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Just compared 2SC5551 to 2SC3357 in an LZ1AQ amp. There is almost no difference in IP2/IP3 and frequency response. I was going to post to say the 2SC3357 are available, but looking at Digikey there are only 9 in stock. It says one week factory lead time and new product, so I assume they are still in production. -- =================================================================== Mike M

I am curioues if any one tested THE lZ1aq Active Antenna Amplifier (model AAA-1C) with 3m wire loop or even longer wire? 73 Lars sm4ive

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: 1. Output Transformer Issues Output transformer has too low an inductance (18?H, actually likely ~10.2?H). Results in too high a lower cutoff frequency (~500kHz or even 800kHz). Incorrect dimensioning limits low-frequency performance rather than the input resistance or loop inductance. 2. Base Circuit Design Issues Separate base voltage supplies used instead of a proper differential amplifier. Better approach: Connect bases directly for true base-coupled differential amplifier. Eliminates unwanted differential voltages. Improves symmetry, reduces component count, lowers noise. No issues with biasing due to resistor tolerances. Enhancement: Replace lower divider resistor with an LED for thermal compensation and power indication. 3. Emitter Circuit Design Issues Same as above: Should be a true differential amplifier. Converting saves components, improves performance, no downside. Output drive capability remains unchanged. 4. Signal Tapping at Collector Resistors Output should be collector current/voltage across resistors, not collector voltage to ground. Incorrect method introduces power supply noise into the signal. Fix: Use PNP emitter circuits or PNP differential amplifier for: Massively better power supply rejection. Eliminating the need for regulated supply voltage. Improved output drive capability and fewer components. 5. Frequency Response & Component Choice Original upper cutoff frequency: ~10MHz, due to capacitances in base/emitter circuits. Author claims flat response up to 40MHz—but only due to input VHF filter resonance. Better solution: Use 2SA1015/2SC1815 instead of 2N2222A for: Lower noise, better linearity, smaller capacitances. Higher cutoff frequency, higher slew rate. Lower input resistance → Better low-frequency response. 6. Final Circuit Comparison New design vs. original tested with 1m, 3.4mm AL loop, no VHF filter. Same input & bias currents, measured max output level. Conclusion: Much better performance with significantly less complexity. 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: Proposed circuit 1 Source: https://www.mikrocontroller.net/topic/523344?page=1#6790749 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. Proposed circuit 2: Source: https://www.mikrocontroller.net/topic/523344?page=2#7450453 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.

Hi group! 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). 73's Hans / LB6GG Sola, Norway

I just saw this RCA rotor on sale, I don't know that is is precise enough, because it is programmable for every 10 degrees. I haven't read the manual far enough to see if you can precisely set direction to null your noise sources or if you can fool it to ever 5degrees by only turning 180 degrees. It is $89 on sale with rebate. $14 shipping, at least to me in Fl. https://www.menards.com/main/electrical/electronics/antennas/rca-outdoor-digital-tv-antenna-auto-rotator-with-remote/vh226f/p-1544513354915-c-1454940301502.htm Here's the manual, https://www.rcaantennas.net/docs/common/VH226E/VH226E_OM.pdf Mikek

Good Afternoon all, After years of chasing MW DX with "real" hardware, I'd like to try SDR and would appreciate recommendations about what I need to get started. In particular: (1) Are any of the inexpensive USB dongles suitable for MW, or are they "toys" and I should look at more expensive hardware? (2) At the entry level, whose hardware is generally accepted as being good, which should I avoid? (3) Is a frequency upconverter required to receive MW Thanks for any comments or recomm

Found this on another group and thought it might interest someone here, but not for the budget minded: https://www.netsandmore.com/products/fishing-accessories/fiberglass-hoops

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. If there is any interest, please contact me off list at everettsharp (at) aol com. Everett N4CY

Hi Folks, I recently built the PA0FRI active loop receiving antenna for HF (shortwave) use. The reception results have been highly impressive, especially considering the extremely constrained space where the antenna is installed. I have made the entire project open at the following URL: https://github.com/kholia/DDX/tree/master/Active-Antenna Total cost: Roughly 10 dollars (including professional PCB, BOM, IP65 casing, aluminum loop and all). I hope this work is useful for you. Feedback is welcome! Cheers, Dhiru (VU3CER + WQ6W)

