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Also most of the important bolts and screws are wire tied on aircraft.?

Hi ...

Some months ago I think a saw a msg where Martin G8JNJ described an of RLC network that creates sort of "pre-emphasis" across the HF spectrum (e.g. 3dB attenuation @ 30MHz and lets say 30dB attenuation @ 3MHz). I think that this subject was in this group.?I used the search tools with some regular expressions with no luck (rural noise, ITU noise etc).

My apologies if this msg was not posted on this group and If someone can refresh this topic I'll appreciate.

73
Marcus PY2PLL + PY3CRX

I loathe "delete if not allowed" posts. Ask the moderator if you aren't sure.

In this case, I think this is a worthy post that has good reason to be here. And since you haven't already posted before, you were on moderated status as is everyone until they post a few times.

So I did approve this post.

--
Steve Greenfield AE7HD

Let me know if this is too far off topic and I will delete it.

Exterior loop antennas are exposed to the wind, the wind causes vibration, vibration can cause nuts and bolts to loosen. Many of us have used split lock washers to prevent loosening.

We ran into this on a piece of farm equipment. A critical bolt/nut kept coming undone and locktight wasn't a good choice because the area has oil drip on it during normal operation.

?

https://www.linkedin.com/pulse/nasa-split-lock-washers-useless-roger-bogrash

------------------------------

NASA: Split Lock Washers Are "Useless"!

?

Roger Bogrash

Published Aug 30, 2019

?

"I know we have a problem with loosening but I don't understand why...we use split lock washers everywhere".

This is not the first time I've had this conversation with an engineer, customer or even an experienced distributor. Engineers know a lot especially in their field but they don't always understand everything when it comes to fasteners - so when a bolted joint comes loose and they are using a DIN, ASTM or other standard "locking fastener" they scratch their heads.

I get it, its effectively a spring and pushes against both the nut and/or bolt and the work surface or flat washer placed on the work surface. The force it exerts on the work part(s), the axial load and the sharp edges of the cuts in the washer, that will surely prevent loosening - well, not really.

So often I talk to engineers and explain that there are many factors that contribute to loosening, and until that conversation the logic is - lets just throw on something that is called a lock washer and let it do exactly that, be a washer that provides locking. Well, there's your problem -?they don't work! Don't take my word for it, here is NASA concluding they do not help prevent loosening and they have known about this for decades!?

“The typical helical spring washer … serves as a spring while the bolt is being tightened.?However, the washer is normally flat by the time the bolt is fully torqued. At this time it is?equivalent to a solid flat washer, and its locking ability is nonexistent.In summary, a?lockwasher of this type is useless for locking.”

??-?

NASA, these are the brilliant minds that send people into outer space. They put the lives of astronauts on the line and the futures of their families into darkness if things go wrong - because if something goes wrong, it really goes wrong BIG. It would make sense that they would invest time and money into making sure that every nut, bolt and washer is up to spec and does what it is supposed to do because they simply cannot afford an accident or a maybe.

Yes they are cheap but how does that help solve a problem if they don't work? There are a lot of locking fasteners out there; lock washers, lock nuts, thread lockers, pins, welds and others - how do you choose something that works for you and how do you know it will work in solving your problem?

First off, please do not use split lock washers to prevent loosening - don't.

The next step is to do your own research, understand the pros and cons of each option. There is no perfect solution, some locking fasteners work in some applications but not in others - for example you would want to avoid serrated washers in areas with extensive and repeated impact shock or substantial settling in the work part(s) or surface, but they might be fine for no or low vibration applications without impact shock or settling.

Talk to the company you are considering and of course they will tell you the benefits but, always try to understand the downsides or limits of each option - when is this option NOT suitable or when will it NOT work. This simple piece of advice most companies do not follow is a major reason split-lock washers are sold in in enormous quantities to end users that simply don't know any better.

Parameters to keep in mind when choosing a locking fastener are:

• Maintenance: Will this require a lot of regular replacement or repeated re-torquing. Is this a locking fastener that is known to come loose over time or has it been tested to stay secure even under vibration?
• Time: How long will this product last? How long does the installation/disassembly take?
• Effectiveness and Performance: Will it actually work in YOUR application? Will it work in the specific type of vibration you are dealing with and do you know what the different types of vibration are? Does the guy selling you fasteners know?
• Cause Of The Problem(s): Do you fully understand what is causing loosening in your joint and what result actually matters to you? Are you speaking with someone that can answer that?

Split?lock washers are a discussion I've had many times, yet it never seems to go away. I have seen them used just about everywhere, I've found them coming loose in the gym, on bridges, tractors, mining equipment the list goes on. With time they will hopefully be used less and less, but in the meantime - be cautious.

If you found the above helpful, feel free to share it and leave a like or comment to let me know. To be notified of future articles, you are welcome to follow me and if you have questions or need input relating to this topic, feel free to contact me.

Written by Roger Bogrash, Director of Business Development @??Locking Fasteners

-----------------

The NASA report on fasteners can be found at:

https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf

?

We solved our problem with a nut with a an internal nylon insert and replace the nut every time it is removed.

