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J-pole in gear leg fairing vs. belly whip test

rvmills

Well Known Member
A quick call to the FCC today yielded a shiny new tech license (as yet virtual, but legal just the same). It was very timely, having just buttoned up after installing the APRS below the panel, and the Ryan Howell J-pole antenna in the right gear leg fairing.

VAF's "guccidude1" Dan came by with his null modem cable, and assisted (or supervised, depending on who you ask) as we configured both profiles on the MT8000FA.

I then launched on two quick flights...one using the J-pole, and one using the Comant belly whip (stolen from COMM2). I was a bit skeptical about what we'd see with the J-pole being so close to so much metal (the gear leg and the engine mount...pics of that install are in this thread).

However, I was pleasantly surprised by the results. I have some more testing to do, and am certainly open to ideas from "Team APRS". The short version is that it appeared to transmit good positons/tracks with both antennas (though the whip looks stronger, as was expected). I also tested the Primary and Secondary profile on each test, by running primary on the way out (shows MIC-E "En Route"), and switching to secondary (shows MIC-E "Returning") on the way back in. Pretty cool stuff! If you want to look at the tracks on aprs.fi, the link to my APRS track is now in my signature block.

Here are a few screen shots.

The first is both tracks superimposed. Both flights were at 8500' MSL (approx 3-4K' AGL). The inside circle is the J-pole flight, and the larger circle is the external whip flight.

aprs5janboth.jpg


Looks like the whip was a bit more consistent with its position reports at altitude, though both antennas performed well when smart beaconing.

Where I saw the biggest difference was back at Stead in the pattern. I only did one landing with the J-pole, and three with the whip, but the J-pole dropped me as I turned downwind, while the whip kept tracking through the three circuits. Here are two shots zoomed in at Stead with TO and LNDG(s) for each flight. (I took off R-L on 26, turned right and departed to the NW...off screen right. Then came in from the upper left on the 45 to right traffic for 26).

First the J-pole:
aprs5janfirst.jpg


Next the whip:
aprs5jansecond.jpg


Pretty marked difference...though I'm hoping that the J-pole will show more, given "equal time" in the pattern. I will go out tomorrow and do some more test runs, and do some more low work, to test the performance more fully. I'll also swing by the avionics shop on the field and do some SWR testing of each antenna combo, to see what it shows.

If Sam, Pete, Allen, or any other APRS gurus have any ideas on tuning, or other measures to increase effectiveness, I'm all ears.

Given my desire to do live APRS tracking during SARL races, the low altitude performance is a key factor. I'd feel pretty good tracking normally (X-C etc) with the J-pole, and could use the whip for racing only (don't need the SAR radio then!)...however...

I did have a downside with the whip. Every time the APRS transmitted with that antenna, it broke squelch on my SL-40 (Comm1). Just a short burst as the packet was sent, but it'd be very annoying, long term. And when I was monitoring approach and later ASOS on the SL-40 STBY freq, when a packet launched and the SL-40 broke squelch, the STBY freq muted. So that is a no-go, till I get it resolved.

gucci Dan suggested I just turn up the squelch...will give that a try tomorrow.

The antennas for COMM1 and COMM2 are 28 inches apart, and line abreast on the belly. Not sure if that is a factor. I've not yet used the SAR radio in flight, so I do not know if it causes similar interference with COMM1 (we can't get the radio programmer and my schedule in sync, and I can fly missions without that radio, so just not done yet.)

Both antennas on the belly are COMANT 122s, and the SAR antenna has not been trimmed (still 22" long). I have another CI-122SP that I can trim down for 2 meter 1/4 wave and swap in for COMM2/APRS, and perhaps that will stop the RFI...not sure.

Will report back on further testing, and open to any suggestions ya'll may have!

Cheers,
Bob
 
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Bob,

Looks like your tracker config is working fine.

Your results with the antenna comparison is pretty much what I would expect. At 3000'AGL a coat hangar would probably be an effective antenna. But low to the ground is where the efficiency of an antenna is demonstrated. Like you, I want max performance at low altitude so someone can determine either which airport I hit or which cotton field to search. ;)

I doubt antenna "tuning" is going to make much difference since our trackers operate on the "brute force" protocol. An airborne tracker is going to have so much line-of-sight range that even sub-par antennae installations will be effective enroute. Where you may get some benefit in tuning the whip is in reducing the squelch problem. That may be due to a high SWR reflecting RF back into the plane and tripping the the squelch.

If all else fails, install the flux capacitor!
 
No refunds!!

Bob,

Sorry, you opened the package, NO REFUNDS!! :D

I am actually surprised it worked at all next to the gear leg, so it is a good data point.

The whip will always be better, as theoretically the J-pole should not work at all. However, it is cheap and easily hidden, so it provides a good compromise.

Let us know when the RV-6 AWACS is fully operational!
 
Bob,

Looks like your tracker config is working fine.

