J Model Comm Antenna: The "7" Vs. the straight

[201Steve]

Hey Guys,

Has anyone ever replaced their "7" comm antenna from the F's and early J's to the newer style "straight" antenna? If so, is there any mounting changes or holes needed drilling etc? I am going for paint this year, and have wanted to convert the look of my "7" antenna to a newer style, just wondering what the best route for this would be, and what would be the most minimally invasive.

[Jblanton]

They mount the same without modification I'm pretty sure. The forward one has the connector offset to clear a tube.  I have a nice used set if interested.  

[201er]

42 minutes ago, 201Steve said:

Hey Guys,

Has anyone ever replaced their "7" comm antenna from the F's and early J's to the newer style "straight" antenna? If so, is there any mounting changes or holes needed drilling etc? I am going for paint this year, and have wanted to convert the look of my "7" antenna to a newer style, just wondering what the best route for this would be, and what would be the most minimally invasive.

I believe @jetdriven did his. In fact he also changed the towel rack to blades and a bunch of other stuff. Might be able to tell you if it made a speed difference or not.

[MikeOH]

Hmm, I've always thought the "7" on my plane looked kinda of cool.  Guess I'm just not up on airplane fashion trends

[BlueSky247]

Following. May be looking to do the same in the future.

[EricJ]

52 minutes ago, MikeOH said:

Hmm, I've always thought the "7" on my plane looked kinda of cool.  Guess I'm just not up on airplane fashion trends

You can't get new ones any more, so if one gets broken or the base corrodes, there isn't much choice.   I've wondered whether one is any faster than the other.

[MikeOH]

9 minutes ago, EricJ said:

You can't get new ones any more, so if one gets broken or the base corrodes, there isn't much choice.   I've wondered whether one is any faster than the other.

Yeah, I've wondered the same.  Probably lost in the rounding, but I once watched an old MIT aerodynamics movie that showed what enormous drag a circular cross section wire has; it was pretty startling!

While an EE, I was never an RF guy, so wondered what the radiation pattern (gain) of the "7" antenna is; seems pretty asymmetrical to have a circular pattern (which, I'd think would be ideal), but I have no real idea.

[EricJ]

42 minutes ago, MikeOH said:

Yeah, I've wondered the same.  Probably lost in the rounding, but I once watched an old MIT aerodynamics movie that showed what enormous drag a circular cross section wire has; it was pretty startling!

While an EE, I was never an RF guy, so wondered what the radiation pattern (gain) of the "7" antenna is; seems pretty asymmetrical to have a circular pattern (which, I'd think would be ideal), but I have no real idea.

I'm a comm guy, but not strictly RF, and I've wondered the same.    It shouldn't affect power output, but would probably alter the pattern and polarization a bit.    That said, it'll probably get rid of the end null that most rod antennas have.   It's really not any different than the bent rod antennas that are out there, especially the ones bent flat for use on the belly.     Like a cat whisker VOR antenna, too.

[MikeOH]

1 hour ago, EricJ said:

I'm a comm guy, but not strictly RF, and I've wondered the same.    It shouldn't affect power output, but would probably alter the pattern and polarization a bit.    That said, it'll probably get rid of the end null that most rod antennas have.   It's really not any different than the bent rod antennas that are out there, especially the ones bent flat for use on the belly.     Like a cat whisker VOR antenna, too.

I always thought that VOR (cat's whiskers) and MB (bent rod belly) were horizontal polarization, and COMs stuff was vertical; BWTHDIK?

[OR75]

4 hours ago, 201Steve said:

Hey Guys,

Has anyone ever replaced their "7" comm antenna from the F's and early J's to the newer style "straight" antenna? If so, is there any mounting changes or holes needed drilling etc? I am going for paint this year, and have wanted to convert the look of my "7" antenna to a newer style, just wondering what the best route for this would be, and what would be the most minimally invasive.

the 7 antenna is a CI156. the replacement for is CI-196 (same nuts / bolts footprint so no need to drill new holes)

the rear one is fairly easy to change,   easy hat rack headliner to remove / get access 

the front one is a bit more involved  .... 

 

[EricJ]

8 minutes ago, MikeOH said:

I always thought that VOR (cat's whiskers) and MB (bent rod belly) were horizontal polarization, and COMs stuff was vertical; BWTHDIK?

