Need help designing attenuator pad to help signal tracing anHW-12A

[w6cux@earthlink.net]

Bernie
Your math is correct. However, I don't think your approach is practical.
The leakage through the case of the generator, down the power line and
around the attenuator would defeat any attempt at precision. RF generators
made for this kind of measurements include lots of internal shielding and
filtering to assure that a known level of signal appears at the output jack.
And they cost a lot of money.

If you decide to proceed anyway, you should make the attenuators as
several 20 db pads and series them to get the 60 or 80 db. An ARRL
handbook of the 70's have a good design.

73, Stu W6CUX

> [Original Message]
> From: VE3FWF <ve3fwf at SYMPATICO.CA>
> To: <HEATH at LISTSERV.TEMPE.GOV>
> Date: 10/3/2004 4:58:44 PM
> Subject: Need help designing attenuator pad to help signal tracing
anHW-12A
>
> The HW-12A that I purchased a while ago needs some signal tracing to find
> out why there is significant sensitivity loss in the receiver. The S meter
> reads S-1 on signals that should be many db over S-9. All resistance
checks
> and static DC voltages seem OK. I did find a bad tube socket and that has
> now been replaced. I suspect the problem is in the first or second IF
stage.
>
> According to the Heathkit manual,  I need to inject  2305 KHz at 15000 uV
at
> test point R2, 1500 uV at test point R3 and 50 uV at test point R4 with an
> impedance of 50 Ohms.  My old Heatkit signal generator is a rather
primitive
> device and is not calibrated.
>
> My thought was to calibrate my signal generator with my scope at the 1.5
> volt level and then build an attenuator pad to reduce the generator signal
> voltage level to the required level for testing.
>
> 15000 uV is  1.5 x 10**(-3) volts or a reduction of 1000   or db = 20 log
> (1000/1)   = 60 db
> 1500   uV is  1.5 x 10**(-4) volts or a reduction of 10000 or db = 20 log
> (10000/1) = 80 db
>
> If some EE type of this list could verify the above calculations, that
would
> be great.  Based on the above
> calculations (if they are correct)  I would need to build a 60 and 80 db
pad
> with a 50 ohm input and output impedance for test points R2 and R3.
>
> I've browsed with Google but have not found anything too useful on this
> topic.  If anyone could point me to a good reference on the design of a 50
> ohm to 50 ohm attenuator pads, it would be greatly appreciated. If anyone
in
> the Ottawa area has a calibrated signal generator that I could borrow,
that
> would even be better.
>
> 73, de Bernie, VE3FWF, Ottawa, Canada.
>

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