Any Way to Build a Marker Beacon TRANSMIT Antenna?

MBDiagMan

MBDiagMan

Final Approach
Joined
May 8, 2011
Messages
5,016
Location
NorthEast Texas
Display Name
Display name:
Doc
I finally have my Marker Beacon antenna in place, whew! I would like to tweak it.

I have a signal generator buried in some old stuff in my shop. Is there a way to make an antenna that I could use to transmit to the MB? If so, could I accomplish this with a sine wave only, or would there have to be some sort of modulation?
 
All it takes is a yard of wire connected to the antenna connector of your ersatz transmitter. A quarter wave at 75MHz is 37".

However unless you are using very tiny amounts of RF (milliwatts) you're breaking the law.

You'll need to figure out how to amplitude modulate your 75 MHz frequency with an appropriate frequency (400, 1.3K or 3K Hz) if you want your aircraft receiver to do anything with the signal. Contrary to what you saw in Die Hard 2, other modulation is going to be filtered out by the receiver.

Frankly, taking it up and flying over the ILS course would probably be easier.
 
flyingron said:
All it takes is a yard of wire connected to the antenna connector of your ersatz transmitter. A quarter wave at 75MHz is 37".

However unless you are using very tiny amounts of RF (milliwatts) you're breaking the law.

You'll need to figure out how to amplitude modulate your 75 MHz frequency with an appropriate frequency (400, 1.3K or 3K Hz) if you want your aircraft receiver to do anything with the signal. Contrary to what you saw in Die Hard 2, other modulation is going to be filtered out by the receiver.

Frankly, taking it up and flying over the ILS course would probably be easier.
Click to expand...

First thing I thought, "Damn, must live a long way from an ILS to do all that."
 
Henning said:
First thing I thought, "Damn, must live a long way from an ILS to do all that."
Click to expand...

Yep, even with the disappearing marker transmitters it's not that hard to find. It still annoys my wife when one goes off when we're out tooling around.
 
It is indeed a pretty good flight to the nearest Marker Beacon. I was just trying to figure out how to peak up the antenna. The sled antenna is adjustable, and I have the connection at what looks like about the right place according to the picture.

I guess if it works, peaking it up is probably just a bunch of wasted time.
 
Yeah, pretty much, it sounds or it doesn't, not like the needle is going to waver.
 
MBDiagMan said:
I finally have my Marker Beacon antenna in place, whew! I would like to tweak it.

I have a signal generator buried in some old stuff in my shop. Is there a way to make an antenna that I could use to transmit to the MB? If so, could I accomplish this with a sine wave only, or would there have to be some sort of modulation?
Click to expand...

Put the signal generator out by the wingtip. Most signal generators will AM the RF at either 400 or 1000 Hz. If it is 400 you are in business as this will light the outer marker (blue light). Connect a 39" piece of wire to the RF output and try to get it horizontal. Adjust the sig gen RF output until the OM light just barely glows, then peak the antenna for maximum bright from the OM light.

Jim
 
weirdjim said:
Put the signal generator out by the wingtip. Most signal generators will AM the RF at either 400 or 1000 Hz. If it is 400 you are in business as this will light the outer marker (blue light). Connect a 39" piece of wire to the RF output and try to get it horizontal. Adjust the sig gen RF output until the OM light just barely glows, then peak the antenna for maximum bright from the OM light.

Jim
Click to expand...


Thanks Jim! I knew that you'd come through for me!
 
flyingron said:
Yep, even with the disappearing marker transmitters it's not that hard to find. It still annoys my wife when one goes off when we're out tooling around.
Click to expand...


Only flying directly over an inner marker (if you can find one) is all that annoying.

Outer and middle ain't so bad.

You should find an inner to fly over just to annoy her sometime if she's that easily bothered. ;)
 
Good news is that the antenna works great. Bad news is that I'm getting audio, but no lights. At least the antenna issue is put to bed.

Thanks for all the help and comments.
 
MBDiagMan said:
Good news is that the antenna works great. Bad news is that I'm getting audio, but no lights. At least the antenna issue is put to bed.

Thanks for all the help and comments.
Click to expand...

You will get audio WAY before you get lights (from an RF signal strength point of view). What frequency of modulation were you using? If you were using the relatively common 1 kHz. modulation, you never WILL get a light. The blue light will ONLY light with 400 Hz. modulation, the amber light with 1300 Hz., and the inner/fan marker with 3000 Hz.. The tone filters are quite sharp.

Which one were you using? And are you sure of the audio frequency?

Jim
 
Thanks for your response Jim!

I wasnt clear in my last post. I didnt end up digging out the signal generator and seeing if it still worked. I flew the ILS and everything worked well except i never saw marker beacon lights on the audio panel or LOC/GS receiver, either one. I cant get enough access to the back of the audio panel tray to tell how it is wired. It can be wired to have the light signals from the NAV or ve used as the marker beacon receiver itself.

I am getting the audio from the NAV, by pressing the NAV 1 button on the audio panel and turning up the volume on the receiver. I never saw the lights on the receiver itself. From what you said, maybe I'm not getting a strong enough MB signal to trigger the lights.

Thanks again for sharing your expertise.
 
What LOC/GS receiver are you using? Why does it have anything to do with the marker beacons?
 
flyingron said:
What LOC/GS receiver are you using? Why does it have anything to do with the marker beacons?
Click to expand...


Logical question.

I don't have the exact model numbers at hand, but it is a panel that was custom built in the early eighties with an integrated, all Narco system.

It has two VOR's, one of them having the LOC/GS/MB all in the same instrument. The VOR with the MB, has MB lights and transfers audio to the audio panel. This allows selection of NAV 1 in the Audio Panel and turning up the NAV 1 volume on the receiver to give MB audio.

To answer your specific question, I THINK that the Narco Model numbers are; NAV 121 & NAV 122. One of them a standard VOR and the other the LOC/GS/MB.
 

Attachments

  • C140Panel.jpg
    C140Panel.jpg
    94.3 KB · Views: 19
Last edited:
I should have guessed it was a Narco kludge. The NAV122 is one of those all in one things that has the VOR receiver integral to the indicator along with it's own marker beacon receiver. Are we talking about that receiver that's integral to the indicator or do you have two?
 
Sorry guys, but I'm just a poor boy trying to maintain an affordable way to fly. You can insult the panel all you want, but it's getting the job done.

The NAV 122 has a Marker Beacon receiver including the lights. The audio panel ALSO has a Marker Beacon receiver capability, or it can use the NAV 122 for it's receiver and indicate there as well, but it's not wired that way currently.
 
So you didn't answer, is the radio in question the one in the NAV122 or a separate one you are trying to hook up? If you have two, how are they connected to the antenna?
 
When the panel was built originally, a V antenna on the tail fed a splitter mounted to the rear of VOR 1, a NAV 122. The splitter fed MB, GS & VOR TO VOR 1 and VOR signal to VOR 2, a NAV 121 all from the same antenna. This did not provide a strong enough MB signal.

I bought a splitter for GS & VOR from the V antenna on the tail and installed a dedicated MB antenna that fed the MB connector on VOR 1.

Now, GS, LOC & MB work perfectly except I have not seen MB lights anywhere.
 
Last edited:
You must log in or register to reply here.
Back
Top