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Bob archer antenna

Denok

Active Member
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First, I hate having things sticking out of my 7 so I thought a Bob Archer wingtip com antenna would do the trick. Turns out it preforms ok when the wingtip is off and I use a bonding strap to ground the antenna to the aircraft but when I install the windtip with all screws I see gremlins everywhere. My Dynon HTX engine monitoring quits and all engine parameters go wild, a real mess. Hints anyone?
 
I might be wrong... and it happens a lot...

I believe is you are talking about the NAV antenna, it?s made so that the screws and nut plates should be the same ones that connect the plane to the wingtip (so hard connected and not grounding strap). It?s made so that it it actually turns the aircraft into the directional of one side, and the wingtip is the other side.

Maybe with a try of reinstalling.

X
 
1. As mentioned by others, the Archer has a "ground leg" which should be electrically tied to the end rib of the wing by as short a route as possible. Some have riveted that leg directly to the rib, or an angle on the rib; design calls for that ground leg to be under the wingtip screws (make sure there is no paint under the screws - you want a short electrical path to the rib. If mounted correctly I'm not sure how the tip mounting screws could subsequently make contact with the radiating part of the antenna.
2. Mount the ground leg as high as you can, and bend the leading edge down around 30 deg or so, as far as the tip will allow, to get as much vertical polarization as possible. (You can also mount the ground leg near the bottom of the rib, and bend the antenna up, and hold it up with fiberglass.). This is for the com antenna; for the nav version, just lay it flat (you want horizontal polarization for the nav).

Any chance of a photo? worth a 1000 words.
 
First, I hate having things sticking out of my 7 so I thought a Bob Archer wingtip com antenna would do the trick. Turns out it preforms ok when the wingtip is off and I use a bonding strap to ground the antenna to the aircraft but when I install the windtip with all screws I see gremlins everywhere. My Dynon HTX engine monitoring quits and all engine parameters go wild, a real mess. Hints anyone?
I'm a simple man so let me ask these dumb questions. The antenna is for NAV? Where does the coaxial go, a NAV unit (VOR/LOC/GS) somewhat separate of the Dynon. What does NAV have to do with the engine monitoring side of your glass display except provide some basic VOR/LOC/GS data Left/Right/Above-Below GS ? Just asking.

Even if it is a COM antenna is attached to a COM transceiver, I don't see the connection (no pun int ended) between the antenna and your Engine monitoring function.
 
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Even if it is a COM antenna is attached to a COM transceiver, I don't see the connection (no pun int ended) between the antenna and your Engine monitoring function.

This is not an uncommon symptom of RF energy radiating where it's not wanted. What happens is the antenna or antenna coax is screwed up. As a result the RF is reflected back up the coax along the outside of the shield where, like an antenna, it radiates. If enough is picked up by the EGT, oil sensor, etc., wires, trouble follows. Curiously enough, old fashioned current gauges were pretty immune to this. Not so modern electronics.
 
The Archer COM antenns has never been considered to be a very good performer in our RVs due to the wingtip shape. The NAV antenna on the other hand is a good option.

I think at some point you will decide to mount a conventional COM antenna....
 
Just checking the facts...

The Archer COM antenns has never been considered to be a very good performer in our RVs due to the wingtip shape. The NAV antenna on the other hand is a good option.

I think at some point you will decide to mount a conventional COM antenna....

Not really sure that this comment is correct. I have a Bob Archer and from my experience it is very good. I do know that users who have made their own antenna from plans and have had issues. I do know that Bob was a Communications specialist and custom tuned each antenna before sending out. My understanding was that the originals operated to a very high standard.

That being said, for my own interest and comfort, do you have any details, reference material or statistics to support the comment "The Archer COM antenns has never been considered to be a very good performer"?
 
That being said, for my own interest and comfort, do you have any details, reference material or statistics to support the comment "The Archer COM antenns has never been considered to be a very good performer"?

