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Author Topic: Pa0rdt Mini-Whip Active Antenna  (Read 26971 times)
PBPP
Member

Posts: 40




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« Reply #15 on: May 28, 2014, 06:56:00 AM »

KD8IIC,

I'm sure you've got room for a 10 foot antenna and probably longer, right? 

Just so you know, a random wire antenna with a LC tuner will vastly outperform
the four overpriced active antennas, the virtues of which you are extolling. 
Since you haven't provided us with any verifiable data, one can only conclude
your claims are without merit. 

Sorry, but buying any of these active antennas is foolish waste of money,
no matter what type of abode you live in.

~ Mitch ~ 
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K0OD
Member

Posts: 2533




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« Reply #16 on: May 28, 2014, 09:34:21 AM »

Quote
Considering the fact that some of us do not have the room for a 43ft vertical or any wire antennas

I sometimes DX the AM BCB with my ancient Panasonic RF2200 on my BASEMENT workbench. No outside antenna at all. I presume everyone has room for the 8" ferrite rod on top of the 2200.

Heck, one of my wristwatches sets itself using 60 kHz time signals from WWVB in Colorado 800 miles west of me.  The antenna (I Guess there is one) couldn't be more than the watchcase.

On lower frequencies where atmospheric noise is the limiting factor, sometimes a costly antenna helps, but often much less performs just as well. Start with some random hookup wire dangling out a window.
 
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KD7RDZI2
Member

Posts: 62




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« Reply #17 on: May 28, 2014, 11:15:24 AM »

KD8IIC,

I'm sure you've got room for a 10 foot antenna and probably longer, right? 

Just so you know, a random wire antenna with a LC tuner will vastly outperform
the four overpriced active antennas, the virtues of which you are extolling. 
Since you haven't provided us with any verifiable data, one can only conclude
your claims are without merit. 

Sorry, but buying any of these active antennas is foolish waste of money,
no matter what type of abode you live in.

~ Mitch ~ 


Well, I don't know anything about the Pa0rdt Mini-Whip, but active antennas ARE NOT a foolish waste of money. If you are interested in SWL try the efficiency of a long wire antenna on the LF. How long should be the wire to get the same efficiency of an active antenna? More, active antennas, excluding active loops, are omnidirectional usually vertically nearly isotropic polarized. A random wire has a distorted pattern and is deeply influenced by both the lengh and the height of the wire and the ground. I am not saying active antennas are better, they are different. Some cost a lot, maybe they are overpriced for what they are, but they can be put close to the ground, you don't need a tower and you save time and sometimes money to install it. Yes they amplify noise too but noise figures are very low often below the atmospheric noise and the amplifier serves more for matching than for amplifying the signal itself. And you don't need a tuner, it's wideband, no switches ... just very convenient.

If you say  that using a simple wire saves you a lot of money I would not be so sure: you cannot leave the wire on the ground: add the costs of a mast, and the tuner, better external, that's also is a lot of money! and still you won't have the LF, the pattern can be distorted on the HF, and you need to tune everytime you move the VFO...
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G8JNJ
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Posts: 473


WWW

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« Reply #18 on: June 10, 2014, 04:02:42 AM »

Hi All,

Active antennas are a perfectly valid concept and are frequently used by the military and other agencies.

As long as the intermod performance is adequate for the intended purpose and the noise figure is low enough to be masked by the external noise floor, they can work surprisingly well, particularly on the LF and VLF bands.

If you want to see how well a Pa0rdt Mini-Whip can work when installed properly, try using the University of Twente WEB SDR

http://websdr.ewi.utwente.nl:8901/

This uses a Pa0rdt Mini-Whip with an active receiving element of about 5 by 10 cm. Such an antenna only works well with a good grounding. This one is on top of a 20m high building, the upper part of which is all metal.

A summary of various Active antennas can be found at

http://g8jnj.webs.com/activeantennas.htm

My own design, mounted on a 3m high metal mast, works at least as well on RX as a 10m high vertical and buried radial system. On the LF bands, where the ambient noise level is the determining factor, the active antenna is probably better in terms of RX S/N ratio.