Your results with the antenna comparison is pretty much what I would expect. At 3000'AGL a coat hangar would probably be an effective antenna. But low to the ground is where the efficiency of an antenna is demonstrated. Like you, I want max performance at low altitude so someone can determine either which airport I hit or which cotton field to search. ;)

Concur Sam...whether racing or (more critically) in an emergency off-airport landing, I too would like to have it track me down as low as possible. I brought a coat hangar and a pair of rabbit ears with tin-foil for today's test...results below! ;)

Flew two test flights out to Truckee and back, with pattern work at each, and a mock search pattern on the way out. Some low work at 1K AGL or above with some psuedo terrain masking and some high work (8500' like yesterday). Probably a pretty challenging scenario for an APRS transmitter, due to terrain and some remoteness.

The whip again did better in the pattern (no hits in either pattern with the j-pole), and neither of the antennas hit repeaters in the mock search (that was where the red dot is painted into the picture below). Interestingly, the jpole did better on the first launch (the part furthest north), and aprs.fi tied the last hit on the first flight to the first hit on the second flight (when I was actually on the ground swapping antennas). Kinda hard to differentiate between the two flights, but here's a pic to show the terrain it was in and around:

aprs6jan.jpg


I doubt antenna "tuning" is going to make much difference since our trackers operate on the "brute force" protocol. An airborne tracker is going to have so much line-of-sight range that even sub-par antennae installations will be effective enroute. Where you may get some benefit in tuning the whip is in reducing the squelch problem. That may be due to a high SWR reflecting RF back into the plane and tripping the the squelch.

Had the same issues with the squelch-breaks today, and adjusting squelch had no impact on the RFI. The avionics guys were clobbered, so no SWR testing available till next week. One gent there said my 28" separation is causing coupling. He said they need to be farther apart (36" as Comant states), or closer together (he made no recommendations on that distance though...gotta dig some on that).

I spoke to an antenna maker, who said they can only put out the 36" min...but he said that if I can't space them wider than I have now, the situation might be improved by moving them closer, and separating them by the length of the straight part of the whip antenna. Just so happens I have a Monroy ATD TED antenna halfway between the whips (14" from each), and that's where my COMM1 ant originally was before I added the COMM2 (so it has the holes for the COMANT).

I have a CI-122SP, which is passive and thus can be clipped. So I'll experiment with it, and clip it, then mount it in the current 28" location. If it still breaks squelch on #1, I'll swap the Monroy and COMM2 antenna locations, putting the COMM2 14" from the COMM1, and see how it works. Turns out the straight part of the whip will be pretty close to 14" after I clip it...hmmmm.

Any thoughts?

If all else fails, install the flux capacitor!

Still looking for my "Mr. Fusion"...I know it's in the hangar somewhere...probably under the L-29 carcass my hangar-mate is storing for a friend!

Bob,

Sorry, you opened the package, NO REFUNDS!! :D

I am actually surprised it worked at all next to the gear leg, so it is a good data point.

The whip will always be better, as theoretically the J-pole should not work at all. However, it is cheap and easily hidden, so it provides a good compromise.

Let us know when the RV-6 AWACS is fully operational!

Pete,

No refund desired...I'm gonna play with it for a while, and if the squelch issue is not solvable, I may use the j-pole for all but racing, and just deal with the short squelch's for those short events (and smart beaconing will be off for them, so it won't be that bad). If I do find a way to make another antenna work, then I'll save the j-pole for a mobile igate set up for the races. Win-win! :)

Either gucci Dan or my HAM Father-in-Law mentioned looking into auto windshield antenna's...the kind that are fine-wire (or similar) and attached to or imbedded into the glass. It was postured that there may be such a thing made for 2 meter...or adaptable to it. Gonna look into it, but have you guys ever heard of such an animal?

Oh, and gucci Dan is the AWACS bird...I'm his fighter escort! :D

Cheers,
Bob
 
Canopy antenna

Bob - working on some ideas for a canopy or cowl antenna - will keep you posted. I'll get my geek on....;)
 
Bob - working on some ideas for a canopy or cowl antenna - will keep you posted. I'll get my geek on....;)

I know a good RV-6 beta tester in Reno...that'll cover the cold-weather portion of the test...wait, you got that covered, don't ya! OK, the hi DA airport and mountainess area range testing...yeah, yeah, that's it! :)

And he'll be happy to invest in the equipment prior to the test...not lookin' for freebies! ;)

Lemme know if I can help...or test 'bout anything!

Cheers,
Bob
 
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DDRR

No, it was cannibalized for another um...project, but that is where I am going. It was ugly, but it worked well.

DDRR%20005.jpg


I have a slim jim (modifed J-pole) in my wing tip now.- It works pretty well, too. Wind chill is well below zero, so I will have some time to noodle this weekend......

Bob - I've got a budget of about $30. If something works, we will strike a deal involving.... BEER...

