Using a standard 10:1 CRO probe connected via a high voltage DC
Block (min 200V) to the 50 ohm SA input will present Low C / Hi Z to
the DUT and also gives about 60dB attenuation to the SA input. Handy
around tube and FET circuits.
A DC Block is just a capacitor in series with the centre conductor
of the adaptor. You can get them in SMA, BNC, N, etc.
Be careful to check the specs of the DC Block, a lot of those on
Ebay, etc are only around 25-50V.
HTH...Bob VK2ZRE
On 19/05/2025 11:45 pm, Mike EI9FEB
wrote:
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As soon as I got my S/H HP141T SA years ago I made a noise
source using a zener diode, high pass filter and MAR6 wide band
amp on stripboard.
I've not tried it yet with IFTs and the TinySA basic, or my
Rigol SA, but it has advantages over a tracking generator as it
can be used at RF in of radio and connect IFT out to SA. Note
some kinds of IFTs, especially on valve (tube) gear would be
detuned and Q reduced by load of the SA. You need a remote FET
buffer (I use J310 because I have them).
I had a wobbulator and the noise source plus SA was far
superior. You can use a tracking generator if driving a filter
direct, but again you may need a buffer (output to simulate
normal driving device) or be misled.
Even changing the mixer or amp device with a different part may
need the IFT to be retuned (i.e. swap 1L6 to a DK92), so unless
it's SAW, ceramic or crystal IF (easy to have a passive match on
input and output) tuning or examining an IFT directly with any
test gear is fraught with pit-falls, especially other than a
secondary to a bipolar transistor.
