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LORAN/APRS Antenna Progress

Pat Hatch

Well Known Member
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Allen,

Pretty good thread drift here...perhaps record setting! So Pat, how's that Loran antenna working on your APRS, and Allen, any pics of your ground assault vehicle with the CI-122SP sticking out of its forehead? :D

Cheers,
Bob

THANK YOU, Sam!:D

OK, can we get back to LORAN antennas now?:rolleyes: Wow! My head was about to explode! So, assuming we get off that treadmill in one piece, here's my plan: this weekend I'm going to trim off 5.5" of my CI-122SP LORAN antenna and dip the end in a urethane clear coat. My antenna came coated with that P-Stat clear coat as advertised. Need to drill the holes in the belly, install doubler, pull the interior, run coax, etc., so I don't expect to be airborne for tests until early next week. Bob, I'll test fly and report my findings then!

Still waiting to hear from you, Allen, on your ongoing SWR tests and whether you decide to trim the antenna, etc., that is, if we can drag you away from your "other" discussion forum for a minute! :)

P.S. My purpose for continuing this thread is to try to determine definitively if these discarded LORAN antennae are going to serve as suitable APRS antenna alternatives. So far all indications point to the affirmative. Considering that they can be picked up for around $10 on eBay, that they are structurally very robust, and that the Comant versions are remarkably similar to their VHF COM antennae that many of us already have installed, I believe this to be a worthy endeavor.
 
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Pat,

Let us know when you test fly, and we'll tune in. Concur with you...a very worthy endeavor. I'm bettin' you'll have good performance and no noise!

Cheers,
Bob
 
Loran antennae

I am waiting for my wife to go out of town before I install the antenna on my minivan! I expect if anything, an improvement in SWR by adding the mass of the vehicle for a ground plane. I plan to throw a low power signal source on the antenna and compare it to our standard magmount antenna, measuring the relative effective radiated power.

Even if these are not perfect antenna ( and there is no such thing anyway) for your applications, they seem like a really sweet deal! A 10.00 buck antenna that we know in advance is suitable for an aircraft install-awesome.

If I mount the antenna on a treadmill moving away from me at the speed of light, how long does it take for the radio wave to be received? (answer: 7)

Allen
VHS
 
I am waiting for my wife to go out of town before I install the antenna on my minivan! I expect if anything, an improvement in SWR by adding the mass of the vehicle for a ground plane. I plan to throw a low power signal source on the antenna and compare it to our standard magmount antenna, measuring the relative effective radiated power.

Even if these are not perfect antenna ( and there is no such thing anyway) for your applications, they seem like a really sweet deal! A 10.00 buck antenna that we know in advance is suitable for an aircraft install-awesome.

If I mount the antenna on a treadmill moving away from me at the speed of light, how long does it take for the radio wave to be received? (answer: 7)

Allen
VHS

Yeah, I just love the idea of getting a $200 antenna for $10 and at the same time recycle at least some of LORAN antennae that will end up in the trash heap at avionics shops. And I figure the price won't go up because certified airplanes will probably not easily adapt to APRS, if at all.

You know Allen, when your wife gets home and sees the van, you better have a treadmill that moves at the speed of light.
 
This is a good effort

When I finally get around to buying an APRS system, I want an external antenna despite the possible drag impact.
 
Pat and Allen: I brought this over from the new product thread so I could post my results today using my Loran antenna (and compare it to guccidude's bent whip). Will do that in a separate post...here's your posts:

Cheers,
Bob

I mounted the new CI-122SP LORAN antenna on the belly as shown below and it ended up being about 74" from the COM 1 antenna on the left in the photo. Clearance off the ground from the tip was about 5". I ended up shortening the antenna about 3.5 inches, still might be a little long, but I don't think it's going to make any difference at 10 watts!

Bob Mills graciously offered to monitor my flight in real time, so I called him on the phone as I was taxiing out and we were conversing for the whole flight. I was at 2,000' for most of the flight and pretty much tracked the same as I had on the first flight, which Bob had posted in the thread that preceded this one. I really can't tell any difference between this antenna and the CI-122 COM antenna that I was borrowing from my COM 2. So I guess we can pronounce the LORAN antennae a success as APRS alternatives!

Here's my ground track:

APRSTrack2-25-10.png


And here a photo of the antenna installation relative to the two COM antennae.

