Hello all,

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I'm clipping an onto a W2LI magnetic loop antenna. I'm puzzled by something: the point at which it shines brightest is consistently about +20 kHz above what a NanoVNA (and the transceiver) indicates is the bottom of the SWR curve (on 40M).

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What explains this? Is this a case where lowest SWR isn't necessarily where the maximum RF radiation is? Defective unit (would love to know what's inside)? User error?

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Thank you!

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-Todd

Dear people,

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What a great quick support offers from you.

I have made a deal with Matt to help me getting those PVC boxes.

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Those, together with my own Alu bending machine and the N4CY PCB which fit perfectly in those boxes, will complete my home made loop :factory"...hi.

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I will post a picture as soon all is fixed.

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Thanks agn fr the great support!

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73e Michael

PA5M

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Did anyone mention CPC? may also be available through Farnell their parent company.

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73

Nick

It seems that the exact Schneider part is also available from:

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and

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Feel free to email me directly (correct on qrz.com) if I can help.

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Matt

M0LMK

KI5GXV

I would be happy to post you some of these if you cover the cost.

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Matt

M0LMK

KI5GXV

Hi, Jorge here (M0LDW...also LW5DX) in Leeds. I found them in different variants in Amazon UK. I don't think there will be an issue with the stock.

The way to search is looking for: "20mm Conduit 2 Way U Box" if galvanised metal, "2-Way Through Box, 20 mm Syste m, White", "2 Way Through Junction Box 20MM BLK, Conduit Fittings Bodies/Boxes Cable Management", or "PVC Conduit Circular Boxes Two-Way-Through- 20mm / 25mm".

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I hope it helps and keep me informed on the advances!

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73 DX DE Jorge, M0LDW in IO93FU

Dear UK ham,

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I am building my Wellbrook copy with the PCB from Everett.

This PCB fits into the original enclosure: 20mm 2 Way Through Junction Box - White.

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Unfortunately it is out of production with Schneider Electric as of Octiber 2024, but I found an online shop who showed they them in stock.

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I am not sure if those are still commonly used in the UK, but perhaps you can give me advice.

Tnx in advance!

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73e Michael

PA5M

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Goodmorning, An answer to your appreciated questions...

Ratzlaff - I posted a picture of the edge of my NanoVNA on S11 port, it says "+10 dBM - 10 VDC Max". I think the signal processing levels are these... /g/loopantennas/photo/299839/3874275?p=Created%2C%2C%2C20%2C2%2C0%2C0

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Dave Martin - What can I say, I use these capacitors in all my electronic constructions... I can say that I can trust them...

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W0LEV - In fact the reason for my schematic was to know exactly how to do the amplifier test chain with the NanoVNA. I have updated the drawing, also based on Tom Anderson's indications. Here is the updated image: /g/loopantennas/photo/299839/3874274?p=Created%2C%2C%2C20%2C2%2C0%2C0

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Tom Anderson: As stated before, I have updated the image for the chain test NanoVNA - LN Amp: /g/loopantennas/photo/299839/3874274?p=Created%2C%2C%2C20%2C2%2C0%2C0

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FEI666888 - Winding is correct as in the drawing. The secondary of T1 is unpaired, you can check this easily seeing one of my boards pics: /g/loopantennas/photo/299839/3872459?p=Created%2C%2C%2C20%2C2%2C0%2C0 and /g/loopantennas/photo/299839/3872458?p=Created%2C%2C%2C20%2C2%2C0%2C0

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Thank you all again, Francesco Caizzi IU4TSV.

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I agree that oscillation is possible, but it should be noted that the amplifier is push-pull, and the 1T coil driving the transistor needs to be in opposite phases.

You can view the schematic diagram here

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I used a stereo microscope at work daily for the last 10 years of my electronics career. The B&L were most common, but I used my personal Zeiss scope. The B&L scopes were used with fiber optic halogen light sources that could brand your skin if you touched the bright end. My scope had a florescent ring light. In my opinion the ring light gave the most even lighting, but it had cool white color spectrum and that made reading resistor color codes a problem. I do not have any experience using LED ring lights made for video cameras but I expect they would be perfect for the purpose. ALL of the scopes had added 0.5x adapters added to the final lenses. That halves the total magnification but doubles the working distance under the scope. That is really a requirement. The adapter lens is also cheap protection for the expensive lens system of the microscope. You absolutely want to protect the expensive scope from deposits of crud from solder smoke and spitting flux or anything else coming off your work piece. All of the B&L scopes had 10x eyepieces. The 0.5x adapter made that 5x actual optical magnification. My scope had 15x eyepieces, but I used it at 0.5x zoom level. The added 0.5x adapter made that about 4x optical magnification. I preferred having slightly more field of view but could still zoom in if I needed more detail. In actual fact, many of the other techs used their florescent adjustable arm bench lamps with a 6" glass lens in the middle. With young eyes that gave enough magnification to do the work but I could always tell the difference when I compared their work against similar work done under a microscope.

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Those bench lamps had around 2x-3x magnification but had excellent eye relief and around 6" (15cm) working distance. It is critical to have enough working distance to get your soldering iron under the lens system. The more magnification, the less working distance. The 10x 4" adjustable arm desk lamps I see on Amazon claim to have useful working distance. When I tried a 3x headband, I was worried I'd burn my nose with the soldering iron.... I tried a 10x jeweler's eye loupe but that was useless except for doing close inspection. I haven't tried a video camera system but I look at them online. I've considered playing around with cheap USB computer cameras, USB inspection cameras, or fancier DLSR cameras with close-focus lenses. For a DIY system I'd recycle a gooseneck desk lamp as the camera mount and use a LED ring light with the camera. I've ordered a 10x 5"x3" magnifier adjustable lamp from Amazon to try. I ordered one with 19" arms so it can mount further back on the table.

What I mean is that the input coupling capacitor may not be the value it's marked with.? In 40 years of repairing electronic equipment I've run into many cases of mismarked, or maybe just floor sweepings parts.? We had a package of .1 uf bypass caps that all measured about 15pf and a bunch of 2N3055 transistors that were PNP not NPN and the best ones were 1% resistors that measured not closer than about 20%.? My "guess" is just that like all the other guesses you have received.? I've found it pays to not overthink the problem until you have checked the simple things first.? I've been guilty of not checking the power supply first, many times, when I was in a hurry.? 73? Dave

The saturated output power of meany of the decent loop amplifiers is >+20dBm, which can easily damage a Spectrum Analyser input.

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I was always taught to put an external 20dB attenuator on the input to the SA, as a sacrificial item, in case you accidentally squirt too much RF or DC into it. This was back in the day, when SA's could easily cost >$50,000. But even with a $150 item, I still think it's worth doing, as you hardly ever need to use the SA full input sensitivity, and you nearly always remember to take more care if you have removed the attenuator for some reason.

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Regards,

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Martin