 W station.
>
> Al  W6LX
>
>
>
>
> >>> That said, is suppose it IS possible that a tuner/antenna combination
> >>> just happened to have a deep null right on the frequency of a nearby
> >>> broadcast station
>
>
>

--
Scott  K9MA

[hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]