Pete, are you still using that microwave-lookin' antenna in the wingtip?
 
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Breaking Squelch

While it is possible that your radios just have a sloppy front end, I think that is unlikely. If you try to power the Micro-Trak with a battery pack, and the squelch problem stops, this suggests that the problem is RF and harmonic byproducts getting into your other radios through your power bus. The solution for this is a a power filter ( A big coil, or choke) on the Micro-Trak. You can also turn the power down on the Micro-Trak in a pinch.

I suspect that your landing gear install is highly directional, and not very efficient.

The theory that your problems might be ameliorated by placing the antennas closer will probably not fly. (so to speak) The problem is not that they are placed at a harmonic distance, but that the antennas are within the "near field" (one wave length) and the coupled power is just too high.

Has anyone mentioned that the wing tip is a really good place for one of the Howell-brand antennas? Just asking.....

Allen
VHS
 
choke

Allen,
what would you suggest for a choke? I have tried turning down the power but still get some rf issues. Also, where would the choke be placed to produce best results, near the unit in the wing tip(for me) or closer to the power bus.
 
Chokes

Gary,

Ordinarily, placing a choke at the power feed to a transmitter will keep RF from bleeding back. I would try that first, but again, you can tend to prove or disprove that as a cause by running the tracking transmitter on a local battery. RF tends to be a little like witchcraft, and all of our wonderful theories are frequently just totally wrong! I believe that Radio Shack has 12 volt chokes designed for Car Radios which should serve nicely. Mount it as close to the power input terminals on the tracking transmitter as you can.

We found at one point that most GPS receivers produce a pulse of RF noise squarely in the middle of the aircraft AM band.....ordinarily, not a problem, unless that's the frequency you use to talk on!

Allen
 
choke

Allen,
Good info, I will try the Radio shack choke and different locations and see what happens. Now, if we can get out of this deep freeze, it would make it a lot easier to work in the hanger.
thanks.
 
Allen, I cut and pasted a few of your quotes, so I could comment and ask a few questions (mine in red)...thanks much for the info and ideas! Here goes:

While it is possible that your radios just have a sloppy front end, I think that is unlikely. If you try to power the Micro-Trak with a battery pack, and the squelch problem stops, this suggests that the problem is RF and harmonic byproducts getting into your other radios through your power bus. The solution for this is a a power filter ( A big coil, or choke) on the Micro-Trak. You can also turn the power down on the Micro-Trak in a pinch.
snip>
The theory that your problems might be ameliorated by placing the antennas closer will probably not fly. (so to speak) The problem is not that they are placed at a harmonic distance, but that the antennas are within the "near field" (one wave length) and the coupled power is just too high.

Well today's testing proved you absolutely right.
- Switching the second bent whip from a normal aviation comm antenna to a passive bent whip that I clipped to 20.5" (correct for 144.39, if my calcs are correct) did not stop the squelch issue, with the antennas located the original 28" apart.
- Moving that same antenna to the center of the airplane, which is 14" from the other bent whip, did not alleviate (or ameliorate ;)) the squelch issue either. Nertz!

Got home and read your posts, and the tracker and the radio are indeed powered via the same avionics buss. Different CBs, but same buss. Will test with a spare battery I have, and if the issue goes away in the test, will "choke" it...I'm hopeful about a choke doing the job! Couple Q's on that below.

Before reading your posts, I started considering notch filters on the Garmin radio to block 144.39 +/-, but know little to nothing about that, and would be concerned about degrading the performance on the COMM radio...don't want to do that! Any thoughts...wrong rabbit hole, stick with the choke idea?


Gary,
Ordinarily, placing a choke at the power feed to a transmitter will keep RF from bleeding back. I would try that first, but again, you can tend to prove or disprove that as a cause by running the tracking transmitter on a local battery.
I believe that Radio Shack has 12 volt chokes designed for Car Radios which should serve nicely. Mount it as close to the power input terminals on the tracking transmitter as you can.

Would you recommend placing the choke between the MV-12 and the tracker, or where the power comes into the MV-12 from the aircraft buss?

I found this on the Radio Shack website:
rschoke.jpg


It's described as a 100 microHenry RF choke. No voltage listed. They had this, a couple torroid chokes and a couple coax chokes. Will do some more research, but does this look like the right type of item? ($1.39!)


I suspect that your landing gear install is highly directional, and not very efficient.

Has anyone mentioned that the wing tip is a really good place for one of the Howell-brand antennas? Just asking.....
Allen
VHS

I think you're right about the gear leg...would like to see how it performs in the flatlands as well, just for the data point. I may keep it as an alternative antenna, depending on how the whip squelch issue turns out.

I was actually going to do a wingtip install, but then decided to make some flat racing wingtips...wanted to be able to do quick swaps and keep APRS capability in the races (we may try to get multiple racers with APRS to show tracks simultaneously to give remote viewers some entertainment...will see!) Such a simple idea...look what it got me! ;) Fun to experiment though!


