I checked the specs for the 4815A (in the '73 catalog)
and it doesn't say - the specs for the 4193A regarding
output appears thusly:

  "Test Level: constant current source"

and shows a small chart describing the RF currents used
on each.

Briefly, the max voltage appears to be 1 V RMS for the
100K Z range (given a constant RF I of 10 uA) -

- to 1 mV RMS for a current of 100 uA on the 10 Ohm Z range.

Of course, when measuring the low-level input Z of a
pre-eamp *any* setup of equipment has to be verified
NOT to be driving the pre-amp into non-linear region
of operation ...

I measured the input Z of some popular 2-Meter rigs once
upon a time over 20 years ago using an HP 8405A - and
kept the RF level as low as possible to avoid over-driving
the first RF stage. As I recall - the input match was horrid!

On the order of 10 to 11 dB RL at 146 MHz! (On a Yaesu FT-227
"Memorizer" I think it was.)

Jim

----- Original Message -----
From: "Peter L. Peres" <plp@ACTCOM.CO.IL>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, July 09, 2002 3:46 PM
Subject: Re: [EE]: Directional couplers & T/R test sets


> (Jim?) does anybody know how small a signal can be while the HP4815A still
> reads right ? I.e. can it be used to measure verly low signals (say 10mV
> pk-pk) and give meaningful results ?
>
> Peter
>

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