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File upload: Rotable FLAG-antenna
Hi group!
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If you're interested, I just uploaded the file "The Growing FLAG", which is a building instruction for my Rotable FLAG-antenna, which is somewhat smaller than traditional FLAG-antennas. I have been using this small antenna since the beginning of October 2024 on the MW Broadcast band, with surprisingly good results (conditions permitting).
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73's
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Hans / LB6GG
Sola, Norway |
Re: LZ1AQ possible changes
Mike,
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It is easy to increase the current, which would improve the IMD, but it will increase the noise. Everett On Monday, February 10, 2025, 5:59 PM, Mike M <groups@...> wrote:
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Re: LZ1AQ possible changes
I have built essentially the same circuit as Everett's and see essentially the same performance. I also wonder how that can be improved. Maybe show some measurements of the current and improved circuit?
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=================================================================== Mike M |
Re: Entry Level SDR recommendations
开云体育Thanks Bob. On 2/10/2025 3:42 AM, Bob W8RMV via
groups.io wrote:
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Doug
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Re: LZ1AQ possible changes
The present commercial LZ1AQ product claims to be "an enhanced and improved version with different active elements (low noise VHF transistors)."
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The present version of the AAA-1C specifies:
Frequency response:? 0.35 – 51 MHz; (within 3dB ) usable frequency range: 0.02 – 55 MHz ?
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regards, Fred
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File /BD3OLH.rar uploaded
#file-notice
Group Notification
The following items have been added to the Files area of the [email protected] group. By: 钱志豪 <qianzhihao2002@...> Description: |
Re: LZ1AQ possible changes
On Mon, Feb 10, 2025 at 12:41 PM, Nils wrote:
The transformer there ist trifilar with 18uH each (5 trifilar turns on a toroidal core, u=1000, 10x6x4 mm). He probably recalculated the inductance. In the older original LZ1AQ AAA-1B that i own, the transformer is on a 10 mm diameter blue coated Siemens/TDK Sifferit N30 toroid core, ?i = 4300.
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5 turns wound on this core would give an inductivitiy of approx. 45 ?H. The lower -3 dB cutoff frequency of a transformer is determined by the point where the transformer's primary inductance has the same impedance as the impedance driving it. Let's assume 50 Ohms. That results in a lower cutoff frequency of roughly 170 kHz. Below the cutoff frequency the transformer behaves like a low pass filter with a slope dropping with approx. 6 dB / octave. I dont know, wether the newer versions now have a different output push-pull transformer.
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If i did a mistake in my calculation please correct me.
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regards
Fred
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Re: LZ1AQ possible changes
Hi Nils,
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On my Improved LZ1AQ design the inductance @100Hz is 610uH on each winding and with the two in series it is 2,395uH. The gain from 100kHz to 20MHz is 30dB? and is 27dB at 30MHz. I don't Know how you can improve on that? Also I am using the lowest NF transistors you can find, which is a 1dB NF.
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Everett N4CY
In a message dated 2/10/2025 6:41:48 AM Central Standard Time, nilsp@... writes: ?
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Re: LZ1AQ possible changes
On Mon, Feb 10, 2025 at 07:19 AM, Fred M wrote:
I dont know where he takes this value from? I think he ist referring to the original schematic on the LZ1AQ website. The transformer there ist trifilar with 18uH each (5 trifilar turns on a toroidal core, u=1000, 10x6x4 mm). He probably recalculated the inductance.
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Best regards,
Nils |
Re: Entry Level SDR recommendations
I've been using SDR receivers since the first softrock kits and have several along with classic receivers from AOR,JRC,Drake etc. Here's a couple of my observations. Firstly the available software for any SDR is as important a consideration as the hardware itself. I find that SDR's are (generally) a little noisier in terms of weak signal intelligibility, but this is software related and can be overcome. Receive antennas with their own ground are to be avoided if an SDR is to be used on a PC. If you go cheap and buy an RTL dongle have fun but don't regard that as a benchmark for SDR performance. Of the lower cost SDR's I own I'd recommend the SDRPlay RSPDuo, the diversity receive function coupled with the SDRUno software is unbeatable at the price point for MW DX IMO, but make sure the software has the features you need. To get any worthwhile hardware improvements above this price point you have to look toward ELAD/Perseus/WinRadio etc, but once again check software support, they are a significant investment and the improvement in performance is marginal.
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Lastly, don't forget that using a budget SDR as a panadaptor for your existing hardware receivers is an option. The visual signal navigation and processing experience can be had providing your traditional receiver has a wide enough IF output connection, or can be modified to provide an IF tap for the SDR, and both your radio and SDR software support CAT control via omnirig.
HTH.
73's
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Re: Entry Level SDR recommendations
On Sat, Feb 8, 2025 at 06:02 PM, JohnT wrote:
After years of chasing MW DX with "real" hardware, I'd like to try SDR@JohnT... Could I suggest visiting groups.io "mwcircle" where there are many like-minded DXers?
