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I've uploaded to the Files a relatively simple one transistor 50 ohm preamp with +30 dBm OIP3 that can be built using common transistors and used to check your own IMD test set. I tried seven different transistors, three different types, different brands. Use a power supply you can set to 12.0 volts, as IMD is sensitive to supply voltage, to obtain the same results that I got. /g/loopantennas/files/50%20ohm%20Preamp%20with%20+30%20dBm%20OIP3 73, Steve AA7U

Raphael Wasserman <wassermanr46@...> added the photo album Short Current Mode of SMA : Equivalent Circuit of Small Closed Loop Antenna

Addressing skin depth: For copper: Conductivity: σ = 6.30 E +7 S/m Resistivity: 1/σ = 1.60 E -8 Ωm Skin Depth: 2.47 E-5 m Frequency of following analysis: 7.000 MHz For the above, refer to: https://www.nessengr.com/techdata/skin/skindepth.html and https://www.everythingrf.com/rf-calculators/skin-depth-calculator From the same reference the resistance due to skin depth can be calculated: For my 36-inch diameter loop made of 0.5-in copper tubing (and converting everything to the MKS system) the resistance due only to skin depth comes out to be: 0.0952 ohms At 1 MHz, this will be "roughy" 0.1X of that value and at 100 MHz, this will be "roughly" 10X of that value. These are only roughly. But it does indicate some frequency dependance. However, in all cases from 1 MHz through 100 MHz, the added resistance is considerably greater than the DC or radiation resistance. So, I'd conclude current in the loop should vary with frequency as a result of skin depth. In addition, the variation between "DC" and 30 MHz should be only a factor of "roughly" 10. Interestingly this goes against the EZNEC analysis presented earlier. It showed current pretty much constant even up to resonance. Guess someone needs to actually measure current as a function of frequency with a constant RF input level. I can short my 36-inch tuned loop to do that. Anyone else want to contribute in this measurement???? Dave - W?LEV

Addressing skin depth: For copper: Conductivity: σ = 6.30 E +7 S/m Resistivity: 1/σ = 1.60 E -8 Ωm Skin Depth: 2.47 E-5 m Frequency of following analysis: 7.000 MHz For the above, refer to: https://www.nessengr.com/techdata/skin/skindepth.html and https://www.everythingrf.com/rf-calculators/skin-depth-calculator From the same reference the resistance due to skin depth can be calculated: For my 36-inch diameter loop made of 0.5-in copper tubing (and converting everything to the MKS system) the resistance due only to skin depth comes out to be: 0.0952 ohms At 1 MHz, this will be "roughy" 0.1X of that value and at 100 MHz, this will be "roughly" 10X of that value. These are only roughly. But it does indicate some frequency dependance. However, in all cases from 1 MHz through 100 MHz, the added resistance is considerably greater than the DC or radiation resistance. So, I'd conclude current in the loop should vary with frequency as a result of skin depth. In addition, the variation between "DC" and 30 MHz should be only a factor of "roughly" 10. Interesting this goes against the EZNEC analysis presented earlier. Guess someone needs to actually measure current as a function of frequency with a constant RF input level. I can short my 36-inch tuned loop to do that. Anyone else want to contribute in this measurement???? Dave - W?LEV -- Dave - W?LEV

The following photos have been uploaded to the Short Circuit Current for SMA photo album of the [email protected] group. Small-Magnetic-Loop-Antenna_0002.jpg By: Raphael Wasserman <wassermanr46@...>

Raphael Wasserman <wassermanr46@...> added the photo album Short Circuit Current for SMA : Based on Chavdar Levkov's paper "Very Weak Signal Reception with Small Magnetic Loop Antenna". I added my remarks by handwriting.

Raphael Wasserman <wassermanr46@...> added the photo album Short Current Mode of Small Loop Antenna : Chavdar Levkov's published article

Hi everyone, I know it's a bit of an off topic but I'd like to have recommendations on good preassembled mini-Whip antenna. Either as an assembled board without the housing or 100% assembled in the housing with connectors. Want to play with diversity receptions a bit more by accompanying my Loop receive antennas with mini-Whip. I see some being sold on eBay/Amazon/AliExpress. Not sure which ones are better design and which ones are not. I found some recommended designs but from years ago. Need something good currently available. Thank you, Simon KM6MUL

