Van's Air Force
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Antenna Musings....
- Thread starter Ironflight
- Start date
Yes, I am satisfied with the Nav performance once I set up the separate GS antenna.Comm performance is still much better with the "Real" Acer than with my imitation, and adequate for ATIS up to 50 miles. It is still not a substitute for a belly antenna as a primary Comm, but for a secondary, it is acceptable.
DIY Glide slope
I spoke with Bob Archer today about his VOR wingtip antenna. The instruction drawing shows a 40" long piece of aluminum on the opposite side of the wing tip (on the top if the vor antenna is on the bottom) for a Marker Antenna. I asked him if this would work for the GS and he said no. He suggested this: in the opposite wing tip, place the coax parallel to the span. Strip the shield and fold it back over the coax. Trim the folded over shield to be 8" and tip to be 8" long. He suggested a little heat shrink over the stripped shield to prevent it fraying. I think I will go ahead and install the coax when I build the wings.
Good question Gil - I actually replaced the splitter with a known good one (that we had taken out of Mikey) a few months back. Now I have TWO surplus, expensive splitters.....
I thought I remember the same thing about a copper foil GS antenna in the cowl - searched and couldn't find it. The stripped Coax helped me confirm that I want the separate antenna - now I'll do a little more research before making my final version - anyone know if there is a better length than 16" (I got that from Knuckoll's dipole design in his book)?
Paul
I spoke with Bob Archer today about his VOR wingtip antenna. The instruction drawing shows a 40" long piece of aluminum on the opposite side of the wing tip (on the top if the vor antenna is on the bottom) for a Marker Antenna. I asked him if this would work for the GS and he said no. He suggested this: in the opposite wing tip, place the coax parallel to the span. Strip the shield and fold it back over the coax. Trim the folded over shield to be 8" and tip to be 8" long. He suggested a little heat shrink over the stripped shield to prevent it fraying. I think I will go ahead and install the coax when I build the wings.
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I've been very happy with my "stripped Coax" GS antenna - it works great! In the -3 we're building, I am going to do the same thing use the Archer in the tip for VOR/LOC and put a GS antenna in the leading edge of one of the gear fairings - the length will be perfect to hide the antenna, and i really only want reception when I am pointed at the transmitter, so I think it will be a good solution.
Paul
az_gila
Well Known Member
Paul, shouldn't the GS antenna be horizontal, not vertical as in a gear fairing?
The typical glideslope transmitter is usually located 750 feet from the beginning of the runway and radiates a 5-watt RF signal from a horizontally polarized antenna array at an inclined glidepath angle of 2.5" to 3.00. The glide slope transmitter operates on one of 40 available channels provided by 150-kHz spacing in the UHF frequency range of 329.15 MHz to 335.00 MHz
You could very well be right Gil, but it will be interesting to try. My current GS antenna follows the contours of the RV-8 roll bar, so it has both vertical and horizontal components.
Paul
ColoCardinal
Well Known Member
Bob Archer
Here's something from Bob Archer I ran across while trying to make my antennae decisions:
http://home.hiwaay.net/~sbuc/journal/bob_archer.htm
This forum has been a lifesaver for me.
Here's something from Bob Archer I ran across while trying to make my antennae decisions:
http://home.hiwaay.net/~sbuc/journal/bob_archer.htm
This forum has been a lifesaver for me.
kbehrent
Well Known Member
GS & MB antennas
I have belly mounted Comant comm antennas for my 530W and SL-40.
For the NAV side, I have the Archer VOR/ILS/GS antenna that will be mounted in the left wingtip. I definitely want a separate GS antenna to eliminate the diplexer.
Would it be ok to mount the Archer MB antenna in front of one of the gear faring?
For the GS antenna, I see Paul was successful with a 16" stripped piece of coax mounted on the front roll bar. I also read the Archer may have recommended the same 16" piece of coax, but with 8" of the shield folded back over the coax. Anybody else tried this? Also, would like to confirm that the GS antenna is installed along the span, i.e. 90 degrees to the ribs?
Pictures would be great too!
Paul, love your idea about installing the GS in the gear faring. I would like to hear if anyone has actually tried this out yet.
I have belly mounted Comant comm antennas for my 530W and SL-40.
