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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
Hi Leong,
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Wow, so I was right, that makes a change :-)
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It's a common problem, especially with baluns and RF transformers, there are frequently many imperfections in "real life" components, that are often difficult to include in models.
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I spend a lot of my time trying to reconcile such inconstancies, which is what make it fun...
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Regards,
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Martin
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On Sun, Oct 13, 2024 at 06:21 AM, <biastee@...> wrote:
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Re: NF of devices used in LZ1AQ Preamp
On Sat, Oct 12, 2024 at 12:40 PM, JohnG3PQA wrote:
The NF of the PXT2222a is listed as 4dB under their test conditions. The noise figure? of max 4 dB as specified in the PXT2222A data sheet refers to a frequency of 1 kHz. That says not much about the broadband noise behaviour at HF Frequencies, which is mainly determined by the base resistance thermal noise. Especially at low frequencies various other noise causes exist.
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regards
Fred |
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Re: Looking for a good cheap antenna analyser
You may wish to look at the RigExpert AA-55 Zoom. Several people I know find them good for a basic but accurate analyser.
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I have used a Sark-110 for years and find it excellent simply because of the wide range of facilities , user intuitive software, small size and long battery life. Goes up to 200MHz.
Another good accurate analyser is the FA-VA5 which can also run on the excellent DG8SAQ software when used in the shack with VNA accuracy. 600MHz.
Unfortunately both these are not in current production but you see them s/h.
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All the above are are single port analysers.
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The NanoVNA is a two port VNA, in my opinion unfortunately the software is very tortuous, takes a lot of getting used to and is rather clunky compared to the DG8SAQ VNWA and other analysers. It is the cheapest though, when bought new, has wide frequency range, is very accurate and has many fans so perhaps I am in the minority here.
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I guess it really depends what you want to do, but if it is only quick SWR measurements around 50 ohms and basic X measurements up to 500 ohms, also for measuring L and C and cable loss, then the old MFJ259b takes a lot of beating. Particularly with its analogue meters is the best way of adjusting an ATU rather than having to wait for sweeps.
John |
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Re: NF of devices used in LZ1AQ Preamp
It's a pity that low noise, robust, medium ft transistors like 2SC5551a are discontinued. Actively produced BFU590 are low noise and high gain, but need to be treated like a high ft device and lack the robustness of a 2SC5551 or 2N5109 (NT278).
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The xx2222A is not a specific RF-device but a kind of swiss army knife among the transistors. Since 1962 it is one of the most common, versatile and commercially successful transistor types. Nearly every semiconductor manufacturer has a silicon-die in its portfolio which can be labeled and sold as xx2222A. The JEDEC registration of a device xx2222A ensures particular rated values will be met by all parts offered under that number. However the manufacturing processes and the die layout varies significantly from foundry to foundry. Some xx2222A types just meet the requirements, others exceed some values due to modern sophisticated silicon processes.
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To find out, which of the countless xx2222A transistor types has a lower noise figure at shortwave frequencies than specified in the data sheet you need to do your own tests (or check Steve Ratzlaffs list). The SOT89 versions PXT2222A for example are available from Nexperia, Good-Arc Semiconductor and Micro Commercial. It may well be that they have different noise figures. The PZT2222A in rugged SOT223 case are manufactured from Nexperia, Onsemi and Micro Commercial.
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regards
Fred
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
On Mon, Sep 30, 2024 at 01:13 AM, Martin - Southwest UK wrote:
Hi Martin,
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You are right. Placing the balun after the L-network causes problems. ? The simulator showed similar result, regardless of whether the balun is placed BEFORE or AFTER the L-section. This deceptive result arises because the simulator's ideal balun was capable of tolerating high Z, whereas the real balun requires ~50 ohm to work properly.
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When the L-network's impedance is measured without the fabricated balun, it shows the expected trajectory, with a resonance at the modelled 30 MHz (black trace). However, after the balun is added, i.e. AFTER the L-section, the resonance mysteriously shifts down to 13 MHz (red trace).?
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The problem can be rectified by moving the balun L2 to a position before the L-section. With the balun in the new position, the impedance locus is as modelled with a resonant at ~30 MHz.
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Additionally, the previously measured LZ1AQ's gain peak at 22 MHz, also correctly shifts back to the modelled 30 MHz.
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73, Chin-Leong Lim, 9W2LC
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
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On Oct 12, 2024, at 4:51?PM, Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
Shape is not that critical, but a circle provides the lowest inductance for a given loop area. The thinker the diameter of the conductor, the better.
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Regards,
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Martin
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On Sat, Oct 12, 2024 at 06:52 PM, Tom ANderson wrote:
I have always heard shape is not that critical in a receive only loop |
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Re: NF of devices used in LZ1AQ Preamp
Fred and Andy,
Many thanks for your replies and the list of transistors.
