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Feb 18, 2016, 03:39 PM
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If you are alternating LH and RH polarization, you will be able to get more than 5 in the air.
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Feb 22, 2016, 11:50 AM
Registered User
Quote:
Originally Posted by Jon h2
If you are alternating LH and RH polarization, you will be able to get more than 5 in the air.
My doubt is if helicals are better than mini patch antennas at receiving circular polarized signals.

We alternate right and left mini patch IRC, first diversity with 2 right, next diversity-frequency with 2 left ....
Feb 26, 2016, 07:17 PM
mstevenson1972's Avatar
Quote:
Originally Posted by Jon h2
Those are pretty good combos, I think it will work.

However, I ran them, and there are 4 IMD products that come close and could cause some problems. Maybe Rob can chime in and check my work.

Generally, we have tried to make sure IMD products are >= 20MHz away from any desired frequency. Three combos in your frequiences fall below that, but it still may work fine.

The IMD products are in yellow, with potential problems in orange: (EDIT: 5915 should also be highlighted as a potential problem)



Making some of the antennas LH polarization will help, too.
Why 5860 and not 5840?
Mar 02, 2016, 09:16 PM
Registered User
techspy's Avatar
Just an FYI, we have resorted to using 2 groups and have had no interference issues since.

5645 (Red), 5705 (Blue), 5740 (Red), 5780 (Blue), 5800 (Red), 5820 (Blue), 5860 (Red), 5885 (Blue), 5945 (Red)

Red will fly for approx 15 min, then Blue, then back to Red. This helps immensely with video interference. If your color is not flying, you are not allowed to power on your video transmitter.
Mar 03, 2016, 10:02 AM
Let's FPV in Middle TN!
moteasa's Avatar
Quote:
Originally Posted by techspy
Just an FYI, we have resorted to using 2 groups and have had no interference issues since.

5645 (Red), 5705 (Blue), 5740 (Red), 5780 (Blue), 5800 (Red), 5820 (Blue), 5860 (Red), 5885 (Blue), 5945 (Red)

Red will fly for approx 15 min, then Blue, then back to Red. This helps immensely with video interference. If your color is not flying, you are not allowed to power on your video transmitter.


5860 (Red), 5885 (Blue)

was this separation to prevent the IMD? 5885 not up closer to 5905 for that reason?
Mar 15, 2016, 01:40 PM
Registered User
lpabmendez's Avatar
We currently use these 6 frequencies:

5645
5685
5760
5800
5860
5905

Wondering if we can also use 5945 as a 7th frequency?
Last edited by lpabmendez; Mar 15, 2016 at 01:53 PM.
Mar 18, 2016, 10:30 AM
Registered User
Jon H2,
With some of the new TX/RX modules coming out http://www.laforgefpv.com/, the frequencies can be changed in code, so we wouldn't be limited to the current bands. What kind of band plan could you come up with to minimize interference and stay within the Ham band with that freedom?
Mar 22, 2016, 10:12 AM
Dirt Dobbins
Quote:
Originally Posted by lpabmendez
We currently use these 6 frequencies:

5645
5685
5760
5800
5860
5905

Wondering if we can also use 5945 as a 7th frequency?
Using 5645 and 5945 in the USA could cost you a hefty fine... stay within 5650-5925 MHz...
Mar 25, 2016, 12:15 PM
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Thread OP
Quote:
Originally Posted by andmiller
Jon H2,
With some of the new TX/RX modules coming out http://www.laforgefpv.com/, the frequencies can be changed in code, so we wouldn't be limited to the current bands. What kind of band plan could you come up with to minimize interference and stay within the Ham band with that freedom?
There are many many groups that can work, and many that can't. you will have to try them and do the math to identify which is which. The groups listed in this thread will be a good start.

If I were to start from scratch to identify a new group, I would choose frequencies that are well spaced from one another and make the spacing not the same between each channel (even spacing tends to make the IMD problem appear, per the simple math of it).
Mar 25, 2016, 02:39 PM
Let's FPV in Middle TN!
moteasa's Avatar
Quote:
Originally Posted by Jon h2
There are many many groups that can work, and many that can't. you will have to try them and do the math to identify which is which. The groups listed in this thread will be a good start.

If I were to start from scratch to identify a new group, I would choose frequencies that are well spaced from one another and make the spacing not the same between each channel (even spacing tends to make the IMD problem appear, per the simple math of it).
Say that we are racing in a cave, and raceband will be used. Since we are in a cave, would 5645 and 5945 still be considered off limits in the US?
If not, how would 5645 and 5945 fit in the IMD chart for raceband?
Has anyone done an IMD chart for raceband to see where the trouble spots are?
Mar 26, 2016, 11:08 PM
Registered User
Quote:
Originally Posted by moteasa
Say that we are racing in a cave, and raceband will be used. Since we are in a cave, would 5645 and 5945 still be considered off limits in the US?
If not, how would 5645 and 5945 fit in the IMD chart for raceband?
Has anyone done an IMD chart for raceband to see where the trouble spots are?
Per the FCC it is not lawful to transmit on those frequencies anywhere in the US, although if you were in a shielded environment, it would be hard for anyone to pick up the transmissions.
Mar 26, 2016, 11:10 PM
Registered User
Quote:
Originally Posted by Jon h2
There are many many groups that can work, and many that can't. you will have to try them and do the math to identify which is which. The groups listed in this thread will be a good start.

If I were to start from scratch to identify a new group, I would choose frequencies that are well spaced from one another and make the spacing not the same between each channel (even spacing tends to make the IMD problem appear, per the simple math of it).
I have tried to find the formula to calculate multiple frequency IMD, but haven't found it yet. Any tips?
Mar 28, 2016, 09:46 AM
Team AlienWarpSquad
Quote:
Originally Posted by andmiller
I have tried to find the formula to calculate multiple frequency IMD, but haven't found it yet. Any tips?
n*f1 + m*f2 = f3
n*f1 - m*f2 = f3
n*f2 + m*f1 = f3
n*f2 - m*f1 = f3
f1 & f2 = the two primary frequencies of 2 transmitting channels
n & m = integers from 1 to infinity (typically limited to 5, 7 or something).

If the result (f3) is another channel then that can cause IMD interference.
Mar 28, 2016, 04:43 PM
Registered User
Thread OP
Quote:
Originally Posted by waltr
n*f1 + m*f2 = f3
n*f1 - m*f2 = f3
n*f2 + m*f1 = f3
n*f2 - m*f1 = f3
f1 & f2 = the two primary frequencies of 2 transmitting channels
n & m = integers from 1 to infinity (typically limited to 5, 7 or something).

If the result (f3) is another channel then that can cause IMD interference.
To clarify for others, you will want to have f3 be a given distance from any of the desired frequencies. We often aim for 15MHz away here.
Mar 29, 2016, 07:45 AM
Team AlienWarpSquad
Thanks for clarifying Jon.


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