The International Cessna 170 Association

I've got one that is in immaculate/restored condition and although I have no plans to use it, I consider it too valuable as a spare to sell it for anything reasonable, therefore I cannot place a price upon it. The value of such item is in the eye of the buyers/sellers, IMO.

Bruce Fenstermacher wrote:

DaveF wrote:Do you think the stab-mounted antenna would be an eyeball hazard if it pointed forward instead of aft?

No. But I didn't put it that way on mine because I wasn't willing to except less performance considering the work it took to do it.

Bruce, I thought I'd read that the VOR antenna has equal or nearly equal response fore and aft, so it doesn't matter which way it points, but I can't remember where I saw that. Do you have information on the radiation pattern of the VOR dipole?

DaveF wrote:

Bruce Fenstermacher wrote:

DaveF wrote:Do you think the stab-mounted antenna would be an eyeball hazard if it pointed forward instead of aft?

No. But I didn't put it that way on mine because I wasn't willing to except less performance considering the work it took to do it.

Bruce, I thought I'd read that the VOR antenna has equal or nearly equal response fore and aft, so it doesn't matter which way it points, but I can't remember where I saw that. Do you have information on the radiation pattern of the VOR dipole?

Dave, I am pretty sure Bruce was referring to the aircraft speed loss with the whiskers facing forward as opposed to rearward. And if there was a significant difference in the radiation pattern of the VOR dipole one would think we would see a lot of the Narco Masts reversed so that the whiskers faced forward. My whiskers are located in the top of the vertical stab, they face the rear giving great vor/loc reception and I have had no issues with them poking any part of my anatomy.

Oh, that kind of performance. Well, here's a plot of the electromagnetic performance, run on an antenna modeling program. Looks very symmetrical fore/aft.

I was talking about reception performance but of course pointed aft does look faster.

When it comes to such things electronic, specially antennas and transmissions of all types, I default to my friend Dan Mitten who I fly with nearly every time I fly for fun. He's been partly responsible for such things over the years as bouncing signals off the moon and whatnot for the space program, top secret defense stuff and lately some of the cell and high speed internet service we use.

When I asked him which way I should mount the antenna in the vertical stabilizer he said point it aft. He was probably thinking if I had any hope of picking up stations 75 miles out I better point it that way. In reality of normal expectations either direction probably works just as well. But at least I haven't had to hear Dan tell me I pointed the antenna the wrong way when he tried to tune and receive morse code from that distant VOR while we flew to breakfast. He does those things.

DaveF wrote:Oh, that kind of performance. Well, here's a plot of the electromagnetic performance, run on an antenna modeling program. Looks very symmetrical fore/aft.

VOR ant - Azimuth plot.pdf

Dave, are you certain that plot is of a swept-whiskers reception antenna? Many modern antennas are "towel-bar" or blade types. I'm wondering if your plot doesn't apply to those types.

I doubt it matters which way the antenna "points" since no one can predict from which direction the VOR station being navigated by is located. It could be ahead...or behind...or way off to one side ahead...or quartering/behind... etc etc. The whiskered antenna is capable of receiving regardless.

Think about a > ... or a < or a /\ or a \/...

If ahead or behind ...the signal pattern is the same regardless. If off to one side...again the same, except that one whisker might be hidden from view (from the perspective of the transmitting VOR) by the vertical stab... however the opposite side will not be so shielded. (Unlikely to matter in VHF band, but just making the point.)

The worst case scenario might be if one whisker was pointing exactly AT the VOR station.... but in that case, the opposite whisker will be approximately perpendicular and still see the signal.

I have flown lots of them in various mounts and have never noticed any difference. In fact, my Bendix-Kind KY-99 has a VOR receiver in it and it uses a little, bitty, flexible, mono-pole WHIP, and it does just fine, even INSIDE the cockpit!

After all, VORs are line of sight...they are a short-range navigation system. It's not likely that reception is a problem at such short distances.

Yes, that was a computer simulation of a swept whiskers antenna, each element quarter wave, and 90 degrees between the elements. I ran the simulation because Bruce's comment made me think about what I thought I knew about these antennas, that they're dipoles bent into an acute angle to create a more omnidirectional receive pattern. Straight dipoles have a figure-eight receive pattern, with no sensitivity to the sides.

The towel bar antennas are loop antennas, a different and smaller way of doing the same thing as the whiskers.

Aryana wrote:Mine is also pointed forward on the vert stab and has never been in the way or contacted anything.

Thanks for the pictures. What kind of antenna is that? I have a nice new VOR antenna, but it has a disc base that's 2.5 inches diameter, too large to fit entirely inside the vert stab.

For the most part, aren't VOR's pretty much obsolete? They still work, but with GPS being substantially better why would one want to use them except for fun and/or keeping their plane to some degree original. Sort of like DME's. I haven't had a VOR receiver in my plane in many years and haven't missed it at all. I finally unscrewed the whisker antenna's after determining they were worthless except for using as a place to hang a towel to dry when camping. (Not trying to stir the pot here )

170C wrote:For the most part, aren't VOR's pretty much obsolete? They still work, but with GPS being substantially better why would one want to use them except for fun and/or keeping their plane to some degree original. Sort of like DME's. I haven't had a VOR receiver in my plane in many years and haven't missed it at all. I finally unscrewed the whisker antenna's after determining they were worthless except for using as a place to hang a towel to dry when camping. (Not trying to stir the pot here )

For the most part you are correct about VORs, however, if you fly instruments you still need the antenna for the localizer on an ILS approach.

Just to stimulate thinking. Pointed forward could be a trash catcher such as anything flying from the cockpit, don't ask. Swept rearward any trash would fly off.
I don't think it matters as far as functionality other than any reflections.

John

lowNslow wrote:

170C wrote:For the most part, aren't VOR's pretty much obsolete? They still work, but with GPS being substantially better why would one want to use them except for fun and/or keeping their plane to some degree original. Sort of like DME's. I haven't had a VOR receiver in my plane in many years and haven't missed it at all. I finally unscrewed the whisker antenna's after determining they were worthless except for using as a place to hang a towel to dry when camping. (Not trying to stir the pot here )

For the most part you are correct about VORs, however, if you fly instruments you still need the antenna for the localizer on an ILS approach.

Bang vs. buck. For not much money, VHF nav allows the occasional IFR flight and, as Karl said, an ILS approach. GPS costs more to buy, plus the database updates, and the units go obsolete alarmingly quickly.

For a strictly VFR aircraft, you are correct, Frank.
For those who fly IFR... VOR is required to be legal, even if a GPS is installed.

I got my hands on a Narco antenna off of Ebay.
I figured for $50.00, it was worth the gamble. It turned out to be in good shape but I'll strip, paint and re-wire the thing anyway.

What's the best material to use as a base gasket? This one had a thick layer of RTV on it.

Does the top cap get a gasket as well? this one didnt have one but it seems like there should at least be a thin paper one up there.

Arash,

Kenny Faeths in Sac has a bunch of them. I can grab on for you next time I'm there if you want. If I remember right, I think I got it out of there for 20 bucks.

Mike