Evening all, I am working on building NCPL antennas. One question, what difference can I expect by laying it horizontal compared to vertical? Also, Would it perform differently horizontally at different levels off the ground? On the ground 5 feet off the ground, 10 feet??? TIA

Good morning, I wanted to tell you about a problem I'm having with the BFU590s (assuming they are) with which I made a replica of the ALA1530. The one I've used so far has always worked well but it uses PN2222. I then made a second version but with BFUs instead of PNs. The BFUs are marked "S59 W42" and I got them on the Italian TME ecommerce platform (www.tme.eu) and not on Aliexpress or some China page on Ebay. In practice it is impossible to calibrate the 100 ohm trimmer to 0 volts, the absorption always tends to rise, sometimes 140 mA, then it goes to 170 or worse, sometimes then it drops to 160-150 then rise again... and in any case the amplifier doesn't work. There is no point in trying to calibrate it even finely, sometimes I see the voltmeter pointer vary on its own (self-oscillations?). The rest of the circuit is built exactly like the version with PNs, same values ??and everything has already been verified several times. If you have any suggestions for me, I would be grateful. Greetings, F.

Hi, I have scanned and uploaded my collection of (historical?) Wellbrook price lists and data sheets from 1999, 2004 and 2007. Hopefully that may help people trying to date the various products and the development. /g/loopantennas/files/wellbrook_datasheets Also worth mentioning that the polarity of the antenna interface connector changed from +ve to -ve inner at some point, and maybe changed back again on later models? I have some from 2007 that are -ve inner that came with LFL1010 loops and the instruction manuals reflect this. 73 Nick

Hi - I am trying to calculate a small transmitting loop from LMR400 using the Pacific 66 calculator site. Does anyone know the actual diameter of the LMR400 shield once the black insulator is removed? The actual diameter size is required form accurate calculation. Appreciateyour help. John - W3JED

I just finished building another batch of LZ1AQ loop amps to fit the Wekkbrook ALA1530 loop. If interested please contact me off lis tat everettsharp@... everettsharo (at) aol com Everett N4CY

Hi All - Does anyone here use the W2LI magnetic loop from TriCountyRadio.org? They used to sell direct, more recently they sell through eBay. I have read the eHam reviews and it sounds like in addition to the advertised 20, 30, and 40 meter transmit, they also can transmit on 17 meters with workable SWR. I was just curious if anyone has used one of these and can also verify if they work for 17 meters. I have an Alpha Antenna 100W mag loop and its great across these bands, but the W2LI looks a bit more compact/portable when broken down and definitely less expensive to take in the field than the Alphaloop (which I leave set up and use at home). If you have experience with the W2LI, I would greatly appreciate your inputs. Many thanks, John - W3JED

Hi All, Today's amusing fact. The Chinese MLA-30 loop, that I reverse engineered some time ago, and then put my version of the circuit on my website, has been cloned by the Chinese :-) The original PCB had no component designators, but one of the clones I have seen photo's of has, and they are the same as I used in my circuit diagram. You couldn't make it up... Regards, Martin

Mostly by dumb luck I've managed to build a SW loop that seems to work well. It's made of 1/2" OD copper tubing, about 34" across, with a 10" x 7 1/2" coupling loop made from 8 AWG copper wire about 1/16" (the thickness of a ty-wrap) from the main loop. The coupling loop is connected to a dual banana female socket with banana connectors. On the other end a 15' length of RG-58 goes from the BNC to the back of my radio. The antenna has prominent nulls and is very directional. Combining that with an old 3-section variable capacitor allows me to tune from ~4500 kHz to ~18000 kHz. The only reason I went into the above is that I'm always looking for suggestions to make it even better. If anyone sees anything I'm missing here I'd certainly appreciate hearing about it... thanks! Earl

Given my off topic thread won't die, it's clear I'm not up to be a moderator on this group. Meaning well isn't enough in life and I demonstrated an atrocious failure in judgment by starting the eterna-thread, a failure of judgment that demonstrates I'm not suited to be a moderator. I hope the remaining moderators can continue to act as weed killers and kill each and every post regarding MJ growhouses. I've enjoyed being a member of this group, learned a lot, I'd like to thank Martin for confirming a goniometer is less then optimal for electronically steering the aim point of two cross phased loops and I'd like to thank Everett N4CY for offering high performance loop at an extremely reasonable price. This would turn into something the length of War and Peace if I tried to thank everyone who has helped me understand the subtleties of loop antennas, so a bit thank you to the entire group. I've learned more about loops in the few years I was a member of the Loop Antennas IO Group, but I believe it is time for me to leave the group. Good luck to group members and, to those offended by my eterna-post, I'm sorry. Accepting responsibility means accepting rational outcomes.

I'm not sure when the ALA1530LN version was first introduced. I've saved this Wellbrook ad of April 2021 which talks about an improved version with higher gain--note the ad does not mention comparing it with his earlier ALA1530 (now WellGood version): -------------------------------------------------------------------------- "A new version of the world famous Wellbrook Active Loop ALA1530 50kHz-30MHz 1m dia. Aluminium Loop---- As of April 2021 the amplifier gain has been increased to +28dB. This Balanced low impedance Magnetic loop has enhanced performance compared to shielded and Moebius loop types. The new JFET design affords a considerable reduction of noise compared to low cost loops using MMIC (Monolithic MicrowaveIntegrated Circuit). MMICs are designed for Microwave use and therefore are unsuitable for LF to HF loops. Furthermore, MMICs use integrated resistor feedback, which limits the noise figure to a minimum 3dB at HF. At Medium Frequencies loops using MMICamplifiers can have a Noise Figure as high as 8dB plus high IMD (Intermodulation Distortion). Compared to the W6LVP loop, the ALA1530LN affords a much lower noise floor with an average of 6-8dB higher gain with much lower IMD. The ALA1530LN has a noise figure of approximately 0.2dB which give a noise floor that is 13dB lower compared to a similar gain loop amp with a noise figure of 3dB. This antenna and its big brother, the ALA1530LN Pro Imperium are the only 1m dia. Active loops in production to use an ultra low noise JFET design. The loop has recently had a significant design change to improve LW/MW and SW reception. The ALA1530LN has been engineered to increase the LW and MW signal to noise ratio s/n by up to 10dB and provide an increased s/n on the HF bands. The LW and MW 3rd order IMD is now approx. 20dB lower. This being a combination of reducing the gain a little and the lower IMD of the JFETs. The new ALA1530LN is the second generation of this antenna and uses 8 very high gain JFETs in parallel push-pull with a Bipolar transistor cascode stage for extended bandwidth. A very low amplifier noise floor is achieved by dynamically decreasing the JFET Source resistance to a fraction of an Ohm. This is achieved using a proven technique developed in the 1980s by coupling the FET Gate to the Source with a phase inverting transformer. The loop works by designing the amplifier so that the very low noise of the loop's real resistance is mismatched to the input impedance of the low noise amplifier. Hence, reducing the amplifier noise floor by up to 13dB compared to more conventional low noise amplifiers.Also JFETs are less noisy at low frequencies compared to Bipolar transistors. The amplifier also has a rising input impedance versus frequency to match the loop's reactance; this together with Ultra low noise JFET design is a technological breakthrough. The mechanical design is now improved to afford increased reliability and to facilitate ease of servicing. The amplifier is now housed in a separate module, thus isolating the electronics from the mechanical stress caused by wind loading on the loop. The amplifier to loop wire terminations use tin plated silicone insulated wire and crimp terminals rated down to –40 Celsius. The module sits on top of the loop box and is secured by stainless steel screws. The base of the loop is now reinforced with an acetal rod to minimise damage due to weather extremities. The amplifier module can be easily replaced in the unlikely event of a failure, without the customer having to purchase a new loop antenna with the associated higher shipping costs. A resettable fuse and a power-on LED are now fitted to the Antenna Interface. Additionally a power limiter is fitted to reduce overload of receivers co-located with transmitters." ------------------------------------------------------------------------------- I would say the jfet version has a little higher gain than the bipolar version, and has a lower noise figure. Obviously with 8 jfets it's quite a bit more complex. But my own tests have not really shown much actual difference in

I'm building a medium wave antenna, 24" x 24" box loop, 20 AWG wire, 365 pf air gap variable capacitor (at least that's what I'm starting with). I'd certainly appreciate suggestions on the best design for a coupling loop for such an antenna, thanks! Earl

Kits and Parts has been my go to source for ferrites and other RF odds and ends. A friend just told me Dieter "Diz" Gentzow, W8DIZ, lost his battle with his illness yesterday, March 3rd, 2024. I have no idea how long Kits and Parts will continue, so it might be a good idea to think about parts they have that you will need and get that order in pronto.