Gerhard Hoffmann wrote:
Am 29.11.2014 um 20:01 schrieb Gerhard Hoffmann:
Am 29.11.2014 um 19:08 schrieb Thomas S. Knutsen:
2014-11-29 16:24 GMT+01:00 Dave M <dgmin...@mediacombb.net>:
Yeah, that's a good way to completely avoid the issue. Since I'm
the only
target audience for my efforts, then I don't mind the extra
components. I'm beginning to realize, as I get deeper into building
my own stuff, that
a VNA is quite a desireable piece of equipment. Unfortunately, I'll
have
to make use of my spectrum analyzer and RLC meters instead.
Ok, I volunteer to measure the S21 of a dc-force-fed T1-1 or T4-1
next weekend, when
I'm back home. (DG8SAQ VNWA and / or W&G TSA-2)
Really, on osc, a voltmeter and a DC source are enough.
Here it is: Mini circuits T1-1T, new very old stock, still in black
case, not
one of the new whitish ones that turn brown in the week after
soldering.
0 / 25 / 50 / 100 mA on the secondary side from Agilent 6633B dc
supply. It is nice that you can directly type in the voltages or currents.
But you better do not take this thing for anything that is sensitive
to noise.
DG8SAQ VNWA, my best DC block from PSPL because it also has the
lowest lower corner. It took some experimenting to find a choke that
would not modify S21 and carry the current. Finally: a medium size
red Amidon core & two 220uH Siemens chokes with a looong air gap.
<
https://picasaweb.google.com/103357048842463945642/Tronix?authuser=0&feat=directlink
The low frequency corner suffers already at 25 mA. The high frequency
side is unimpressed by the current. Just what one expects from a
transmission line
transformer that gets ferrite as an anabolicum for the low
frequencies.
The transformer survived 1A for a short time and did not seem to
suffer from that abuse s-parameter-wise.
regards, Gerhard
Many thanks for the graphs, Gerhard. I suspected that the low end would be
the first to suffer, but didn't know how much. Those curves explain the
reason for the 30ma limit; it's to keep the devices' specs definable. With
a higher limit, the insertion loss specs would be terrible, and nobody would
buy them.
The text on the screen shots is a bit hard to read, but I think the curves
told me what I wanted to know..As with most other devices, it's best to stay
away from the Max figures on the datasheet.
Thanks for taking the trouble to make the measurements and share the
results.
Dave M
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