There you could find out what a difference SDR makes in the MW context and get more targeted advice on a suitable SDR.
An important consideration will be if you want to go down the rabbit hole of "medium wave carrier offsets".
MW DX can be just fun or suck you into an obsession :)
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Re: LZ1AQ possible changes
On Mon, Feb 10, 2025 at 05:43 AM, John Kolb wrote:
Doesn't ANY diode generate noise?? Reverse biased diodes in breakdown like Avalanche and Zener-diodes generate noise, a normal diode does it nor or much less. Diode based transistor biasing is frequently used and proven in audio amplifiers.
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regards, Fred |
Re: LZ1AQ possible changes
I suspect that ArnoR has not yet tested an original LZ1AQ amplifier and he did not evaluate it's performance on the bench nor in the field. Some of his judgement seems to be based on simulations and his assumptions, some of which are obviously inaccurate, but some of his suggestions are worth thinking about, e.g. replace the 2N2222A with better performing RF-transistors. ArnoR may be very experienced in analog transistor circuit design. As far as i know, he himself did not yet provide measurement plots proving the achievements of his proposed design compared to the performance of the original LZ1AQ amplifier.
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For example claim 1:
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Output Transformer Issues
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This assumption, IMHO, is ridiculous. The output transformer has not a "too low" inductivity of 10.2 ?H. I dont know where he takes this value from? The push-pull output transformer is wound on a high-permeability ferrite core. The open circuit incuctance of the transformer is likewise in the range of several hundreds of ?H. If he had measured this circuit on the lab bench, he would have known that the frequency range of an original LZ1AQ amplifier goes down much much lower than 800 kHz. In the files section there are many frequency plots which prove that.
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regards
Fred
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Re: LZ1AQ possible changes
开云体育
I would disagree with
calling either this circuit or the LZ1AQ circuit differential.
Both are two separate amplifier chains fed with a differential
signal. The only differential coupling in the amplifier is the
output transformer. Doesn't ANY diode
generate noise?? The green LED provides a stable voltage to
protect against power supply variations, but putting a noise
source on the base just feels wrong.? John Kolb?? KK6IL On 2/9/2025 5:26 AM, Nils via groups.io
wrote:
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Re: Entry Level SDR recommendations
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Re: Entry Level SDR recommendations
开云体育Do you have a link to the F/W update you mention. I don't see it on the Airspy site. Thanks Doug WA6VYN
On 2/9/2025 3:56 AM, Bob W8RMV via
groups.io wrote:
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Doug
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Re: LZ1AQ possible changes
Should you not add my suggestion of a Full Wilson Current Source for each of R1 and R2 of present Everett Sharp circuit.? ( On the other hand, one could try the simple single BJT or FET constant current source firstly......again the THAT CORP 300 series of 4 transistors is a good start....likely they have a SPICE data model available) That can be modelled....anyone out want to try that and see any affect on IP3 best wishes Paul EE VE3PVB
On Sunday, February 9, 2025 at 08:26:29 a.m. EST, Nils via groups.io <nilsp@...> wrote:
? Hello everyone, ? a while ago there was a discussion in a german forum where forum member ArnoR proposed modifications to the original LZ1AQ circuit. The modifications seemed plausible to me but as an electronic hobbyist with little knowledge (but a lot of passion!) I had difficulties understanding them. A circuit (and later an updated version) was presented as an improvement over the original LZ1AQ design that i know has been in use for years (and has highly regarded updated versions published in this forum). Since I don’t have the experience to evaluate the design myself, I thought I’d bring it here, where the level of expertise is much higher. My goal is not to argue for or against the changes but simply to understand whether and why they might be beneficial—or if they introduce new drawbacks. Even if there is no benefit, the proposed changes are still interesting from a circuit design perspective. I would appreciate any insights you can share! (I created some LTSpice files for the proposed circuits, they do run but are not refined enough to do a proper circuit simulation. They should be seen as a starting point for experimentation. They are called Arno_V1.asc and Arno_V2.asc in the files section.) ? Here is a summary of the changes:
2. Base Circuit Design Issues
3. Emitter Circuit Design Issues
4. Signal Tapping at Collector Resistors
5. Frequency Response & Component Choice
6. Final Circuit Comparison
? I’d love to hear your thoughts. Could they offer any advantages, or might they introduce unintended issues? Looking forward to learning from your insights! Best regards, Nils Just to be super clear: none of this is my original work, all work was done by ArnoR. I just translated his post to post it here and condensed it for clarity. ? For reference i include the original forum post in translated form: ? Source:
? Since I previously criticized LZ1AQ’s circuit without providing specifics, I now want to briefly address this to avoid the impression of baseless complaining. Let us start at the very end. The output transformer supposedly has a winding inductance of 18?H. With the output resistances of the emitter circuits (220Ω), which generate the output voltage, and the load resistor, the resulting lower cutoff frequency is around 500kHz. This means the inductance is far too low if one intends to amplify cleanly down to the longwave (LW) range. *) The core is specified with ?=1000 and core size R10. According to the Epcos catalog, this core has an AL value of 407, which, with 5 turns, results in an inductance of only 10.2?H. This would place the lower cutoff frequency at about 800kHz. Thus, the lower cutoff frequency is not limited by the input resistance of the circuit and the loop inductance but by the incorrect dimensioning of the output transformer. The two base circuits are powered by separate base voltage supplies. However, the circuit is actually supposed to amplify the differential signal between the emitters. This only works properly if there is no differential voltage between the base connections. Here, this is achieved for AC signals using bypass capacitors. A much more natural approach would be to connect the base terminals directly, thereby constructing a true base-coupled differential amplifier. This would require only a single bias voltage divider, with changes in base currents perfectly canceling each other out. No interference voltage could be coupled between the bases, and there would be no difference in operating points due to resistor tolerances. This results in better symmetry, saves some components and power, and delivers improved performance without any drawbacks compared to separate base circuits. The frequency response remains identical to that of the separate base circuits. At the same time, the lower resistor of the divider could be replaced with an LED, which provides good thermal compensation of the operating point while also serving as an operating indicator. The same mistake as in point 2 has also been made in the emitter circuits. These, too, can be converted into a true differential amplifier without any drawbacks. This again saves several components and improves performance—without even affecting the output drive capability (large-signal behavior). The most serious error, however, is the incorrect signal tapping at the 220Ω collector resistors. The output signal of the base circuits is their collector current, or the voltage across the collector resistors—not the voltage at the collector relative to ground. If, as in LZ1AQ's circuit, the emitter circuits are driven against ground, then the supply voltage and any noise on it appear directly in the signal. Additionally, the operating point becomes highly dependent on the power supply. For these reasons, the circuit can only be operated with a stabilized supply voltage (the 10V regulator). This issue can be easily avoided by using PNP emitter circuits or a PNP differential amplifier. This improves power supply rejection by orders of magnitude compared to the original circuit, eliminating the need for supply voltage stabilization, reducing component count, and increasing output drive capability. The upper cutoff frequency of the original circuit is about 10MHz. It is determined by the effective capacitances at the collector resistance of the base circuits: the Miller capacitance of the emitter circuit, feedback and output capacitance of both the base circuit and the emitter circuit itself. The transistors are no longer suitable for these frequencies or dimensions because their capacitances are too large. According to the author, the circuit is supposed to maintain a flat frequency response up to about 40MHz. However, this is due to the input-side VHF filter introducing a resonance peak in the 10MHz–40MHz range, which compensates for the amplifier’s frequency response roll-off. I consider this an unclean approach. Much better performance can be achieved with more suitable transistors, such as the 2SA1015/2SC1815. These transistors are extremely low-noise, highly linear, have much smaller capacitances, and are very inexpensive. With these transistors, one achieves a significantly higher upper cutoff frequency, a higher slew rate, and a lower input resistance than with 2N2222A, leading to a lower cutoff frequency at the loop. Finally, I present the circuit resulting from the above considerations in the attached images and compare its characteristics with the original circuit. In both cases, the same 1m, 3.4mm AL loop was used, and the VHF input filter was omitted to focus solely on the amplifier’s characteristics. The input signal was kept the same in both setups, slightly into overdrive, to show the maximum output level. The operating currents of all stages are identical in both circuits. Conclusion: Significantly better performance despite much less effort. ? Source:
? Transistors T1/T2 and T5/T6 each form a composite transistor (Sziklai pair) configured as a common-base circuit. The base is clamped (via D1/C1), and the input signal is fed into the composite emitter. This composite transistor has a significantly lower emitter input resistance compared to a single transistor, which is essential since the lower cutoff frequency of the circuit is determined by the relationship: fu=re2πLf_u = \frac{r_e}{2\pi L}fu?=2πLre?? The two composite transistors operate as a base-coupled differential amplifier for the floating magnetic loop, which is connected to the two blocks at the bottom. The output signal from this input differential stage is amplified by the emitter-coupled differential stage T3/T4 and then fed via C8/C9 into a balun, which sums the output signals and provides high common-mode rejection. The resulting 50Ω output is floating (potential-free). C11 and C12 limit the upper frequency response and must be selected according to the desired bandwidth. I have used only C12 with a few picofarads. The input impedance of the circuit is 0.4Ω differentially (i.e., 0.2Ω per side), which allows for a lower cutoff frequency of approximately 20kHz (-3dB) with a 1m loop. The balun is simply a bifilar winding on a toroidal core and is connected like a standard common-mode choke, meaning both winding starts are connected to C8/C9, and the winding ends go to the output. The core must have low losses in the desired frequency range, and the winding inductance should be at least 100?H. ? ? ? |