What is the ideal ILS antenna?

[billkennedy3]

Questions for Jim Weir, or other knowledgeable folks:

I've got a couple of questions about an ideal antenna for ILS use.

My Comm/Nav radio uses one antenna for both ILS and VOR. I rarely use
VOR so I'd like to optimize an antenna for ILS use (a side note -- my
current antenna sucks for both VOR and ILS). My plane is fiberglass.
I'm thinking a "V" shape may give me a stronger lobe toward the front
but don't know what the angle should be.

So, my questions

Is a "V" array a good idea for directional gain? What angle?

Should the top of the "V" be oriented forward to maximize reception
from that direction?

How long should the elements be for optimum reception of a 109MHz
signal?

Thanks – Bill Kennedy
N42BK


--
billkennedy3
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[TaxSrv]

"billkennedy3" wrote:
> So, my questions
>
> Is a "V" array a good idea for directional gain? What angle?
>
> Should the top of the "V" be oriented forward to maximize
reception
> from that direction?
>
> How long should the elements be for optimum reception of a 109MHz
> signal?

Jim can advise on the specifics if he desires, but to avoid
potential contradiction, I'll say only there's more than enough
signal strength available from the ILS antenna for practical IFR
use. So, the effect of optimizations you propose will not give you
anything you'll ever notice. I imagine for something as
safety-critical as an ILS, FAA gotta send you enough RF energy to
allow for things not being quite up to snuff on your end, or
seriously still shooting a LOC approach with a ratty old Genave
Alpha 200...

But what's your theory on why your present antenna sucks for both
VOR/ILS? Might it be the receiver, or coax? Did you install a
balun, or if self-fabricated with RG-58, are the dimensions
correct? Are the tips located near to any lengthy run of metal?
Optimizing a replacement antenna won't make up for the problems
these items can cause.

Fred F.

[RST Engineering]

As Taxsrv noted, your current antenna "sucks for both VOR and ILS". Let's
explore that before we design you something that will suck for the same
reasons.

Jim


"billkennedy3" > wrote in
message .. .
>
> Questions for Jim Weir, or other knowledgeable folks:
>
> I've got a couple of questions about an ideal antenna for ILS use.
>
> My Comm/Nav radio uses one antenna for both ILS and VOR. I rarely use
> VOR so I'd like to optimize an antenna for ILS use (a side note -- my
> current antenna sucks for both VOR and ILS). My plane is fiberglass.
> I'm thinking a "V" shape may give me a stronger lobe toward the front
> but don't know what the angle should be.
>
> So, my questions
>
> Is a "V" array a good idea for directional gain? What angle?
>
> Should the top of the "V" be oriented forward to maximize reception
> from that direction?
>
> How long should the elements be for optimum reception of a 109MHz
> signal?
>
> Thanks – Bill Kennedy
> N42BK
>
>
> --
> billkennedy3
> Powered by www.flight.org
>

[Dave S]

If he is using the SAME antenna for both glideslope and localizer/VOR
its understandeable how one or BOTH recievers are doing poorly.

Correct me if I'm wrong.. Glideslope receivers are UHF band (400 mhz
range??) while the LOC/VOR is in the VHF band (109-117 mhz range). He
did not explicitly state he had glideslope, using the term "ILS" which
im not sure if he's referring to Loc/GS or Loc alone.

The a/c is a lancair 320 (if the N number search is correct). Where is
the "per plans" antenna location for the nav and GS antennae?

Dave

RST Engineering wrote:

> As Taxsrv noted, your current antenna "sucks for both VOR and ILS". Let's
> explore that before we design you something that will suck for the same
> reasons.
>
> Jim
>
>
> "billkennedy3" > wrote in
> message .. .
>
>>Questions for Jim Weir, or other knowledgeable folks:
>>
>>I've got a couple of questions about an ideal antenna for ILS use.
>>
>>My Comm/Nav radio uses one antenna for both ILS and VOR. I rarely use
>>VOR so I'd like to optimize an antenna for ILS use (a side note -- my
>>current antenna sucks for both VOR and ILS). My plane is fiberglass.
>>I'm thinking a "V" shape may give me a stronger lobe toward the front
>>but don't know what the angle should be.
>>
>>So, my questions
>>
>>Is a "V" array a good idea for directional gain? What angle?
>>
>>Should the top of the "V" be oriented forward to maximize reception
>>from that direction?
>>
>>How long should the elements be for optimum reception of a 109MHz
>>signal?
>>
>>Thanks – Bill Kennedy
>>N42BK
>>
>>
>>--
>>billkennedy3
>>Powered by www.flight.org
>>
>
>
>

[RST Engineering]

Dave ...

