Was this a good-to-go ground test .....or am I grounded??
 

I'm asking this same question at the other RC place too, so pardon if it's a repeat to you, but I'm trying to get as much input as I can to make a decision before I go flying tomorrow.

OK.....this afternoon I did final preperation and a ground check on an electric PT-40 for a maiden flight I intend to do over the weekend. I've got a proven 8103 FM 72mhz radio and receiver I've used many times before. I placed the plane in the grass with the nose facing me. The receiver antenna runs through the length of the fuse with about 10" of antenna exiting out of the bottom of the fuse and laying in the grass. I stood with the radio and antenna down, about only 30 feet or so downrange from the plane. In between the plane and my radio I have a gazebo with metal corner panels and a metal patio table and metal chairs. All the plane surfaces fluttered and moved like crazy back and forth with no control. I changed out the receiver thinking maybe it was bad, but got the same bad ground test results with the next receiver I tried. I pulled the radio antenna up about 12" to see if that made a difference but the plane was still acting crazy.

I then moved the plane to my cementy driveway to do the ground test. I had the same 10" of antenna exiting the plane as before, but lying on cement this time and not in the grass. This time too there was no patio furniture in between anything. It was basically a straight shot visually between my plane and the radio with no patio furniture in between. I left the radio antenna down and walked away 75 feet and everything worked fine. No more crazy flutter.

Is this good to go, or is a phantom waiting to strike?

OK, I'm nothing even close to any kind of radio guru (still use 72MHz on ALL my planes), but I'm rather sure I'm going to be pretty close to right in my views on this one. Remember, this is LIMITED KNOWLEDGE of radio, but also 40+ years RC experience.

Question: did you purposely place plane/radio in it most compromised-possible position or is this a joke of some sort?

Nose facing you = least possible radio antenna reception

150 lbs of metal between xmtr and rcvr = nothing but interference possible

10" antenna exiting bottom of plane (assuming, at the rear) = no problem. ALL my planes are similar, all have been flying for a minimum of 20 years in this configuration - a couple since 1974-75.

I dunno - maybe this really is some kind of joke and it's on me after all.

Range checks must be line of site. That means nothing between you and the airplane. Also an engine off range checks is only half a range check, the next step is a range check with the running an momentarily throttled up to full power working with an assistant of course. This is even doubly important for the FM,AM systems.

The figures you got are OK but back when I used 72Mhz I preferred to see antenna down at least 100 feet. Some brands struggled with that though.

John

Skylark,
I was suspicious of some of the details myself (the ones that you highlighted in red for me), and this is why I was sure to mention them. Because I had never flown a plane with a gazebo or metal patio furniture surrounding it up in the sky, I wasn't informed of the path by which the radio waves worked. As a novice pilot, I had some how assumed that the "FM" in a JR receiver worked like my "FM" car radio with unhindred penetrating reception. I was NOT aware that our FM toys were suseptible to "multi-path" radio interference. (a term somebody explained to me at the other websight)

John,
Thank you for that simple confirmation that it should be a direct line with nothing between it, and that is how it was intended to be. As I explained to skylark, that while it makes sense NOT to fly the plane around patio furniture or inside of tree tops, I had thought the FM signals worked differently with a broad range that penetrates obstacles. BTW....as mentioned in my post, the plane is electric and not glow.

Thank both you gents for the help.

Where di you ever get the idea that FM in a car has unhindered radio reception? Have you never seen the antenna in the windshield?

ALL RADIO SIGNALS ARE LINE OF SITE, REGARDLESS OF FREQUENCY BAND!!!!!!!!!!!!!!
In the case of your car's radio, there is so much power being transmitted by the radio station(100,000 watts minimum), that it still gets reception when traveling behind obstacles. You R/C transmitter, on the other hand, only kicks out .5 watts.The signal can't force it's way around obstacles and, therefore, anything getting in the way will cause problems

Hydro Junkie,
Thank you for that simple explanation. Easy enough for me to undertsatnd without my knowing squat about radios.


UPDATE;
I finally had to change out the receiver from FM to SPCM to stop the uncontrolled fluttering.

I'm glad I had done another ground test today in the driveway to observe the flutter problem reappear! The fluttering occured at only 25 feet away!! (no gazebo and no metal patio furniture this time to blame) Two different FM receivers (JR600 and JR700) with two different #29 crystals didn't fully eliminate it. So finally I put an SPCM JR 770 receiver in the plane and all tests well at 105 feet away now with the radio antenna down.

Moral of the story, this impressed me just how important a good ground check is!!! http://static.rcgroups.com/forums/im...lies/smile.gif I'll be sure to check it out in the field tomorrow one more time before maidening. I've never noticed intererference issues during the last 15 years I've lived at this house. Evidently, something has changed recently!!

Are there more houses in the area? Any new businesses?
If there are more houses, that means more electricity and that means more static and magnetic interference. It could also be more wireless alarm systems, new wireless gaming(Wii, PS3/4,etc) and WIFI jamming up the airwaved
New businesses means the same thing but, more so. More florescent lighting(more magnetic fields), more video security(transmitting to a monitoring site) and more electricity(again, more or stronger magnetic fields).
These are all things you didn't really need to worry about a few years back

It's been my experience that usually something like this being caused by what I refer to as " interior RF " in other words there is something inside the airplane that is causing the problem. Being an electric model add slightly to the mix. Are you using the BEC in the speed control or a separate RX battery? Is the RX mounted closely to the speed control or motor batteries? What brand controller do you have? If you are running BEC then I would suggest installing a separate RX battery and testing again with the FM RX. If there is a problem with the BEC introducing dirty voltage to the RX it may get worse and the SPCM RX may have difficulties rejecting the noise at an unpredictable time.