[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

RE: Info needed for MBM88 Antena



Here are the specs I have from the manufacturer:

MBM88
fREQUENCY RANGE: 420-450
Impedence: 50 ohms
Gain: 18.5 dBi
Bandwidth (e) 23 deg
	    (h) 28 deg

Boom Length: 13 ft


73
Barry

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of i8cvs
Sent: Saturday, June 23, 2001 8:00 AM
To: Shlomo; AMSAT-BB; Neill Taylor
Cc: George Liepins
Subject: R: [amsat-bb] Info needed for MBM88 Antena


Hello  Shlomo,

Tank you for this information but there is someting  wrong somewhere because
the specifications published in VHF Communications magazine 2/1975 are 17.3
dBd for the model MBM46/70 wich is 2.65 meter long and 18.7 dBd for the
model MBM68/70 wich is 3.00 meters long.
The above gain are well specified Gain/Dipole
I cannot understand why the MBM88/70 wich is 3.98 meter long should have a
gain of only 16.3 dBd
Probably the best source of data is the manufacturer but i dont know if
J BEAM is still in business or not.

73 de i8CVS Domenico

----- Original Message -----
From: Shlomo <4x1as@netvision.net.il>
To: i8cvs <domenico.i8cvs@tin.it>; AMSAT-BB <amsat-bb@AMSAT.Org>; Neill
Taylor <neill.taylor@ukaea.org.uk>
Cc: George Liepins <gliepins@nc.rr.com>
Sent: Saturday, June 23, 2001 7:37 AM
Subject: Re: [amsat-bb] Info needed for MBM88 Antena


> Hi Domenico, I think you have wrong specifications on the JBEAM MBM88
> Here are the factory specifications;
>
> Frequency  430-440 mhz
> GAIN (dbd)   16.3 dbd
> FRONT TO BACK RATIO 22db
> 3db BAND WIDTH   H 28
>                                    E 23 ? (not clear on my page)
> DESIGN IMPEDANCE    50 OHMS
> POWER RATING (Peak)      1 KW
> BOON LENGTH    3.98 Meters
> LONGEST ELEMENT 42 cm
> TURING RADIUS  2 METERS
> WINLOADING AT 80 MPH    21.4 Kg
> WEIGHT     4.7 KG
>
>
> ;
>    73s Shlomo
>
>
> AO-16,UO=22,KO-23,KO-25  Amsast U.K member #3406. QTH LOCATOR KM71JV.
> Internet address  4x1as@amsat.org , 4x1as@netvision.net.il
> 4X1AS. Shlomo Menuhin, 30 Uriel Menuhin,Rehovot,76655, Israel, KM71JV
> ----- Original Message -----
> From: "i8cvs" <domenico.i8cvs@tin.it>
> To: "AMSAT-BB" <amsat-bb@AMSAT.Org>; "Neill Taylor"
> <neill.taylor@ukaea.org.uk>
> Cc: "George Liepins" <gliepins@nc.rr.com>
> Sent: Saturday, June 23, 2001 00:47
> Subject: R: [amsat-bb] Info needed for MBM88 Antena
>
>
> > The Multibeam MBM88/70 cm was produced by  J BEAM in 1975 and virtually
> > comprises four 22 element yagi antennas that have been stacked and bayed
> to
> > form a single,compact array.
> > Gain of MBM88/70 is 19 dBd ,i.e over a dipole or  21,14  dBi ,i.e over
> > isotropic
> > The antenna is linearly polarized and each of the 22 rods is
approximately
> > one wavelength long.
> > Each rod can be seen as two 1/2 wavelenght  elements connected togheter
> with
> > the center of this rod fastened to the boom with a  plastic insulator.
> > This particular assembling is not  convenient because the maximum
voltage
> > point is exacly where the element is fastened in to the plastic
insulator
> > wich represent a source of  losses particularly with high humidity,rain
> and
> > ice.
> > The slot-feed driving element is a balance one and the antenna has a
> baloon
> > made with coax cable rolled up and contained in to a small plastic box.
> > All J BEAM antennas supplied for Italy at that time were for 50 ohm
> > transmission line.
> > In order to connect two MBM88/70 in Right Hand Circular Polarization
> first
> > of all it is
> > necessary to look at the baloon box from the reflector side and ascribe
to
> > each of the two screws a simmetrical polarty for both antennas and mark
> them
> >  (+) (-)         ( +) (-)
> > Than put  both antennas on a boom and  mount the left antenna orizontal
in
> > order to see the screws like this   (+) (-)
> > Than rotate vertical  the right antenna by 90° clockwise in order to see
> > the screws like this   (+)
> >                                      (- )
> >
> > Now consider that the (+) screws are to be connected to the inner
> conductor
> > of the coax cable and the (-) screws to the braid of the coax cable.
> >
> > In order to get RHCP it is necessary to connect the vertical antenna
with
> a
> > transmission line wich is electrically 1/4 waveleght longer than the
line
> > suppliyng the orizontal antenna.
> > This line is well know as a delay line or a 90° delay line and its
lenght
> > must be calculated taking in to account the velocity factor of the coax
> > cable used for it.
> > Since the 50 ohm coax to the orizontal and vertical antennas are
connected
> > in parallel  and forms 25 ohm in their junction,it is now necessary to
use
> > one
> > of the many existing sistems to transform 25 ohm to the 50 ohm impedance
> > of the transmission line.
> >
> > 73 de i8CVS Domenico
> >
> >
> >
> > ----- Original Message -----
> > From: Neill Taylor <neill.taylor@ukaea.org.uk>
> > To: <amsat-bb@AMSAT.Org>
> > Cc: George Liepins <gliepins@nc.rr.com>
> > Sent: Friday, June 22, 2001 11:02 AM
> > Subject: Re: [amsat-bb] Info needed for MBM88 Antena
> >
> >
> > > "George Liepins" <gliepins@nc.rr.com> wrote:
> > > >Some years ago I bought two MBM88 70cm yagies made by Jaybeam Limited
> in
> > UK.
> > > >I was going to phase them, but never got to it.  Instead I kept the
> > HyGain
> > > >70 cm for satellite work.
> > > >
> > > >I have a friend who is interested in my antena, and wonders if it is
> > > >"circularly polarized."  As far as I can tell, it can be set up for
> > vertical
> > > >or horizontal polarization, but circular?  The technical specs don't
> > mention
> > > >polarization specifics, except mentioning beamwidth E and H plane
 28
> > and
> > > >23 deg's respectively).
> > > >
> > > >Can someone , please, enlighten me concerning this antena, and how it
> > could
> > > >work as uplink for AO-40.
> > >
> > > You are right, the Jaybeam "Multibeam" MBM yagis are linearly
polarized.
> > The design is effectively a double-yagi with a slot-feed driven element.
> > Since you have two of them, of course you could put one in each plane
and
> > phase them for circular polarisation like any other pair of linear
> polarized
> > antennas.
> > >
> > > Be careful about the matching of the phasing harness, though.  My
> > recollection is that these yagis are 75 ohm impedance.
> > >
> > > Neill
> > > G4HLX
> > >
> > > ----
> > > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
> >
>





----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home