RF tends to be a little like witchcraft, and all of our wonderful theories are frequently just totally wrong!

Yes, feeling a little spellbound right now! :eek:

Cheers,
Bob
 
Allen,
Good info, I will try the Radio shack choke and different locations and see what happens. Now, if we can get out of this deep freeze, it would make it a lot easier to work in the hanger.
thanks.

Gary,

How ya doin' up there, brudda!?! If I find something that works, will let ya know. If you beat me to it, please do the same!! Thanks!

Say hi to Tom and Wayne!

Cheers,
Bob
 
Choking!

Don't panic when choking. A properly designed RF choke will keep noise from passing either way. Our goal is to pass only DC, without alternator whine, or RF signals or harmonics. What I had in mind for a choke for you is something like this: http://www.powerwerx.com/oem-connectors-filters/dc-line-noise-filter-oem-t.html

You could certainly try the 100 mH chokes, but I would use two: one for each of the power legs, ground and +12. My hunch is that this won't do much to block noise in the range you are interested in blocking, but on the other hand, it will only cost $2.00 to find out! Although the MT-and GPS can draw a a couple of amps during transmission, its a very short time period, about 300 ms with a MIC-E position report, so I think the 100 mH chokes would not burts into flames. Try it away from your ship first, just to be on the safe side, if they get warm or smoke, thats bad.

Allen

ps I will give you a call today.
 
Don't panic when choking. A properly designed RF choke will keep noise from passing either way. Our goal is to pass only DC, without alternator whine, or RF signals or harmonics. What I had in mind for a choke for you is something like this: http://www.powerwerx.com/oem-connectors-filters/dc-line-noise-filter-oem-t.html

You could certainly try the 100 mH chokes, but I would use two: one for each of the power legs, ground and +12. My hunch is that this won't do much to block noise in the range you are interested in blocking, but on the other hand, it will only cost $2.00 to find out! Although the MT-and GPS can draw a a couple of amps during transmission, its a very short time period, about 300 ms with a MIC-E position report, so I think the 100 mH chokes would not burts into flames. Try it away from your ship first, just to be on the safe side, if they get warm or smoke, thats bad.

Allen

ps I will give you a call today.

Thanks very much Allen, and thanks for the call!

Based on this post and the call, I ordered the PowerWerks choke (20A max oughtta cover what the tracker puts out during its brief transmissions...certainly don't wan't to go cheap and test R.Shack chokes for smoke content! ;))

For Gary and other readers that may want to add a choke later, Allen confirmed that a choke would go on the ground and on the 12v lines to the tracker. With the RS chokes, that would be one per line. The PowerWerks choke has black and red wires, with quick connectors, so for $29.99, it seems like a reliable and simple solution.

I'm on the road for a few days, but when I get back, will do a test using a separate battery, and then will post the results of the choke install.

Thanks again!

(Anyone else think it's way cool that we have the developer of the tracker talking and working with us like this!! Thanks Allen!)

Cheers,
Bob
 
[
(Anyone else think it's way cool that we have the developer of the tracker talking and working with us like this!! Thanks Allen!)

Cheers,
Bob[/QUOTE]


((((((Blushing))))))))

Allen
VHS
 
DDRR - The Phoenix

Well, it is -2F here today so we fired up the antenna factory for Rocket Bob!

Our latest offering is a DDRR in this particular instance, it stands for:

Directional Discontinuity Rocket Radiator

Here are the parts:

Rocket%20Radiator%20001.jpg


Base is bolted and soldered to the "stalk" (nut is soldered in the stalk)

Rocket%20Radiator%20003.jpg


Rocket%20Radiator%20005.jpg


Next, the ring is soldered in place

Rocket%20Radiator%20007.jpg


The coax feed points are located and optimized by trial and error. We got the SWR down to just over 1.5:1.

Rocket%20Radiator%20010.jpg


Test setup - Choco puddin' is key for snack attacks - Holy cow, my desk is a mess!

Rocket%20Radiator%20011.jpg


Ready to ship - Bob - send me an email with your address! They serve beer at the air races, don't they????

Rocket%20Radiator%20013.jpg


This puppy was smacking packets off the Igate up by the airport 12 miles away just sitting on my desk. I am anxious to see what it will do under the cowl (if it fits).
 
Wow, Pete...that is both really cool and really cold (the DDRR, and the OAT at your house, respectively!) :D

E-mail sent, and as soon as I get home I'll pull the cowl, and find a 9x9x3 area to mount it. Temporarily at first, then more permanently if (ahem, when) we have success. I'm thinking lower right corner, keeping it out of the exit air and away from the motor, exhaust manifold and firewall as much as possible. Will use the same penetration for the feed line that I'm using for the J-pole.

This'll be fun! Thanks to all of Team Howell for doing this!!

