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

Re: phasing two arrows



Hi guys,

First to answer Chris:  You state "I have had luck with using nothing more
than a 1/4 wave section of
RG-62 joining the driven elements through a BNC T-connector. Worked great."
 Are you sure you used RG-62?  It is 93 ohm impedance which would not match
two 50 ohm antennas with 50 ohm coax at a Tee.  RG-11 or RG-59 which are 75
ohm are close to the right value for a two-way splitting 1/4 wave
transformer line.  Page 8-22 in the original edition of the Satellite
Experimenters Handbook shows the right set up in fig. 8-11b.  Note that
RG-62 is used in fig. 8-11a for a polarity switching configuration.

Hasan:  Your comments about stacking two yagis are correct when the object
is increasing gain.  The object being to space them so their aperatures
just touch for max increase in gain.

But what if your object is to provide a set of orthogonal positioned
elements to generate circular polarization?  The classic case has the two
sets of elements mounted on the same boom {i.e. zero spacing}.  

Therefore, I think you could space the two Arrows for 0.8 wavelength {as
recommended on page 7-8, Fig. 7-7} at 436 MHz and feed the 2m and 70cm
sections separately using normal 90 degree phasing harnesses to produce
circular pol.  Since the two antennas are at right angles the proximity of
the 2m elements should not produce much coupling or detuning providing that
the cross boom and mast are non-metallic.  I would mount the antennas in
the / and \ position vs H and V.  I think you would get fairly clean
patterns but little or no stacking gain.  {you would gain 3 dB for matching
circular polarization, though}

I hope someone will try this out and tell us how it worked.

Ed  
PS: per usual there were some comments after Hasan.  Spacing farther than
optimum does produce bad side lobes, but under spacing, up to a point,
usually has the effect of reducing sidelobes.

If someone would fwd me the dimentions of the Arrow antenna: element dia,
lengths, spacing; boom dia. and length and driven antenna matching method
{i.e. gamma, T,...}, I will attempt to analyze a two antenna phased system
with NEC4WIN.

>From: "hasan schiers" <schiers@prairieinet.net>
>If you're talking about the dual band antennas, you can't stack them for
>both bands. The spacing will only be correct for one of the two bands.
>
>If you do stack two single band yagis, you have to decide on what
>polarization you want. You can get linear vertical, linear horizontal, or
>circular. The circular will require a delay line to one of the two antennas.
>
>The dual band arrow antennas are not suitable for stacking because of my
>initial comments above. I wouldn't bother, it can't possibly work right on
>one of the two bands.
>
>73,
>
>hasan schiers
>schiers@netins.net
>N0AN
>
>
>----- Original Message -----
>From: "Christopher Cox" <cobox@urec.net>
>To: "Cordill,Jim" <JCORDILL@cerner.com>; "'amsat-bb@amsat.org'"
><amsat-bb@AMSAT.Org>
>Sent: Thursday, November 30, 2000 3:49 PM
>Subject: Re: [amsat-bb] phasing two arrows
>
>
>> Well, it depends.
>>
>> Are you going to try 2 stock Arrows, or put all the 2 meter elements on
>one
>> boom and all the 70 cm on the other?
>>
>> I have not tried 2 stock Arrows, but I would make sure they where canted
>45
>> degrees from each other instead of 90 degrees.
>>
>> If you are going to combine 'like kind' elements onto their respective
>> booms, I have had luck with using nothing more than a 1/4 wave section of
>> RG62 joining the driven elements through a BNC T-connector. Worked great.
>>
>> Regards
>>
>> Christopher Cox
>> KC8FRJ
 
----
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