011pp.jpg


I'm still getting feedback from the tracker on COM 1, but only on the ground, and not as often as before. I did not notice any interference in flight at all, so that's an improvement. What I am getting is not really that objectionable, actually. It kind of serves as an indicator that the tracker is working as you taxi out.

Thanks to Bob for giving me real-time feedback as I was flying! A plug here for the Zulu headset: reception was perfect throughout the flight using the Bluetooth feature of the headset.

In conclusion, if you're thinking about APRS at all, grab one of these LORAN antennae off of eBay for about $10 while you can still get them. They come in two varieties, bent whip or straight. It would be interesting to compare the two, obviously the straight will probably have a little better performance, but does it matter?:)

Pat,

Glad to hear that it worked well. I looked at your track on aprs.fi and saw that you primarily hit one digi and an I-gate about 10 miles north of you. It looks like there are not a lot of digis out there? I did not see any evidence though that the antenna had anything other than good omnidirectional patterns. My kudos to whoever came up with using the LORAN antennas as VHF transmitters. You have done your Nation a great service!

Allen
VHS
 
Follow-on to the above post...

Pat, it was quite the experience watching you in near-real-time, while talking with you on the phone live. What a world we live in!

First, on your Zulus...man do I want a set now! I couldn't believe it when you said you were taxiing, and it was just as clear when you were flying. I couldn't hear any background noise...you could have been next door in a quiet office! As I mentioned, I could hear your transmissions to tower too (but not their replies). Tell ya what, if you combine the real-time tracking with the voice calls, this combo could be a neat way to watch and hear SARL racers on the course as well.

On the tracking, even with a slow connection from a wireless router in a nearby hangar, I was able to watch you move almost in real time. Most of the time your location was very close to what you were calling, your speeds were right on, and in turns, new points were dropped showing you in nearly the same heading as you were calling out on the phone. Really really cool! There were some small gaps, and I had to refresh twice, but I attribute that to a bit of a fragile connection on my end.

That was a great test of the CI-122SP! I know you followed me on my test hop and GPS speed runs, and thanks for texting me what you saw. We'll be able to talk when I save up and get some Zulus! ;)

After we talked on the ground, I was called out on a SAR mission, and was able to put the CI-122SP though some more paces. As you can see from the pics below, it did very well. In those pics, guccidude Dan is the green track, and I am the blue. Dan uses a basic bent whip (the kind with the round white insulator at the base) and was the high SAR bird at 11,500'. I was the low search aircraft, and with the CI-122SP, I tracked well from Stead, through a quick stop at a nearby dirt strip to pick up my observer (the small pattern at Nevada Flyers Airport), along the east side of the ridge while conducting the search (500 agl and below), and when circling over the command post (the small circles to the southeast). Dan and I each did a flight before the mission, and those are the hits to the west of Stead...the mission was to the east, south of Pyramid Lake:

aprs25feb1.png


aprs25feb2.png


I thought is was very good performance, so its another plug for the Loran antennas. Heck, it even tracked me through a loop on the first hop (the three hits right on top of each other in the upper left corner of each pic...on aprs.fi, it shows the different altitudes!)

By the way Allen, Pat came up with that idea at about the same time our local avionics guy gave me a spare CI-122SP off his dusty back shelf. So the credit goes to Pat, and Lynn at Aviation Classics (two really smart guys!!) :D

And Pete...a little tidbit on the j-pole: I used it to talk with the CP and to talk with and deconflict from the SAR helo Dan and I were working with. Dan reports I was a little scratchy on it, but with the capability to switch between the two antennae, its a very workable set-up. Still gotta get rid of the noise from the APRS, but Pat may have solved that (or proven where mine's coming from!) Still working on a "speedy" solution for that one! :)

All in all, a very good bi-coastal APRS kinda day!

Cheers,
Bob
 
Perfect: a very good bi-coastal APRS kinda day! Great description, Bob!

After I landed, I got on aprs.fi and watched your test flight in real time as well--as you mentioned in your post above. You've got one fast RV-6, buddy! I was seeing 245 mph pretty consistently, but the coolest thing was your loop. I didn't notice it in real time, but after you texted me, I was able to go back and follow the breadcrumbs up and over!

