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Bob Archer Nav Antenna Performance

Bill.Peyton

Bill.Peyton

Well Known Member
I am starting to take a look at my avionics plan and I am trying to decide on a Nav antenna. I see a lot of builders are usint the Archer antenna and would like to get some feedback. The only real alternative is the cat wisker V dipole mounted in the lower or upper rudder fairing which does not look as nice.
Performance is obivously the most important decision factor. Does anyone have any good data on this?
Bill
 
I know of a few that seem happy with it, but I can't say any of them were IFR airplanes.

I've talked to numerous IFR folks who have not been happy with the performance of the antenna and I've spoken with several more who have removed it completely and installed the whiskers after the fact.

I liked the idea at first, but I'm going the whisker route. I looked at Vic Syracuse's plane a few days ago and he's got whiskers mounted on the belly and directly below the Horizontal Stab to keep people from walking into it.

That's the route I'm headed down.
 
I had a pair installed in my RV-10 (430W and SL30) and both worked great. For maximum success you have to follow the install instructions to the letter. Anything short of that will absolutely provide degraded performance. Intuitively I would have thought that you'd want them as far aft of the lights & strobes as you could get. I discussed this with Bob Archer via email and he said that no, you want the antenna close and reiterated the wire routing instructions. He also said to install as close as possible, but not touching the foil heat shielding for the landing light. I did this and did not see any issue at all. While normally fly with GPS, I tested VORs at 75nm on both radios and had solid reception. ILS localizer and glideslope also solid with no blanking that I could detect. Not to say you couldn't get some wierd reception problems, I never experienced that though.

With that said, Bob Archer himself will tell you that his wingtip comm antenna is not very effective in an RV because you can't get enough vertical height in the wingtip.

Bob
 
Just thought I would add my comments here. I have no experience with the Bob Archer antennas. In all of the RV's I have built, I have installed external antennas almost always in the same approximate locations. The nav whiskers have always been installed on the belly just forward of the tail tie down or tail wheel, using a doubler, with the point of the V towards the nose of the aircraft. At normal cruise altitudes of 8K'-12k' I can pick up VOR's 80-90 miles away. I have always equipped my airplanes for IFR, and I want them to work when needed. Also, there are still some parts of the country where you actually do still need to receive FSS voice on the VOR to activate flight plans, etc. It's nice to hear them clearly. :)
The same for the com antennas---always external, and RG-400 coax. A number of times I have heard apporach say "there are multiple aircraft talking at once, 4VC go ahead." that made it worthwhile.


I did make them removable so if I ever decide to race I can remove them. :)

Vic
 
Phil said:
I know of a few that seem happy with it, but I can't say any of them were IFR airplanes.

I've talked to numerous IFR folks who have not been happy with the performance of the antenna and I've spoken with several more who have removed it completely and installed the whiskers after the fact.

I liked the idea at first, but I'm going the whisker route. I looked at Vic Syracuse's plane a few days ago and he's got whiskers mounted on the belly and directly below the Horizontal Stab to keep people from walking into it.

That's the route I'm headed down.
Click to expand...

I have an Archer Nav antenna in my right wingtip, with careful attention to the instructions and wiring.

performance with an SL30 is excellent, and slightly outperforms the certified setup with dual GNS430s in the Cirrus I also fly a good bit.

I have intentionally looked for airframe shadowing with weak signals (distant VORs) and been unable to demonstrate it.

In both airplanes I tend to cruise higher than a lot of others (9-12K) and usually pick up VORs at 100+miles with enough signal for the SL30 to decode the identifier. Neither of the GN?S430s in the Cirrus does as well, but I suspect that is the antenna.

In a practical sense though, VOR navigation is like ADF was maybe 15 years ago, clearly a dying art. The only practical use for the VOR is flying ILS approaches and in that case you're so close to the navaid even a crappy antenna is OK.

If you set up an airplane for "IFR light" to avoid GPS subscriptions, you might fly an occasional VOR approach but the same thing applies.

I really wish they had killed off enroute VORs rather than LORAN :(

Now, with WAAS approaches, there is little practical advantage to ILS except as a backup that doesn't require expensive database updates.

I'd suggest that the Archer antenna will be more than adequate, especially if you take some care with the installation.
 
my experience

I have an IFR equipped RV7A with an Archer NAV antenna tied to a 530 and SL30. I have been flying for 3.5 years with good performance from this antenna. As I upgrade my RV10 to IFR this winter, I will be using the same antenna.
 
I wouldn't expect any blanking in the Cirrus.

