开云体育

tried this today and it did not fix it.

If you own or still use the ol HP 65/67/41C series RPN machines, I have a copy of Medleys microwave routines text.
Routines include analysis and synthesis of networks driven by S data.

If interested, reply offline direct. TNX...

73' Alan W4AMV

For me too
Opens fine
Dg9bfc sigi

Am 11.11.2022 12:57 schrieb "Max via groups.io" <kg4pid@...>:

Power MOSFETS are specified in terms of max Rdson. At high frequencies one must also include the drain/source capacitance as well as gate-drain and gate-source capacitances. Spice models typically include those capacitance parameters so an AC simulation at the frequency of interest should shed light on the performance as a “switch”.

-CT

On Thu, Nov 10, 2022 at 07:53 AM, Manfred Mornhinweg wrote:

Elecraft went another path, and used an RF oscillator to generate the high
voltage needed to bias 1N4007 and 1N5408 diodes pressed into PIN diode
service.

Is this saying that they use 1N4007/5408 as PIN? If so, any details?

It opens fine for me.
Max

On Thu, Nov 10, 2022 at 11:36 PM, Michael wrote:
Michael -

Found this a long time ago and not sure if this will be useful to anybody. See
attached.

Your "cross_ref_list.pdf" sort of opens - appears blank and closes immediately.
--
Doug, K8RFT

What is needed is some kind of NTE/ECG/SK catalog for most of the makers/seller of core material. Found this a long time ago and not sure if this will be useful to anybody. See attached.

Also, is there an SDK-ish docs on interfacing with the Nano? I was a fair programmer and I am learning to use my Nano better or at least trying to.

Michael

On 11/10/22 5:53 AM, Manfred Mornhinweg wrote:

Jim, yes, ready-made DC-DC converters are inexpensive these days, and are a good option in many applications. But for RF switching, I don't see the one you linked as very usable. 15V is definitely not enough reverse bias in any solid-state RF switch that has to handle the typical power used by hams, exccept with some types of true PIN diodes. Also the DC isolation provided by these converters is rarely required in RF switches. RF isolation is indeed required, but these ready-made converters don't provide it, having 20pF of capacitance between input and output. So the RF isolation has to be provided by means of RF chokes and/or high value resistors, in any case.

You can stack them for higher voltages. The DC isolation lets you do that.
Yeah, filtering for a specific application would be application specific.

As for RFI from voltage converters, I love to run mine at a very low frequency, such as 1kHz, taking advantage of the fact that only very low power is needed for reverse biasing RF switches. So even at that low frequency the transformer can be tiny. Where the interesting radio spectrum begins, we are already at several hundred times the switching frequency, and the harmonics up there are weak and very easily suppressed.

Yes, that works.

Elecraft went another path, and used an RF oscillator to generate the high voltage needed to bias 1N4007 and 1N5408 diodes pressed into PIN diode service. They placed the oscillator between two ham bands, locking it to a crystal to make sure it won't wander away. They also made sure that its harmonics don't fall on ham bands. A brave design, I would say! But later design changes seem to suggest that they still got RFI from these converters, maybe in the form of IMD with strong broadcast signals.

Locking the converters to an internal oscillator is a common strategy. It's used in most spacecraft for instance (it's even in JPL's "Design Principles") - I have a system that is locked to the divide by 64 from a 50 MHz reference oscillator, and we just accept that there's a noise spur every 781 kHz. Other systems with lower sample rates have locked the switching rate to the sample rate. The noise appears at DC, then.

Jim, yes, ready-made DC-DC converters are inexpensive these days, and are a good option in many applications. But for RF switching, I don't see the one you linked as very usable. 15V is definitely not enough reverse bias in any solid-state RF switch that has to handle the typical power used by hams, exccept with some types of true PIN diodes. Also the DC isolation provided by these converters is rarely required in RF switches. RF isolation is indeed required, but these ready-made converters don't provide it, having 20pF of capacitance between input and output. So the RF isolation has to be provided by means of RF chokes and/or high value resistors, in any case.

As for RFI from voltage converters, I love to run mine at a very low frequency, such as 1kHz, taking advantage of the fact that only very low power is needed for reverse biasing RF switches. So even at that low frequency the transformer can be tiny. Where the interesting radio spectrum begins, we are already at several hundred times the switching frequency, and the harmonics up there are weak and very easily suppressed.

Elecraft went another path, and used an RF oscillator to generate the high voltage needed to bias 1N4007 and 1N5408 diodes pressed into PIN diode service. They placed the oscillator between two ham bands, locking it to a crystal to make sure it won't wander away. They also made sure that its harmonics don't fall on ham bands. A brave design, I would say! But later design changes seem to suggest that they still got RFI from these converters, maybe in the form of IMD with strong broadcast signals.

