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  #21  
Old 04-27-2017, 05:41 PM
jweir43 jweir43 is offline
 
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Quote:
Originally Posted by j-red View Post
I've got about 16' of RG174 which has a similar impedence to the rg400. I'll head out to the hanger again tomorrow morning when the weather is clearer and give it some more time.
Thanks for the input.
RG-174 is quite appropriate for this purpose. It has almost exactly twice the loss of -400 so the minimum and maximum lengths are cut in half. I copied a page out of the RST Engineering Appareo Installation manual and will be happy to email you antenna installation images and such. I'm also happy to answer questions in this ng or by email if you prefer.

If somebody knows how to attach a pdf file to this thread I'll be happy to post the antenna page. jim@rstengineering.com

Jim
RST
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  #22  
Old 04-27-2017, 05:47 PM
jweir43 jweir43 is offline
 
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Quote:
Originally Posted by BobTurner View Post
Bottom line: This is a TSO'd device, and must be installed per the manufacturer's instructions, or technically it is not legal.
Bob ... sort of. The way the regulation is written, the ESG has to MEET the requirements for TSO, not BE TSOd. And, with experimental aircraft rules, I would suspect that if you can show that you used a cable with the appropriate loss factor that would MEET the same requirements you would be good to go.

The actual requirement is for a cable with between 2 and 7 decibels of attenuation, however you choose to get it. Appareo SUGGESTS using -400 but the requirement is for the attenuation, not one specific cable.

Jim
RST
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  #23  
Old 04-28-2017, 09:26 AM
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jjconstant jjconstant is offline
 
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I am about to be doing this upgrade. Regarding the cable length...not having read the manual yet, is it really a minimum length and not a maximim? If I have a shorter run of RG 400 it won't meet the spec and/or risk not working? It needs the resistance?
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  #24  
Old 04-28-2017, 09:38 AM
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Quote:
Originally Posted by jjconstant View Post
I am about to be doing this upgrade. Regarding the cable length...not having read the manual yet, is it really a minimum length and not a maximim? If I have a shorter run of RG 400 it won't meet the spec and/or risk not working? It needs the resistance?
Garmin has the same minimum requirement of 10', which is an expectation of the installation in most airplanes, apparently. Shorter runs essentially provide too much signal strength to the receiver, is what I was told.
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  #25  
Old 04-28-2017, 11:48 AM
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carlrai carlrai is offline
 
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Default Here's a quote from the manual

Quote:
Originally Posted by jjconstant View Post
I am about to be doing this upgrade. Regarding the cable length...not having read the manual yet, is it really a minimum length and not a maximim? If I have a shorter run of RG 400 it won't meet the spec and/or risk not working? It needs the resistance?
I had a short length of rg400 originally and no GPS. Finally read the manual again and found this. All works now.



As pointed out earlier by those smarter than I, there are other alternatives but you have to deal with picking the length to obtain the 50 ohm impedance.
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  #26  
Old 04-28-2017, 01:38 PM
BobTurner BobTurner is offline
 
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Quote:
Originally Posted by carlrai View Post
As pointed out earlier by those smarter than I, there are other alternatives but you have to deal with picking the length to obtain the 50 ohm impedance.
If you use something other than the example given, it still has to be 50 ohm cable, and its loss has to fit the minimum and maximum given. So 16' of RG-174 does work; but 19' would be too lossy.
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  #27  
Old 04-28-2017, 02:54 PM
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Tommycat Tommycat is offline
 
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Interesting... So when trying to hit the SWEET spot. Which would be better?
A coiled up long piece of RG-400... or a 50 percent shorter piece of RG-174?
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Last edited by Tommycat : 04-29-2017 at 03:12 PM. Reason: corrected comparison figures...
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  #28  
Old 04-28-2017, 04:11 PM
jweir43 jweir43 is offline
 
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Quote:
Originally Posted by carlrai View Post
As pointed out earlier by those smarter than I, there are other alternatives but you have to deal with picking the length to obtain the 50 ohm impedance.
That's not quite true. It will be 50 ohm cable no matter how long you make it. Coax impedance is a function of the outer DIAMETER to the center conductor, and length has nothing to do with the matter.

However, the antenna they chose (and I have no idea why they chose that big klunker) has 30 decibels (dB) of gain and that just blows away the front end of the GPS when the satellites are dead overhead, making anything NOT dead overhead impossible to hear. They came up with a solution of running the gain down by loss in the cable. Why in the world they chose heavy expensive -400 is, again, a mystery.

Coming up with LOSS is trivially simple and good old RG-58 would have had a minimum of 7 feet or so, and tiny little-174 is about 5 feet minimum. Again, if anybody can teach me how to post a pdf to this forum, I've got a full page (with pictures) explaining the whole thing.

Jim
RST
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  #29  
Old 04-28-2017, 04:20 PM
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Sam Buchanan Sam Buchanan is offline
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Quote:
Originally Posted by jweir43 View Post
Coming up with LOSS is trivially simple and good old RG-58 would have had a minimum of 7 feet or so, and tiny little-174 is about 5 feet minimum. Again, if anybody can teach me how to post a pdf to this forum, I've got a full page (with pictures) explaining the whole thing.

Jim
RST
Jim, here is the link with instructions for inserting images:

http://www.vansairforce.net/articles...ums/images.htm

I'm interested in your data because a Stratus install is in my near future.
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  #30  
Old 04-28-2017, 04:25 PM
jweir43 jweir43 is offline
 
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Quote:
Originally Posted by jjconstant View Post
I am about to be doing this upgrade. Regarding the cable length...not having read the manual yet, is it really a minimum length and not a maximim? If I have a shorter run of RG 400 it won't meet the spec and/or risk not working? It needs the resistance?
OK, here is the link to the full installation manual and a whole bunch of other stuff that I send out with my Appareo ESG units. You all might just as well have access to what I have as it doesn't cost me a penny for you to download all my information.

Yeah, I sell the thing and I'm NOT trying to scam you into reading my ads. I'll tell you right up front that it is halfway down on the web page and is highlighted in blue as a download link. Bypass all the hucksterism if you wish, but please use the documents with my blessing.

Use this URL: http://www.rstengineering.com/rst/pr...b/password.htm

Use this password: eaa73aopa88 (Do NOT cut and paste, it doesn't work).

Jim
RST
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