A random wire and tuner is OK if you wish to stay on one frequency, but if you do a lot of tuning around, or want to monitor propagation beacons or similar, it's not really viable to keep on having to re-tune every time you change frequency.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

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KD8IIC
Member

Posts: 152




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« Reply #19 on: June 10, 2014, 05:59:16 AM »

 Hi Martin ; Great info on the web pages. Now we just have to wait and see what the real "Experts" who have unashamedly chimed in to correct us Neanderthals in this thread have to say to correct you on..
I must be a real dolt, my ten feet of wire using a simple LC tuner doesn't work half as well as claimed, maybe it's because I'm using insulated wire and not bare, hi.
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PBPP
Member

Posts: 40




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« Reply #20 on: June 12, 2014, 11:49:50 PM »

The links Martin gave show no real information on the Pa0rdt antenna, only a similar circuit.

Still waiting for KD8IIC to provide us with some verifiable data on just how well this whizbang active antenna works. 
So...... how about it there Lane?? Care to educate the experts? 

~ Mitch ~
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G8JNJ
Member

Posts: 473


WWW

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« Reply #21 on: June 13, 2014, 09:24:58 AM »

http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf

http://dl1dbc.net/SAQ/Mwhip/pa0rdt-Mini-Whip.pdf

Plus others referenced from my active antennas webpage

http://g8jnj.webs.com/activeantennas.htm

Regards,

Martin - G8JNJ

www.g8jnj.net




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KD7RDZI2
Member

Posts: 62




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« Reply #22 on: June 13, 2014, 10:51:48 AM »

The links Martin gave show no real information on the Pa0rdt antenna, only a similar circuit.

Still waiting for KD8IIC to provide us with some verifiable data on just how well this whizbang active antenna works. 
So...... how about it there Lane?? Care to educate the experts? 

~ Mitch ~

I remember a nice chapter on  active antennas on WRTH 1988. There some of the best active antennas of that time were discussed vs longwires (with high impedance ununs), dipoles and other antennas. Not rocket science but from the practical point of view quite a honest and objective picture of antennas of that era. Strangely enough at that time the best  active antenna were offering quite a higher IP3 than most of the active antennas you find today such as the Pa0rdt. I think the relatively high price for the active antennas you find today might be due to a lack of competition.

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PA0DGL
Member

Posts: 1




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« Reply #23 on: June 17, 2014, 10:56:29 AM »

The performance of active antennas like the mini whip can be verified rather well with modeling. But before I did that, it was already noticed that there were serious issues:
1. the J310 has relatively high Cdg and Cgs. In a good design, the influence of the first would have to be minimized by bootstrapping whereas the influence of the second can be made small by taking care of a near 1 gate - source voltage gain. Simulation shows a 2.5 dB loss instead so the effective Cgs is rather high.
2. An emitter follower has a very low output impedance and should be connected to the coax via a resistor of the proper value. That also will half the (already <1) gain.
3. For the relatively high input capacitance, the sensor / whip must be much larger.

So my 10 meter vertical wire in a tree, with 9:1 impedance transformer and proper ground worked much better than any active antenna. That was about 30 years ago. Living in Panama now, lightning storms are a big issue and the hills at my property would require 30 meter or larger towers to erect a horizontal antenna. So I took a second look at active antennas.

A test as in the video that started this thread was changed into a mobile job: portable radio and active antenna on a battery, to discover locations with the lowest RFI where the active monopole can be erected. An active whip with imperfect ground works like an asymmetric dipole IOW no problem. The result was so good (MW stations were heard with good S/N that were inaudible on the ferrite antenna of the Tecsun PL-660) that I designed (and tested) a symmetrical active dipole with, similar results. For the S/N to be comparable to the (now destroyed by a storm) 85 m uphill long wire (slope ~40 degrees) a whip aka dipole half has to be more than half a meter in my designs. No commerce intended - I used to work as designer for a Dutch magazine.

Jan
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