Still hoping for some good input. Or maybe everyone's hunkering down waiting for this to blow over? Or maybe everyone stacked up for a smooth transition through some months of turbulence?
Thank you,
Radu.
On Thu, May 8, 2025 at 12:04?PM Radu Bogdan Dicher via groups.io <> <vondicher@... <mailto:[email protected]>> wrote:
Hi all,
This may of particular interest to US members, but I am wondering
how others are handling the effect of tariffs (in particular with
China) on your PCB fabrication needs. Though I should say,
recommendations on reliable, good fabricators is likely information
that everyone could use.
I have two raiser cards I designed (for Fluke
instrumentation/calibrating equipment), and maybe I should just wait
for all this to blow over (assuming it settles somewhere different
than where we are), but I'd rather plan for tough times. I used to
use JLCPCB, but with the additional costs triggered by the tariffs,
I may be looking at about two or three times the cost (rather closer
to the latter than the former), and that just makes is unfeasible to
offer this product. At what hobbyists are willing to pay for
something like this (which, myself being one, I fully understand),
I'd be losing money on each one I'd make.
Are there some good options others have figured out where tariffs
are not quite so onerous?
I looked, for instance, at a place in India, which looks decent
enough and not crazy expensive - though distinctly more expensive
than JLCPCB - but they don't seem to have some of the capabilities I
want, such as beveled card edge and so on. Their features seem to be
about half as many as a place like JLCPCB offers.
There are some places in the US - and OSH Park need not apply, as
these are large and really need volume discounts - but they seem to
be very low tech in terms of getting online quotes (=0 capabilities
for such at what likely is the most affordable ones) and so it's
very hard and time intensive to investigate. But if any of you knows
a good, affordable and reliable place, I'd love to hear about it.
From what I gather, at this point, offshoring this kind of thing is
by far the most affordable and ultimately lucrative option.
particularly at hobbyist level.
With some places that can price me upon uploading my gerbers, I'm a
bit antsy about giving them away. I heard stories where once
uploaded, you essentially are giving away your IP and the design may
pop up in mass production somewhere.
Thank you,
Radu.

Still hoping for some good input. Or maybe everyone's hunkering down waiting for this to blow over? Or maybe everyone stacked up for a smooth transition through some months of turbulence?
Thank you,
Radu.

On Thu, May 8, 2025 at 12:04?PM Radu Bogdan Dicher via groups.io <> <vondicher@...> wrote:

Hi all,
This may of particular interest to US members, but I am wondering
how others are handling the effect of tariffs (in particular with
China) on your PCB fabrication needs. Though I should say,
recommendations on reliable, good fabricators is likely
information that everyone could use.
I have two raiser cards I designed (for Fluke
instrumentation/calibrating equipment), and maybe I should just
wait for all this to blow over (assuming it settles somewhere
different than where we are), but I'd rather plan for tough times.
I used to use JLCPCB, but with the additional costs triggered by
the tariffs, I may be looking at about two or three times the cost
(rather closer to the latter than the former), and that just makes
is unfeasible to offer this product. At what hobbyists are willing
to pay for something like this (which, myself being one, I fully
understand), I'd be losing money on each one I'd make.
Are there some good options others have figured out where tariffs
are not quite so onerous?
I looked, for instance, at a place in India, which looks decent
enough and not crazy expensive - though distinctly more expensive
than JLCPCB - but they don't seem to have some of the capabilities
I want, such as beveled card edge and so on. Their features seem
to be about half as many as a place like JLCPCB offers.
There are some places in the US - and OSH Park need not apply, as
these are large and really need volume discounts - but they seem
to be very low tech in terms of getting online quotes (=0
capabilities for such at what likely is the most affordable ones)
and so it's very hard and time intensive to investigate. But if
any of you knows a good, affordable and reliable place, I'd love
to hear about it. From what I gather, at this point, offshoring
this kind of thing is by far the most affordable and ultimately
lucrative option. particularly at hobbyist level.
With some places that can price me upon uploading my gerbers, I'm
a bit antsy about giving them away. I heard stories where once
uploaded, you essentially are giving away your IP and the design
may pop up in mass production somewhere.
Thank you,
Radu.

What would you use a scalar analyser for these days?
The only place I've seen them still in use in recent years is older microwave antenna measurement ranges. Those were old existing facilities.

?

Robert.

On 10 May 2025, at 10:53, Patricio A. Greco via groups.io <patricio_greco@...> wrote:

?I use 3458A to measure Vrf and a very good tracked 34401a for Vref and I have good results. I check que bridge with calibrator each two or three years. That’s all! There are no news.?

Ing. Patricio A. Greco
Taller Aeronáutico de Reparación 1B-349
Organización de Mantenimiento Aeronáutico de la Defensa OMAD-001
Gral. Martín Rodríguez 2159
San Miguel (1663)
Buenos Aires
T:?+5411-4455-2557
F:?+5411-4032-0072

On 10 May 2025, at 10:11, jmr via groups.io <jmrhzu@...> wrote:

?