That doesn't happen to be true. What you say about the signals is correct
.... Loc/Vor is 108-118 MHz. and glideslope is 325-340. An antenna, to work
well, needs to be an *ODD* quarter wavelength per element. Note that a
1-quarter wave at the Loc/Vor just happens to be a 3-quarter wave at the
glideslope, and as such, will work quite well for both frequencies.

It is traditional to make a "splitter" to take each signal off unaffected by
the other signal. Such a splitter can be made from two cents worth of parts
and a few bucks for connectors and metalwork. You can go one step further
and for half a buck's worth of coax have a two-radio VOR/LOC splitter plus a
glideslope splitter in the same box.

Now, back to the original question. Where is the CURRENT antenna located
and why is it performing so poorly. No bandaids before we do the analysis.

Jim



"Dave S" > wrote in message
ink.net...
> If he is using the SAME antenna for both glideslope and localizer/VOR its
> understandeable how one or BOTH recievers are doing poorly.
>
> Correct me if I'm wrong.. Glideslope receivers are UHF band (400 mhz
> range??) while the LOC/VOR is in the VHF band (109-117 mhz range). He did
> not explicitly state he had glideslope, using the term "ILS" which im not
> sure if he's referring to Loc/GS or Loc alone.
>
> The a/c is a lancair 320 (if the N number search is correct). Where is the
> "per plans" antenna location for the nav and GS antennae?

[billkennedy3]

I'm using a Archer antenna in the top of my Lancair 320 fuselage just
aft of the baggage compartment. I tried to do a careful job of
installation but I'm a klutz. Not only that, I'm a 200 pound klutz and
the area behind the baggage compartment was designed for very small
non-klutz persons.

So, I confess, I don't have a clue if my problem is from poor
installation or from installing a poor choice of antenna. I've sent
for Jim Weir's antenna kit, so I'm going to install another come hell
or high water. I'll rig it temporarily above the baggage area (for
reasons mentioned afore). So, back to my original questions:

Is a "V" array a good idea for directional gain? (My space available
make the "V" very tempting)

What angle?

Should the top of the "V" be oriented forward to maximize reception
from that direction?

How long should the elements be for optimum reception of a 109MHz
signal?

How fat?

Thanks -- Bill Kennedy


--
billkennedy3
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[RST Engineering]

"billkennedy3" > wrote in
message .. .
>
> Is a "V" array a good idea for directional gain? (My space available
> make the "V" very tempting)

The V antenna may be made at any angle up to a 90d right angle, but the
optimum for omnidirectional reception (which you want for VOR) would put the
angle of the V somewhere around 120-140d. The V antenna will have SLIGHTLY
better reception in the apex of the V -- that is, this V antenna will pick
up slightly better towards the top of the page than the bottom, but will
have no effect for all practical purposes.




>
> How long should the elements be for optimum reception of a 109MHz
> signal?

Why 109? The center of the localizer band is 110 and the center of the
whole nav band is 113. However, to answer your question directly, about
23.5" for each element. If you wanna split hairs l = 2575 / f where l is
the length of an element and f is the frequency in MHz. In this case, the
number works out to 23.62, but this is also like building a house with a
micrometer.
>
> How fat?


We've found that 1/2 " copper tape is about the best compromise between
bandwidth and work-ability.


Jim

[UltraJohn]

RST Engineering wrote:

> the length of an element and f is the frequency in MHz. In this case, the
> number works out to 23.62, but this is also like building a house with a
> micrometer.
>>
>> How fat?
>
>
> We've found that 1/2 " copper tape is about the best compromise between
> bandwidth and work-ability.
>
>
> Jim

Hey Jim like we used to say in the Navy, "Measure it with a micrometer, mark
it with chalk and cut it with an axe!"

Have a good day
John

[billkennedy3]

"...mark it with chalk and cut it with an axe." Thanks guys, I can
really relate to this. And, beyond the construction tips, thanks for
the technical advice as well.

Bill Kennedy


--
billkennedy3
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