[ARC5] A simple receiver improvement

[Ian Wilson]

Ken,

In principle you could just use an L-network or something to couple more
energy
from the antenna to the tuned circuit of the first RF stage. However ..
this will
reduce the selectivity of that tuned circuit, so you may run into
diminishing
returns.

73, ian K3IMW



On Tue, Jan 14, 2014 at 12:50 PM, Kenneth G. Gordon <
kgordon2006 at frontier.com> wrote:

> On 14 Jan 2014 at 12:15, Ian Wilson wrote:
>
> > A couple of schematics - sorry, didn't have time to check for the R-26
> > specifically - show values for C1 of 8.5pF and 11pF. At 3.5MHz, 11pF
> > looks like 4.1k of reactance.
>
> Now, this makes me wonder if one couldn't build a 4K:50 ohm balun fairly
> easily, and what improvement that would make.
>
> What would this be? An 80:1 balun? Or a 40:1? I can't remember how that
> works.
>
> It certainly shouldn't be all that difficult to make one for each range,
> since the
> receivers are relatively narrow banded, covering only one "band".
>
> Perhaps the right kind of toroid and some few turns of small wire?
>
> If I remember correctly, it would be something like 2 turns on the primary
> and
> 40 turns on the secondary...maybe?
>
> I guess I'll go dig out my documentation...
>
> To get some sort of idea about this, I could connect the 300 ohm sides of 4
> of the baluns in series to the receiver input terminals, and use one of
> the 75
> ohm inputs to connect to my antenna to see if there was any improvement.
>
> That would be an "interesting exercise" at least.
>
> However, last night, even with the 300:75 ohm balun, in many cases (like
> for
> 5.0 MHz WWV) I could not turn the RF gain down far enough to silence the
> receiver. Even with the RF gain as low as it would go, WWV was still
> copyable from the speaker.
>
> Perhaps a 4K:50 ohm balun would be very serious "over-kill".
>
> Ken W7EKB
>