Ooohhh, alnost forgot...I may have seen a beer vendor or two at the races! Better yet, how 'bout a hangar to hang at, with a fridge full of your favorite suds! :)

Cheers,
Bob
 
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Ext 12V check for noise

Before testing Pete's DDRR antenna, I ran Allen's recommended ground test for my belly whip noise problem. I used a spare battery to power the APRS and my Kenwood SAR radio (one at a time) to see if the squelch breaks on COMM 1 stopped...i.e., checking to see if it was power system noise rather than antenna coupling noise.

Unfortunately, in each case, the bleed over remained when either the APRS (144.39) or the SAR radio (155.205) transmitted via the belly whip (recall the two whips are 28" apart...a known defeciency). I could hear the noise on the SL-40 primary freq (122.7) and when monitoring ASOS (135.17) on the secondary, any APRS transmission still breaks squelch on the primary and silences the secondary. Bummer!

Allen (or others), wondering if you have any thoughts. Seems that choking may not do anything if the noise remains on the ext 12V source. Would you concur...or should I give it a whirl anyway?

If the DDRR works out, I can live with the rare occurence of the SAR radio bleeding to my COMM 1 (rarely, if ever, do I need to use both simultaneously). Can't move the antennas laterally farther apart, as my roll servo prevents moving one of them. Might consider staggering them, but am averse to drilling more holes in the belly. Fuselage top is possible, but still thinking drag reduction.

Anything up any sleeves? Anyone know of a super-stealth low-profile 144.39 antenna form? Pete...you inventing one? ;)

DDRR test hop 1 in next post!

Cheers,
Bob
 
DDRR Test Hop 1

After careful consideration as to the mounting location for the R&P Howell DDRR "Rocket Radiator" Antenna, I came up with this:

ddrronback.jpg


Great radiation pattern, but not quite the drag reduction I was looking for! :p

OK, yeah, it's backwards...nyuk, nyuk...that pic's just to show the rubber hose lengths I epoxied to the ground plane edges, to provide some protection for it, and the surrounding structure in this first test mount:

ddrrengine1.jpg


Bottom of the ground plane is the green phenolic. A few tie wrap mounts, a few stand-offs, a little threading of the heat exchanger in/out hoses, and it was pretty stable, albeit tightly packed.

ddrrengine2.jpg


Pete and I discussed this install, and agreed that being surrounded by the engine mount, firewall and engine, not to mention the scat with metal winding in it, just might degrade the signal (which should radiate out and down in this orientation).

Ran a hybrid course that included some low work to the west of Stead, and a trip around Pyramid Lake, so it would have some of each of my routes when the J-pole and Whip were tested. Here's the APRS pic:

aprs13janpost.png


Descent performance up hi, but nothing below 800' AGL (or higher in some areas), and some areas with somewhat long gaps between hits. Pete was following along, and we texted along the way (when I had a signal...don't tell the flight attendant! ;)) as to where I was and what he was seeing.

So not bad, given all the challenges of install location and terrain. But still not what I'd like down low.

So tomorrow, I'll use an idea proffered by guccidude1 Dan...move it to the cowl bottom, and gorilla tape it upside down (same orientation as shown here) to the glass, just below the right exhaust manifold. Pete sez the antenna should ignore everything on the green side...up in this case, so the manifold and the big hunk of metal above it should be a non-factor (and nothing but glass below the antenna, so keep your fingers crossed!

I wanted to test the engine mount idea first, as I may have some lower cowl mods coming for cooling drag/racing...but this location may be OK, even with those that I have in mind. Will be watching those CHTs (1,3,5) to see if it affects things just from being stuffed in there. I'll shim the "halo" with a plastic tube opposite the copper tube strut, to strengthen and stabilize it as well. We'll give this a good workout! More results and pics tomorrow!

Cheers,
Bob
 
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"stealth antennae"

Based on your battery test, I think that the choke would just add weight. The break-over on your com radio is no doubt due to the near-field effect of your antennae. You could turn the power of the Micro-Trak down, and even a little less power is likely to give you considerable effect in the squelch problem. A small power loss will not significantly effect your overall range.

If you need to do a very low profile antenna, there are a number of "Stealth" antenna out there that mount on an NMO mount. ( you need to drill a 3/4 hole to install one) They are not nearly as effective as a full size whip, but offer a very low profile. Here is one from Antennex: http://cgi.ebay.com/Antenex-VHF-Pha...emQQptZLH_DefaultDomain_0?hash=item3357cbe3fd

Allen
VHS
 
Looks like you went a bit wide on the unlimited course on that last race.:D

As long as you don't say I cut a pylon! :D

Yanno, I think I may need to do some testing in some flatter, more populous areas...hmmm SACTO might do...wanna visit in the next few weeks (after the next storm passes through!)

Cheers,
Bob
 
DDRR Test Run 2...progress!