I tried to follow recommendation from Chavdar's app note in regards to feed cable location (for vertical dual loop configuration). Here is a picture: https://photos.app.goo.gl/P1vSAeefdMkj4WYc8 Although in the notes Chavdar recommends 1-2m offset for the cable behind the loop's plane. I only have ~60-70cm (2ft) due to some space restrictions. I noticed that in Dipole mode I see about 5dB drop in AM BC station images in the lower 80m band. That's due to CM issues in dipole mode. Not sure if that was worth the hassle as loop mode is still superior in my noisy environment (semi-urban location). I also noticed that top loop (Loop A) usually provides better s/n ratio compared to lower loop (loop B) and cross-parallel connection of both loops. I see that on most HF bands. Sometimes LoopA=A+B but usually I just use loopA. I was wondering if that's due to the cable that was hanging right across the lower loop. New cable placement improved things a bit but I still see LoopA normally being better or equal to A+B configuration. LoopB is still normally worse than other two configs (A, or A+B). Next I may try to put more clip on ferrites along the portion of the cable that hangs below LoopB. Maybe mix31 and mix75 clip-ons combined on the length of 1-3m up to the point where cable comes to the wall. I already have a stack of two FT240-31 with ~6 turns of CAT before cable leaves the amplifier box and a stack of three FT240-31 with 6 turns before it enters control switch box. That actually helped a lot but I wanted to improve things even more. I wonder if Loop A is better simply because it's higher in the air and further away from my "shack" that's 2-3m away from the antenna physically. Also may try to place Yaesu GS-050 mast bearing a bit lower. Right now it sits right below the lower loop. Wonder if that can create any un-balance issues. Regards, Simon KM6MUL

I am thinking of making a VLF loop out of a 10 ft piece of PEX pipe with many turns of wire inside the PEX and a plastic junction box on the bottom. I have read several articles about doing the same thing with copper pipe as the shield and making a gap in the top center of the pipe. The purpose of the gap is to shield the windings from electrical noise and allowing the magnetic waves inside the pipe. There are several articles on how to shield VLF antennas ie; Ferrite Rods, from electrical noise. Making copper pipe loops and metal electrical boxes at the bottom and cutting a gap in the pipe at the top is basically the same as shielding the Ferrite Rod with aluminum and leaving an air gap for the magnetic waves. Pex is a different animal as if you cut a gap in the top of a PEX loop, you lose the round loop. So my question is this. What if I keep the round loop attached to the plastic electrical box and shield the entire round loop with #80 copper mesh and not the box, would I have the same shielding as an the copper pipe loop? Fred N4CLA

The following items have been added to the Files area of the [email protected] group. /BD3OLH.rar By: 钱志豪 <qianzhihao2002@...> Description: 我设计了一个分裂定子蝴蝶电容，有需要的可以看看

Just tested the LZ1AQ amp with BFU590QX. Performance equivalent to the 2SC5551. As with the 2SC3357, the max voltages are lower for the BFU590 than for the 2SC5551. However, just like with the 2SC5551, the voltages in the LZ1AQ circuit have plenty of margin. Both Mouser and DigiKey have the BFU590QX in stock. -- =================================================================== Mike M

Hi all, I have been reading with lots of interest the post by AA7U Steve on his findings and modification experiments with his GA-450. Steve, did you find that after doing the modification to power the RF board directly with 12 volts DC, that there was less noise generally, or was that only in this particularly troublesome MW to 3MHz section? I have been having fun experimenting with my as yet unmodified GA-450 and, providing I turn my radio's gain way down low, have been rather impressed with the results. It's an improvement over the telescopic whip and it's nice to be able to have some directivity. However, the gain is rather excessive in my opinion and I wonder if anyone has any ideas how that might be reduced......? I have no experience with varactor-tuned loops, but have buils lots of other types, and my latest activie antenna for MW and HF can have the gain adjusted by reducing the voltage to the AMP. I'm guessing a similar arrangement will not have quite different results with the varactor set-up and just lower the maximum tuned frequency........ The photos you have posted in the files section Steve will be invaluable if I decide to do any modifications. But it would be sad to lose it's portability. Anyway, hope someone can offer a little bit of advice! Thanks. Adam (M6RDP

