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Redesigning my CP antenas

3zuli

Junior Member
#1
Hi guys, I've been flying FPV for about 6 months (I love my Bixler v1 :D). I'm using 200mW 5.8GHz with homemade cloverleaf and SPW antennas. However, these antennas are pretty worn out now, especially the CL which is on the plane and took lots of hits while landing into tall grass.
Right now I'm building a new CL/SPW set and I decided to do some more research (since this second build is supposed to be a bit "advanced"), but this has led me into some questions.
I decided to check, if there's a recommended max length of the coaxial feed. I didn't find the answer, instead I found IBcrazy saying that RG174 cable isn't suitable for 5.8G and RG316 should be used instead. I've been using RG174 till now, since it is cheap and easy to get where I live (Slovakia) and I didn't have any significant problems with it. Max ground test distance I've been able to make (with LOS and no obstacles) was around 450m (actual range should be ~700m). I had about 20cm of RG174 in the entire system, which should be a ~0.4dB loss. Long stroy short, here are my questions:
1. Is it really so critical to use RG316? Can I still use RG174 instead?
2. Assuming the above, I should keep the total coax length under 30cm or so?
3. To protect the antennas, I'm going to enclose them into table tennis balls - this won't hurt the performance too much, right?
I hope there's someone who can answer :)
Thanks for help.
 

Tritium

Amateur Extra Class K5TWM
#2
Actually RG-316 is not rated for more than 3GHz. You want RG-316D which is double shielded RG-316 and is rated to 6GHz. Also you want to keep the antenna stub less than 15cm and even better at half that length. The Table Tennis balls will not have a lot of impact but at 5.8GHz EVERYTHING adds up to lower performance very quickly. Done correctly you should get 4km with a 200mW transmitter. If it were me I would build a 5 turn helical antenna for your receiver (See IBCrazy's tutorial at RCGroups).

RG-174 looks good to 6GHz also according to this spec sheet:
http://datasheet.octopart.com/7805-0101000-Belden-datasheet-24331.pdf


Thurmond
 

3zuli

Junior Member
#3
I've been chatting with IBcrazy and he keeps telling me, that RG316 is better than 174. I don't know, I guess I'll stick with my RG174 and keep it short.
BTW I have a 3 turn and a 8 turn helical ready, I just don't feel like doing long range / planed flights yet. But I want to :)
 

Tritium

Amateur Extra Class K5TWM
#4
I've been chatting with IBcrazy and he keeps telling me, that RG316 is better than 174. I don't know, I guess I'll stick with my RG174 and keep it short.
BTW I have a 3 turn and a 8 turn helical ready, I just don't feel like doing long range / planed flights yet. But I want to :)
Absolutely do not take my findings over Alex. His comes from practical real world experience over time.

Thurmond