Pretty good test today with the DDRR mounted on the bottom of the cowl (right side, under the heater muff). Here's a couple pics:

First I bolstered the ring with a few pieces of hose tie wrapped throught the middle of the hose and around the ring. It'll be mounted upside down, so the ring will support the structure on the cowl. It's very light, but don't want to break it!

ddrrwithsupports.jpg


For the test it's mounted with gorilla tape, as is the feed line. If all tests go well, then I'll use plastic adels and red RTV to secure it a bit more permanently. Here's one pic looking through the cowl exit forward and to the right, and another looking down past the cylinder and heat muff.

ddrrcowlbottom2.jpg


ddrrcowlbottomfromabove.jpg


Taxiing out, I saw Greg Arehart's truck at his hangar, and called him and asked if he could come out and play. Good to have a partner on test hops...even if its just to see a nice sunset!

Test went well, with Pete watching and texting us along the way. Looks like it tracked us down to 5300' (1000 or so AGL) over Pyramid Lake, and down to 300' AGL in the pattern! Woo hoo, this thing works!!

aprs14jan.png


Right traffic 26...looks like it picked me up in each crosswind turn (Pete texted and said I flew sloppy patterns...yikes! :p)

aprs14janpattern.png


Pete evaluated the raw data, and saw many packets that were sent and received, but were not processed correctly (evaluated as moving too fast or turning to slowly). He recommended disabling MIC-E and retesting, then playing with the power on the MT8000FA. Will do so next week when back from "paying for the gas".

Thanks Pete for following along, for all the help and for the Directional Discontinuity Ring Radiator...quite a mouthful for a Navy guy...is it OK if I call it a P-Triple R (Pete and Ryan Rocket Radiator)? :D

Cheers,
Bob
 
Question for Sam or Pete...

What do you guys think of the possibility/efficacy of using the ELT antenna that many of us have mounted under the tail fairing? Cons would be that it is horizontally polarized and probably a little too long for APRS freqs? I am thinking about taking the ELT out entirely and just going APRS, but thought I might be able to use the antenna, possibly shorten it a little. I think I know the answer: try it and see how it works! And would the correct 1/4 wave length be about 18 inches? Thanks for your input!

ELTantennaRV6.jpg


Do you guys think this has any chance of working? Allen, please feel free to jump in. Thanks!
 
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What do you guys think of the possibility/efficacy of using the ELT antenna that many of us have mounted under the tail fairing? Cons would be that it is horizontally polarized and probably a little too long for APRS freqs? I am thinking about taking the ELT out entirely and just going APRS, but thought I might be able to use the antenna, possibly shorten it a little. I think I know the answer: try it and see how it works! And would the correct 1/4 wave length be about 18 inches? Thanks for your input!

Do you guys think this has any chance of working? Allen, please feel free to jump in. Thanks!

Pat, I think you provided my answer, "try it and see how it works!". :)

Be absolutely positive the antenna can't short to the airframe. The 1/4 wave length for 144.390 is ~19.45" but there is so much theoretically wrong with this antenna setup that having a radiator the wrong length may be the least of the sins. ;)

Let us know how it works!

P.S. Eliminate the ELT????
 
Pat, I think you provided my answer, "try it and see how it works!". :)

Be absolutely positive the antenna can't short to the airframe. The 1/4 wave length for 144.390 is ~19.45" but there is so much theoretically wrong with this antenna setup that having a radiator the wrong length may be the least of the sins. ;)

Let us know how it works!

P.S. Eliminate the ELT????

Thanks, Sam! My thought with the length was only to try to match impedance as much as possible, standing wave and all that. And I have those two nylon clamps securing the antenna which I would think should be enough to prevent it from shorting to ground. So I'll try it and see how it works and let you know! The more data points the better I guess.

ELT? Yeah, what good is it now? I would leave it in as long as it's mandatory, but I think those days are probably numbered.

Any chance APRS could play a role?

P.S. After reading Mel's response, I guess my assumption is that the whole regulatory thing on ELTs will probably be re-worked soon to include the new 406 ELTs or possibly other alternatives like PLBs, etc. Then there's Canada and Mexico. In the meantime, I am going to play with an APRS rig until everything gets sorted out.
 
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P.S. After reading Mel's response, I guess my assumption is that the whole regulatory thing on ELTs will probably be re-worked soon to include the new 406 ELTs or possibly other alternatives like PLBs, etc.
The new 406 ELTs are already included in the regs. They are just not mandatory. I'm pretty sure PLBs will never be an alternative to ELTs unless they have some sort of automatic activation.
 