1. There are some poor installations, that of course work poorly. I’ve seen a photo of a ‘poor performer’ that was installed upside down-the ground leg was out in the wing tip, the radiator up against the rib!!
2. I’ve seen some home brews that don’t understand and/or fail to replicate the matching capacitor.
3. Some don’t get it that you need to maximize the vertical distance of the leading edge, to maximize the vertical polarization. This is really the main issue. In some not well controlled tests (different receivers/com transmitters) I’d say my Archer has 75% of the useful range of my belly whip. Is this ‘not a good performer’? Opinions vary.
 
This is not an uncommon symptom of RF energy radiating where it's not wanted. What happens is the antenna or antenna coax is screwed up. As a result the RF is reflected back up the coax along the outside of the shield where, like an antenna, it radiates. If enough is picked up by the EGT, oil sensor, etc., wires, trouble follows. Curiously enough, old fashioned current gauges were pretty immune to this. Not so modern electronics.
Thanks Bob...initially I was going on this was a NAV antenna and there were no issues until the wing tip was installed.... there was no PTT or transmitting involved like the other thread.

When I say it should not matter if it was COM antenna, it shouldn't especially if not transmitting (which was not mentioned).. However you are right RF leaking in the cabin and/or poor grounds/shielding might cause issues with flight instruments or autopilot.
 
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Not really sure that this comment is correct. I have a Bob Archer and from my experience it is very good. I do know that users who have made their own antenna from plans and have had issues. I do know that Bob was a Communications specialist and custom tuned each antenna before sending out. My understanding was that the originals operated to a very high standard.

That being said, for my own interest and comfort, do you have any details, reference material or statistics to support the comment "The Archer COM antenns has never been considered to be a very good performer"?

My statement is based on nearly twenty years of reports by RVers who have installed the Archer COM antenna in RV wingtips. The issue isn't the RF properties of the antenna rather the consequences of a primarily horizontal orientation in the RV wingtip.

(My observation is based on installations in two-place RVs.....perhaps the RV-10 wingtip is a different scenario?)

COM antennae are designed for vertical polarization and the RV wingtip doesn't accommodate the Archer in a vertical orientation. This results in performance that is less than a properly installed 'whip' COM antenna. There have also been reports of significant 'shadowing' (not sure if that is a technical term) supposedly from the proximity of the antenna to the metal wing. The Archer COM antenna installed in a composite aircraft that allows vertical orientation would most likely be a good performer.

The Archer NAV antenna in my RV-6 wingtip works very nicely because NAV is designed for horizontal polarization which the RV wing tip accommodates well. There is some shadowing at the fringes of coverage range but overall it works well in my RV. But for me it's a moot point since I don't fly IFR and no longer use VOR navigation. :)
 
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I have made the Archer antenna for most of my RV builds. In my experience, they perform acceptably as a NAV antenna when navigating with VORs. Where they shine IMHO is as a LOC/GS antenna. Rock solid. I am sure that has something to do with being close to the station and the airplane pointing directly at the transmitter. If that's all you use it for, it can't be beat.

One of my homemade versions is installed into our East Coast RV-14A, N914VA. Worked great while I had the airplane. Might ask our rep, Zack for his experience.
 
This is not an uncommon symptom of RF energy radiating where it's not wanted. What happens is the antenna or antenna coax is screwed up. As a result the RF is reflected back up the coax along the outside of the shield where, like an antenna, it radiates. If enough is picked up by the EGT, oil sensor, etc., wires, trouble follows. Curiously enough, old fashioned current gauges were pretty immune to this. Not so modern electronics.

I believe this is precisely what is happening. Sorry for not mentionning it before but my problem is with a right side com antenna and yes it only happens when PTT is engaged. The install has changed since these pictures were taken as the inboard part of the antenna is now installed on the top part of the wingtip.

https://photos.app.goo.gl/TaoYR2oZ7ALdenzp7
 
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(My observation is based on installations in two-place RVs.....perhaps the RV-10 wingtip is a different scenario?)
:)

I believe the -10 (and -14) wings are thicker than other RVs, allowing more vertical throw. They also are wide enough fore-aft to allow you to mount the leading edge of the antenna radiator at that thickest point of the wing - NOT full forward - again, giving you as much vertical polarization as possible. As I said, it is not as good as an external antenna but for my use - ATIS and backup - it works for me.
 
