Re: Why not a resonant loop?
This subject was extensively covered and commented on a few months ago.? I'd suggest you check the archives.
Personally, I don't want to tune the loop every time I chase something else.? They are extremely high-Q and tuning is required at BCB and HF frequencies for even a couple of 10 kHz.? No thanks.? My untuned loops work just fine!? I do have a single tuned 1-meter diameter loop I occasionally use for RCV and XMT on 40 and 20-meters during lightning season.? But on 40 the 2 : 1 bandwidth is roughly 6 kHz.? I don't use it too often.
Dave - W?LEV
On Sat, Mar 8, 2025 at 7:48?PM VLF Dilletante via <brownpiggin= [email protected]> wrote: I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
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?I am glad it was free. They are expensive capacitors!
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Re: Why not a resonant loop?
I have made several similar loops for BCB and NDB work. I wind the loop to about 330uH and use a BB112 Variactor to? resonate it, fed from a 0-10V Bias-Tee (indoors) . Very sharp / hi-Q and nothing expensive.
Here's the circuit, but with a different model loop using ferrite. Both the 1-meter loop and the rod loop work nicely with the BB112 circuitry.
Bob, N1KPR
-
- Youtube: N1KPR
- Youtube: Ham Radio Doctor
Engineering, where enigma meets paradox
On Saturday, March 8, 2025 at 02:48:51 PM EST, VLF Dilletante via groups.io <brownpiggin@...> wrote:
I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
?
?I am glad it was free. They are expensive capacitors!
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Re: Why not a resonant loop?
I like tuned loop antennas for AM BCB as well as for NDB chasing. I have a 45 inch on a side box 8 turn loop wound with
#12 magnet wire and also use it as a crystal radio set. A good tuning capacitor is essential. I recently was given a Comet vacuum variable
8 to 1000pf capacitor and it is great for tuning the loop. Very sharp tuning and no need for a vernier. Better Q than my air variables for the BCB band as the tuning peak is sharper and the signal is stronger.
?
?I am glad it was free. They are expensive capacitors!
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If anyone is interested in a loop amp, or a phaser, please contact me off list. everettsharp (@) aol.com
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Everett N4CY
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Re: LZ1AQ amp With 2SC3357
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
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Re: LZ1AQ amp With 2SC3357
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
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Re: LZ1AQ Active Antenna Amplifier (model AAA-1C)
yes any off your question
Den 2025-03-01 kl. 14:17, skrev Fred M
via groups.io:
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Show quoted text
What is meant?
Circumference of 3m or Diameter 3m?
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regards, Fred
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Re: LZ1AQ Active Antenna Amplifier (model AAA-1C)
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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LZ1AQ Active Antenna Amplifier (model AAA-1C)
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
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Re: LZ1AQ possible changes
Hi All,
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Very interesting thread.
I looked at the circuit introduced.
I felt nostalgia for the 2SC1815 and 2SA1015.
They like staple foods for us from the 1980s until around 2010.
The 2SA1015 was surprisingly low noise and was used for Rx Preamp in the then hit CB Band Amplifire.
I hadn't used a parts with legs in years, so I wanted to build one.
I wrote about it on my blog.
It is in Japanese, but I think it makes sense with machine translation.
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73, Hisami 7L4IOU
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Re: TX protection on RX Loop
A helpful free book on PIN Diodes:
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Regards, Fred
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Re: TX protection on RX Loop
Sure, there are several measurements available in the web:
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Thanks for pointing to the minority carrier lifetime (Tau) measurement.?
The paper reported the 1N4007's Tau = ~7 uS, phew! This value is way higher than what I have encountered in real PIN diodes (see below).?
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Tau (uS) ? ?Use
0.07 ? ?limiter
0.2 ? ?low-current switch
0.5 ? ?high-linearity switch, low-current attenuator
1.5 ? ?high-linearity attenuator
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If the reported 7 uS Tau is correct, then the 1N4007 will NOT be suitable for limiting because its turn-on threshold will be too high to be useful. If used as a switch, e.g. K2, then it will have very low distortion, but needs high bias current.?
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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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Re: TX protection on RX Loop
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
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Re: TX protection on RX Loop
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
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Re: TX protection on RX Loop
Guessing and throwing ill conceived "fixes" at an ill defined and misunderstood problem is certainly the average amateur method of "solving" misunderstood glitches and possible damaging conditions.?
Why not invest $100 in one of the NANOVNAs and actually MEASURE the isolation over frequency between antennas.? Then you will 1)? solidly conclude you do or do not have a potential problem, and 2) you will know how much protection is required, if any.? Hopefully, one can add and subtract (grade school exercises) simple values of attenuation.??
Dave - W?LEV
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 low frequencies is also well documented
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Re: TX protection on RX Loop
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
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Re: TX protection on RX Loop
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.
Getting special performance from simple components!
Andrew VK5CV
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Show quoted text
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:
?
The use of an 1N4007 as P.I.N. diode for low frequencies is also well documented
?
?
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Re: TX protection on RX Loop
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:
?
The use of an 1N4007 as P.I.N. diode for Shortwave frequencies is well documented. See Jims link:
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Re: TX protection on RX Loop
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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PIN diodes are segregated into either attenuating, switching or limiting applications depending on their minority carrier lifetimes. 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?
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73, Leong, 9M2LCL.
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Re: TX protection on RX Loop
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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https://qrp-labs.com/images/qdx/schem4.png
Bob, N1KPR
Everett N4CY
James Redding WA9VEZ