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Old Oct 09, 2012, 11:41 PM
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United States, TX, Austin
Joined Sep 2012
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I'd like to hear from 72MHz techno-geeks (Noobs don't reply)

I have an issue with a JR XP 6102 FM transmitter and various brands of receivers: Berg and Corona. Basically, they will NOT ground range check beyond ~10' but all of them will fly a small homebrew foamie to ~half mile out at ~300' altitude and back. It's when I get into this pattern below I have a plane plowing into dirt:

..........._________ <------- (begin left turn toward self)
........./
....... /
........\
........ \___x___ (~10' altitude heading to my right, x = start of down elev.)
....................... \
........................V
...................smash!
........................|
........................|
........................| (~20' distance)
........................|
........................|
........................|
.......................o
........................|
........................|
................... __|__
....................| o o |
....................|_ :: _|

This has occurred at 3 different locations and the pattern/altitude is roughly
the same. Also note Austin Texas is a major league Wifi/Cell-aholic town.

Does anyone know of new signals being incorporated by municipalities which have a harmonic which could interfere with our 72MHz equipment? This town does have a "safety signal" which takes control of Austin Power's (no pun!) thermostats to keep your inhouse climate locked at ~74 degrees year 'round. I'm thinking MAYBE that is throwing a harmonic that may effect range checks (all controls flutter wildly beyond 10', so it's getting something from someplace!).
Whatever it is, it's reserved to low altitude near the ground. My local club is getting hit on Spektrum equipment also.

The heading of the plane (10' flying left to right ~25' out) is always the same, the rest of the flight proceeds uneventful. This leads back to the radio gear itself but the altitude issue makes me question if it's an external source of aggravation.

Any insight from RADIO GUYS only please? Thank you

Oh yeah, crystals have been matched to the receivers and Tx mast fully extended for flight.
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Old Oct 10, 2012, 09:42 AM
AndyKunz's Avatar
Illinois
Joined Sep 2001
25,233 Posts
Check the FCC frequency chart: http://www.ntia.doc.gov/files/ntia/p...3-allochrt.pdf

That's an old chart, but the blue areas on either side of our 72-75 area are now "white space" and unused. Some people are putting their own things into those areas to experiment.

Notice that 72 has both "fixed" and "mobile" stations in there. This corresponds to things like wireless mikes in studios/stadiums/churches/etc. (fixed) as well as us (mobile). There are also things like pagers in that band, but they shouldn't cause you much problem. In fact, as long as people are operating legally, you shouldn't have any problem from other users.

Andy
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Old Oct 10, 2012, 10:03 AM
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whitecrest's Avatar
Orleans, MA
Joined Feb 2007
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Quote:
Originally Posted by XtalHunt View Post
. . . Basically, they will NOT ground range check beyond ~10' but all of them will fly a small homebrew foamie to ~half mile out at ~300' altitude and back. . .
You should be able to go out to about 100' for a range check. I'd check for low transmitter output or a loose antenna. That may explain the erratic control you have been observing. Without a solid signal, the receiver will be more sensitive to other extraneous signals that may be nearby.
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Old Oct 10, 2012, 10:55 AM
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LesUyeda's Avatar
San Diego, California
Joined Dec 2004
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Once upon a time, at some field or other, we had similar problems. Turned out that we were flying over an old land fill that was used when you could dump ANYTHING and people dumped old cars, refregerators, stoves, etc. This would cause interference patterns, where the direct signal was interfered with by the signal reflected off the ground, and just slightly out of phase.

Les
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Old Oct 10, 2012, 04:50 PM
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richard hanson's Avatar
United States, UT, Salt Lake City
Joined Oct 2007
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I miss my old 72--- like I used to miss the pot under the bed -
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Old Oct 11, 2012, 02:29 PM
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E-Challenged's Avatar
United States, CA, Garden Grove
Joined Oct 2000
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Somebody gave me an old Airtronics RD-8000, lots of features, works nicely on 72Mhz CH 42, no interference yet. Probably because everyone else is using 2.4GHZ . Used to have problems at same field on CH 13, 47, etc. with Hitec Prism XMTR
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Old Oct 11, 2012, 02:44 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
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I understand the railroad systems use 72 MHz as part of their ops.

Also, there was once a discussion about running internet through the thrid rail and that this was going set-off 72 MHz interference.

I don't know if either could be a problem for you.


HOWEVER

When you range check your plane, where are you placing it? Where is the antenna? Is it fully deployed or bundled up somewhere? is it on the ground?

Good to range check with model off the ground, say on a wood table or with someone holding it so that the antenna is in a normal configuration. Many power guys have the antenna taped or rubber banded to the verticle fin.
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Old Oct 11, 2012, 03:55 PM
AndyKunz's Avatar
Illinois
Joined Sep 2001
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Also BPL Broadband over Power Lines was in the same area.

