[Elecraft] RX noise and 2-wire lines

[Drew AF2Z]

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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