One question: what is that donut in the lower right corner of your SAR flight? Possibly the rescue sight?

Allen, thanks for your comments. Yeah, I can see a digi and I-gate in my future out at the hangar!
 
One question: what is that donut in the lower right corner of your SAR flight? Possibly the rescue sight?QUOTE]

Pat,

The donut is actually where the Sheriff's ground Command Post was. The search was for a possible downed aircraft, which was last seen heading NW from about that donut area towards the higher terrain at a very low altitude.

The Sheriff's helo and I did contour searches along the ridgeline, starting high to low, and dropping 500' on each pass to cover a lower part of the terrain. We deconflicted by me staying well above his altitude. Dan circled high overhead and did a birdseye search as well. After covering the area well, the helo landed on the dirt road near the CP and went over the area covered with the boss, and I circled overhead waiting for further assignment. I was then sent to search further to the NW and then the search was called. The eye witness report was a bit sketchy, and since the area was clear, it was assessed that the airplane departed the area to the NW and was OK (no crash was reported, just a low-flying aircraft). But we were able to do our civic duty with an RV-6 and an RV-9A! (all captured on APRS!) ;)

Cheers,
Bob
 
Have we determined what the optimal amount to trim off of these antennas is yet?

John, both Bob Mills and myself cut 3.5" off the end and both or our antennae are working great. I think Bob measured a VSWR of 1.6:1 with his, excellent. We're waiting to hear from Allen Lord and the results of the experimentation with his LORAN antenna. You could probably trim off another couple of inches to really tune the antenna, but there's a little bit of guess work involved. If these were true ground plane 1/4 wave antennae, 19.45" would be the correct element length. But with the current SWR, I doubt if you will see any actual improvement with your tracker by trimming any more off. I defer to Allen...
 
You guys are spending too much!

I stopped by the local avionics shop today and asked if they had any old LORAN antennas still sitting around the shop. A trip up to the scrap pile yielded several antennas. I picked one and headed back to my shop to begin testing.

Total cost - $0:D

Well, I guess I'll drop a little cash his direction next time I have to do my transponder/altimeter cert.
 
Scott,

Mine came to me the same way...toughest part was getting the dust off! Price was definitely right!!

Purty neat stuff in those avionics shop scrap heaps, eh. I'd like to be cut loose in there for an hour or two ;) (Hey Stein, if you read this, I'll clean your scrap pile up if I can keep what you don't want anymore...I'll probably have to stand in line for that job though!)

Pat, you may have started a national run on old Loran antennas! :D

Cheers,
Bob
 
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Scott,

Pat, you may have started a national run on old Loran antennas! :D

Cheers,
Bob

Bob, you too; how come we didn't have the foresight to figure out a way to make a small fortune on the idea?! Like cornering the market on used LORAN antennas or something! Actually, if this results in the advancement of airborne APRS, then we are all better off for it.:)
 
Bob, you too; how come we didn't have the foresight to figure out a way to make a small fortune on the idea?! Like cornering the market on used LORAN antennas or something! Actually, if this results in the advancement of airborne APRS, then we are all better off for it.:)

Pat, you mean like that pile of Loran antennas I'm building up as I buy every one on e-bay I can find...

Nah, I'm kidding...foresight in business opportunities has never been my strong suit. Is it too late? We could clean 'em, paint 'em, and sell them for a huge profit...except for that discount to RV APRS bubbas, then it'd be perhaps a buck a piece! Oh wait, that is the market...oh well. :D

You've heard the old saying, "How do you make $100K in aviation?", right! ;)

Oh, and your last line hits in on the head!

Cheers,
Bob
 
Another LORAN Antenna

I picked up this out of the trash from a local avionics shop.

Trivec-Avant, model NY154. Also has a Foster Airdata Systems sticker on it.

Complies with TSO-C60A

Any idea if this may be suitable for APRS?
 
Yes!

I picked up this out of the trash from a local avionics shop.

Trivec-Avant, model NY154. Also has a Foster Airdata Systems sticker on it.

Complies with TSO-C60A

Any idea if this may be suitable for APRS?

Ron,

I looked at a picture of your antenna on eBay and it looks exactly like the Comant CI-122SP that we have been using successfully for our trackers. Perhaps manufactured by Comant under contract? I see no reason why this shouldn't work for you. I wouldn't bother trying to shorten it the 3.5" that we did--no sense messing up that P-Stat coating that's on it! Let us know how it works out!
 