I intend to replace every nut and split lock washer with a Nylock nut.
?

https://en.wikipedia.org/wiki/Nyloc_nut

You have reported a couple of messages from the group as spam. Groups.io removes members for this. Nothing to do with me, but I'm not against it, as this can seriously affect the group. In addition, neither of the messages you reported are spam in any way, shape, or fashion.

This may be why you aren't receiving messages, although I can't find where you are bouncing. Perhaps your ISP is now putting all group emails into your spam folder.

If you feel a message in the group is spam, send notification to the listowner address. Please do not report it as spam in your email program. Repeated reporting of group messages as spam will get you blocked from the group.

gareywittich2000

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Talk to me off-list. This subject was covered when we first moved over to groups.io. This topic is locked.

Steve Greenfield
listowner loopantennas
--
Steve Greenfield AE7HD

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Yes, similar.
But there is no output transformer in my preamp. The NE592 OUT- is connected to my preamp output directly with? a 220nF capacitor.

Is your circuit similar to this one?
/g/loopantennas/files/MLA30LF.pdf
Tom

Now I found some time to measure my 1 turn SRL with NE592 preamp:
I could get a relatively flat S11 response from 100 kHz to 31 MHz with deep resonance at 37 MHz.
I even tried S21 with a small exciting coil 2m away from the loop and found a response from about 50 kHz to 200 MHz.
Not sure how to interprete this... Perhaps measuring nonsense.

Amazon has MG Chemicals 419D Acrylic Conformal Coating, Clear Finish, 12 oz. Aerosol for $30. Might be cheaper elsewhere.
Just spray on from different directions. Clean the board with toothbrush and alcohol before applying.? Acrylic coatings are easy to remove if you ever need to replace a component.
N3UMW

Jinze,

Let's put our semantics on side...
The bottom line is you wish a practical means of? discrimination from unwanted EMI. You may use a tuned loop antenna at each frequency of interest? in order to minimize the effect of EMI, testing it in your city EMI environment.
For this severe EMI enviroment a proper impedance matching will not help at all.
Again all your tested amplifiers will not minimize external picked up by antenna electrical noises. Loop antennas with their directivity pattern might not help either ( let's say your broadcast signal comes from same direction as EMI source ).
You may try a space diversity antenna arrangement. However, none will have 100 % proofed solution for you.?
Raphael

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Science or technical applications start with appropriate measurements and decision making

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I guess you designed this amplifier with recommended LCR equalization circuit in front of it. It is possible two capacitors in series 120 pF each together with the inductance of your transformer winding creates that parallel resonant

On Mon, Dec 5, 2022 at 09:16 PM, Raphael Wasserman wrote:

mpedance matching for a broad band application can be discussed? when Ra + j Xa of? antenna impedance can transformed in R inp + j X inp in such way to achieve a maximum power transfer when?4 R a x R inp / | Z a + Z inp | ^ 2 = 1 - |Gamma|^2 for a specified bandwidth from f min to f max of design interest. Have you ascertained that ? That is the function of matching network between antenna and input of your amplifier.

I'm not a math expert, I think for enthusiasts, we just want to know the performance of the equipment, we can't really test the antenna's pattern in the standard electromagnetic shielding laboratory,
we can only try with simple equipment at hand learn.
For the impedance and matching of the common 1m diameter loop, I mainly obtained it by reading Martin's website. I think it is a very intuitive conclusion.

“Assuming a typical loop of 1m diameter with an inductance approximately 2 to 3uH, used over the frequency range of 20KHz to 30MHz.

At low frequencies<1MHz? the loop behaves as a current source, and the loop needs to have a low value of DC resistance matched by an amplifier with a low value of input impedance.

At mid frequencies, typically >1MHz and <10MHz the loop impedance is in the order of tens of ohms and nearly any amplifier with an input impedance in the range >10 Ohms & <200 Ohms will work to some degree. Many poor designs are judged on the basis of signals received in this frequency range, which can be misleading.

At higher frequencies when connected to the amplifier, a 1m diameter circular loop, tends to have a resonance at around 30MHz (or just above it), and so it effectively becomes a high impedance voltage source, which requires an amplifier with a much higher value of input impedance, typically peaking to values of around 500 to >1000 Ohms at 30MHz.”
I guess the easiest thing is to make the input impedance of the amplifier conform to this conclusion

Raphael ，
I know that the 22M input impedance becomes 244.5 ohms, which cannot match the common 1m diameter loop. I don’t know if the early resonance is caused by the large inductance of the TC1-1t+ I used. I will try to wind one myself. balun, but I would say that this kind of test can tell if the input impedance of the amplifier is as expected

Jinze,
My understanding is you used mini-circuits RF transformer that has winding ratio 1:1 to connect VNA to your designed LZ1AQ amplifier with balanced input and measured Z input of your antenna amplifier.?
Your plot shows a peak of measured impedance |Z| = 244.5 ohm at frequency 22 MHz.
I do not follow? your explanation "this is more in line with the impedance matching expactation of the loop". How come ?
Impedance matching for a broad band application can be discussed? when Ra + j Xa of? antenna impedance can transformed in R inp + j X inp in such way to achieve a maximum power transfer when?4 R a x R inp / | Z a + Z inp | ^ 2 = 1 - |Gamma|^2 for a specified bandwidth from f min to f max of design interest. Have you ascertained that ? That is the function of matching network between antenna and input of your amplifier.

Raphael