Re the overload concern with active 4 sq receive antennas (although the
IP3 is quite high for DX Eng and Hi-Z).
For the upcoming Mellish DXpedition VK9MA, the team leader Rob N7QT
asked if I could help build a passive 4 sq, inspired by a comment from
K3LR and some ideas from http://www.w5zn.org/160%20Meters.html . The
VK9MA overload concern with active antennas is 4 simultaneous QRO
stations on a couple of acres of sand, all verticals. With generous
support from DX Eng. for the Hi-Z boxes, chokes, bases, and aluminum we
built a passive 4 sq with top loaded whips, see W8JI for the antenna
design (25' whip, 4x 25' wires at 45deg, 4x 54' ground wires each). A
simple tuner box is needed at each antenna, some switchable L to
resonate on 160 and variable R to load and match 75 ohm cables. We
don't know the VK9 ground conditions so they will tune the antennas on
site, but they tuned easily to 1:1 with a SARK in my front yard. There
was almost no interaction in the tuning with them all up. Each whip was
connected without amps to the Hi-Z phasing box which had delay cables
cut for 70' on the square side. Then with 70 to 50 ohm transformers and
50 ohm 160m low and high power bandpass filters overload should be
manageable, we hope. We had the chance to test a little bit and saw
expected F/B etc against a daylight BCB station just in time to ship to
VK land (Cairns) staging. vk9ma.com
Fingers crossed that it helps the 160 effort at VK9MA. They will also
have some DHDL's up, proven winners on prior DXpeditions.
Grant KZ1W
(also happy at my QTH with my DXEng active receive 4sq.on 160)
On 10/22/2017 10:33 AM, Mike VE3CKO wrote:
I do have K9AY loop system, and it did get some direction from it, had
it on the only place it can go in a side yard but was too close to
lots of metal objects and power lines. Basically useless so I'm
holding on to it as we have our eye on a few properties out in the
country so believe me, if the move happens I've to lots of wire and
aluminum to put up. 4-square on 80m, play around with bent vertical
160 4-square around a tower, and 2 bi-directional beverages.
73, Mike Kovacich - VE3CKO
On 10/22/2017 11:51 AM, K4SAV wrote:
*Mike, while reading your message on Towertalk, I decided to give you
a few of my thoughts on 160 antennas.**
**
**You could be right about the inverted L not having enough punch
with only 2 radials, especially if those radials are on the ground.
I tied that once with a couple of radials on the ground. It was
terrible. I think K2AVs folded counterpoise is probably a good
choice for those on city lots and don't have a lot of room. He seems
to do very well with it and others that have tried it report the
same. I haven't tried it myself. If you do that, be sure to
construct it exactly as he describes. The operation of that system,
especially the transformer, is not obvious.**
**
**Receiving is always a problem on 160 and it makes a huge difference
in working someone if you can hear them well. Noise from a city is
difficult to solve when you live in or near a city. Best solution is
to clean up the noise from your own house and find a way to put up
some kind of receiving antenna. That can also be difficult when you
don't have much space. **
**
**If you have local noise from just one direction, a receiving loop
can be used to null that. If the noise comes from all directions or
is atmospheric noise, a loop won't help very much. The first level
of receiving antennas consist of the single element loops, like a
K9AY, flag, pennant, delta, diamond, etc. Those all perform about
the same because they all work like two short phased verticals. The
main difference between those is in the effort to construct them and
the difference in their susceptibility to common mode noise from the
feedline (which is always a major concern with low gain receiving
antennas). Note: The K9AY is the easiest to construct if you want
the capability to switch directions. The ones that use a ground rod,
are easier to control the common mode noise.**
**
**There is an antenna called a double half delta (DHDL). Put "DHDL
antenna" into Google and you will get several hits. It takes up a lot
less space than a BOG or Beverage and works very well. It works best
when that bottom wire is near the ground, maybe about 2 ft from
ground. That is the only thing I don't like about it. This antenna
should beat a short Beverage or BOG. They come in various sizes.
You will need two supports of at least 20 ft high to construct a good
one for 160.**
**
**I have been playing with BOGs for years and they are good receiving
antennas, although they may be too long for a city lot. I have tried
various lengths and found anything between about 200 ft to 370 feet
to be good on 160 and 80. The shorter end of that range works a
little better on 40. I live in a rural area and don't have a city
noise problem. I attached a short mp3 file that I made of 3C0L on
160. That was made with a 365 ft BOG. At the time I was making this
recording when listening on my inverted L, the noise was about the
same level as their signal.**
**
**Another step up with small receiving antennas is to phase some of
the single element antennas. I have phased EWEs for 4 directions.
Those are small but they are more difficult to construct. They work
very well and I can leave them up all the time, unlike the BOGs,
which have to to rolled up during the summer.**
**
**Then there are the commercial receiving antennas consisting of
active verticals. Those work well but you will have to part with
some bucks for those. Occasionally I think about constructing a
system like that, but then I am reminded of the AM radio station
about 1700 ft from my antennas that would probably overload it. I
also have a lot of lightning, which would probably take out the
active circuits of this antenna, even with close strikes. So I think
it would not work at my location.**
**
**Good luck with the 160 problems. Only until the last 12 years have
I been able to get away from the city and move to a location that is
a lot more friendly to radio. I know the problems with living on a
city lot.**
**
**Got to get ready for the next major DX operation, 3Y0Z, Bouvet Is,
last of January. That will be huge. It will be a difficult path
(significantly worse than West Africa) but at least we will have a
chance because there is significant time of common darkness between
us and them.**
**
**Jerry, K4SAV*
On 10/22/2017 8:41 AM, Mike VE3CKO wrote:
I've got 3C0L on 17m, 15m and 12m but the challenge is as always top
band. I have an inverted-L with just a couple radials at this time.
Noise floor at my QTH in the city is just so high with the
inverted-L and could not hear 3C0L but when I switch to an
experimental vertical setup which right now is just a 20' 2"
aluminum mast on a 4 x 4 post 8' high with a K2AV FCP (80m), 3C0L
was very readable much of the night. Using the 20' vertical as a
receive antenna and the inverted-L as the resonant tx antenna even
with the help of an Alpha 87A, I too was unsuccessful when he was
making stateside and the odd VE contacts. I did spend too much time
during time frame he was working the EU. I blame the lack of radials.
If we end up staying at this QTH I will certainly try a 160m folded
counterpoise.
73, Mike Kovacich - VE3CKO
On 10/17/2017 12:29 PM, Charlie Young wrote:
My station has not been configured for Topband for this season
yet. All rx antennas are disconnected/removed and my inverted L
has not been inspected yet. Usually the elevated radials need
maintenance after the summer if the wire is still up.
I saw 3C0L spotted for some time but did not listen because of the
antenna situation. After finally deciding to listen, the station
on 1821 was so strong there was no way it could be 3C0L. But it
was. I thought it was a NA signal.
Found that my inverted L VSWR was good, which indicated the antenna
was still up and the elevated radials were still intact. The
pileup was big and wide, but he seemed to be working folks above
1830 so we parked on a frequency and started calling. Glad to work
him for a new 160 Challenge point.
Great operator and signal. For the time I was listening he was at
least 2 S units above my noise, many times peaking over S9 on my
inverted L. Whatever he was running sure did the job on Topband,
plus he was hearing well also.
GL in the chase.
73 Charlie N8RR
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