[amsat-bb] NASA Helical Antenna Question

[Wendy and Terry Osborne]

Hi,

Yes, it's an 8 turn helix with a Gamma match (50 ohms to 120 ohms).
The advantages of ring reflector are in an IEEE Transactions paper 
somewhere. (about 25 years ago?).
Not sure what the VHF 1 and VHF 2 frequencies are but if they are more than 
a few MHz apart, that would explain the use of a helix
rather than a crossed yagi antenna.

The other picture (existingvhf.jpg) on the web page shows a 4 crossed yagi 
array with rotators.

73,
Terry Osborne ZL2BAC


-----Original Message----- 
From: John Mac
Sent: Tuesday, May 08, 2018 1:51 PM
To: Glenn Little WB4UIV
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] NASA Helical Antenna Question

Hi.

Not sure its a standard 8 turn helix, the feed looks totally different and
looks like it has a ring reflector..

John

On Tue, May 8, 2018 at 9:39 AM, Glenn Little WB4UIV <
glennmaillist at bellsouth.net> wrote:

> Looks like a standard 8 turn, axial mode, helix to me.
>
> see https://en.wikipedia.org/wiki/Helical_antenna#Axial-mode_helical
>
> Looks like about 8 dBi gain.
>
> 73
> Glenn
> WB4UIV
>
>
>
> On 5/7/2018 6:57 PM, Steve Bossert via AMSAT-BB wrote:
>
>> I am curious about the helical antenna in the article just released late
>> last month:
>> https://www.nasa.gov/feature/goddard/2018/nasa-upgrades-spac
>> e-station-emergency-communications-ground-stations
>>
>> This one:
>> https://www.nasa.gov/sites/default/files/thumbnails/image/
>> upgradedvhf-antenna.jpg
>>
>> While I await a reply from the article author, I wonder if anyone may
>> have some details on this antenna.
>> Looks like a good candidate as a functional lawn ornament that is not
>> another QFH for more garden modern art satellite installation.  I would
>> like to author a construction and theory article for the HVDN.org 
>> website
>> in the "notebook" section.
>>
>> Thanks,
>> Steve
>> Steve Bossert K2GOG at yahoo.com 914-573-1799
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>
> --
> -----------------------------------------------------------------------
> Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
> Amateur Callsign:  WB4UIV            wb4uiv at arrl.net    AMSAT LM 2178
> QTH:  Goose Creek, SC USA (EM92xx)  USSVI LM   NRA LM   SBE ARRL TAPR
> "It is not the class of license that the Amateur holds but the class
> of the Amateur that holds the license"
>
>
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_______________________________________________
Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
to all interested persons worldwide without requiring membership. Opinions 
expressed
are solely those of the author, and do not reflect the official views of 
AMSAT-NA.
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Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb