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Technical Topics => Equipment => Topic started by: Rafman on September 02, 2014, 2259 UTC
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I have been poking around here lately & found these 2 offerings very interesting...
Antenna Amplifier & Delay Line: http://active-antenna.eu/
Anyone use these?
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Chavdar Levkov, LZ1AQ does some good work, and if you pick and poke around his site there is some very useful info.
I have seen these amps, but have no use for them at the present time.
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Yes, one of my favorite antenna sites.
His antenna amplifier design is one of the best available anywhere.
Plus plenty of good loop info...
Of course, JFarley has a lot of good loop info as well....
You might also enjoy looking through the VE1ZAC site as well. Lots of excellent antenna discussions: http://www.ve1zac.com/ (http://www.ve1zac.com/).
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Radio Netherlands used offer instructions on a 1 meter square MW loop, which worked fine by itself. However they included a schematic of a simple low noise preamp you could use with it. (Building the RN MW loop is the step that started my addiction to the things. Be careful! )
I've got the schematic of the amp but my copy is so grainy I can barely make it out as is. Maybe one of the web wizards that reside here can find a clear schematic of the RN MW loop pre-amp online?
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He has a pdf file with several loop antenna designs here: http://active-antenna.eu/tech-docs/3_ActiveAA_Antena_11.pdf
I'm curious what folks think about the last antenna in the file: 3.7 - 2/4 crossed parallel loops and symmetrical vertical dipole
A question for jFarley - are there technical reasons why the amplifier uses BJTs rather than an MMIC?
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Chris,
That last array has me intrigued but I wonder what the patterns would look like for each mode...
I think F2DX provided the best view of what a quality build of it would look like. Almost looks commercially produced when the elements have custom mounting blocks?
Check out his photo set of it: https://picasaweb.google.com/108459637204329481149/LoopReceptionF2DX#
What an awesome [and EXPEN$IVE] antenna farm!
Rafman
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Rafman, that is indeed a top quality build. Looks like he got around half a uH of inductance, from the LCR meter reading.
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The best build I have seen yet, of all I have looked at... However, we all know that looks isn't always what works. It has stirred further study for me though...
Well I have taken the plunge... I have ordered an LC meter to start. I intend to use some "surplus" 1/2" LDF4 hardline for the 2x loop(s)... I intend to try a single loop or an offset eggbeater [1 loop over another/offset by 90 degrees] to get away from using any rotor... However, that 4x really has my curiosity...
I am in the experiment mode this season... I now have enough quiet SDRs but the quest for a quiet antenna is endless ;)
Rafman
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He has a pdf file with several loop antenna designs here: http://active-antenna.eu/tech-docs/3_ActiveAA_Antena_11.pdf
I'm curious what folks think about the last antenna in the file: 3.7 - 2/4 crossed parallel loops and symmetrical vertical dipole
A question for jFarley - are there technical reasons why the amplifier uses BJTs rather than an MMIC?
Out of my area of expertise here, but here is a WAG.
In the linked document, the author mentions that (In the section "Some comments on the amplifier schematic") that "The amplifier is a standard common base differential amplifier. The differential input resistance of the amplifier is around 3 ohms at 1 MHz...". The antenna is being used in current source mode, and perhaps the MMICs (which as far as I can tell are tailored towards 50 ohm systems) are not appropriate here. Just a guess.
Another guess...maybe the amp is a tried and true design in his arsenal, and he just used something he felt comfortable with. I myself have been using the same old amp design in my resonant loops for over 20 years. I have often thought about seeing what could be done to simplify or upgrade the design, but just never seem to get around to it.
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I'll throw in my own WAG, based on having worked in RF amplifier production...
MMICs typically have 3 detrimental characteristics:
1) Higher Noise Figures
2) Lower Compression Points [driving the amp out of linearity, producing distortion]
3) Very WIDE frequency ranges [Studying Mini-Circuits' MMIC listings, their low frequency offerings are spec'd at 0.1-1000MHz] thus they must be filtered more than discrete circuits
Just my WAG as JFarley offered... What amp design have you used for 20 years? I'm curious...
Rafman
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Thanks, Rafman. Good points all and I'll take your word.
The amp is a balanced Hi-Z JFET cascode of minimal gain which is suitable for use with resonant parallel LC loops. Here is a link to an rar archive of schematics in .png format.
http://www.mediafire.com/download/5hmfdoqj03f6z8v/Package_2.rar
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Thanks Rafman and jFarley.
I'm trying to decide if that "2/4 crossed parallel loops" implementation would have any advantages over my existing antennas (the huge sky loop and the sloped folded dipole).
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What I find most interesting is the use of CAT5 as balanced 100 ohm line + power injection...
I have long wondered about using CAT5 cable in listening antenna applications...
I have to get to work after my LC meter gets here. I received my amp yesterday ;)
Rafman
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What I find most interesting is the use of CAT5 as balanced 100 ohm line + power injection...
As long as the DC power is well filtered, there is no reason to worry excessively about multiplexing power on an RF signal line. Be sure that decoupling chokes can handle the current level; I tended towards using wound toroidal cores rather than molded chokes for this function.
Note that that amp I referenced also provides the tuning voltage for the back to back varicaps. I can get 3 functions (RF, Vdd, and tuning voltage) multiplexed on a single coax cable which makes it VERY difficult to wean myself off of loops tuned electronically.
Gentlemen: start your soldering irons!
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I always start yearning to try some new antennas this time of year.
Since this amplifier has a balanced output, it is ideally suited for use with twisted pair cabling such as CAT5. Even more so if you have a receiver with a balanced antenna connector -- you would not need a balun.
Rafman's points regarding MMIC's are right on; The BJT makes it easier to design a gain stage with high OIP3 (>40db) performance than with the MMIC's that my limited experience is familiar with (I haven't used any MMIC's in the last 15 years, so there may be better ones out there now). If OIP3 in the 30 db range is okay, then MMIC's would be an easier solution, especially if you don't have any transmit antennas in the vicinity.
I'm planning to try some of the loop designs from his site next year, getting ready to play with short vertical whips this year.
Plus playing with ferrite mixes for chokes to improve my VLF receive capabilities. Any VLF antenna gurus out there?
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I finally dug deep enough to find some patterns on the loops [I think I'm addicted?]
The initial LZ1AQ design notes [2011]: http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm