Topband: 8 circle: DXE vs Hi-Z
n4is at comcast.net
Thu Dec 18 10:08:31 EST 2014
Hi David and Don
I understand your point. Gain is cheap and quite easy to get with a good low
noise amplifier, but to keep the common mode noise out of it is very
expensive, and could be very complicated. The beverages are very forgiveness
and does not requires much amplification. It is an ideal antenna.
The noise measured at 500Hz BW on my TX antenna, varies from average -90
dB, when I do not have power line noise to -100 dB few mornings during
winter. The noise floor from my HWF is - 120dB (500Hz BW) after a 43db gain
preamp (.5dB NF). I have no space for beverages and my station with all
antennas uses only 150ft x 100ft. Using 100 Hz BW the noise floor drops to
-145dB during the day. Connecting the HWF on the 43db gain increase the
noise only 0.2db , you can't hear the increase of noise, I measured it with
QS1R SDR, basically the noise is below the sensitivity of the receiver.
I can hear very well on 160m. not bragging but just for reference, 4W6, 9M0,
9M4,9M2, HS, DU, XU, and other very weak signals logged in 160 since 2006.
Doug worked 292 and I worked 275 on 160m from city lot. The new stuff works.
But as I said, it is very expensive. Also the implementation was not
possible without the information shared by K9YC, W8JI, and others how to
control common mode noise, grounding, shielding and best practices. The list
of MUST do things to implement the new stuff is very long
The signal above noise is there at the RX array, to bring it at the station
and amplify only the signal coming from the RX array without adding common
mode noise is very touch. Here is a sort list of must do things
1- Detune all resonant antenna, feed line, rotor cable tower, any metal
thing over 90 ft. long .
2- Ground everything at the tower, outside the shack, and in the shack
3- Choke every single cable that enter your radio system, including the
preamp. 100's of toroid's is quite common, and few toxoids does not get the
4-All electronics' must be shielded with steel boxes, aluminum does not cut
magnetic field and does not help below -120dB noise floor. If possible run
all cables inside galvanized grounded water pipes or hot deep galvanized
5- All cable inside the tower and grounded at the top and at the bottom
6- NO ground loop with the AC lines, isolation transformer and one point
ground for the system, your house wires is an effective way to drive noise
into the RX system.
A good RDF RX antenna does not fix the issues above. There is no allowance
here, all points above can deteriorate your RX signal to noise ratio. Using
Horizontal antenna does help a lot with interaction with TX antennas but do
not eliminate the common mode nose or ground loops problems.
Even a single flag is complicated because the feed line can introduce common
mode noise, and turn the flag into a loaded vertical. There is only two
solution, choke the line overkilling the common mode noise , or use
unshielded 100 ohms twisted pair cable. See T6LG results on his web page,
only after replacing the coax with twisted pair he was able to work 100's of
DX from a military base in YA on 160m.
The results using the new RX system varies form excellent to a perfect
disaster depending on the points above.
From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of David
Sent: Thursday, December 18, 2014 1:01 AM
To: Don Moman VE6JY; Topband at Contesting. Com
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
My experience is similar to Don's outlined below. Both gain and noise
figure are important in very low noise environments. In my own case, I have
a noise floor from my TX array in the high -120s or -130s assuming a quiet
atmosphere. A high RDF performance RX array often brings virtually no
improvement. In my case, since the RX arrays lack gain, they often don't
have the horsepower (gain) to reach down and hear the super low level
signals picked up by the TX array. Switching from the TX antenna to the
high RDF receive array not only fails to make the signal "jump out of the
noise" (what noise?) but fails to hear the signal at all. In these
circumstance both gain and noise figure become very important factors.
73. . .Dave, W0FLS
----- Original Message -----
From: "Don Moman VE6JY" <ve6jy.1 at gmail.com>
To: "Topband at Contesting. Com" <topband at contesting.com>
Sent: Wednesday, December 17, 2014 10:53 PM
Subject: Re: Topband: 8 circle: DXE vs Hi-Z
> Well I disagree that gain isn't important. Maybe you topbanders in the
> better areas of propagation can afford to throw away many db to get a
> better rdf, but that sure isn't the case up here in mid-northern VE6 land.
> I have numerous receive antennas including many beverages and Wellbrook
> loops (large area) and the Hi-Z 4-8PRO 8 element circle. They all work
> more or less as expected on the "easy" stuff and show reasonable
> directivity but when I need help for the weaker dx, there just isn't any
> signal there to work with. The beverages do the best of the bunch, they
> aren't anything special - typically in the 700-1100 foot range. With the
> many vertical structures I have there is no doubt their patterns are
> somewhat affected but they seem to work fine for Eu and JA bcb dx vs the
> loops and the 8 verticals. Not that this has been a good year for much of
> anything on the low bands in this area.
> The HI-Z was erected quite aways from anything else which involved
> bushwhacking and clearing the entire circle, trenching almost 1200 feet of
> feedline etc so there was a lot of sweat work done on that project. But
> on 160 and 80 where I have the tx antennas to use as a comparison, the
> specialized rx stuff just doesn't hear the weaker stuff. And it's not
> I have a pristine "can hear a pin drop low noise qth", esp on 160 - plenty
> of flare stack ingitors plus the usual powerline and smps junk. It's
> especially frustrating to hear all the glowing success stories of these rx
> arrays and how they make the dx just jump out of the noise and into your
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