I also had another look at the block diagram of the Tegam 1830A in application note 217. I've amended it to suit operation with the 478A sensor as this sensor has one end grounded. So parts of the Tegam circuit aren't needed here. See the diagram below.

?

Assuming I understand it correctly, I think the bridge balances when the voltage across 200R resistor Rref (circled in pink) is the same as the voltage measured at S+ (circled in sky blue).

?

I think it relies on being able to measure the 200R resistance of Rref to better than 0.1% accuracy and the two differential amplifiers need to be able to measure all the relevant voltages with any offsets correctly trimmed out. These offsets have to be correctly trimmed for the case when RF is off and when it is on and it needs to be able to do this over the full 30mW input power range where the voltages will change quite a bit between RF off and RF on.

?

It also has to measure the temperature compensation bridge in a similar way but I guess the offset issue is less critical here as long as it is stable. However, any tens of uV drift measured by the system should be due to the thermistor temperature changes and not due to the summing of offset drifts in any of the four differential amplifiers when operating in compensated mode.

?

I don't have much experience designing precision instrumentation/differential amplifiers but the gain of each amplifier will also have to be precisely defined (using precision resistors?) and all offsets carefully managed. The accuracy of the ADC used to measure these voltages needs to be managed and any non-linearity issues across the ADC range must be correctly managed.

?

I think this is why the Tegam manual shows various offsets and gain calibration constants. Maybe this stuff is trivial to manage with modern amplifiers and components but there seems to be an awful lot of things to manage here.

?

By contrast, if I look at the HP 432A system, once the mount resistance is measured using a 4 wire bench DMM to <= 0.1% accuracy, the DC substitution is all about how good the external DVM is. Obviously, the mismatch uncertainty and sensor efficiency are also important but these factors affects both the 432A and Tegam meters equally.

?

A decent external 6.5 digit DVM should be good enough for most 432A users but Keysight seem to recommend using a $$$ 3458A 8.5 digit DVM for the N432A. Maybe this has the required linearity and accuracy to get the most out of the system? I don't see how the Tegam meter can compete here, but maybe I'm missing something. Either way, any differences are likely to be so tiny that only places like NIST and maybe Keysight need to be concerned about this.

?

I would choose the N432A over the Tegam meter for various reasons, even if the accuracy is the same or regardless if one is ever so slightly better than the other. But then again, I think I prefer the HP 432A for home use because it just needs a decent 6.5 digit DVM to operate it with DC substitution. No ned to return it for an annual calibration :)

?

?

<tegam_block.gif>

On 10 May 2025, at 10:11, jmr via groups.io <jmrhzu@...> wrote:

?

I also had another look at the block diagram of the Tegam 1830A in application note 217. I've amended it to suit operation with the 478A sensor as this sensor has one end grounded. So parts of the Tegam circuit aren't needed here. See the diagram below.

?

Assuming I understand it correctly, I think the bridge balances when the voltage across 200R resistor Rref (circled in pink) is the same as the voltage measured at S+ (circled in sky blue).

?

I think it relies on being able to measure the 200R resistance of Rref to better than 0.1% accuracy and the two differential amplifiers need to be able to measure all the relevant voltages with any offsets correctly trimmed out. These offsets have to be correctly trimmed for the case when RF is off and when it is on and it needs to be able to do this over the full 30mW input power range where the voltages will change quite a bit between RF off and RF on.

?

It also has to measure the temperature compensation bridge in a similar way but I guess the offset issue is less critical here as long as it is stable. However, any tens of uV drift measured by the system should be due to the thermistor temperature changes and not due to the summing of offset drifts in any of the four differential amplifiers when operating in compensated mode.

?

I don't have much experience designing precision instrumentation/differential amplifiers but the gain of each amplifier will also have to be precisely defined (using precision resistors?) and all offsets carefully managed. The accuracy of the ADC used to measure these voltages needs to be managed and any non-linearity issues across the ADC range must be correctly managed.

?

I think this is why the Tegam manual shows various offsets and gain calibration constants. Maybe this stuff is trivial to manage with modern amplifiers and components but there seems to be an awful lot of things to manage here.

?

By contrast, if I look at the HP 432A system, once the mount resistance is measured using a 4 wire bench DMM to <= 0.1% accuracy, the DC substitution is all about how good the external DVM is. Obviously, the mismatch uncertainty and sensor efficiency are also important but these factors affects both the 432A and Tegam meters equally.

?

A decent external 6.5 digit DVM should be good enough for most 432A users but Keysight seem to recommend using a $$$ 3458A 8.5 digit DVM for the N432A. Maybe this has the required linearity and accuracy to get the most out of the system? I don't see how the Tegam meter can compete here, but maybe I'm missing something. Either way, any differences are likely to be so tiny that only places like NIST and maybe Keysight need to be concerned about this.

?

I would choose the N432A over the Tegam meter for various reasons, even if the accuracy is the same or regardless if one is ever so slightly better than the other. But then again, I think I prefer the HP 432A for home use because it just needs a decent 6.5 digit DVM to operate it with DC substitution. No ned to return it for an annual calibration :)

?

?

<tegam_block.gif>