The fiberglass structure of the Cirrus would we transparent from an RV perspective. The only blanking that could occur would be the engine or the metal control surfaces.

Phil
 
Another vote for Bob's antenna. I have one installed (following the instructions to the letter) in the right tip of my RV-9. I have an SL-30 and get 80NM+, much better than I was expecting.
 
Certified Glass vs Exp

Phil said:
I wouldn't expect any blanking in the Cirrus.

The fiberglass structure of the Cirrus would we transparent from an RV perspective. The only blanking that could occur would be the engine or the metal control surfaces.

Phil
Click to expand...

My guess is the Cirrus, like all other certified glass aircraft I'm aware of, has a conductive mesh in the glass layup for lightning protection. If that is the case then there isn't much difference from a metal aircraft. That's why they have all their antennas on the outside.
 
dhammer said:
My guess is the Cirrus, like all other certified glass aircraft I'm aware of, has a conductive mesh in the glass layup for lightning protection. If that is the case then there isn't much difference from a metal aircraft. That's why they have all their antennas on the outside.
Click to expand...

Exactly right. There are "windows" in the mesh for GPS antennae, but there is mesh under most of the skin.

One annoying problem we had initially (2003 model) was shadowing of the transponder antenna. Center would complain they had lost the transponder, but a few seconds of rudder to change aspect and they could see us again.
 
Bob Archer

I have not been as happy with my performance of the Bob Archer antenna and have advised others to use the whiskers on the plane. I feel like I have installed and grounded the antenna per the instructions. It works great when your close to airports and VOR's but does not appear to have as much range as an external antenna.

One of these days I am going to put an external antenna on.

Just my thoughts.
 
Having done quite a bit of exploration of this topic, I think that my conclusions are best summed up this way. If I need ultimate performance in a VHF Nav antenna, I'd go with external cat whiskers. If I am only going to mostly use it for VOR/LOC, then the Archer antenna works just fine. Personally, I have enough GPS's to see me through so long as the system is working (high probability), so the Archer suffices for me. But it is not as good as the cat whiskers. Does it need to be? That depends on how you are actually going to navigate....

Paul
 
It sounds to me like the Archer antenna works, but not as well as the external, which is kind of what I would suspect. I have not used a VOR for navigation since I put my first GPS in my current plane. The only reason to have a VOR reciever it is for the occasional VOR/LOC/ILS approach these days.
Scott, what is your primary complaint? VOR reception or ILS?

My plane is for a full IFR platform, but I am still leaning toward the archer antenna.

I assume Bob Archer is easy to get a hold of?

Bill
 
Bill.Peyton said:
It sounds to me like the Archer antenna works, but not as well as the external, which is kind of what I would suspect. I have not used a VOR for navigation since I put my first GPS in my current plane. The only reason to have a VOR reciever it is for the occasional VOR/LOC/ILS approach these days.
Scott, what is your primary complaint? VOR reception or ILS?

My plane is for a full IFR platform, but I am still leaning toward the archer antenna.

I assume Bob Archer is easy to get a hold of?

Bill
Click to expand...

Bill:

I respectfully disagree with your summary.

The Bob Archer VOR antenna works better than the external VOR antenna. In my RV-6, I can always pick up a signal on a distance VOR before I can pickup the ID code.

Been using the Bob Archer VOR over 13-years and would not use anything else. Yes I have strobe power supply, strobe, nav, and landing light in the wing tip with wires routed as close to Bob's instructions as possible.

I purchased my Bob Archer VOR antenne directly from Bob and picked them up at his house.
 
I was just commenting on the results of the replies, but I did do a search on the performance and came up with great reviews. I plan to use the Archer, and if I am not happy I can always change my mind.

What I would really like is a MB antenna to fit in the lower rudder cowl

Bill
 
Bill.Peyton said:
I was just commenting on the results of the replies, but I did do a search on the performance and came up with great reviews. I plan to use the Archer, and if I am not happy I can always change my mind.

What I would really like is a MB antenna to fit in the lower rudder cowl

Bill
Click to expand...

Put the marker beacon antenna in the engine cowl.
 
If you're looking to also include an MB antenna in combination with his wingtip VOR/ILS antenna, Bob Archer suggests either the copper foil (or just stripped coax) on the lower surface of the wingtip parallel to the edge of the wing. Don't recall the exact distance away re recommended. The VOR/ILS antenna would then be installed in the top of the wingtip. He said that doing this would result in slightly degraded performance. I had 2 of his VOR/ILS antennas and an MB also in one side. I had great reception with both (SL30 and 430W) and in actual flight I could never tell any difference in range.

