Antenna Replacement

[PilotDerek]

I am looking at replacing my radio antennas and was looking for some insight. Has anyone replaced the mooney roof antenna shaped like a backwards 7? My two vhf antennas are the one on the rook like I mentioned and one on the belly which is a metal one bent back at an angle. Has anyone had any issues replacing these? Did you do it yourself or just have a shop do it? As a ground radio guy I know the in & outs on radio installations and cabling, although I am not looking foward to figuring out where my antenna cables are ran, as I am going to replace them as well. Everything is original 1967 cables and antennas. Any input is greatly appreciated.

[jetdriven]

Make sure the antenna is bad with an SWR meter before tossing out the 7 antenna.  Check th coax cable also.  I reently resealed my roof antenna and am considering replacing the rear, I think its bad.  Only transmits 10 miles.

The correct coax replacement is RG-400. It is low loss, double insulated, with a low drag teflon jacket.  About 2$ a foot.  Check ebay also.   You can get a RG-58 crimper for 20$, it has the same dize dies to crimp RG-400.  You can get the new BNC or TNC connectors to crimp on for 5-10$ from places like Mouser or Frys.  Get a couple extra, and a coax stripper, like  a palladin 1255 LC-CST from Amazon. As you can tell we just did all this ourselves.

  4 Bolts screw into the base of the antenna. (Might also be studs and nuts) Remove those and the BNC antenna connector.  The correct replacement is a Comant CI-196.  It has the offset BNC at the base and the proper bolt pattern.  Reinstall the antenna per the MFR directions but be sure to use star washers under the bolt heads (along with the proper flat washer)  to bite into the aluminum skin and make a good ground plane.

[PilotDerek]

Quote: jetdriven

Make sure the antenna is bad with an SWR meter before tossing out the 7 antenna.  Check th coax cable also.  I reently resealed my roof antenna and am considering replacing the rear, I think its bad.  Only transmits 10 miles.

  4 Bolts screw into the base of the antenna. (Might also be studs and nuts) Remove those and the BNC antenna connector.  The correct replacement is a Comant CI-196.  It has the offset BNC at the base and the proper bolt pattern. 

[PilotDerek]

I guess I should mention that my job in the Marine Corps is communication electronics maintenance. I have access to all the test equipment and tools that would be needed for this job.  

[jetdriven]

Derek, at the bottom is good reading about this subject.  Perfect SWR is 1:1.  all of the energy goes out the antenna, but is not achievable.  So anything numerically lower than 2:1 is good. Thats about 80% delivery.   You have to have an SWR meter that can measure a 50 ohm load and in the 118-135 Mhz band. the CB SWR from radio shack wont.  Also, you have to fab up a test cable to insert the SWR meter into your BNC COMM antenna line, as the SWR meter I have has a screw on CB type connector.  I bought a 6' CB extension, then cut in two and put a male BNC on one and a female BNC on the other.  Calibrate the SWR meter as the MFR of it says to do, then measure SWR by keying the mic away from any buildings, trees, structures etc.  I suppose inflight is best. 

I have all this, and didnt read the directions on setting the meter.  So I need to do it again, as out COM/NAV 2 recieves 80 miles but only transmits 10.

AFAIK the CI-196 is a drop in for the CI-156, it just doesnt look as 60s cool.

What kind of COM do you have? You might just need it looked at and aligned.

I shoud mention that replacing antennas is not someting allowed under FAR 43 as owner approved maintenance.  Also not likely is a fed jumping out from behind a tree demanding to see the log entry for that shiny, stock appearing antenna.  However, a helpful A&P you have an agrement with can supervise the work and do the log entry returning to service.  Those kinda guys are the best you can get.

http://www.firestik.com/Meas-SWR.htm

 

 

[PilotDerek]

I have Narco radios. I plan on replacing them down the road. I have a great A&P that has no problem supervising/inspecting my work and logging it. How did you figure out that you could recieve 80 miles but only transmit 10?

[jetdriven]

I went up and called a few towers, and on an XC  coming back, just kept calling SGR tower until they answered back.  Ten miles, but we could recieve ATIS, VOR, and DME at 80 miles.  Mine is the 7 antenna as well.

[Jerry 5TJ]

Quote: PilotDerek

I guess I should mention that my job in the Marine Corps is communication electronics maintenance. I have access to all the test equipment and tools that would be needed for this job.  

[takair]

Good input above. If VSWR checks good then you may want to check the bonding under the antenna. This is is especially true for planes that were painted within 2 or 3 years. It seems to take about that long for chemical stripper wick its way under the antenna leaving a poor ground. This is critical, especially in transmitt. The old cork gaskets seemed especially prone to this. One method is to use a gasket impregnated with metal. However, you can also clean the ground plane on the antenna and fuselage mounting. You can treat with alodine and be sure to clean up the screw holes. Whether you use the gasket or not, be sure to seal the antenna.

[SkyPilot]

Quote: PilotDerek

I am looking at replacing my radio antennas and was looking for some insight. Has anyone replaced the mooney roof antenna shaped like a backwards 7? My two vhf antennas are the one on the rook like I mentioned and one on the belly which is a metal one bent back at an angle. Has anyone had any issues replacing these? Did you do it yourself or just have a shop do it? As a ground radio guy I know the in & outs on radio installations and cabling, although I am not looking foward to figuring out where my antenna cables are ran, as I am going to replace them as well. Everything is original 1967 cables and antennas. Any input is greatly appreciated.

[M20E-1964]

Is the 7 better or worse than the modern replacement?  I'd like to convert mine back to the 7's.  Like the look better. 

[PilotDerek]

Quote: gmcd

Is the 7 better or worse than the modern replacement?  I'd like to convert mine back to the 7's.  Like the look better. 

[N601RX]

The straight antenna will provide a stronger signal all things else being equal.  The "7" antenna was orignally developed because of clearance issues when mounting the antenna on the belly.    It also has slightly less drag than the straight antenna. 

[jetdriven]

Update, 

After having the COM 2 radio checked out (it was fine, 200$), and replacing all the RG-58 coax antenna cable in the plane with RG-400 (60$ and removal of left sidewall plastic and seats), the COM 2 would still only transmit 10 miles. Taking it to an avionics shop was going to generate a 150$ airplane cost and a 200$ bill to diagnose it,  so we rolled the dice and blew 360$ on a new Comant CI-196 antenna to replace that rear "7" antenna.

Yes, it kinda hurts to even admit that. But it wasnt going to fix itself, and we have been screwing around with it for a year.  Anyways, I had plenty of time to install it correctly with the engine off.  The first flight, from 1400' above the ground, we were able to reach a control tower 45 miles away.  Later testing reveals it transmits over 90 miles above 6,000 feet.  A KX-170B from 1980. (A "high serial number" one). I love those radios.

It doesnt look too bad either.  Neither did the old antenna. Looks can be deceiving.

[PilotDerek]

Bryon,

Where did you buy your antenna from? I will be replacing mine shortly. Glad everything is working for you now. My turn to get to work and fix my Comm problem.

[jetdriven]

Chief Aircraft.

[OR75]

exact same foot print  ? and direct R&R exercise ?

[jetdriven]

The holes in the airframe were rather hacked out, and it took about 15 minutes of elongating a couple by 1/16" or so to get the bolts to fit.  But overall, a pull and swap deal.

[buckfever06]

I know this topic hasn't been revisited since 2012, but I recently broke off my comm1 (forward) "7" antenna while putting my Bruce's cover on just before a thunderstorm. The wind was whipping and it didn't even seem like the cover torqued the antenna that much, but it snapped off. I found a good used Comant CI-196 antenna as a replacement. I was slightly disapointed that the antenna I purchased looked white in the photos online, but arrived as a grey color. The photos didn't depict the actual color of the antenna. It isn't ugly, but doesn't match my aft antenna. I am planning on having my mechanic supervise me in replacing the antenna and will let everyone know how it goes. I am even considering buying another (grey) CI-196 so I have matching antennas. I figure I can find someone who needs a "7" antenna and make up the purchase price of a couple of slightly less aerodynamic CI-196 shark fin antennas. I recently went on an IFR cross country flight 730 miles each way using only my comm2. I found I was able to still listen to AWOS and ATIS that weren't too far away on my broken antenna, although I didn't try to scientifically figure out how far I could listen, and I didn't even try to talk to ATC on my broken "7" antenna. More to follow...

[buckfever06]

I returned the grey antenna to the seller today and they agreed to immediately ship out the white one they had in stock. I still may replace the aft comm2 "7" antenna someday. Does anyone know the model number for the "7" antenna? I need to figure out how much it is worth so I can decide whether to replace it with a Comant CI-196. maybe someone else is in the same boat and doesn't want to pay $1000 for a matching "7"!