Manfred

I found this data a year ago -

"The easiest way to identify most ferrite materials is to wind about four turns of wire through the core and then measure the lowest frequency at which the value of reactive impedance equal resistive impedance i.e. X=R. There will be some variation between different batches and sizes of materials. But if you can plot the results graphically you can easily identify the 'signature' of each material.

Here are my references for some common ferrite materials

FT240-77 0.74MHz
FT240-31 3.5MHz
FT100-33 7MHz
FT240-43 17MHz
FT240-K 22MHz
FT240-52 31MHz
FT240-61 58MHz

Iron powder has a slightly different 'signature' it usually has a very low resistive component, which peaks to a higher value near self resonance. The more lossy the material the broader and lower value of resistive peak is apparent.

T200-52 40MHz Lime Green (& Blue or Red) colour common in PC switch mode power supplies - moderate loss
T200-26 60MHz Yellow & White colour common in PC switch mode power supplies - high loss
T200-2 60MHz Dark Red colour used for HF tuned circuits (& Ruthoff Ununs) - high Q low loss
T200-1 70MHz Blue colour not common - moderate loss
T200-6 100MHz Yellow colour used for VHF tuned circuits - high Q low loss

To illustrate this point here are some loss measurements made on ring cores recovered from switched mode power supplies.

In each case the windings were 5 turns of 1mm wire bifilar wound as a 1:1 transformer. As you can see there is great deal of variation between the results depending upon the type of core material.

Powdered iron cores are popular for high power baluns, but they don’t offer much inductance per turn of wire, so their effectiveness when used as baluns can be limited. Ferrite materials provide a much higher impedance value per turn of wire and are much more effective over a wider frequency range, but they can be very lossy when connected to a mismatched load, and heat up to a point where irreversible damage occurs."
----------------
At this web address:


Using G8JNJ's data for matching the crossover frequency where X=R for the toroid being tested, I believe I've determined the mix type for a few unknown cores. The two I was most interested in were both roughly 2 inches diameter, but one was thick, heavy and all black and the other is painted gray with yellow around one edge. The X=R points were very close to the same value for each of those two cores, and were the same as Mix 77.

G8NJNJ's page was the only place that I found the crossover X=R frequencies data listed. I feel very grateful to him for publishing the data.

--
Doug, K8RFT

On 11/9/22 3:54 PM, Manfred Mornhinweg wrote:

Don, I have seen that RF rectification technique used to bias switching diodes. But personally I don't like it much, at least not generally. Maybe in a specific application. Bias development by that method will always lag a little behind the RF signal. This means late switching, and distortion (harmonics, IMD).
It's easy enough to make a small self-oscillating flyback converter to generate a high bias voltage. It might take just seven parts or so. So that's what I would rather do. Or use a 555 to drive a small pulse transformer, with a voltage doubler at its secondary. 10 parts. But after adding all the chokes and capacitors and other parts of the switching circuit (with FETs or diodes), the total parts count gets into the range where a relay looks really tempting...

I'd buy an isolated DC/DC integrated converter something like Cui PQME1-S12-S15-M -- 12V in 15V out. $5 each



You can also get the 5V in. So you can drive them with all manner of switching circuits to turn antennas on and off.

They stack and come in different voltages.
I've used a bunch of their other parts in various configurations, often to take 12V battery (which is really 9-18V) and make regulated voltages. Like the PQP3-D12-S5-M - they're a bit pricier, $9.



They're fairly quiet RF wise if you put the right capacitors around them. Because all the current loops are inside a tiny package, they don't radiate much H field noise. It's hard to do that with a discrete design, just because of the physical size of the components.

If you need to knock down the noise, then a LT3042 post regulator (>70dB PSRR at 10 MHz) works.

Packaging and layout are the key.

Don, I have seen that RF rectification technique used to bias switching diodes. But personally I don't like it much, at least not generally. Maybe in a specific application. Bias development by that method will always lag a little behind the RF signal. This means late switching, and distortion (harmonics, IMD).

It's easy enough to make a small self-oscillating flyback converter to generate a high bias voltage. It might take just seven parts or so. So that's what I would rather do. Or use a 555 to drive a small pulse transformer, with a voltage doubler at its secondary. 10 parts. But after adding all the chokes and capacitors and other parts of the switching circuit (with FETs or diodes), the total parts count gets into the range where a relay looks really tempting...

Manfred

Gary, that was an interesting read!

But if I understand integrated SOI FETs correctly, then they have no body diodes, and very low capacitances! So the main two problems of common MOSFETs for RF switch use aren't present in SOI FETs. This indeed makes SOI FETs good devices for integrated RF switches. But using commonly available, cheap, discrete MOSFETs in the same role, with their high capacitances and their body diodes, is something completely different.