Antenna troubleshooting

Can anyone tell me how to test my antenna to make sure that I have good connections and signal?

OK, here's the story. I've got the Bytronics APRS transmitter and the magnet mount antenna that comes with it. The transmitter worked just fine when I tested it on my truck - got good coverage and all was good. After removing it from my truck, I flew with the transmitter and magnet mount antenna on my other plane for a couple of months. All good.

Jump to the present. I want to mount my APRS transmitter in my RV-7, but the magnet mount antenna just isn't going to work. So I aquired a Loran antenna and mounted it on the belly of the beast. Made all of the connections from the GPS, power, panel mounted LED lights - all good. When I fly, the LED lights indicate properly to show that the APRS is getting a good GPS sentence (steady green LED) and the APRS is transmitting (short burst of red LED approx every 60 seconds or so).

But the problem is that the signal is not making it onto any of the APRS mapping sites such as www.aprs.google.com or www.aprs.fi.

Since I'm getting the correct LED signals, I'm assuming that maybe my antenna isn't working correctly???

Any suggestions?
 
Can anyone tell me how to test my antenna to make sure that I have good connections and signal?

OK, here's the story. I've got the Bytronics APRS transmitter and the magnet mount antenna that comes with it. The transmitter worked just fine when I tested it on my truck - got good coverage and all was good. After removing it from my truck, I flew with the transmitter and magnet mount antenna on my other plane for a couple of months. All good.

Jump to the present. I want to mount my APRS transmitter in my RV-7, but the magnet mount antenna just isn't going to work. So I aquired a Loran antenna and mounted it on the belly of the beast. Made all of the connections from the GPS, power, panel mounted LED lights - all good. When I fly, the LED lights indicate properly to show that the APRS is getting a good GPS sentence (steady green LED) and the APRS is transmitting (short burst of red LED approx every 60 seconds or so).

But the problem is that the signal is not making it onto any of the APRS mapping sites such as www.aprs.google.com or www.aprs.fi.

Since I'm getting the correct LED signals, I'm assuming that maybe my antenna isn't working correctly???

Any suggestions?

Scott,

You might try some simple stuff first (you may have already done some of this):

1) A careful visual check of all the connections

2) Disconnect the coax at the tracker and antenna and use an ohmmeter or test light to confirm continuity of the coax from the tracker to the antenna. Make sure the inner conductor isn't shorting to ground.

3) If good, check continuity between inner conductor of antenna connector and the antenna element (assuming you can get the probe on the element, it may be encased in epoxy or somethin'). Make sure the inner contact isn't shorted to ground.

4) Your loran antenna may have some sort of loading coil that is bad. Make a test flight with your proven mag antenna taped to the inside of the canopy and see if the tracker comes back to life.

Hope this helps,

Sam
 
The easiest and most efficient way to tune or check an antenna is to use an antenna analyzer. Find the local amateur radio club and ask the president of the club if he knows anyone that has one. I have the MFJ-259B and it works very well.

Takes about 10 minutes to tune the antenna to the resonant frequency on the 2 meter band.
 
Scott,

This is a long shot, but could it be possible that you didn't turn up the gain the last time you configured your tracker? I'm imagining a scenario where you took the tracker out of your truck and decided to adjust a couple of the parameters on your tracker configuration, turned down the gain as called for in the instructions, and perhaps forgot to turn it back up? :(

Just trying to think of anything Sam might have missed. Otherwise, you might have a bad antenna. Could be they threw it away for good reason. Also, you could put your tracker back on the truck and see if it's still working OK. If so, time to tune your antenna as Marty suggested.
 
Thanks...

Looks like a good weekend to do some troubleshooting. Thanks for the suggestions.

I'll follow up when I figure out what's up.
 
CI-122SP vs CI-122

As I read the specs, it appears that the SP was intended to only receive, while the CI-122 can TX & RX. If one can be obtained cheaply enough, wouldn't a trimmed CI-122 work as well (better?). Any comments?
 
Mark,

The CI-122 should work just fine. Problem is they are pretty expensive, even used, whereas the CI-122SP's have been available on eBay for around $10 or so since the demise of LORAN.