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The last time I bought any RF transistors was a few years ago before Covid and Brexit, when RF transistors and FETs seemed far more plentiful.
I have just done a search and see that apart from European suppliers on Ebay, Digikey stock the PXT2222a for a very reasonable cost . At least that will make buying enough to match pairs and experiments affordable. The NF of the PXT2222a is listed as 4dB under their test conditions.
Digikey also stock the 2N5551BU, NF listed as 8dB and BFR92 NFlisted 1-2dB.?????? Farnell also stocks the 2N2222a.
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I last tested discrete 2N5109, 2N2222a and 2N3904s in a simple 50 ohm Norton amp drawing about 20mA AT 12V using a calibrated noise source at test frequencies 2 to 20MHz some years ago and the results (at 50 ohms using the "noiseless single ended 11dB Norton amplifier") were:-
2N5109 = 3dB
2N2222A = 5dB
2N3904 = 5dB
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My noise source is faulty at present, when I get it repaired and cal checked I plan to use the Norton to test the Digikey PXT2222a and 2N5551 and will post the results here. With these latest devices I hope it is nearer the 1-2dB region found by Steve when he tested them in the LZ1AQ design amp !
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John
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Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
There is no way to run a proper IMD without a band stop filter that rejects the 2 tones and a band pass filter for each of the tones.
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Everett N4CY
In a message dated 10/12/2024 11:55:40 AM Central Daylight Time, martin_ehrenfried@... writes: ?
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Re: Looking for a good cheap antenna analyser
I second that recommendation, old style antenna analysers seem to be very expensive for what they are, and will only provide you with limited data.
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I have a LiteVNA 64, which was an upgrade from an original NanoVNA, and I now tend to use it more than my previous AIM's, WVNA's and the rest. They still get used occasionally for specific tasks, but the ability to just switch it on and make a measurement, quickly recall previous sweeps and setups is fantastic. In addition, because it is so small and self-contained, you don't have to worry about the contribution of interconnecting connecting cables to any measurements, as it is effectively a "floating" instrument. Plus, you can export s1p files into other applications, such as SimSmith, which provides even greater scope for analysis.
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Highly recommended, as is the TinySA Ultra. Owning the pair gives you a complete RF workshop in your pocket.
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Regards,
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Martin
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On Sat, Oct 12, 2024 at 03:23 PM, Fred M wrote:
Why not a NanoVNA |
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Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
Absolutely, it's no good unless you can notch out the fundamental tones.
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My own notches provide about 40dB rejection, which is just about good enough.
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Regards,
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Martin
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On Sat, Oct 12, 2024 at 03:21 PM, Fred M wrote:
Definitely, but without? notch filters for the original 2-tone signals the tiny-SA will become overloaded. It's own IP3 is about +17 dBm. |
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Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
On Sat, Oct 12, 2024 at 07:28 AM, Martin - Southwest UK wrote:
Every time I make comparisons against my other Spectrum Analysers, including HP 8500 series, I gain more respect for the TinySA Ultra.Definitely, but without? notch filters for the original 2-tone signals the tiny-SA will become overloaded. It's own IP3 is about +17 dBm. ?
regards
Fred |
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Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
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Incidentally, I've just been comparing IMD measurements using a Rigol DSA815 and a TinySA Ultra.
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I've been using my own test source and notch filters, and providing the notched test tones are kept to a level of -60dBm or lower, the TinySA Ultra actually produced better results.
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Every time I make comparisons against my other Spectrum Analysers, including HP 8500 series, I gain more respect for the TinySA Ultra.
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Regards,
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Martin
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On Mon, Oct 7, 2024 at 04:19 PM, Fred M wrote:
Besides the TinySA, whose own IP3 is 17 dBm at best |
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
Nice loop, but could you state the loop inductance ?
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Regards,
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Martin
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On Fri, Oct 11, 2024 at 09:39 AM, Fenu wrote:
Rectangular loop 1000x800mm: 0.8m2 |
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
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Stainless-Steel Loop with Wellgood 4.1 Amplifier
I would like to introduce you to my latest loop.
Ideally, a loop should be round, but because the production costs for a round loop with a diameter of 1m are very expensive, I decided to make the loop rectangular. The surface area is slightly larger than that of a round loop with a diameter of 1m. Round 1m loop: 0.785m2 Rectangular loop 1000x800mm: 0.8m2 The loop is screwed onto a Bakelite plate, which is also very stable.
The housing is IP65 and is equipped with a ventilation membrane. In terms of reception, the difference is not noticeable. Even if the loop is made of stainless steel, there is no noticeable difference to aluminum.
But why stainless steel? Quite simply. It is much more durable and stable than aluminum.
This is an antenna without ifs and buts.
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See here:
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Everett N4CY
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