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TX protection on RX Loop
Hi, I have made an indoor active broadband loop for HFusing the LAMB-1B amp board from Casarain.
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Having now got back into amateur radio I want to know if there is anything I can build on the lead to protect against accidental transmission from my rig.
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If someone could point me in the right direction of a simple circuit Id be much appreciated. Thks. Adam
M6RDP? |
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Re: Entry Level SDR recommendations
We have to distinguish between functional ground/earth, which is needed for the proper functioning of a device and the mandatory protection earth and equipotential bonding. The latter dos not care that an antenna system actually works, only that it be safe. It is required by electrical safety standards, in the US by the National Electrical Code. Here in Europe by EN IEC 60728-11. You have no choice, you are reqired to comply (or you take the risk of liability).
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regards
Fred |
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Re: Entry Level SDR recommendations
Yep!? Computers are major RFI generators!? Dave - W?LEV On Mon, Feb 17, 2025 at 11:17?PM Tom ANderson via <SDR_Radio=[email protected]> wrote:
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Dave - W?LEV |
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Re: Entry Level SDR recommendations
开云体育Dave,I eliminated a good part of EMI from my computer by grounding all of my equipment to a central point on the computer.
Additionally, using the original mini whip it is recommended to ground the coax shield to earth ground.
? ? Tom Anderson SDR_Radio@...
On Feb 18, 2025, at 3:22?AM, W0LEV via groups.io <davearea51a@...> wrote:
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Re: Entry Level SDR recommendations
Why would one need an extra "ground" for an SDR??? Dave - W?LEV On Mon, Feb 17, 2025 at 8:43?AM Tom ANderson via <SDR_Radio=[email protected]> wrote:
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Dave - W?LEV |
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Re: LZ1AQ possible changes
Before considering changes, the objectives that you want to achieve should be clearly defined. For example
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a) improved sensitivity/noise figure
b) improved gain / gain flatness
c) improved frequency range
d) improved linearity / intermodulation performance / IP2, IP3
e) lower/higher/tracking input-Z
f) lower/higher supply voltage/supply current/power consuption
g) minimum Common Mode Rejection Ratio over frequency h) lower costs
i) common availability of quality components
j) ESD hardening
k) environmental conditions
k) else . . .
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Some of these requirements compete with others, some come with a price. Some of them ar very specific or are of limited relevance for general receive purposes. For example, an exeptionally good CMRR, which is achieved over a certain frequency range only may have no practical advantage, because the overall antenna CMRR is limited by external factors. IMHO, implementing changes just for the sake of change makes no sense. It should be known what goals you want to achieve with it.
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regards,? Fred
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LZ1AQ with a protective Relay
There has been interest in my improved LZ1AQ with a relay added. The new design has an added relay on the board that, when off, (NO POWER) the relay contacts short both loop legs to ground.
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If there is any interest, please contact me off list at everettsharp (at) aol com.
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Everett N4CY
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Re: LZ1AQ possible changes
The other issue that many loop? experts dont want to accept is that for a the typical 1 metre? to 2 metre loop size? the antenna factors cant be improved to the point where it drops the inherent amplifier or system noise floor.
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If the ultimate objective is a better signal to noise ration then a better antenna design should be pursued rather than making miniscule changes in loop amplifier design that does not change? noise or floor antenna factor by much.? Then again I am not surprised because even the likes of the FCC, OFCOMM and several other regulatory agencies use measuring loop antennas whose? noise floor is higher than the noise that they are trying to measure.? They just dont want to get it!
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The only thing that will improve antenna factor? to get a better signal noise ratio for a 1? to 2 metre loop size is to implement a tuning/tracking system that gives anything from 6 to 10 db improvement. The only professional company that "gets it" is R&S whose model? HM525 loop has a tuned or amplified mode that results in a substantial signal to noise floor improvement that allows noise measurement? or signal reception close to ITU rural noise levels.
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So I question the value of pursuing the miniscule improvements in pursuing? minor amplifier and transistor improvements beyond what is necessary for the antennas antenna factor that it will be used in. It seems to be an exercise in futility when the majority want to use a small 1 to 1.5m loop diameter.
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When someone develops a loop antenna amplifier and small loop? antenna that improves 10db over the existing 1 metre designs I will take notice. That is not to say that all this research and? endeavour is not technically interesting? because it does advance everyone's technical understanding which is great. Ultimately it comes down to antenna factor that nobody wants to talk about!