Bob
 
Archer and MB

I have both a comm and nav Archer antenna. The NAV works great, the COMM not so much. I also have a stripped coax in the same tip with the NAV antenna, and that works great as well. I fly IFR and am very comfortable with NAV the antenna performance.
 
Archer

Bill, the Bob Archer antenna works perfect for VOR and ILS approaches like Paul said. I feel it lacks the range on long cross country flights but like Paul pointed out, GPS works great for that (since I have 4 GPS's I should be fine). I feel like I use to pick up VOR's at much longer range in "rental" planes than I do with this antenna.

Since I only have one NAV antenna I think I would personally just put one on the outside but I am probably about a 20% range improvement, not 100%.

I don't want to talk you into either one, just my feelings.
 
My conclusion is that each installation may result in it's own set of performance parameters, but in general the Archer antenna works just fine. It appears that some get a little better performance than others, but all get performance good enough for approaches and terminal area usage and, as a minimum, acceptable performance for enroute use.

I like the fact that its hidden and one less ugly thing to hang on the outside.

Thanks for all the feedback!
Bill
 
Comm experience

At height, my comm reception with the Archer antenna is around 25 miles, based on recent flights trying to pick up Potomac Approach and AWOS.

Doug.
 
A cuve ball question

What about the Bob Archer wingtip nav antenna with the Hotel Whiskey wingtip tanks?

I wonder if the close proximity of the aluminum in the wingtip tanks will kill the effectiveness of the antenna.

Anybody tired both?
 
I have the HWA wing tip tanks and the Archer Navs in each wingtip. I get really solid performace out of the SL30 but the 430w is lacking. I am not sure if I loose some performance do to the diplexer. My plan it to install the cat wiskers under the tailcone and hope that solves it. I see no ill effect of the tanks on the Nav antenna as they are on the bottom. I was glad it worked as I did not know of anyone at the time with the tanks and antennas, it could have been a pain to change.

The SL30 and the 430w will fly the fully coupled ILS just as well as one another but the range in not there on the 430. I plan to swap the antenna first to see if it just a bad connection as I would expect the 430 to be superior. Not sure if that is the right assumption.
 
TroyBranch said:
I would expect the 430 to be superior. Not sure if that is the right assumption.
Click to expand...

My experience has been that the SL30 is just a better VOR nav radio than the 430. I have used pre-waas 430s in several airplanes, and the SL30 in my RV-8 has always performed better for VOR navigation than the certified airplanes I also fly.

I should point out that the 430 is -way- better for flying WAAS approaches :)
 
I was told.....

I was told that 2 Bob Archer VOR antennas (one in each wingtip) work better than one.

The theory is that they work together and enhance the reception.

I am not a radio guy, so hopefully someone who is can re-explain the phenomena?
 
GAHco said:
I was told that 2 Bob Archer VOR antennas (one in each wingtip) work better than one.

The theory is that they work together and enhance the reception.

I am not a radio guy, so hopefully someone who is can re-explain the phenomena?
Click to expand...


NEGATIVE. IF the two signals are in PHASE, they cancel each other out. DO NOT connect two antennae to one radio.
 
Did not and will not.

RV6_flyer said:
NEGATIVE. IF the two signals are in PHASE, they cancel each other out. DO NOT connect two antennae to one radio.
Click to expand...

Did not and will not. Having the antennas in both wingtips as individuals is supposed to be better, from what I was told, I will try to find out why.
 
GAHco said:
Did not and will not. Having the antennas in both wingtips as individuals is supposed to be better, from what I was told, I will try to find out why.
Click to expand...

A single antenna for each radio works best. When there is one antenna, a splitter, and two NAV radios, the best signal you can get is 1/2 signal strength at each radio. That is assuming the splitter has no loss. Splitting the signal reduces the signal 3 dB. 3 dB drop is 1/2 power.
 
All clear!

RV6_flyer said:
A single antenna for each radio works best. When there is one antenna, a splitter, and two NAV radios, the best signal you can get is 1/2 signal strength at each radio. That is assuming the splitter has no loss. Splitting the signal reduces the signal 3 dB. 3 dB drop is 1/2 power.
Click to expand...

Like your tag line say's

"I must have read the newspaper:confused:= misinformed"

I do know what I have will work, thats the good news!

I appreciate the insightful input:cool:
 
RV6_flyer said:
NEGATIVE. IF the two signals are in PHASE, they cancel each other out. DO NOT connect two antennae to one radio.
Click to expand...