Manfred

On Wed, Nov 9, 2022 at 07:52 AM, DougVL wrote:

several unknown cores to investigate.

Try it with some known cores first.
--
John AE5X

On Wed, Nov 9, 2022 at 11:17 AM, Manfred Mornhinweg wrote:

So to use a MOSFET as RF switch, you need to bias its drain to a high voltage
to turn the switch off. High enough to be comfortably above the peak RF
voltage, so that even at the negative RF peak the MOSFET has enough positive
drain-source voltage to keep its capacitance small enough.

Often a voltage doubler or tripler is used to "steal" some of the incoming RF, rectify it, and derive a high bias voltage that way, which will always be high enough to avoid conduction, since it will track the incoming RF.
Best regards, Don Brant

Again, Fair-Rite has a wonderful YouTube presentation that outlines how to
determine the mix of a ferrite. There's also a lot of additional
information which may be quite useful. Visit the Fair-Rite site and
explore their presentations.

Dave - W?LEV

On Wed, Nov 9, 2022 at 7:35 PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

The subject of measuring toroid characteristics (ferrite and powdered
iron) has been discussed in this group before. When Rune added the
graphing capability of S11 R/ω & X/ω to NanoVNA Saver there was a post on
this subject. The post is 68 comments long and only a few pertain to this
topic. The need for a decent test fixture and how to interpret the results
is covered. Links to reference papers on the subject are provided.

/g/nanovna-users/message/6896

There was also a suggestion to add calculation of the complex permeability
parameters ?' and ?'' to NanoVNA Saver on github. A lengthy discussion
with spreadsheet calculations, test jig photos and documents on the subject
were posted. Very interesting reading but it was never implemented in
Saver.



The bottom line of all this discussion above is that it takes some effort
to get accurate measurement results and it will be difficult to determine
the manufacturer and mix type of an unknown toroid. If one knows the
manufacturer (i.e. Fair-Rite) then determining the initial permeability and
crossover frequency and comparing to data sheets will determine the mix
type.

Roger

--
*Dave - W?LEV*
*Just Let Darwin Work*


--
Dave - W?LEV

I didn't see this topic after a brief search, so here goes. My NanoVNA H3 (ver. 3.3) randomly reboots for no apparent reason, and it won't save configs. It's even happened when in DFU mode, fortunately I was able to jumper the BOOT and VDD pins and flash it a second time.
Doesn't matter if i'm holding it, or just letting it sit on a firm surface.
I've tried several different firmware versions, and it makes no difference whether it's running in standalone configuration, connected over USB, battery connected or not, powered by USB or thru battery.
I've tried wiggling the power switch to see if it's perhaps a cold / cracked / loose solder joint.
It also will not save its configuration; i.e. I can set it up to show certain traces, save the config, then after it reboots it goes back to the original config.

It works fine otherwise, I mainly use it to measure SWR, return loss, and use Smith charts between 3 and 30 MHz.

For what a replacement would cost, I'm not inclined to tinker with SMD components or reflow soldering the entire board. That being said, any ideas on a possible cause or fix?

Sometimes it will run for a couple of minutes before rebooting, sometimes 10 seconds...Seems completely random.

73 and thanks for any observations or tips concerning this!

The subject of measuring toroid characteristics (ferrite and powdered iron) has been discussed in this group before. When Rune added the graphing capability of S11 R/ω & X/ω to NanoVNA Saver there was a post on this subject. The post is 68 comments long and only a few pertain to this topic. The need for a decent test fixture and how to interpret the results is covered. Links to reference papers on the subject are provided.

/g/nanovna-users/message/6896

There was also a suggestion to add calculation of the complex permeability parameters ?' and ?'' to NanoVNA Saver on github. A lengthy discussion with spreadsheet calculations, test jig photos and documents on the subject were posted. Very interesting reading but it was never implemented in Saver.



The bottom line of all this discussion above is that it takes some effort to get accurate measurement results and it will be difficult to determine the manufacturer and mix type of an unknown toroid. If one knows the manufacturer (i.e. Fair-Rite) then determining the initial permeability and crossover frequency and comparing to data sheets will determine the mix type.

Roger

On 11/9/22 10:09 AM, Miro, N9LR via groups.io wrote:

On Wed, Nov 9, 2022 at 08:48 AM, Jim Lux wrote:

UM9415

Yes, with 1kW PIN that affordable I question my attempt to use MOSFET with all the inherit problems it comes with

Yeah, that's cheaper than some relays.

Of course, a relay won't vanish in a puff of smoke if you accidentally hook up line voltage or the B+ anode supply shorts to the output.