Re: Don't run QCX at 19V


Arv Evans <arvid.evans@...>
 

Popular idea seems to be that a lower frequency scope is not useful for
measuring HF signals.  This is true for unmodulated signals, but not true
if the signal is modulated and the audio scope is equipped with an RF
detector probe.  If modulation is at or near 100 percent the detected
RF at AF frequency is a fairly good way to trace signal levels and to
determine if the signal is present or missing.  It is not perfect, but if
the alternative is no measurement, it can be helpful.

It is also possible to build a "chopper" circuit that converts HF/RF into
lower frequency AF or MF and then measure that on a lower frequency
scope.

Of course, just a diode detector and a VOM is also very useful when
tracing RF signals.  It is more an issue of operator understanding than
of instrument requirements.

Arv
_._


On Tue, Jun 15, 2021 at 12:55 PM Yury Krasouski <krasoffski@...> wrote:

On Tue, Jun 15, 2021 at 07:10 PM, VK5EEE wrote:

I don't have an oscilloscope but definitely must order one of those low cost basic ones Hans demonstrated in his alignment video.

Lou, scope from Hans' video is good only for tracing audio signal but does not allow to measure power output from PA or Vpp on BS170 drains. I would recommend to look at something like FNIRSI 1C15, Hantek 2C72 or smth with price around $55-$75.

This is VERY compromise devices and from my perspective. E.g. for FNIRSI 1C15 working frequency is about 7-10MHz despite spec value 100Mhz.

But for debugging PA it is enough built-in RF PWR meter. Pa calculated like Pa = Vrms/50, where Vrms = Vamplitude * 0.7071 ( I know that PA out is no a sine-wave)

Thus, from internal PWR meter you might get some amplitude value for PA bs170 drains.

From my IMO I would buy Hantek DSO2C10 or RIGOL DS1102z.

BWY, I would like, than Hans add ability to show measured voltage used for PWR calculation.

P.S. Also you can build RF Probe for digital multi-meter like https://www.hamshop.cz/data/items/169_39.pdf I used probe like this for power measurement before.

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