With our ~7.5m wingspan, if the antennas were in free space and at the wingtips, you'd have about 3 and 1/8 lambda spacing. Here is a free-space plot of two antennas spaced out by 3.125 wavelengths. Up in the plot would be forward in the aircraft.


xcqafa.jpg


Yes, very 'lobey' but not unusable. BUT! Its not so simple with antennae on a small aircraft. The whole aircraft is part of the antenna. I don't have an EM model for any aircraft or the Archer antennas but I'd expect the pattern to be somewhat complicated. My gut feel is that the nulls won't be as deep, and the peaks will be wider, since you have two antennas that are effectively much closer together (basically a co-linear antenna array), using the big horizontal wings as elements. The consequence of moving charges in one area (the antenna) is that you're 'pushing' against charges elsewhere (the aircraft). I'd rely on real experience, and if they say it helps, then it probably does help to use two antennas. Anyone out there using two archers that can chime in?

Also, if two signals are in phase at a given point in space, they add, not subtract. If they were 180 degrees out of phase, then they would subtract at that point. The datasheet for the Comant CI 5120 splitter, for example, suggests to me that it is a transformer type coupler, which has 180? outputs, instead of equal-split 0? (in-phase) outputs as a resistive divider would have. (I might be totally wrong on the Comant, though).

A single antenna for each radio works best. When there is one antenna, a splitter, and two NAV radios, the best signal you can get is 1/2 signal strength at each radio. That is assuming the splitter has no loss. Splitting the signal reduces the signal 3 dB. 3 dB drop is 1/2 power.
Click to expand...
Agreed. But if you find you have bad coverage dropouts, having some signal at all angles is better than having no signal at some angles.
 
Interesting post, Jeff

It makes sense, too. Last year while flying to Panama City, Fl., I tuned to the Marianna, Fl. VOR and the SL-30 caught it about 85 miles away, on the Bob Archer antenna in the right wing. The 430W caught it about the same distance with its cat's whisker mounted on the rear, lower fuselage.

I was impressed with the Archer antenna's distant reception in my -10 with much longer wings than the 2 seaters.

Best,
 
Bob Archer Instructions are interesting; a portion:

"A note of caution : the same noted antenna guru as noted above recommends connecting two wing tip antennas together through a two set coupler and then dividing the signal again through another coupler to two receivers in order to attain better coverage all the way around the aircraft. Though this sounds like a logical thing to do it is very poor antenna practice. Unless you REALLY know what you are doing I would say NEVER connect two antennas together in a way that would sum the signals. Because of the distance between the wing tips as the aircraft rotates about its vertical axis the distance from the antennas to the station will change causing the signal to arrive at the antennas at different times. There will therefore be times when the signals arrive at the antennas with zero difference in time and are then said to be in phase and the signals will add, but there will be angles where the signals will arrive at times when the signals are a half a wave different and they will then be 180 degrees out of phase and they will add negatively and there will be no net signal. The radiation pattern will then look very much like the petals of a daisy"
 
What I'm advocating for is experimentation. I believe that one VHF antenna (or one per radio) properly installed, should provide good performance due to the aircraft acting as part of the antenna. But, if you find the performance lacking, there is no reason to say 'never do it this way'. Rather, experiment, take good notes, and find out what works best for you. With the RV series, what works best for one person should work well for others. For the record, I believe that one or two antennas hooked simulataneously to two radios won't be the best solution due to mentioned inefficiency. That doesn't mean you can't try it.

I'll work on a model for the RV series and report back to the group on both COM and NAV antenna modelling. This will take some time, and I'll start a new thread once its ready, so as to not hijack this one any more.

Hmmm... data for notes/comparison: Perhaps useful data for comparison would be to find a ground station and determine the fade out distance vs aircraft heading. This could be done by flying a coarse grid over the volume of coverage of the station -- essentially a SAR radio location pattern. Use GPS to note where signal was lost. This will give you a good indicator of relative performance between configurations on your own aircraft and those of other aircraft using the same ground station for comparison.
 
Bill.Peyton said:
I was just commenting on the results of the replies, but I did do a search on the performance and came up with great reviews. I plan to use the Archer, and if I am not happy I can always change my mind.

What I would really like is a MB antenna to fit in the lower rudder cowl

Bill
Click to expand...

Why waste time and money on a MB antenna? The FAA is decommissioning virtually all of the marker beacons except inner markers for Cat II and III approaches. I don't expect anyone is trying for Cat II approval of their -10.
Perhaps different in other countries, just like ADF.
 
I did not realize that the MBs were being decomissioned. I think the easiest solution, since I already have the 8000b w/mb, is to use a strip antenna in the wingtip with the NAV antenna. A simple dipole should do the trick.
Bill
 
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