Some of us using the CI-122SP's have trimmed them about 3.5" in an attempt to tune them to 144.39 MHz, but it is not known if this has improved performance. I don't believe it has hurt either, it's just that the power put out by these trackers kind of overwhelms any antenna inefficiencies. In any event, mine works perfectly on the belly of my RV-6.

I kind of thought the SP stood for special paint, as these antennae feature a P-Stat anti-precipitation coating and are finished in a white Skydrol resistant polyurethane paint (according to the Comant catalog that I have).
 
troubleshooting complete

Looks like a good weekend to do some troubleshooting. Thanks for the suggestions.

I'll follow up when I figure out what's up.

I spent a couple of days trying various methods to make my APRS work with a "recycled" LORAN antenna. I wasn't able to get the LORAN antenna to work at all. I'm not saying that a generic LORAN antenna won't work. I'm simply saying that the particular antenna I had, didn't work! Maybe a failed BNC connector, or bad ground connection to the ground plane, or something else???:confused:

Anyways, as I've posted in other threads, I figured I should close the loop in this thread as well.

I finally purchased a Phantom Stealth 1440 antenna. I installed it a couple of weeks ago in the same hole that the LORAN antenna came out of. The Phantom Stealth antenna cost about $65. It comes in Black or White, and has a fairly small and aerodynamic size.

The signal is completely satisfactory. I've made several local flights, and a cross-country from Washington to Utah. I was very happy with the results. I enjoyed trying the LORAN antenna, but I'm glad to have a working APRS tracker now.:D
 
An old idea revisited

While cleaning off a storage shelf, I found my Morrow LORAN antenna that I had planned to install on my mini-van ( which just gave up the ghost) I decided to check it out, and driving it with a Micro-Trak RTG FA, I had an SWR of 1.5 with the antenna just clamped to the bench vise. It should only improve with ground plane of the my new car, a little Toyota. I plan on mounting it on the trunk providing I can open the trunk without the antenna smashing out my rear window. This will be the first hole I bore in my new Corolla........., but it should look cool! If I had a pair, I could mount one on the port and starboard sides for my voice radio! My wife is going to freak....

By the way, we are completing software revisions and firming up board designs for our new MT-TT4 transceiver. Frequency agile, 10 watts, ps/2 Keyboard input and 4 X 20 LCD output for a display ( of course you could plug it into a GPS too....)

I will try to post photos of the antenna on the car.

Allen
VHS
 
By the way, we are completing software revisions and firming up board designs for our new MT-TT4 transceiver. Frequency agile, 10 watts, ps/2 Keyboard input and 4 X 20 LCD output for a display ( of course you could plug it into a GPS too....)

Excellent. I missed out on the previous MT-TT4. I wanted it to be able to find other APRS aircraft. I went back to check a previous discussion about the TT4. At that time, the RANGE/BEARING functionality to another APRS aircraft had not been implemented in the TT4. Is that being included with the current TT4?

http://www.vansairforce.com/community/showthread.php?t=36779
 
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Ron,

Byon added range and bearing to a reporting station that can be viewed on the LCD display. I am hoping I can convince him to add a selective screen to show R & B to Icons of things that are up in the sky, balloons, mountaintops, aircraft, gliders, UFO's etc.

One thing we have to consider for airborne operation is that generally a transceiver will hold off transmitting until it hears a clear channel. Airborne, you have line of site and can "hear" transmitters out to the optical horizon plus about 15% beyond that, so your transmitter would never transmit again.....I am not sure that our chip has the computing power to evaluate a signal instantaneously and say "you are too far away, so I am going to transmit anyway!" I am leaning towards just ignoring other peoples transmissions while airborne and brute forcing a transmission. As long as you don't do this too often, no one should complain. The idea of changing the configuration to change power and digipath as a function of altitude and/or velocity are also on the to-do list.

Allen
 
I was once told that these Loran antennas are physically identical to the their VHF comm antenna counterpart, the only difference being that an antenna matching box was used inline with the coax to re-tune for the Loran's longer wavelength, and they were given a different part number to be sold as Loran antennas. Anybody know if that's actually true or not?
 
I have no idea of the electronic issues of a LORAN antenna. I do have a Foster Model NY154 antenna that I intend to try once I get a system.
 
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