Looking for threaded antenna

[RangerConlin]

Greetings!

I'm trying to find antennas for the mounting in the attached pictures. I need two of them, for the band listed on the sticker. So far I've had no luck identifying what type of connector it is or anything that looks close. Thanks!

 

[jeepsandradios]

Looks like a 1/4-20 stud mount. Lots of antenna's used that size in the early days. May be easier to just order a 1/4 wave NMO and mag mount on amazon.

 

[RangerConlin]

Unfortunately these are specialized and extremely rare mountings that I can't replace.

 

[kf8yk]

Looks like a MobileMark A2111B magnetic mount. Stock versions go as low as 136 MHz, but the spec sheet says they provide custom tuned versions at no additional cost.

 

[RangerConlin]

They're L-Tronics 10129 DF antennas with a switching diode built in to the cable to allow them to work as a phased array. Replacing the mounts is not an option. I just need to find either an antenna that fits that mount or an adapter that lets me use an NMO or similar mount.

 

[kf8yk]

I suspect L-Tronics modified the MobileMark antenna for their DF product. I bet you can call MobileMark & just order replacement whips. Worst case is ordering the entire antenna, spin off the whips & discard the base.

 

[BMDaug]

McMaster Carr sells thread adapters in all sorts of sizes. They are essentially a long nut where half is threaded with size/pitch A and half is threaded with size/pitch B. They also sell thread adapting “Jack screws”. They are usually stainless and would allow you to adapt to any thread size and gender you need for whatever whip you choose.

-B

 

[mmckenna]

Easy way to do this is to take it to a good local hardware store.
Go through their selection of nuts and figure out what it is.

If it's 5/16 x 24 thread, you can take whips off the Larsen NMO-Q series antennas and screw them right on.
Or, these cones and a 0.100 diameter whip will do the trick: Larsen QCONE.100 - Misc Antenna Parts | The Antenna Farm

I have some old/cheap antennas that have a 1/4 x 20, but I don't know the brand.

 

[ko6jw_2]

L-Tronics was run by Bruce Gordon N6OLT. Bruce passed away a couple of years ago. However, I know some other hams that were close to him and involved with the company. I can make some inquiries as whether there are any parts still available. I can't do it until the middle of January because of holiday travel plans. You can PM me with your contact info.

 

[merlin]

I am sure that is a 1/4 X 20 stud. You can get a whip adapter and whip off ebay.
Antenna Specialists Whip Adapter K-50 , 2.5mm Radio Antenna **NEW** | eBay
49" Replacement Steel Whip Rod 2.5 mm 0.1" for VHF UHF CB Mobile Radio Antenna | eBay
If you intend this for transmitting, you will need to cut this to the frequency of use for proper SWR.
Looks air band, so no cutting may be needed.
Cheers

 

[Golay]

I'm with mmcKenna to start. Take it up to a hardware store. Using the nuts out of the bins there, ascertain just what the size and thread count is. Then get back on here and tell us. Without a doubt, more than a few of us have what you want and will throw it in a box for the cost of shipping. If I rummaged around thru boxes here, I myself could probably find two or three of the springs like the one circled in the pix below.

 

[ko6jw_2]

The device in question is an RDF designed to receive ELT's on 121.500 MHz. Used alone it would provide a heading for the signal and by triangulation could be used to locate the beacon. As such the replacement antenna would have to match the OEM antennas as closely possible. There are four antennas. The phase relationship would determine the heading. Thus the need to match the antennas closely. L-tronics also made alerting receivers for ELT's. We had one at our repeater site which would trigger an alarm when an ELT was received. There were several at different mountain to sites. When an alarm was received the RDF could be deployed.

ELT's on 121.500 are being phased out in preference to satellite based 406 MHz systems.

 

[BMDaug]

Just take a 1.5” long piece of 3/4” bar stock, drill and tap 1/4-20 in one end, drill a 1/16th” hole in the other end for a piece of tuned 16 gauge music wire, then drill and tap an intersecting hole for a set screw. Insert the music wire, make sure the whips are tuned. Add thread lock and to the set screw and spray paint. Totally custom and fairly simple.

-B