With the recent talk about oscillation I thought I would share a recent debug. Summary: have multiple ferrite bead types on hand. I made a PCB for the Ikin Norton Amp: /g/loopantennas/files/Wellbrook%2050%20ohm%20Norton%20Preamp/Ikin%20Norton%20Amp%20sch.PNG.jpg It is a 2-layer PCB with ground fills. I built one using 2SC3357 transistors and it worked. I built a second using 2SC5551 and it oscillated at 660MHz. It also did not amplify. I checked and double checked the transformers but could find no difference between the two boards, but then I found the amplification problem: one end of the T1 primary was soldered but had not melted the enamel on the wire so it was not actually connected. But it still oscillated. The ferrite beads I used are Laird MI1206K310R, which are about 41 ohms at 1GHz. I tried replacing them with 68 ohm resistors but no change. I tried replacing the 10pF caps with 39pF, still no change. I then put the 10pF caps back and put Laird LI1206H121R-10 ferrite beads in and it tamed the oscillations. The new ferrite beads are around 135 ohms at 1GHz, so that is what it took. So don't be afraid to use high fT transistors, but make sure you have a ferrite bead in the design as well as a variety of ferrites to test. I just looked at the data sheets. The ZTX327 used in the original has an fT of 800MHz, the 2SC3357 is 6.5GHz and the 2SC5551 is 3.5GHz. So even though the 2SC3357 has a higher fT than the 2SC5551, it did not oscillate. -- =================================================================== Mike M

Hello, lots of great info here. I am new to the group IO format, just created an account. I have been paging through the topics and tags but I cannot seem to find anything that deals directly with the shape of the loop material. I have been debating building an upgraded receive only loop. I see most loops are made of round material, either tubing, wire, coax etc.. i am wondering if using sheet metal cut to a certain width then passed though a 3 pin roller to achieve the correct diameter would be OK? The 3 pin can also take up to 3/8" solid or hollow round stock. How wide would be too wide? Thanks a lot

If anyone is interest in LZ1AQ boards, Transistors, or Built and Tested LZ1AQ amps you can contact me off list. at everettsharp (at) AOL com Everett N4CY

Seeking advice for “upping my receive game” during Field Day Contest operation this coming summer. On Field Day, multiple operators are usually grouped physically (and socially) close but some don’t always respect band schedules & bandpass filters and which means I generally I can talk better than I hear hear because of interstation receive interference. On FD I transmit 20-10M bands using a 17’ vertical + Base autocoupler + directional radials all mounted at 10’ AGL that gives fine directional transmit but my receiver is overloaded with other on-site contestors. I’m wondering if a receive-only loop located as far away from other antennas (up to 1000’ allowed) and taking advantage of loop directionality might help? 1. - Would commercial 1M receive loops be directional enough on 10-30M to be helpful? 2. -Would locating the loop to the edge of the 1000’ contest area, far away from other Hams, be woth the effort? 3. - Would the LZ1AQ likely function OK over that 1000’ length of CAT interconnect? Or, maybe a better approach is the rather expensive DX Engineering NCC-2 Receive Antenna Phasing Systems DXE-NCC-2 to null out local noise with a 2nd local-only antenna? https://www.dxengineering.com/parts/dxe-ncc-2 I’d appreciate anyone’s experience or ideas! 73…John

In case anyone is interested, I bought an LZ1AQ type amp from Everett before Christmas and finally got it up today. I'm using a 4 foot loop made from 1/2 hardline, fed with about 50 feet of RG6, and 8 feet AGL. I was fat, dumb, and happy with my homebrew amp based on the G8CQX design with a pair of 2N5109 transistors and a 3 foot loop of the same material but as a mobius. The difference is amazing. Just as a point of reference for myself , I am now receiving solid copy NAVTEX on 518Khz from Labrador and seeing signals from Greenland. Those stations where not even a squeak previously. Florida and PR boom in like they are local. I am in coastal NJ. NDB stations are all over the place. 160 and 80 are a pleasure with an S1 noise floor and very little reduction in signals from my transmitting antennas. Good stuff!

I had some MPS2222 transistors and built up a quick LZ1AQ and swept it, with the sweeps and picture of the ugly-build added to the Photos. This is only for comparing with Caaarlo's build and sweeps (thanks, Caaarlo, you did a nice job building yours). His nanovna sweep didn't include gain sweep. I used the DG8SAQ VNWA with the same two frequency sweeps, and with calibrated-out 1:1 input transformer (unbalanced to balanced) which shows both input impedance and gain on the same sweep. I used -30 dBm input level to ensure the loop amp is not overloaded. I'm not sure what transformer and turns Caaarlo used; I used a BN73-302 binocular core with 8/8:6 turns which is what I use with a nominal 50 ohm coax cable output. (Same as what Everett Sharp N4CY's LZ1AQ PCB uses.) The transistors run out of gain-bandwidth product at 30 MHz as you can see from the sweep (the gain is rolling off). Caaarlo's loop amp should have similar gain since both used the same transistors. /g/loopantennas/album?id=296351 If that doesn't work, search Photos for "Steve LZ1AQ Sweep".