| Wayne,
I'm going through a similar process on my IV-P right now. I am by no means an expert yet but I have learned a few things which would have caused me to do it all differently if I had known before.
Firstly, carbon or any conductor near your antenna is bad. Hopefully not a problem for you. Jim Weir describes it as "more than an eigth of a wavelength long within a quarter wavelength of the antenna." This basically means that the Bob Archer nav antenna doesn't work in a IVP winglet because Lancair made the top of the winglet out of carbon. ...although interestingly a few people that have a King nav radio are able to function with this setup.
Secondly, if your antenna installation is marginal, you don't want to compromise it with splitters if you can help it. A standard splitter robs 50% of the signal strength which I think Bob Archer says translates to 30% range reduction. Using the standard approach, you would have two splitters on the way to your Garmin. So 25% signal strength. If it were me I would work pretty hard to eliminate the nav1/nav2 splitter and if I could come up with a place for a separate GS antenna I would do it. In Jim Weir's book, however, there's a design for a vor/loc <-> GS splitter which is frequency selective so is supposed to have lower losses than a standard splitter used in that vor/loc <-> GS application. I haven't tried it yet but it sounds good.
You might consider only hooking the new nav antenna to your SL30 only and figuring if that radio or antenna fails some day you are going to be looking for a waas vnav approach.
On the com side, I know Bob Archer has two switches left to select between com units for transmit. but you still have to live with a splitter on the receive side. I like Bob Pastusek's idea of putting in a belly whip better. Bob has a carbon fuselage right there which is probably helping with the ground a bit. In my understanding you need ideally a 22" radius ground plane for optimal performance. You can do that with a foil X with 22" inch legs. Beware the 1/8 wavelength within 1/4 wavelength rule though.
Thirdly, BNC connectors have losses so I would be looking for ways to cut those to a minimum.
I'm not sure which Bob Archer Nav antenna you are thinking of. But the one that is designed for a IV wingtip is looking for a big ground in the inboard side. You'll have to get Bob Archer's advice on doing it in an all glass environment. I do wonder how well it's going to perform sitting behind human water bags and an engine when you are on final approach. Might want to go test that before the glue dries.
Colyn
On Jan 18, 2011, at 9:13 PM, Robert R Pastusek wrote: Wayne wrote:
Installing my avionics and its time for antennas, I installed a comm antenna in the vert/stab years ago and everything is closed back there.
I am installing a S/L30 Nav/Com which has an internal diplexer and the manuel says not to install an external diplexer, however I am thinking
they are talking about using an external diplexer for one antenna for Nav/Com. I am also installing a GNS530W and in the rear of the unit there
is a place for a Nav and GS antenna. My plan is to install a Bob Archer VOR antenna in the ceiling of the baggage area and that would give me
one Nav ant and one Comm ant. I would use a splitter coming from the Nav ant and connect to the Nav port on the S/30 and to the Nav port
and the GS port on the 530W GPS which has two different ports for GS and Nav. I would use a T/R switch for the com on the S/L30 and the
com on the 530W GPS. I emailed Bob about this installation and he said he believed it would be ok but didn't know if the GS connection fr the
splitter to the 530W would completely rob the signal from the S/L 30. Please give me your recomendations as I know there are many 2 place
Lancairs flying with no antenna problems.
Wayne,
Diplexers work, but for the cost of another antenna (probably less than the diplexer?) you can build true redundancy in your radio system, and I’d recommend that. I have a Bob Archer antenna installed in the tail of my IV-P and a “bent whip” antenna on the belly with a 32” aluminum ground plane inside the fuselage behind it. I have an SL-30 for Comm/Nav 1 and an SL-40 for Comm 2. After some testing, I hooked the belly antenna to #1 (the SL-30), and can routinely talk out to the line of sight of the other radio. Not so with my Bob Archer hooked to the SL-40…it’s good out to 40-50 miles or so, and with more static on receive. I often move ATC to the #2 when I need to talk to flight service because of the significantly better range and reception on the #1 system with the whip antenna. The bent whip like I have would easily work on a 2-seat Lancair. My 2 cents… Bob Pastusek
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