Andy
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Old Oct 11, 2012, 04:41 PM
Proud member of LISF and ESL
LI, New York, USA
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Thanks Andy, that was what I was thinking. Not third rail it was the Power Lines. I remember AMA being all concerned about this.
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Old Oct 14, 2012, 04:03 PM
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United States, TX, Austin
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The TX was completely disassembled and cleaned in soapy water and then oven dried. Battery was replaced with an HK Lipo and (2) diodes installed to provide 10.7V full charge meter reading. In the interim, CR2032 button cell went dead and has been replaced since all model memory was being dropped every power-off. While the TX was being externally/internally washed, I did not care for the "looseness" of antenna mast hardware, so all the nuts/washers were tightened up around the base and I also re soldered the output lead from the RF circuit board since that's ~26 gauge multistrand wire there..

You have given me a CLUE here: Berg receiver is using a loaded antenna and Corona is still bundled up from being brand new out of box. Will extend RX wire, see if I gain some footage. These issues had not been apparent with a NEW set won on Ebay before this, this P.O.S. was very used and abused.

Next bit of data I would like to find are the LABELS of the 2 main chokes on the RF board and the RED trimmer pot, which probably is an antenna trimmer. No glypto on any of the components, indicating jackass prior owner may have seriously mucked about in there!
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Old Oct 14, 2012, 04:11 PM
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I also am toying with idea of stealing the GUTS out of that HK TX and switching over to 2.4G. But I want the functionality of the menus at my fingertips since being a slave to a laptop at the field defeats the purpose of leaving the house altogether!

Any of you savvy with the surgery required? Can't be too complex, not with what I've already put into this unit anyway.
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Old Oct 14, 2012, 04:30 PM
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Quote:
Originally Posted by AndyKunz View Post
Also BPL Broadband over Power Lines was in the same area.

Andy
I'm in a student housing complex which is rampant with kiddie-signals, shall we say. Internet, Cell, cable TV, who the hell knows what else. Another thing that annoys me is the city taking control of indoor thermostats by radio signal. Hey, I didn't signup for that!
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Old Oct 14, 2012, 10:05 PM
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Canada, QC, Quebec City
Joined Sep 2006
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Quote:
Originally Posted by XtalHunt View Post
I also am toying with idea of stealing the GUTS out of that HK TX and switching over to 2.4G. But I want the functionality of the menus at my fingertips since being a slave to a laptop at the field defeats the purpose of leaving the house altogether!

Any of you savvy with the surgery required? Can't be too complex, not with what I've already put into this unit anyway.
The 2.4Ghz RF board in these HobbyKing(FlySky)radio is separate from the encoder. It can be easily installed in any Tx using the existing encoder since it uses ppm,V+ and ground only. The RF board in the radio you linked id the same a what is in the Turnigy 9X and this one:
http://www.hobbyking.com/hobbycity/s...2_Mode_2_.html
Or you could just use one of the many DIY modules, FrSky is very popular and better than the FlySky system. There is several posts about doing just that here and in the Electronic DIY forum.
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Old Oct 14, 2012, 10:26 PM
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earlwb's Avatar
USA, TX, Grapevine
Joined Dec 2008
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We discovered a while back that 72mhz on the week days is quite risky to use. In the morning, at around noon, and later in the afternoon (quitting time?) a RC system could be jammed out if it was on 72mhz. We hooked up a frequency scanner, and it lit up like a Christmas Tree at quitting time too. It turned out they put up some pager towers that send out very powerful signals on those frequencies now. So we advise people at our flying field of the risk and that it is wise to convert over to 2.4ghz now. Due to the RF power output of the pager transmitters, they can be miles away and still jam out a RC system.

Another problem is warehouses use overhead cranes inside their buildings that use 72mhz too. But they can have 25watt output transmitters on these things. So they can jam out any 72mhz RC systems flying nearby too.

Some schools use 72mhz radio systems for synchonizing their classroom clock systems. These can put out upwards of 100 watts of power too. They have to have a signal that can penetrate many walls to reach the clocks in the classrooms everywhere.

So unfortunately it is getting pretty risky to fly 72mhz anymore in some locales.
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Old Oct 14, 2012, 10:47 PM
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United States, TX, Austin
Joined Sep 2012
165 Posts
This is all news to me but making lots of sense since the quality of 72MHz link in the last 4 years has been getting steadily more unsteady! Yeah, figured a hardware convert wouldn't be too difficult! Well, it will cost me $23 plus shipping to find out. I just blew a wad on channel 32 crystals for this piece of work besides, damn!

Update: Now I am not sure what to do since that Hobby king crap and the ~35 associated files to go with that TX are not my idea of "keeping it simple, stupid". This is why I never upgraded to 2.4GHz: the consumer treadmill money agenda!

Screw it, I'm not buying any more Chinese B.S. I'll have to get this JR either fixed or retuned. I am not an advocate of any HK product that has current flowing through it! I've always had issues with their electronics since 2008, wish there was an American alternative.
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Last edited by XtalHunt; Oct 15, 2012 at 07:32 AM.
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