Antennae

I had no idea that is how you guys mounted your ELT antennae....Its an absolutely awful way to mount an antenna! It makes me want to drink to kill the pain..... Just terrible. The 121.5 ELT sends a few milliwatts out. The MT sends 8-10 Watts, and the problems with the mount will increase with the power input to the antenna. The MT can tolerate a huge antenna mismatch, since its a very short transmission, and because the amplifier is well designed, but this install could easily convert to a dead short (which it almost certainly would do in a crash, effectively eliminating your ELT from your survival tool chest) Operating an MT into a belly whip cut for an ELT is not a problem. Its a little lossy, since the antenna is cut for a lower frequency, but the power budget is so high, even a few hundred milliwatts of effective radiated power will work great at altitude, and the ELT antenna will do a lot better than that.

Allen
 
I had no idea that is how you guys mounted your ELT antennae....Its an absolutely awful way to mount an antenna! It makes me want to drink to kill the pain..... Just terrible. The 121.5 ELT sends a few milliwatts out. The MT sends 8-10 Watts, and the problems with the mount will increase with the power input to the antenna. The MT can tolerate a huge antenna mismatch, since its a very short transmission, and because the amplifier is well designed, but this install could easily convert to a dead short (which it almost certainly would do in a crash, effectively eliminating your ELT from your survival tool chest) Operating an MT into a belly whip cut for an ELT is not a problem. Its a little lossy, since the antenna is cut for a lower frequency, but the power budget is so high, even a few hundred milliwatts of effective radiated power will work great at altitude, and the ELT antenna will do a lot better than that.

Allen

Allen, I can only imagine how shocked you were to see the ELT antenna installation! :D

Even though I'm creeping the thread a bit, let me offer a little background on the ELT situation since you are a bit new to RV aviation and so you won't think we are totally crazy, and also to ease your pain. :D ELT antenna location was hotly discussed when I was building my plane twelve years ago, and it still appears on the forums several times a year since there are no good solutions.

1) The reliability of the "legacy" ELT's is sketchy at best. The devices seem to be best suited for either emitting false alarms while the plane is hangared or, worse, failing to activate when there is an actual incident.

2) There are precious few options for "correctly" mounting an ELT antenna on an RV, especially when most builders are trying to keep their sleek aircraft from looking like airborne porcupines. In fact, there is no location on an RV-8 that will satisfy the installation documents for an ELT (this is due to the canopy design).

3) Which way will an airframe be oriented following a crash? Who knows...an antenna mounted on the upper or belly surfaces may not survive the accident. Many RV accidents result in the plane flipped on its back so the "legal" installation would have the antenna buried in the ground.

4) Quite a few builders (myself included) have our ELT antenna mounted as described in the earlier post because A) we have little faith in the contraption working when needed (one reason we are huge APRS fans), B) We despise the idea of the ugly ELT antenna protruding from our gorgeous aircraft, and C) If the the thing has little value anyway, why not stuff it somewhere out of sight?

Hopefully this will offer some background. We know under the emp fairing violates about every antenna rule in the book, but............. ;)
 
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I had no idea that is how you guys mounted your ELT antennae....Its an absolutely awful way to mount an antenna! It makes me want to drink to kill the pain..... Just terrible. The 121.5 ELT sends a few milliwatts out. The MT sends 8-10 Watts, and the problems with the mount will increase with the power input to the antenna. The MT can tolerate a huge antenna mismatch, since its a very short transmission, and because the amplifier is well designed, but this install could easily convert to a dead short (which it almost certainly would do in a crash, effectively eliminating your ELT from your survival tool chest) Operating an MT into a belly whip cut for an ELT is not a problem. Its a little lossy, since the antenna is cut for a lower frequency, but the power budget is so high, even a few hundred milliwatts of effective radiated power will work great at altitude, and the ELT antenna will do a lot better than that.

Allen

Thanks for those comments, Allen. OK, how about this plan: I convert to a new 406 Mhz ELT and mount that antenna on the belly and use the existing antenna (that's driving you to drink) as the MT's antenna. Or would it be better to split the new ELT antenna with some kind of switchable splitter? Would the horizontal antenna be feasible at all for the MT, in your opinion, or should I just give up on that idea? I've heard that you can't share an antenna with two transmitters and I guess I was assuming that sharing the ELT antenna wouldn't be feasible. But then I saw a photograph earlier in this thread of what I assume is a switchable splitter for this purpose, so I'm not sure. Can you give me some guidance? Thanks!
 
The new 406 ELTs are already included in the regs. They are just not mandatory. I'm pretty sure PLBs will never be an alternative to ELTs unless they have some sort of automatic activation.

Mel, I hear ya. I know we're stretching this thread a bit, but I think there's a relationship here. There's got to be a better way than ELTs, considering today's technology. I'm not sure a crash should be the trigger that sets off an alert, since there are so many things that can go wrong. A better philosophy might be an alert as a result of the cessation of streaming data. Kind of like APRS would lend itself to. I know, I know, APRS would never work because its an "amateur" system, but perhaps with ADS-B? I was just suggesting that the entire concept of ELTs will eventually be re-thought in light of the huge technological advances we are seeing. And it looks like APRS is leading the way.
 
