[Elecraft] RX noise and 2-wire lines

[Drew AF2Z]

More info about the LZ1AQ loop preamp is here
http://active-antenna.eu/amplifier-kit/

The supplied amplifier, control board, enclosure, etc. make a nearly 
complete package. You fabricate the loop yourself. Various examples are 
shown on associated pages.

I think the main benefit of such a small receiving antenna is that you 
can localize it away from noise sources in houses or power lines. Even 
30 or 40 ft separation might make a difference (the inverse-square law 
is your friend!)

The amplifier seems quite robust. My loop + amp is only 25 or 30 ft from 
my transmitting antenna and tolerates the 100 watt transmitter output, 
no problem. I don't even need any T/R switching; the loop is connected 
directly to my K3's RX port or to my RSP1A SDR. Signal levels are safe 
on all bands.

It receives well on lower freqs especially-- the AM bcst band and LW. I 
can often hear Algeria here in SNJ on winter nights, 252 kHz.

73,
Drew
AF2Z





On 10/28/19 20:04, David Thompson wrote:
> I would like to know more about your receive antenna. At my home, I deal with S7-S9+ noise and am looking for some way to be able to operate besides FT8.
> 
> Thanks…
> 
> David Thompson, AG7TX
> Jack of All Trades
> Master of None
> dbthompson at me.com
> 
> 
> 
> 
>> On Oct 28, 2019, at 14:31, Drew AF2Z <pubx1 at af2z.net> wrote:
>>
>> My RX antenna is a pair of small amplified stacked loops. It uses the LZ1AQ amplifier board fed with common FTP (foil twisted pair) cable, which provides the supply voltage, control lines and a shielded twisted pair for the signal. I don't think you can get any better noise isolation than that.
>>
>> It is a lot quieter than my transmitting antennas; lower signal levels as well, but often a better signal-to-noise ratio than the transmit antennas.
>>
>> 73,
>> Drew
>> AF2Z
>>
>>
>> On 10/26/19 10:11, Victor Rosenthal 4X6GP wrote:
>>> Jim,
>>> I have to disagree about balanced line. Unlike coax, both conductors are exposed to external RF fields, so common mode noise will be rejected. If the antenna and line are properly balanced (not always easy to do, I admit) and if it is fed through a balanced antenna tuner, there is no reason for it to be noisier than coax. Yes, it can't be choked, but it doesn't need to be.
>>> My antenna is a 10m long rotary dipole fed with open line. It has gone through several iterations and I've been very careful to install the line so that it is perpendicular to the antenna for as far as possible, etc. I've tried various balun arrangements, but the system that works best, both for reducing RF in the shack when transmitting and noise immunity when receiving, is a Johnson kW Matchbox.
>>> There is a building taller than mine a few hundred meters away from it, and a very distinct noise peak when the antenna is turned toward it, which seems to indicate that the noise is picked up by the antenna, not the line. I notice the same noise peak with a coax-fed shielded loop antenna, so it is definitely coming from the building, and isn't an artifact of the alignment of the antenna to the line.  I am pretty sure I have at least a 10 dB difference in noise when a band is open (at least, when the antenna is not aimed at that building), but I will wait until the band is solidly dead tonight to check that out.
>>> My pattern is a form of figure 8 on 40-10 meters, but you are right that you can't maintain the pattern over a greater frequency range.
>>> My main point is that there is nothing inherently noisy about a two-wire transmission line!
>>> 73,
>>> Victor, 4X6GP
>>> Rehovot, Israel
>>> Formerly K2VCO
>>> CWops no. 5
>>> http://www.qsl.net/k2vco/
>>> On 26-Oct-2019 10:32, Jim Brown wrote:
>>>> On 10/25/2019 2:01 PM, Bob McGraw K4TAX wrote:
>>>>> Except for my 6M yagi, all of my antennas are non-resonant antennas. My favorite is the 256 ft center fed wire {resonant at 1.825 MHz} with a balanced feed.
>>>>
>>>> Dean Straw, N6BV, retired editor of the ARRL Antenna Book and Antenna Compendiums, is a very smart engineer and a very good friend. But his promotion of this sort of antenna is probably the greatest error of his time in that job, an idea whose time is LONG past, for many reasons. Primary -- 1) it cannot be choked to kill noise on RX, and 99.9% of hams live surrounded by local noise and 2) it's pattern is different on every frequency.
>>>>
>>>> I am a strong believer in resonant antennas for each band, if if the must be multi-band antennas like fan dipoles to fit in the available space. For example, a 20/15/10 fan fits in 33 ft and works great, with a predictable pattern on each band. An 80/40 fan works on 15M, with a predictable pattern on both 80 and 40. Hypower Antenna company sells loaded antennas that are resonant on 80 and 40 and fit into about 100 ft; I used one in Chicago on 30 to great effect. All of these antennas are fed with 50 or 75 ohm coax, and CAN be choked to kill RX noise.
>>>>
>>>> RX noise is a VERY big deal -- if you can't hear 'em, you can't work 'em. If you haven't worked to minimize your RX noise, you're DXing with one hand tied behind your back! My friend AG6EE goes to remote locations in NV, OR, and CA to light up rare grids with 1kW on 6M. Folks trying to work him complain of one-way propagation because he hears them really well and the don't hear him, but the REAL problem is their local RX noise.
>>>>
>>>> http://k9yc.com/KillingReceiveNoise.pdf  Text, NCJ article
>>>> http://k9yc.com/KillingRXNoiseVisalia.pdf  Slides Visalia talk
>>>>
>>>> 73, Jim K9YC
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