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Henry |
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Re: My PA0FRI active loop receiving antenna
Hi Fred & Dhiru,
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Thank you for your kind praises. I am standing on the shoulders of giants, namely PA0FRI & Martin G8JNJ whose loop aerial impedance measurement allowed me to create the dummy aerial.
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Google site doesn't have that feature. One workaround is to use the browser's Print > Save to PDF function because it has the effect of magnifying the images while keeping the text at the same size. Alternatively, let me know which figure/s that you would like to view, and I will post it/them to this group's Photos section.
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I am amazed by your encyclopedic knowledge of transistors! :-) What I am going to write next is heresy - the transistor model that best matches the gain measurement is ..... BC547B! No gain peak artifact, at all!
/g/loopantennas/photo/300703/3886460
However, its S22 has poor resemblance to reality, sigh...
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Anyway, an accurate answer can only be obtained if I were to measure the 2N2222A's s-parameters in a 50 ohm fixture and then compare them to the different models. This is the only way to eliminate the confounding factors due to external components.
I am clueless with regard to the gain peaks. I have tweaked the surrounding components to see if they can affect the peak, but nothing works. So far, only damping the ideal (lossless) balun with R7 to account for the former's loss seems to work.
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However, the absence of the gain peak in simulations with Siemens PZT2222A and BC547B seems to indicate that the gain peak is inherent in the Motorola and Natsemi models.?
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Good discussion. I am glad for the opportunity to get the above information off my chest. :-) Previously, I have thought that nobody here gave a damn to circuit modelling.....
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73, Leong, 9M2LCL, ex-9W2LC
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Re: LZ1AQ possible changes
On Fri, Feb 14, 2025 at 08:33 AM, Martin - Southwest UK wrote:
It always used to amuse me when dealing with one particular make of broadcast transmitter, where individual sections had obviously been designed by graduate engineers, and the feedback around operational amplifier stages used non-standard value, 1% tolerance parts, even though they were intended to be simple, unity gain buffer stages.This example is more about the cost optimization, which is another side of the real life engineering. It applies to hobby projects as well. A hobby design becomes popular only when it balances the performance with cost (and availability of parts). LZ1AQ loop amp is a nice example. But suggesting 2SC1815 for use in it is a step too far in the cost reduction direction :) ?
73, Mike AF7KR |
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Re: LZ1AQ possible changes
Simulations do have their place, and they allow us to quickly try new things, without letting out the magic smoke.
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However, so many graduates these days are trained using simulation tools, without ever touching actual components, so it often comes as a bit of a shock to them, when they have their first industry placement, and have to start actually making things.
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The first challenge is to get them to be able to recognise parts, and the second is in acknowledging that there are various physical constraints that also have to be taken into consideration. Such as power dissipation and cooling, and in the case of RF, screening, stray coupling, including unaccounted for inductance and capacitance, which all need to be taken into account.
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It always used to amuse me when dealing with one particular make of broadcast transmitter, where individual sections had obviously been designed by graduate engineers, and the feedback around operational amplifier stages used non-standard value, 1% tolerance parts, even though they were intended to be simple, unity gain buffer stages.
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This should have really been spotted and sorted out during production engineering, but for some reason it never did.
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Regards,
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Martin
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On Fri, Feb 14, 2025 at 03:02 PM, Mike M wrote:
So simulation-based arguments may be interesting, but unless there is the built and tested prototype it is hard to know whether the simulations represent reality or not. |
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Re: LZ1AQ possible changes
I worked for a company that had among other products a simulator. The architect was somewhat of a curmudgeon but really knew his stuff. He really drove home the idea that you need good measurements to validate your simulations. The best way to enrage him was to show him the all-too-common customer question "why does your simulator give a different answer than this other simulator?".? A much better question would be "why does your simulator not match these good measurements?". There are so many ways that different simulators can vary even with the same models that it is never a fun exercise to determine why they differ.
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So simulation-based arguments may be interesting, but unless there is the built and tested prototype it is hard to know whether the simulations represent reality or not.
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=================================================================== Mike M |
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Re: My PA0FRI active loop receiving antenna
Hi Leong
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With regard to: Fig. 16: Transistor models from different manufacturers exhibit huge differences in gain simulation!
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At present there are mainly PZT2222A from Nexperia/NXP and from Onsemi in active production. Which model is closest to reality?
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I am surprised of the gain peaks with the different SPICE-models and i do not really understand what causes them. It looks like frequency dependant resonances with external components. Any idea?
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regards
Fred
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Adam
Warren Dean / NI5L
Everett N4CY
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