Hi to all the guys,
here i have some news about my experiment of receiving antenna.
Like have you read in my last write, i always combat with my noise
situation, for the local noise produced by the lamp on the street.
Thanks to the advice that i have received, but point to point i want to
explane the results in the follow point:
1) the advice of VK3APN, about the IMD in the front end was really
interesting, so i have measured with an HP spectrum analizer the output of
the vertical slooping dipole, well some signal in AM was -8 dBm, and also
the signal from the high band was so high, i have made a BP aufilter with
some notch on AM, and the noise is changed, so i had some IMD problem for
the high level signal that the big antenna was receiving.
I am waiting also a xtal filter with a bandpass from 1822 to 1850 KHz, is
made by a local OM here and it will be ready in few days.
So, first problem was the IMD!!!!!!!!! (tnx VK3APN).
2) the noise from the lamp to N/W is not deleted, so i was planning a good
balanced antenna sistem that permitt to trasmitt well but also to receive
so well.
The beverage is the best solution but is no easy here in Italy, we do not
have a large field to put it, so i was looking for some antenna for the
time when the beverage is not ready.
On my roof i have a magnetic loop antenna, 2 meters radius, tunable from
1.2 to 7.4 MHz, and some time i use it for receive, during the last CQ SSB
contest i have made a little shielded loop, about 1 meters dia., the
results was incredible, in my sunrise W3LPL was not audible on the slooping
sistem, but was ok on the big loop and also on the little loop in my
room!!!
So i have decided to made 2 of this little tuned loop and put it in a
phased array.
The loop is made by a Andrew cable hardline 7/8" foam, tipe LDF 5-50A,the
dia is 0.98 meters, the capacitor for tune it in 160 is exatly 2435 pF on
all two the loop, at the top the external shield of the looop is cut for
about 1 cm., with a final ros of more than 35 dB measured on the HP network
analizer.
The cable is exatly 90° long, with the delay of more 90° in one loop, all
measured with the network analizer, the cable is RG214.
So, i have put it in the field, at a distance to the tower of about 60
meters, the loop is spaced 40 meters, a quarter wave, direction 310°.
During the first test with a little beacon of 1 mW at 200 meters is no
possible to check corretly the sistem becouse the signal on the loop is not
the same, may be that the distance was little, so we have tried with a
signal generated at about 50 Km far at 2 PM, but also this sistem seems not
work well, there is reflection also at this time so the signal was coming
not on ground, but by the sky wave.
So we have decided to try with NA station in the night.
After some test receiving a signal from G land and SV land, the F/B is in
some test droop from S9 to S2 , only with signal generated by the vertical
antenna, so the F/B is in some situation is very high, more than 35 dB.
This night i have made some call, after 2 JA qso, a D68BW and heard 8Q7IO
with the slooping sistem in east direction i have found that the
propagation was good, the first call to the NA was from Tom W8JI, followed
by K1UO.
The qsb was really fast and deep, and the signal from NA is coming here
about 30-60 minutes later than G land, so i have made this qso:
K3ZO
K1ZG
K9AN
K9UWA
K8IP
W4WN
NA0Y
WOCD
K5ZG
W3RCQ
W8UVZ
N4ZY
WD4JRA
K3AW
K2AV
K2ZJ
K1UW
All this qso's is made using the 2 little loop array for receive, on the
big slooping dipole many times there was no signal, only noise!!!!!!!!!!!!
So, i am very happy for this test, i need a preamplifier becouse the output
of the loop is really low, more low than a beverage, but also the space
needed for the sistem and the loop is little, hi hi.
So, now what can tell more, seems that also the tuned loop may be used for
an array, the next step here is try to put 3 in line feed with the right
phase shift, the azimutal pattern seems more narrower than the sistem using
a vertical in the array.
Ahhh, if you have a good project for a fet preamp., i need it, thanks.
Vy 73 and cul for some new test, Giulio IK2DED.
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|