EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: hamster_nz on February 21, 2017, 10:15:50 am
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I've had a long term project which never made it to the top of the list to spend the time building- a pa0rdt-Mini-Whip LF/MW antenna, for use with a direct conversion SDR rig.
Interesting because of the small physical size - it is capacitively coupled to the e-field. This also gives it a wide flat frequency response.
The transistor footprint was flipped, but tombstoning three 0 ohm resistors and flipping the transistor fixed that. >:D
I'm yet to get it connected to the SDR (need connector), but had it on a USB scope's FFT as a poor man's spectrum analyser. The local MW stations stood out like the proverbial dogs bollocks vs that of a random length of wire, even without a decent ground reference.
Original design details are at http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf, (http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf,) but built with SMD and some of the parts were substituted (esp the JFETs for the front end).
Oh, I must buy some flux cleaner....
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Interesting project.
Here's my experiences when I built one a few years back.
https://www.youtube.com/watch?v=MTkVGN9tgQg (https://www.youtube.com/watch?v=MTkVGN9tgQg)
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Original design details are at http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf, (http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf,) but built with SMD and some of the parts were substituted (esp the JFETs for the front end).
There is an updated cricuit by PA0NHC that uses BF998 for the first FET:
http://www.pa0nhc.nl/Miniwhip/indexE.htm (http://www.pa0nhc.nl/Miniwhip/indexE.htm)
and also a version by RA0SMS, for sale on e-bay. also seems to use BF998.
http://www.ra0sms.ru/p/the-active-antenna-mini-whip-10-khz-30.html (http://www.ra0sms.ru/p/the-active-antenna-mini-whip-10-khz-30.html)
I just tested the original PA0RDT design against a long-wire (around 35m IIRC), looking at some LF time-code signals. The long-wire has a tuning coil for resonance at 136 kHz - so the comparison isn't entirely apples to apples...
Anyway the mini-whip seems to perform quite well and is significantly easier to find space for than the 35-40m wire!
For the TDF signal at 162 kHz the tuned long-wire provides almost the same signal as the amplified mini-whip.
I also made a ferrite-sleeve-loop, and a ~1m diameter coax-loop, but haven't had time to test them properly. For LF it seems SNR is key and it isn't obvious that a bigger antenna or more gain will help...
The time-code transmitters pretty large installations:
Anthorn, https://goo.gl/maps/nVymTZ7zi8L2 (https://goo.gl/maps/nVymTZ7zi8L2)
Mainflingen, https://goo.gl/maps/mKD297oE1rq (https://goo.gl/maps/mKD297oE1rq)
Allouis, https://goo.gl/maps/K71JtKVVGAz (https://goo.gl/maps/K71JtKVVGAz)
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Hi, dont worry, these antennas are quite tolerant to sloppy construction.
I made some of them in different sizes, all work OK:
https://electronicprojectsforfun.wordpress.com/antennas/active-antennas/