For the NAV side, I have the Archer VOR/ILS/GS antenna that will be mounted in the left wingtip. I definitely want a separate GS antenna to eliminate the diplexer.
Would it be ok to mount the Archer MB antenna in front of one of the gear faring?
For the GS antenna, I see Paul was successful with a 16" stripped piece of coax mounted on the front roll bar. I also read the Archer may have recommended the same 16" piece of coax, but with 8" of the shield folded back over the coax. Anybody else tried this? Also, would like to confirm that the GS antenna is installed along the span, i.e. 90 degrees to the ribs?
Pictures would be great too!
Paul, love your idea about installing the GS in the gear faring. I would like to hear if anyone has actually tried this out yet.
Tom Martin
Well Known Member
I followed Paul's suggestion and shoved a piece of stripped coax in the right gear leg of my rocket. Although I have not tested it extensively, it does work.
I do not have a lot of GS experience and so I am not in a position to say it works better or worse then other installations. I had used the diplexer at first and it seems to work at least as well as that installation.
Installation was a simple as I have some foam in the top of my gear leg faring and I simply poked it through the foam and down the leg. It has been secure for more then one flight season, 100 hours.
I do not have a lot of GS experience and so I am not in a position to say it works better or worse then other installations. I had used the diplexer at first and it seems to work at least as well as that installation.
Installation was a simple as I have some foam in the top of my gear leg faring and I simply poked it through the foam and down the leg. It has been secure for more then one flight season, 100 hours.
kbehrent
Well Known Member
Some homeade GS Ant questions
For those making your own GS ant:
1. Are you using RG58 OR RG400?
2. Is the stripped portion 16" long with the last 8" of shield peeled back? Is the shield grounded to the airframe?
3. I hear it needs to be mounted horizontally, can it be mounted in the wingtip parallel with the outboard rib or span wise, i.e across the inside of the wingtip?
I'm mounting the archer nav ant in the left wingtip, GS is the right. I figure if this homemade GS ant doesn't work, I can always buy another archer nav and just use it for the GS.
I'm going to put the archer MB ant in the left gear leg, I really don't care if it works well or not, but it's worth a shot.
For those making your own GS ant:
1. Are you using RG58 OR RG400?
2. Is the stripped portion 16" long with the last 8" of shield peeled back? Is the shield grounded to the airframe?
3. I hear it needs to be mounted horizontally, can it be mounted in the wingtip parallel with the outboard rib or span wise, i.e across the inside of the wingtip?
I'm mounting the archer nav ant in the left wingtip, GS is the right. I figure if this homemade GS ant doesn't work, I can always buy another archer nav and just use it for the GS.
I'm going to put the archer MB ant in the left gear leg, I really don't care if it works well or not, but it's worth a shot.
1) I made mine out of scrap RG58 that was laying around.
2) I stripped 16" of insulation, and the only place I grounded the shield was at the BNC connector - but then, there is only about 12" of shield left anyway, as it comes right out of the radio, through the glare shield, and to the rollbar (in the -8).
3) Mine matches the contour of the rollbar and works fine. Hey, this thing isn't really much more complex than a bent coat hanger, but if I can get the GS at 20 miles, that's all I really need for my purposes....
Paul
Pilot135pd
Well Known Member
...and 9 years later IT'S ALIVE !!!!! Love this thread since I just bought a VAL INS-429 and the antenna issue is important this week when I go to install it all on my RV-8. Thanks to everyone who contributed to this thread !
I see a lot of effort going toward a non-problem. Just use the appropriate splitter off the vor/loc antenna. Because the GS is exactly 3 times higher frequency than the localizer frequencies, an antenna that is resonant at 110 MHz will also resonate at 330 MHz. And, technically, it’s not signal strength that matters, it’s signal to noise ratio. My SL30 doesn’t even offer the option of a separate gs antenna - it has an internal splitter. But if you want a second, GS antenna, a simple dipole (each of the two arms 8”) should work fine. Horizontal, running left to right, do not ground either leg (that includes the leg attached to the braided shield). Lots of Cessnas mounted something like this on their windscreen. Gluing it to the underside of the engine cowling should be okay too. One caution: on any antenna that looks thru the prop arc, its possible to see erratic behavior of the GS needle. If so, just change the rpm a bit.
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