| Subject: |
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Omni Circular Antenna for VHF |
| Name: |
|
Ignacio |
| Date Posted: |
|
Jan 11, 07 - 7:05 AM |
| Email: |
|
eb2gwo@yahoo.es |
| Website: |
|
http://www.geocities.com/eb2gwo |
| Message: |
|
Hello,
first thanks a lot for your great website. I enjoy a lot experimenting with antennas and homebrewing, and for me it's difficult to find someone that is so experienced in many different configurations as you are.
The purpose of my query is to build an antenna to work VHF satellites uplink with a fixed antenna that provides good enough circular polarisation to work it along all pass (or most).
I have some yagis to deal with it when working portable but I'm looking for a solution that provides enough signal without the need of a rotator and a satellite tracking software.
After much searching and reading, I'm convinced that a QHA will do the job, but due to the complexity of this construction I would like to prepare at first your Omni Circular as described in your program CIRPOL.exe. Do you think its performance is comparable with the QHA?
I would like to prepare then one Omni Circular using solid copper rod of 4 mm diameter. Therefore I can not run the program cause the diameter there is fixed.
Question 1: Could you then re-calculate the dimensions with that configuration for 145 MHz? (Please provide the dimensions in mm which is much more easier for me ;o) ).
In the other hand, I need a clarification about the Square area. I understood making it round would be more complex, but maybe you can give me the radius for that area at 145 MHz as a complementary information.
Question 2: when building it square, I need to know if the lenght called "end" in your program applies to every side at right and left of the feeding gap of if it is the total length of this side of the square.
In example: for 145 MHz, I understand the total profile of the square would be (out of Cirpol.exe, in mm):
119,48 + 183,02 + 119,48 (half side) + 119,48 +183,02 + 119,48 (the other half) plus the gaps.
Is that correct?
Question 3: concerning the radius at the corners and when changing from the square profile to the vertical element: do you recommend making them small or big ?
Question 4: concerning the capacitors installed: I understand they are fitted to match the antenna for a 50 ohms direct coax feed.
When using the antenna for transmitting with 20 watt at 145 MHz, what kind of capacitors should I use ?
Any suggestion of electrical characteristics or any web page where I can check what is commercially available?
That's all. I hope I was not so long to bore you but I hope is also interesting for your forum as I didn't recognised such antenna among your questions. Satellite for amateurs is becoming more interesting nowadays.
Thanks again for your support for all hams that are enthusiast like you, and for sharing with us all your experience so open and clear !
Best regards,
Ignacio |
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