See this note from the instructions:

"It has recently been brought to my attention that some folks have experienced problems with RF interference with the late model panel devices. These new devices operate on lower voltages and when the RF energy gets on the bus wires it can travel back to the panel area and cause all kinds of problems. SO, It is recommended that the cable used for the transmitted signals be the double shielded type and the cables should be run as far from Bus wires as possible.
The double shielded types are; RG55, RG142,RG213 and RG400.
These are commonly available types but there are others."

B
 
On the photos it is clear you have NAV/Strobe wire running along the antenna arm. Don?t do that.

Carl

Hmm -- The drawings suggest that this is correct - and cable clamps are included at this location to facilitate this routing.

However, I agree - keep all the wires as far as possible from the radiator (small piece of aluminum on top of the fiberglass) - and route the RG-400 back and away from the radiator.

B
 
Hi Denis
I got the photos you emailed, thanks- the antenna side coax connection looks good. A few questions, still trying to figure out what is going on with your installation:

1. Did you use the single point ground forest of tabs on the firewall?
2. Is your wing painted?

Sam
 
Hi Denis
I got the photos you emailed, thanks- the antenna side coax connection looks good. A few questions, still trying to figure out what is going on with your installation:

1. Did you use the single point ground forest of tabs on the firewall?
2. Is your wing painted?

Sam
Sam,
No. Equipment is grounded at multiple locations and yes, the aircraft is painted and screws make good contact.
 
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It is as per instructions.

The instructions are for when you cannot avoid running wires across the antenna, use the provided clamps. But bypassing the antenna completely, by a foot or more, is better.
The first part of the radiating element (the piece that the feed arm attaches to) appears to be horizontal. For a com you have to bend the entire antenna up or down (depending if the ground leg is riveted low or high) to get as much vertical component in the first part of the antenna (the part that attaches to ground leg) as possible. Otherwise the polarization will be all horizontal, you need vertical.
 
Noted difference


Hi, From looking at this photo, against my installation per the original installation details, I noticed that this is also attached to a Aluminium strip along the bottom of the Wing Tip.

Now I am not sure of whether this would have an impact, however, mine was not connected to any other metal along that strip other than the aircraft via the screws.

As I said, not sure of the impact, just something I noticed and have no idea if that would affect the way in which a signal is then translated.
 
Hi, From looking at this photo, against my installation per the original installation details, I noticed that this is also attached to a Aluminium strip along the bottom of the Wing Tip.

Now I am not sure of whether this would have an impact, however, mine was not connected to any other metal along that strip other than the aircraft via the screws.

As I said, not sure of the impact, just something I noticed and have no idea if that would affect the way in which a signal is then translated.

This should be fine. It will just act as part of the wing skin. What?s important is a good electrical contact from the antenna ground leg to the wing skin to the rib.
 
a finding

I have a Archer antenna in my right wing tip and a marker beacon antenna (a length of stripped coax). I installed my GPS antenna in the right wing tip also and used the coax from my marker beacon and left the marker beacon wire in place disconnected. I noticed my CDI would not capture the ILS as well and VOR performance was diminished. I removed the marker beacon antenna today and low and behold my ILS is smoother than ever.
 
As an update to my antenna problems, I have modified the installation in the windtip to reflect the Sportcraft antennas instructions in order to increase the verticality of the antenna. I have also improved the grounding of the antenna but to no avail. Engine monitoring still goes haywire when PTT is depressed.
see: https://photos.app.goo.gl/TaoYR2oZ7ALdenzp7

One thing that cought my eye in the installation instructions is this (Bob speaking:) )

"It has recently been brought to my attention that some folks have experienced problems with RF interference with trhe late model panel devices. These new devices operate on lower voltages and when the RF energy gets on the bus wires it can travel back to the panel area and cause all kinds of problems. SO, It is recommended that the cable used for the transmitted signals be the double shielded type and the cables should be run as far from Bus wires as possible."
Is return energy normal in well shielded cable?
I guess rerouting the RG400 will need to be looked into. Any (other) ideas?
 
