Re: [amsat-bb] Helical Antenna for 2-meters
Just scale the dimensions proportionally (except wire diameter);
ratio = 144/435
I built a 14 turn 437 MHz helical back in 1996 to receive the MGS beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish feed for AO-40. Plenty information in Amsat Archives. Original Kraus-W8JK design is optimistic in gain calculation. http://www.kl7uw.com/Satellite%20feed.jpg
W9EK had good construction hints in prior publications.
For receive-only do not sweat getting a good SWR. I used a 1/4 wavelength long 1/8 inch wide brass strip, run from connector to beginning turn of the helix for impedance matching. Space the point of connection to the helix about 3/16 inch above the ground plane reflector. Natural impedance of a helix is 140-ohm.
On air experience with the 432 helix was that a ten element CP crossed element yagi is better. But if you desire CP the helix is a natural, though not perfect.
73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: dubususa@gmail.com
I just finished assembly of the Cushcraft cross-polarized yagi which I bought from a fellow Ham. It was like new. Now I remember what I really didn't like like about that Antenna. I put one together back in 1978 or thereabouts. Putting the phasing harnesses on was quite the job! I managed to remember curses in four or five different languages (tnx Army language school). Anyway it's all together and I mounted it vertically on a 10 piece of pvc pipe for testing. SWR was almost 1:1 over the range 432.5 to 437.0 then rose slightly as I approached 437 MHz. I'm a happy guy now. Next project is either the 2-m Helical we've discussed here, or two 3-element yagis with circular polarization. I already have the yagis, so that would be a no cost option.
Thoughts anyone?
73 Dave N4CVX
Sent from my iPad
On Feb 7, 2017, at 18:23, Edward R Cole kl7uw@acsalaska.net wrote:
Just scale the dimensions proportionally (except wire diameter);
ratio = 144/435
I built a 14 turn 437 MHz helical back in 1996 to receive the MGS beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish feed for AO-40. Plenty information in Amsat Archives. Original Kraus-W8JK design is optimistic in gain calculation. http://www.kl7uw.com/Satellite%20feed.jpg
W9EK had good construction hints in prior publications.
For receive-only do not sweat getting a good SWR. I used a 1/4 wavelength long 1/8 inch wide brass strip, run from connector to beginning turn of the helix for impedance matching. Space the point of connection to the helix about 3/16 inch above the ground plane reflector. Natural impedance of a helix is 140-ohm.
On air experience with the 432 helix was that a ten element CP crossed element yagi is better. But if you desire CP the helix is a natural, though not perfect.
73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: dubususa@gmail.com _______________________________________________ Sent via AMSAT-BB@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. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Dave,
It helps to be multi-lingual <smile>. Sounds as you got it under control.
I used a 16 element CC cross-yagi for AO-10 and the phasing harness was not according the dimensions one would calculate but it worked. I traded it for a M2 436CP42UG for AO-40 (which I still have) and the CC 20 element 2m satellite antenna. 2m went kaput early so I used the 432 yagi a lot for uplink in mode-US or LS. I had a 50w linear which was overkill (usually ran about 20w). The dish photo I shared was my mode-S downlink using preamp to two Drake converters.
M2 is marketing an 8 element cross yagi CP antenna for 2m which is probably just right in gain. Its pretty spendy, though. If you have a couple 3 or 4 element yagi's you can combine them for CP and even switchable in sense using a relay or two.
I am using a 2M7 by M2 linear yagi and only have 26 elements of the big M2 436 antenna mounted. Not QRV yet as I am planning major changes next summer.
GL on whatever you decide.
73, Ed
At 03:45 PM 2/7/2017, Dave Mann wrote:
I just finished assembly of the Cushcraft cross-polarized yagi which I bought from a fellow Ham. It was like new. Now I remember what I really didn't like like about that Antenna. I put one together back in 1978 or thereabouts. Putting the phasing harnesses on was quite the job! I managed to remember curses in four or five different languages (tnx Army language school). Anyway it's all together and I mounted it vertically on a 10 piece of pvc pipe for testing. SWR was almost 1:1 over the range 432.5 to 437.0 then rose slightly as I approached 437 MHz. I'm a happy guy now. Next project is either the 2-m Helical we've discussed here, or two 3-element yagis with circular polarization. I already have the yagis, so that would be a no cost option.
Thoughts anyone?
73 Dave N4CVX
Sent from my iPad
On Feb 7, 2017, at 18:23, Edward R Cole kl7uw@acsalaska.net wrote:
Just scale the dimensions proportionally (except wire diameter);
ratio = 144/435
I built a 14 turn 437 MHz helical back in 1996 to receive the MGS
beacon and built a 2.4 GHz 6-turn helical for 33-inch offset dish feed for AO-40. Plenty information in Amsat Archives. Original Kraus-W8JK design is optimistic in gain calculation.
http://www.kl7uw.com/Satellite%20feed.jpg
W9EK had good construction hints in prior publications.
For receive-only do not sweat getting a good SWR. I used a 1/4
wavelength long 1/8 inch wide brass strip, run from connector to beginning turn of the helix for impedance matching. Space the point of connection to the helix about 3/16 inch above the ground plane reflector. Natural impedance of a helix is 140-ohm.
On air experience with the 432 helix was that a ten element CP
crossed element yagi is better. But if you desire CP the helix is a natural, though not perfect.
73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: dubususa@gmail.com _______________________________________________ Sent via AMSAT-BB@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.
Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
73, Ed - KL7UW http://www.kl7uw.com Dubus-NA Business mail: dubususa@gmail.com
participants (2)
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Dave Mann -
Edward R Cole