[Elecraft] Gain calibration

Wed Oct 30 16:51:00 2002

A signal source, like a crystal oscillator, can be battery operated inside a
metal case to  essentially eliminate stray radiation.  The signal can start
out at an amplitude large enough to be measured by a scope for calibration
purposes (a volt or so) and then accurately attenuated so we know the
amplitude of the signal at the input to the rx.  The attenuator also creates
an accurate 50 ohm source impedance.  The same box can include a noise
generator too for filter tests.

Even if the rx input impedance isn't exactly 50 ohms, the overall gain will
still indicate the performance when it's driven by a 50 ohm source.  The
input filter and mixer loss can be measured by increasing the input signal
amplitude enough to use a scope for measurements in the early stages. 100mv
is okay for the first stages when the preamp is turned off.

Then the  amplitude can be reduced to the millivolt range for measurements
in subsequent stages.

A fairly simple addition (NE555) to the signal source is a circuit to turn
it on and off a few times a second. This would allow measurement of the
transient responses of the various filters (for example, ringing and
settling time).  The AGC circuit can be evaluated if the signal is switched
on and off very slowly.

Bob - AG5Q

=========================================================

----- Original Message -----
From: "Don Brown" <[email protected]>
To: "Paul Jensen" <[email protected]>; "Elecraft" <[email protected]>
Sent: Wednesday, October 30, 2002 10:24 AM
Subject: Re: [Elecraft] Re:New Crystals or Not

Hi

A generator to supply 1 microvolt is fairly difficult to design. It is very
hard to keep the signal confined in the generator. The small amount of
leakage can be higher than the desired signal. It's not imposable, it's just
not easy to come up with something with the proper shielding in a kit form.
There is also the problem of calibrating the signal.

Don Brown
KD5NDB

----- Original Message -----
From: Paul Jensen
Sent: Wednesday, October 30, 2002 9:42 AM
To: [email protected]
Subject: RE: [Elecraft] Re:New Crystals or Not

<SNIP>

A simple test might be have a small pc board with a calibrated 1 microvolt
rf signal hooked up to the K2 antenna input.  Turn AGC off, set rf gain to
max, and set volume control to a specific resistance.  The voltage on the
speaker measured with a DVM could be used to calculate the total gain for
the
receiver.

Perhaps this rf signal board could be a kit like the noise generator
board :)  Then we could all post our results and see if our K2 is up to
snuff.

Paul Jensen
AD5IW

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