VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #11  
Old 04-09-2009, 11:52 AM
vonjet vonjet is offline
 
Join Date: Feb 2008
Location: Thousand Oaks, CA
Posts: 183
Default Transmit and signal strength are fine

The motivation for replacing the 58 with the 400 was to get better sheilding as to avoid getting RF interference into the autopilot and magnetometer.
Would I achieve this goal by doing this or no?
Reply With Quote
  #12  
Old 04-09-2009, 02:35 PM
breister breister is offline
 
Join Date: Dec 2006
Location: Atlanta, GA
Posts: 1,231
Default

Maybe a little; you will get more from re-routing the wire than by changing the coax type.

If you can simply pull the wire BACK from the front and then route around the side away from the tunnel, that alone might give significant improvement. You could then leave the existing cable intact and simply add an extender if needed. It is ok to mix types. I fubared all my connections, it might be worth your while to have a length made up for you by Stein.

And I think you already read the thread on the RF filter - have you tried that?
Reply With Quote
  #13  
Old 04-09-2009, 04:22 PM
vonjet vonjet is offline
 
Join Date: Feb 2008
Location: Thousand Oaks, CA
Posts: 183
Default

I bought the filter and got it today. I will be plugging that in this afternoon.
I really cant get my wires routed much different anymore since my interior is done. They are no longer bundled with the other wires but they still run a few inchs away down the center tunnel.
I'm getting close to solving it but I still have the issue of where to place my Magnetometer. Haven't found a spot in the airplane that doesn't cause mass RF problems yet.
Reply With Quote
  #14  
Old 04-09-2009, 04:45 PM
apatti apatti is offline
 
Join Date: Dec 2005
Location: Middle Georgia
Posts: 654
Default

Have you checked the SWR on your antennas? High SWR can exasperate RFI problems.
__________________
Tony
RV8A
N97AP
Warner Robins, GA
Phase I complete
Reply With Quote
  #15  
Old 04-09-2009, 07:10 PM
noelf noelf is offline
 
Join Date: Nov 2007
Location: Cary, N.C.
Posts: 1,216
Default Coax can be a funny animal...

...Although we commonly refer to the outer conductor as a "shield", it is not a shield. The outer conductor is just that...it is the outer conductor.

Coax is constructed with a "center conductor" surrounded by an insulated layer, and then the outer-surround conductor, followed by (optionally) an outer insulated layer. The inner insulated layer is called a "dielectric" separator that keeps the outer conductor and the inner conductor a specific distance from each other.

The combination of inner conductor size, the dielectric material thickness and electrical properties, and the outer conductor size and placement distance from the inner conductor all combine to create the characteristic impedance of the coax cable ( for us, usually 50 ohms).

The outer conductor can be one or several layers of braided wire, or the coax can be of a rigid type...resembling a water pipe (high power applications).

The choice of coax, which incorporates two braided layers in the outer conductor, is generally of a higher quality than a coax with only a single braided outer conductor. Whenever a coax cable is severely bent (at or near its minimum bend radius) the braided outer conductor can be distorted and the individual braid strands can move. This causes the cable impedance to change at that bend position. This is not desirable for the following reason:

As a signal is launched from a transmitter, the Tx circuits are designed for a 50 ohm (in this case) load. The coax transmission line is expected to be 50 ohms, and the target end (the antenna) is also expected to be 50 ohms. If any part of this turns out to not be 50 ohms, then a mismatch is "felt" by the signals, and a "mode" change is the result (technical terms). This mode change point is what allows the signal to "escape" from the transmission line (coax) at some undesirable point, and is also the point at which outside signals can be brought into the coax (think radiated interference).

So, to minimize these negative effects, use gentle bends, as few connectors as possible, and be sure to "match" all items for the proper characteristic impedance.

If you are inclined to shop at your local blister-pack audio store, just be aware that their coax connectors can be 50 or 75 ohm items. They are not marked as to which they are, so you may end up with the wrong impedance stuff, and you will suffer mode change problems.
Reply With Quote
  #16  
Old 04-11-2009, 08:29 PM
breister breister is offline
 
Join Date: Dec 2006
Location: Atlanta, GA
Posts: 1,231
Default

Quote:
Originally Posted by vonjet View Post
I bought the filter and got it today. I will be plugging that in this afternoon.
I really cant get my wires routed much different anymore since my interior is done. They are no longer bundled with the other wires but they still run a few inchs away down the center tunnel.
I'm getting close to solving it but I still have the issue of where to place my Magnetometer. Haven't found a spot in the airplane that doesn't cause mass RF problems yet.
See your pm's since this is not an "RV Solution..."

Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:54 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.