On Sat, Mar 1, 2025 at 05:04 PM, Mike M wrote:

They are listed as a "new" part,

Yes, because it is not the genuine 2SC3357 from NEC/Unisonic, which is obsolete since a couple of years. It is a new part from EVVOSEMI, a fabless Hong-Kong based company, specialised in second sourcing of obsolete discrete semiconductors.

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regards, Fred

Just an update. DigiKey has 2SC3357 back in stock. They only have 1009, so it looks like they just got one reel in. They are listed as a "new" part, so I think the issue has been supply chain related not that the parts are obsolete. They are $0.27 in quantity one and $0.18 in quantity 10, so less expensive than alternatives like BFU590QX.

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Mike M

Lars, what do you mean with "3 m Loop"?

Circumference of 3m or diameter of 3m?

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regards, Fred

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I am curioues if any one tested THE?

lZ1aq Active Antenna Amplifier (model AAA-1C)? with 3m wire loop or even longer wire?

A helpful free book on PIN Diodes:

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Regards, Fred

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On Fri, Feb 28, 2025 at 04:07 AM, Andrew Russell wrote:

Cool stuff!

I have a QDX 80m to 20m band model.

Hans couldn't get the 1n4007s to work on 160m or below so there are single band models for MF , LF and 6m.

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Above 10 * fc, the diode behaves like a resistor. fc = 1 / (2.pi.Tau) = 22.7 kHz. So, ?10 * fc = 227 kHz.?
So, if the 1N4007's reported Tau is correct, then it should work at both 160m and medium wave.?

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73, Leong, 9M2LCL

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OK. Curiosity got the better of me, so I decided to try Dave's (W0LEV) suggestion and make a measurement with my VNA. I happen to have an LZ1AQ loop right under my 80-10 EFHW inverted L. It happens to be about 25 feet from the vertical part, and 25 feet under the horizontal part. The VNA is set up to sweep from 2 to 30 MHz with the output port connected to the EFHW antenna. The input port is connected to the output of my bias-tee. The loop is on a rotator.?

Depending on the rotation of the loop, the various peaks and valleys move around quite considerably. The largest peak occurs when the loop is in alignment with the radiating wire, and is at 3.5 MHz and -18dB. Initially I was surprised by such a large return signal. But then I realized that the LZ1AQ amplifier has a gain of about 29dB. So the actual power into the loop is quite small even at this close distance. I will leave the input voltage calculation up to the mathematicians in the group, but my guess is it's below a volt. Remember that neither the 1m loop's output impedance or the amplifier's input impedance is 50 ohms. According to measurement Steve Ratzlaff (AA7U) recently made on this same loop amplifier design, the input impedance is around 15 ohms at 3.5 MHz. Have fun with the math.

As further background, my LZ1AQ does not have any input protection diodes or an input disconnect relay. I have operated 100W CW on most bands numerous times while the loop has been active without damage. Obviously if I was running a kW and had the loop closer I might have had issues.

73 Tom

If you’re protecting the loop amplifier from own transmission, then you will need to use a relay to cut the power and and ground the antenna input at the loop and the feed. Also placing the antenna several wavelengths and lower power reduces the the need for relays, provided you have a front end protection on each of the loop connections to the amplifier. Some people use back-to-back diodes

PIN diodes have an additional P layer which is why Sarkes Tarzian never got into that part of the technology. ST made some SCR's and 45KV 2 ma diodes were many layers of diodes stacked and soldered together.? Some of the ST "avalanche diodes" were doped with aluminum which is a "P" type material but that was before PIN variable resistance diodes were promoted as commercially useful. That was back in 1972 before we closed all the ST plants. I was a "project engineer" in the back of the ST Broadcast Division lab where we designed and manufactured RS-170 video special effects systems. My later business partner was the manager of the semiconductor manufacturing, the late Al Cain.

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But I need to apologize for diverging off the topic of "loop" antennas. Take a Poynting vector and plop it into:?

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Turn the "crank" and get a voltage out. . .

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Jim/VEZ

Get

On Fri, Feb 28, 2025 at 01:55 AM, <biastee@...> wrote:

I have seen hams using 1N4007 for attenuating and switching, but I think it is premature to decide on a suitable application without first measuring the minority carrier lifetime. Or has someone already measured them?

Sure, there are several measurements available in the web:

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The use of an 1N4007 as P.I.N. diode for Shortwave frequencies is well documented. See Jims link:

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QRP-labs is using 1N4007 as a PIN diode substitute band switch diode in its successful QDX digital TRX, Elecraft used the 1N4007 as PIN Diode in their famous K2 rig.
https://qrp-labs.com/images/qdx/schem4.png

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On Wed, Feb 26, 2025 at 07:13 PM, James Redding WA9VEZ wrote:

It will be informative to follow the link below:

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Hi Jim,
Thanks for referencing my paper. :-)
However, I will not recommend that limiter configuration for protecting the Rx loop. The described Schottky assisted PIN limiter has a ~10 dB lower turn-on threshold than a conventional PIN limiter, but it trades-off linearity; i.e. the Schottky diode is capable of mixing & detecting like a small signal diode. The achieved low threshold is useful for protecting sensitive transistors, but it is not required with the regular BJTs in Rx loops.?

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Some 1N4007 have a long carrier lifetime and behave like a HF PIN Diode.

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73, Leong, 9M2LCL.

Interesting question.?

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There are interesting amateur tests of the 1N4007/1N5408 as replacements for the Unitrode P-I-N characterised diodes. At least one experiment shows that 1N5408's were lower resistance than the purpose designed Unitrodes with one caveat: the recombination time of the 1N5408's/1N4007's is getting skimpy (not long enough) for perfect use at 160M.?

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or

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Considering the unknown sourcing issues of modern devices, and the clever re-marking methods, I have no confidence that parts sold with jedec registered numbers will meet specifications, much less undocumented specifications.

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Or as one person famously said, "Trust but verify!", which is why I included the links.

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Jim/VEZ

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Hi Fred,

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I agree with the points you are raising, with some caveats.

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In a 50 ohm system, a pair of 1N4148's or similar small signal silicon diodes will limit at somewhere around +10dBm, and second and third order (two tone) IMD, at average signal levels, (peaking around-30dBm max) will typically be at, or below, the noise floor of an average receiver, in an average location.

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E-Probe, high impedance, antennas are tricky, and it's usually necessary to and more diodes to a string, or provide some reverse bias, to offset the point of conduction. Loops and relatively short E-Probe type antennas generally don't develop a high enough voltage across the diodes for IMD to become noticeable. Plus, many designs are pretty poor in terms of IMD performance anyway, and I suspect that additional IMD produced by the protection diodes, would probably go unnoticed.

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Sometimes we have to trade one problem for another, and it's a user's choice which is preferable.

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Regards,

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Martin

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On Thu, Feb 27, 2025 at 11:35 AM, Fred M wrote:

Icom uses a pair of 1SS302's to help protect the FE of the IC-R75 receiver.

They are very fast & I use them in a protection circuit I built for my receivers downstairs in the torture chamber (repair lab) where I torture old radios.

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-Bob

It is a common misconception that there is a sharp forward voltage threshold for diodes and that there is no current flow below this "forward voltage". A diode is an amplitude-dependent, non-linear resistor, described by the Shockley equation. The non-linearity also exists at small voltages and is the reason why IM Products occur even with samll RF levels below the "forward voltage".

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regards,? Fred