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Question: Does 72MHz interfere with TV?

colorex

Rotor Riot!
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#1
OK, so here I am in Ecuador, and my friend from the US gave me this 6ch JR 72MHZ computer radio + Rx. I don't have the right crystals yet, but I'm getting the 72.810 crystal.

Now I was looking on Wikipedia the other day and found this. If you look on the South America line, it'll say that channel 4 on broadcast TV goes all the way up to 72MHz. Looking around more, I found this:

Channel--Lower edge--Video carrier-DTV carrier--Audio carrier--Upper edge
---2---------54----------55.25------54.31--------59.75-----------60
---3---------60----------61.25------60.31--------65.75-----------66
---4---------66----------67.25------66.31--------71.75-----------72
---5---------76----------77.25------76.31--------81.75-----------82
---6---------82----------83.25------82.31--------87.75-----------88

According to that, 72.000 MHz is the upper limit of broadcast channel 4.

Will my JR RS600 Rx running at 72.810MHz catch strong interference from TV signals?
 

colorex

Rotor Riot!
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#2
I just checked on my TV, the TV gets strong interference from the Tx... You can hear the PPM signal... don't know about the receiver, cuz I don't have a battery yet...
 

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JimCR120

Got Lobstah?
Site Moderator
#3
Colorex,

Another problem with dealing with strong signals is the possibility of intermediate frequencies. This is where one freq can mix with another and produce others (two, sometimes more). My opinion is, if the air is already cluttered with so many 72MHz users, why risk a crash when there are channelized tx/rc systems that are effective at overcoming those hazards.

Jim
 

colorex

Rotor Riot!
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#4
My opinion is, if the air is already cluttered with so many 72MHz users, why risk a crash when there are channelized tx/rc systems that are effective at overcoming those hazards.

Jim
What exactly do you mean? There are not any 72MHz users, just a TV station that broadcasts on a near frequency...
 

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colorex

Rotor Riot!
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#6
Yeah the 27MHz MIGHT be cluttered sometimes... I remember for a physics class everyone brought their own cheapo RC car... all on 27MHz and Channel A... Weridest thing since the channels were switched on some cars... though spooky with 15 RC cars going crazy...

However if the reciever picks up a tiny band that is tightly stuck between two other channels, it should be able to clear up interference, don't you think?
 

JimCR120

Got Lobstah?
Site Moderator
#7
It all depends on the design of that rcvr. Electronics has it definite benefits but they aren't a replacement for good human judgment. Have you ever been on the road listening to music when somehow your radio locks on to a different signal? These systems are only as "smart" as the instructions they've been given.

Again, there are plenty of very inexpensive 2.4GHz radios out there that will perform just fine. I have my trusty HK-7 that has never given me trouble. My only beef with it is that the documentation on it stinks. It has more capabilities and I don't know how to exploit them.
 
#9
I would turn the RX on with some servos plugged in and see if they move at all for about 10 min or so. If nothing moves and they stay put, i would say your safe to go, plus with your Freq higher on the 72 band you should be fine. If you don't want to chance it go to 2.4 gHz.

I think when they say upper edge of 72 they mean like 71.999 but not above 72.000. You could also get a Frequency Scanner to be absolutely positive.
 

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colorex

Rotor Riot!
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#11
I would turn the RX on with some servos plugged in and see if they move at all for about 10 min or so. If nothing moves and they stay put, i would say your safe to go, plus with your Freq higher on the 72 band you should be fine.
I would too, if I had servos and a battery... I only have the Tx and Rx. I'll try soon to buy HXT900 servos from HobbyKing and see if they arrive, and if I have to pay taxes.

I think when they say upper edge of 72 they mean like 71.999 but not above 72.000.
Are the TV transmissions that accurate?

You could also get a Frequency Scanner to be absolutely positive.
Will try to locate one.

----------------------

Thanks for the feedback. Very good ideas!
 

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colorex

Rotor Riot!
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#14
Thanks! I will try to get my hand on a crystal and a servo, as to test the receiver. Further input about interference is welcome. I was about to consider the Turnigy 9X for a replacement, but then I saw an episode where Chad uses a 72MHz radio to get farther away with FPV. I guess I'll try to revive that ol' system...
 

colorex

Rotor Riot!
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#15
OK I asked on RCGroups, but we didn't get there. http://www.rcgroups.com/forums/showthread.php?t=1534998

I got the idea to call the DHS (Distant Hobby Shop) to ask if they were able to use 72MHz. They said they use them on their flying fields, but their field is far away from the TV transmitter. He said I might have problems using it closer to the antenna than 1 Km. (that is, I won't be able to fly in town)

Anyway, I'll report back when I get my crystals.
 

colorex

Rotor Riot!
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#16
HAHAHA Now after using my Tx for quite some time, I can report back. I'm having glitches a few times (when I walk around with the Tx) but that seems to be a problem of the Tx antenna.

I have gone probably 200-300 meters away without glitches. Haven't range tested yet, but I will get to that.

So far it works for me but it knocks out broadcast TV channel 4 for everyone at two blocks distance and for everyone else too.