VHF 1 is 143.625 MHz (the standard Russian ISS downlink frequency) and VHF 2 is 130.165 MHz (the Soyuz downlink frequency).
The gain of this 8 turn helix should be about 13 dBic.
I once built a 9 turn helix for 2 m. Worked very well.
73, Nico PA0DLO
On 08-05-18 06:30, Wendy and Terry Osborne wrote:
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: [email protected] 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 < [email protected]> 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 [email protected] 914-573-1799 _______________________________________________ Sent via [email protected]. 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. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
--
Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV [email protected] 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"