That's correct.    Polarization can be view from multiple angles, though.    The one we care about is relative to horizontal, so putting a bend in a vertical rod antenna tilts the polarization in the direction of the bend.    For example, tilt a vertical rod antenna toward the tail.   The polarization tilts toward the tail, too, but view from the front of the airplane there's no change in polarization and it's still vertical.     Tilting the VOR cat's whiskers forward from the vertical stab makes no difference in the polarization in any horizontal viewpoint, but looking down at it the polarization from each whisker is tilted toward the front of the airplane (and that's a dipole compared to the comm antennas, which are monopole).

Bending or tilting the polarization of the comm antennas a bit isn't a big deal, though, as at the ground antenna reflections off everything nearby will have random polarizations and only the direct ray will maintain the transmitted polarization.   It doesn't make a big difference.   There is some difference, but it isn't a big deal.

[BlueSky247]

Hey, while we're on the subject - what's up with 10w vs 14w radios?

[MikeOH]

26 minutes ago, OR75 said:

the 7 antenna is a CI156. the replacement for is CI-196 (same nuts / bolts footprint so no need to drill new holes)

the rear one is fairly easy to change,   easy hat rack headliner to remove / get access 

the front one is a bit more involved  .... 

 

YOWZER!!

They sure are proud of that CI-196 vertical blade...like $900 proud!  I'm gonna keep my CI-156 a bit longer, thanks

[McMooney]

I want to replace one of the 7's with a new gps/comm/xm comm antennae,  really want to get rid of atleast one of those warts

[EricJ]

57 minutes ago, BlueSky247 said:

Hey, while we're on the subject - what's up with 10w vs 14w radios?

One transmits 4W more than the other.    It just increases your transmit range a bit.

[M20F]

1 hour ago, EricJ said:

One transmits 4W more than the other.    It just increases your transmit range a bit.

It does make a difference.  My audio panel goes to 11.  

[BlueSky247]

5 hours ago, EricJ said:

One transmits 4W more than the other.    It just increases your transmit range a bit.

Thank you. I wasn’t sure if there might be a different antenna in those cases. 

[jetdriven]

The CI-196 antenna is the only  thing you can buy right now except for the ci-122 for the belly, because the 196 has an offset BNC to clear the stringer. Yes, they’re expensive but that’s the way that is. Plus the drag on any one of these antennas is very minimal.

[Andy95W]

Comant CI-248-5.  Works great, strongly recommend, low-drag profile.  Has a built in notch filter.

https://www.aircraftspruce.com/catalog/avpages/comant248-5.php

[jetdriven]

That antenna is 17 inches tall, which is 4 inches taller than the other antenna and it’s more circular in profile so it’s great for a 182 but not really for Mooney speeds. Plus, I’m not sure it has the offset BNC either and some places will just chop that leg off of stringer, but it’s not really what you should do.

[201Steve]

Anyone know whether the base plates and hardware will match up between the 7 and the blade? I may buy a couple off of ebay, but none of them come with hardware. I'd have to use my existing, not sure if they are the same or would need to source them separately.

@OR75

@jetdriven

 

[OR75]

I have both in my hangar and can check this weekend 

 

[Aerodon]

I removed the front one so I can install a traffic antenna.  Had to take headline off.  I can't remember if there were nut plates underneath the screws, but there are spacers and washers between the mounting plate and the out skin.  So even iff there are nut plates, you don't want those rattling around.

I removed the rear one to install a GPS/Com antenna for my lynx traffic system,  had to move the antenna sideways and drill some new holes.  But there is already a nice triangular doubler riveted to the skin, so no structural issues.

So now I have these two antennas for sale.  Make me a decent offer.

Aerodon

[Will.iam]

On 7/16/2024 at 12:32 PM, MikeOH said:

Yeah, I've wondered the same.  Probably lost in the rounding, but I once watched an old MIT aerodynamics movie that showed what enormous drag a circular cross section wire has; it was pretty startling!

While an EE, I was never an RF guy, so wondered what the radiation pattern (gain) of the "7" antenna is; seems pretty asymmetrical to have a circular pattern (which, I'd think would be ideal), but I have no real idea.

Do you mean this video?

https://www.techtv.mit.edu/collections/ifluids/videos/32599-fluid-dynamics-of-drag-part-1
 

[MikeOH]

16 minutes ago, Will.iam said:

Do you mean this video?

https://www.techtv.mit.edu/collections/ifluids/videos/32599-fluid-dynamics-of-drag-part-1
 

That is the MIT series but NOT the video I recall.  I've tried to find it before with no luck.  But with your link I'm going to try and poke around the site to find it.

Thanks!