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Aug 18, 2017, 02:56 PM
Great Britain
MrBen.'s Avatar
Can anyone suggest a best 7 frequencies set? Determined to get more than 6 pilots airborne as at all UK events we never fly more than 6 and pilots are too stuck in their ways to start running alternate LHCP antennas
Last edited by MrBen.; Aug 18, 2017 at 03:02 PM.
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Aug 18, 2017, 07:11 PM
Registered User
I have looked at the first and last few pages and see a lot of theory and computer analysis; let me present what I tested after we recently encored two goggles conflicting; My tabulation of 5 bands (plus partial R band) by actually transmitting on one frequency and clicking all the receiving frequencies one at a time required about 1,500 test points. Next, a table of the bands and channels was marked with slashes at each frequency received. Then I did a reverse on which channel conflicted with others.
This mess of slash marked frequencies had ONLY TWO FREQUENCIES unmarked........they didn't interfere or be interfered.
I then made all other channels shut off to use and picked the least conflicted ones and discovered that there are TWELVE FREQUENCIES THAT DO NOT CONFLICT when used in any combination of the 12. We might be able to get 4 more channels that can be paired and used with one at a time.
The real bad news is that most of the local FPVers use Fat Shark goggles and these are on band F. There are only 3 clear channels on F
A few minutes ago, a member e-mailed asking if his wireless backup camera could interfere at the field............oh, yes!
We discovered that the dome we fly in has wireless security cameras and at least one is on F.
Our club has 6 FPV flyers so this means we can assign a personal frequency for each. We will do something else when the number reaches 12.
A computer guru took the conflicting channels and made a program to see how bad it was.......after 5 random channels were picked, 30 channels of the 40 total were unusable.
If anyone decides to repeat this testing, have lots of coffee to keep the brain fog in check.
Mar 22, 2018, 04:11 PM
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trojanGoat's Avatar
There's been a lot of talk about using imd channel sets. But one of the recommendations from the video on the first page of this thread was to use a 5db attenuator to reduce the imd products. Has anyone tried using an attenuator? I tried searching on the web and I can't even find a place that sells it.
Mar 05, 2019, 10:16 PM
Registered User
How could we calculate the effects of using CP antennas on IMD? How much better is the rating with alternating polarization?
Jan 18, 2020, 11:12 PM
Registered User
Quote:
Originally Posted by trojanGoat
There's been a lot of talk about using imd channel sets. But one of the recommendations from the video on the first page of this thread was to use a 5db attenuator to reduce the imd products. Has anyone tried using an attenuator? I tried searching on the web and I can't even find a place that sells it.
Do a Google search for SMA attenuators. Amazon even has them. Be sure your receiver and antenna does not use RP SMA connectors.
Jan 18, 2020, 11:28 PM
Registered User
Quote:
Originally Posted by elib100
How could we calculate the effects of using CP antennas on IMD? How much better is the rating with alternating polarization?
I've been away from this forum for along time.

To accurately calculate how much improvement you'd get from using opposite handed CP requires knowing some characteristics of the receiver which I've never seen published for FPV receivers, as well as the particulars of the environment and antenna specs.

But if the antenna gives 20 dB or more opposite CP rejection, I'd expect that to give good results. And that seems to be similar to results some are reporting. Of course if you have more than two users, some will share CP direction.


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