[Elecraft] Seperate Receive Antenna

[jim]

David,

Not sure what ur budget is.

The amp in the Pixel is a Cliffton Labs design, using the Norton  architecture.  Jack of Cliffton labs cannot share info of the amp design, as he is under non-disclosure.  He does sell a great amp, using the Norton structure, that has a gain ~ 50% of the gain of the Pixel amp.  The Pixel amp and his for sale amp use the exact architecture.  The interface to the amp is also well thought out.  The amp is protected if you hook up a signal that goes low when the xmitter is keyed.  It removes power from the loop.

Take a look at Dallas Lankford's page on Yahoo groups.  He has done A LOT of work in the area of low noise antennas and loops with amplifiers, and has some GREAT articles on that Yahoo group page.  He discusses how to use the Cliffton amp with loops with good results.  I just went and bought a Pixel, as I did not want yet another project to get 75% done and then sit.  

Dallas Lankford is a great resource for BCBDX and loops/low noise antennas.

Also, if you "mind the gap" and account for common mode, the LZ1AQ amp would work.  Again, just take note of potential CM issues.

Jim


 

-----Original Message-----
From: David Cutter [mailto:d.cutter at ntlworld.com] 
Sent: Monday, February 2, 2015 10:43 AM
To: jim
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Seperate Receive Antenna

Thanks, Jim, that's opened out the discussion very well for me.  I am not able to determine how bad this makes the performance, since the output is floating and I think hardly susceptible to common mode problems.  I'm in the market for such antennas but most are outside my budget.  I would like to have 2 loops (could be large loops)  a half wavelength apart for diversity reception on 160 and this system with its delay line might do that economically.  2  amplified receive aerials (eg from CCW here in UK) with a phasing box would also be economical.  The next on my list is the shared apex.

thanks again for the link

73

David
G3UNA

Subject: RE: [Elecraft] Seperate Receive Antenna


Dave,

Here is the quote from W8JI


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10-29-2011, 05:36 PM #8

W8JI


Quote Originally Posted by WV6U View Post

Here is one broadband RX loop design that I found very interesting and something worth trying out. Once I am done with my TX loop for 40-15m, maybe I will start with this

http://lz1aq.signacor.com/docs/wsml/...op-antenna.htm

 I would not use that system in the link.

 While a good analysis, the amplifier is ground referenced. It is not a ground independent differential input. An ideal amplifier should have ZERO output if one loop terminal was open circuited. Otherwise, it has less than perfect common mode rejection.

 Bandwidth of the loop vs. noise is a myth. The only reasons a narrow loop bandwidth, or any antenna or amplifier bandwidth, would ever reduce noise or interference are when at least one of two conditions are met:

 1.) The receiver IF filter is wider than bandwidth of the pre-receiver system. This helps because overall bandwidth is reduced. 1/2 bandwidth= 3dB less noise if the signal is still narrower than the narrowest bandwidth

 2.) Something in a stage in front of the receiver narrow filter is overloading, and the system in front of the receiver is narrow enough to reduce the unwanted signal and stop or reduce the overload

 73 Tom


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The link to the above quote is

http://forums.qrz.com/showthread.php?318414-Magnetic-Loop-RX-Antennas


Jim