[ARC5] Visual alignment of BC-454

[Ian Wilson]

Hi Ken,

I worked out your picture numbering scheme and looked at
the new pic. That looks much more reasonable.

As far as coupling into an IF chain I would use a 5pF capacitor
in series with the scope probe. That may have too much hum
pickup if your RF levels are very low, though.

Last time I played with swept analyzers I was interested in
looking at crystal filters. For these you really need a sampling
scope or something, the rep rate becomes so low. Nevertheless
this failed to stop me from picking up a 1DP7 (I think) on eBay
a few weeks back (has a long persistence phosphor).

Very interesting work on the IFs, regeneration, etc. At last
there will be something more quantitative than "wide as a
barn door".

73, ian K3IMW



On Thu, May 23, 2013 at 1:01 PM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 23 May 2013 at 9:21, Ian Wilson wrote:
>
> > Hi Ken,
> >
> > You will see the envelope if you are looking at the output of
> > an AM detector.
>
> I tried that Ian, and got nothing but a big blob. I still can't figure out
> why that
> didn't work. I only got what I have been expecting after I began to use
> one of
> my Heathkit RF probes to connect to the X-axis input.
>
> > If you are looking at the IF then you should see
> > a symmetrical, "filled-in" display.
>
> I don't quite follow you here, Ian. What sort of probe or connection to the
> o'scope X-axis would I use? A straight 11 meg resistor-probe?
>
> > If you have an asymmetric
> > display with fill-in then you are probably looking at the output
> > of a not very linear detector with inadequate filtering :)
>
> Indeed...or an off-center signal generator....or both.
>
> >
> > If you can access the Z axis then you can blank the retrace
> > and clean up the display significantly.
>
> I can access the "Z" axis all right, but I have always presumed that if the
> ramp generator had an infinitely-fast return-to-zero, "Z" axis access
> wouldn't
> be necessary.
>
> > You will still have to wait
> > for the transient response to die away before starting a new sweep.
>
> Yes. That has been clear since the beginning of this experiment.
>
> > It
> > is very easy to do experiments like this if you are messing around
> > with PICs or whatever. It is somewhat more challenging if you are
> > doing this the fun way with 555's, etc.
>
> Yes. From my reading, 555s as ramp generators leave a lot to be desired.
> They need a near-perfect current source instead of a resistor in the RC
> circuit for one thing. And their power output is low.
>
> Well, I am going to continue to play with this setup as it now is in order
> to
> figure out how to get the most out of it.
>
> Have you yet had a chance to look at my latest photo?
>
> Ken W7EKB
>