Antenna Madness

I would not expect to see any major new developments in infrastructure around ELT's. Since the 406 data burst and the sunsetting of the VHF SARSAT birds, I think any new changes are decades away. Most people have not even upgraded to the newest technology, and the jury on its effectiveness is still out. Theoretically, it should be far superior to the old ELT location technology.

It would be possible to multiplex your 144 MHZ and 121 Mhz signals into a single antenna with a diplexer, with some degree of loss in power. I would guess that only experimentals could get away with such a modification.

As far as using the horizontally polarized antenna, Pete's J-Poles are kinda-sorta horizontally polarized, and the text books say they should not work worth a ****, but clearly, they work very well. ( I am going to use that text book to set my drink on while I swear in a curmudgeonly fashion at DDRR antennas under the hood, and search for a bottle of tramadol to kill the psychic pain it causes me) There is no harm in trying the aft-mounted antenna with a Micro-Trak. I would expect performance to be adequate given the drive power and assuming reasonable altitudes. I think at ground level, it would be nearly worthless.

One possible way to use a belly whip for dual purposes would be to use a drop out relay to switch the antenna line, causing the MT to seize the antenna during transmissions. Its fairly doable.

Byon and I had discussed the possibility of decoding ADS-B transmissions and adding the info to the APRS display. You would still need a receiver for ADS-B, and that's a pricey order. Outside the ham bands, Type Approval is necessary for a receiver.

Since most APRS encoders can handle two configurations, I think a very cheap way to add to your safety is to add the "emergency" configuration to your secondary configuration. Use a switch that won't be activated accidentally.(I suppose we could add a G-Switch like an ELT, but these have a tendency to create false alarms) When you send the emergency beacon, the whole ham world jumps out of its chair. As a CAP guy, I can assure you that we don't even think about launching assets until everyone has finished lunch, and the AFRCC has given us the green light to spend Uncle Sam's money to go look for you. I think of how little fun it would be to be hanging upside down in the redwoods with fuel running down my neck waiting for the AFRCC to get off the dime, a process that can take hours. A ham seeing your signal will just start driving to find you , or will call 911. ( remember, when seconds count, police and fire are only minutes away....)

Allen
VHS
 
I would not expect to see any major new developments in infrastructure around ELT's. Since the 406 data burst and the sunsetting of the VHF SARSAT birds, I think any new changes are decades away. Most people have not even upgraded to the newest technology, and the jury on its effectiveness is still out. Theoretically, it should be far superior to the old ELT location technology.

It would be possible to multiplex your 144 MHZ and 121 Mhz signals into a single antenna with a diplexer, with some degree of loss in power. I would guess that only experimentals could get away with such a modification.

As far as using the horizontally polarized antenna, Pete's J-Poles are kinda-sorta horizontally polarized, and the text books say they should not work worth a ****, but clearly, they work very well. ( I am going to use that text book to set my drink on while I swear in a curmudgeonly fashion at DDRR antennas under the hood, and search for a bottle of tramadol to kill the psychic pain it causes me) There is no harm in trying the aft-mounted antenna with a Micro-Trak. I would expect performance to be adequate given the drive power and assuming reasonable altitudes. I think at ground level, it would be nearly worthless.

One possible way to use a belly whip for dual purposes would be to use a drop out relay to switch the antenna line, causing the MT to seize the antenna during transmissions. Its fairly doable.

Byon and I had discussed the possibility of decoding ADS-B transmissions and adding the info to the APRS display. You would still need a receiver for ADS-B, and that's a pricey order. Outside the ham bands, Type Approval is necessary for a receiver.

Since most APRS encoders can handle two configurations, I think a very cheap way to add to your safety is to add the "emergency" configuration to your secondary configuration. Use a switch that won't be activated accidentally.(I suppose we could add a G-Switch like an ELT, but these have a tendency to create false alarms) When you send the emergency beacon, the whole ham world jumps out of its chair. As a CAP guy, I can assure you that we don't even think about launching assets until everyone has finished lunch, and the AFRCC has given us the green light to spend Uncle Sam's money to go look for you. I think of how little fun it would be to be hanging upside down in the redwoods with fuel running down my neck waiting for the AFRCC to get off the dime, a process that can take hours. A ham seeing your signal will just start driving to find you , or will call 911. ( remember, when seconds count, police and fire are only minutes away....)

Allen
VHS

Thanks, Allen. I think what I'm going to do is keep the old ELT/antenna to fulfill the regulatory requirements only. Then find a spot on the belly for a new antenna for the MT (probably bent whip like Sam's). At current prices, not sure I would ever go with the new 406s. And just wait for the ELT saga to play itself out. Sound like a good plan to you? I will experiment with the horizontal antenna on the MT just to see how it compares with the bent whip.
 
Sounds like a good plan to me! BTW, I expect PLB's to come down in cost, and used ones to come on the market. As a rescue radio, its hard to beat.

Allen
VHS
 
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