VHF Antenna Extension Rod Broke at Threads

[kenchim]

I accidentally broke off the small metal extension rod to my VHF antenna while attaching the canvas cover. The piece that broke is about 10” long, screws into the antenna base, and broke at the threads. It’s pretty old and I can’t find anything like it to type the part # here. If reception is OK, can I still use the radios or is this an immediate replacement scenario?

My equipment:
GARMIN GMA 345 AUDIO PANEL
Garmin GTR 225 COM
Garmin GNC 255 NAV/COM

 

[carusoam]

welcome aboard Ken...

First find out what radio it is attached to...
 

No... don’t use it...

Antenna length can harm radios during transmission... it alters power and ruins things...

Or don’t transmit...

what keeps you from getting a replacement?

We have a pre-flown antenna and radio guy around here if that helps...  Look for Alan....

PP thoughts only...

Best regards,

-a-

[kenchim]

Thanks for the feedback on antenna length. This experience made me realize what little I know about my antennas. I do plan to replace it. The plane is just close to annual and I thought I could wait a little longer. I'll find out where it is attached and turn that radio off. 

[EricJ]

10 hours ago, kenchim said:

I accidentally broke off the small metal extension rod to my VHF antenna while attaching the canvas cover. The piece that broke is about 10” long, screws into the antenna base, and broke at the threads. It’s pretty old and I can’t find anything like it to type the part # here. If reception is OK, can I still use the radios or is this an immediate replacement scenario?

My equipment:
GARMIN GMA 345 AUDIO PANEL
Garmin GTR 225 COM
Garmin GNC 255 NAV/COM

That's a key part of the radiating element for one of your voice radios.   The main risk is that it changes the output impedance so much that when transmitting it doesn't radiate all of the applied power and too much of the power reflects back to the transmitter, which can damage the power amplifier.   It won't damage anything if you only use it for receiving, but it probably won't be nearly as sensitive, i.e., the range will be reduced.   The antenna pattern might be a bit wonky as well.

 

[N201MKTurbo]

If you can get the broken piece out, just get a stainless rod and cut some threads on the end and screw it in. You can paint it white if you like. Just make it the same length as the original. 
 

You could just cut some more threads on your existing rod and screw it back in, but it will raise the center frequency Of the antenna a bit.

[kenchim]

I found an exact replacement for my antenna on ebay (lucky me!), but then I noticed that it doesn’t meet the required TSO’s for my new Comm equipment. It would be so easy to just get an exact replacement because the holes will line up, but do I need to get a different antenna that complies with the documented TSO’s?

The old antenna complies with TSO-c60a “Airborne Area Navigation Equipment Using Loran C Inputs”, but the documentation on the GTR 225/GNC 255 states “COM antenna Meets TSO-C37( ) and C38( ) or TSO-C169( ) 50 Ω, vertically polarized with coaxial cable.”  The old antenna seemed to work just fine, but was I slowly destroying my new radio with that old LORAN antenna? 

[carusoam]

There may be a couple antennas inside the one physical structure...

If you look at the base of the antenna, does it have multiple connection points?

I don’t think anything Loran related will be very helpful...   to soon for that...  it will be digital the next time it comes out...

Ken,

Are you flying IFR with this radio?

People have difficulty under the best circumstances getting their radios to work properly...

Mixing and matching radios and antennas isn’t going to be a positive experience...

If you need to save dough... check in with @Alan Fox to see if he has the right antenna for you at his pre-flown avionics emporium...

PP thoughts only, not a mechanic...

Best regards,

-a-

[EricJ]

1 hour ago, kenchim said:

I found an exact replacement for my antenna on ebay (lucky me!), but then I noticed that it doesn’t meet the required TSO’s for my new Comm equipment. It would be so easy to just get an exact replacement because the holes will line up, but do I need to get a different antenna that complies with the documented TSO’s?

The old antenna complies with TSO-c60a “Airborne Area Navigation Equipment Using Loran C Inputs”, but the documentation on the GTR 225/GNC 255 states “COM antenna Meets TSO-C37( ) and C38( ) or TSO-C169( ) 50 Ω, vertically polarized with coaxial cable.”  The old antenna seemed to work just fine, but was I slowly destroying my new radio with that old LORAN antenna? 

I didn't realize that was a LORAN antenna.   LORAN was not the same frequencies as VHF comm, so the antenna was tuned differently.   You should get a VHF comm antenna to connect to your VHF comm radio.   

 

[kenchim]

Thanks for all the help! I’m going to get two replacement antennas that are actually for VHF Comm. I’m hoping Alan can set me up. To think, I would never have known about the wrong antennas if I didn’t break this one. How serendipitous