SNIP... Is return energy normal in well shielded cable? I guess rerouting the RG400 will need to be looked into. Any (other) ideas?[/QUOTE said:
?Return Energy? is a problem if the path of least resistance for the RF energy is not the antenna.

What I do:
- Assume the antenna is not resonant at the desired frequency unless you verified it so. Simple task with an antenna analyzer.
- Assume the antenna lead and connectors are an issue unless you verified them good. Again a simple task with an antenna analyzer.
- NEVER run the nav/strobe wires along the antenna like the instructions say. Move the antenna a little aft a little on the wing root to gain some separation. A few inches can make a world of difference. I suspect this is a common problem with both RF energy going back to the panel and LED noise getting into the radio.
- Assuming you are using modern LED Nav/strobes, feed these strobes via a three #20 conductor shielded wire (leads are power for the Nav, strobe and a strobe sync line, the shield is the ground lead).
- The RG-400 antenna coax can be run in the same bundle as the other wing wires. It will not typically be an issue unless there is a bigger problem with the antenna itself.

Bob Archer type antennas are a good design - I?ve made several (but modified to use the full width of the wing tip). I note however that to get them to work well you should to have an antenna analyzer. Each EAA chapter should have one of these in their shared tool bin: https://www.dxengineering.com/searc...30-mhz-plus-2200-meter-antenna-swr-analyzers?
autoview=SKU&sortby=Default&sortorder=Default

Carl
 
+1 on Carl?s comments. Look hard at the connectors, they?re surprisingly easy to screw up (ask me how I know!).
1. Is there a sharp bend in the coax, about 3? from the antenna connection? Maybe just the photo angle.
2. I bent mine a little differently. I drew a line right down the middle of the ground leg (the long way), clamped the outboard side plus the antenna, then bent the inboard half of the ground leg (with nutplates). Your bend location cost a bit of structural rigidity. In your photos, I can see that (1) you ?lost? the first inch of the radiator - it is horizontal. This is where the max current flows, and where the max radiation comes from. Probably not a big deal. But (2) I can see that the ?feed leg? got twisted a bit. The aluminum is lifted up a bit under the ground connection. (Not a big deal). But I cannot see under the capacitor, a few inches further up the feed leg. If it is also twisted-and has separated at all from the aluminum-bakelite-aluminum sandwich, the capacitance will be changed. That is important.
As Carl said, move the antenna back so the leading edge is near the thickest part of the wing. Then you?ll have the max possible vertical component. Re-route wires to the lights, inside the end rib if possible. Then run them straight across to the lights, well forward of the antenna.
 
Ferrites

After reading Jim Weir, I'm thinking ferrite coils. I would try to slip one over the cable where it leaves the wing tip. Probably a lot cheaper than double-shielded cable.

Just a thought.

Finn
 
Dynon known fault

On a Rv-7 I tested a couple of years ago the same thing occurred. When transmitting the engine readings would go silly.
Turned out it was an early Dynon skyview fault.
The owner swapped a engine monitor box for a later version and all was well.
So possibly nothing to do with the antenna

Regards

Peter
 
On a Rv-7 I tested a couple of years ago the same thing occurred. When transmitting the engine readings would go silly.
Turned out it was an early Dynon skyview fault.
The owner swapped a engine monitor box for a later version and all was well.
So possibly nothing to do with the antenna.

Regards

Peter
This is a known issue with "older" DYNON EMS modules and there are two ways to correct it.

1 - Install a Capacitive Filter like this one on the EMS module plug.

2 - Return the module to DYNON and they will add the additional capacitive filtering inside the module.

I had the same issue so I returned the EMS module to DYNON and they fixed the problem. You can play around with the antenna and the connections but it sounds like this is the most likely culprit.

:cool:
 
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Certainly the Dynon box is not immune to very much EMI in older versions, and I agree, the most direct solution may be to upgraded it. But there is a bit of a gotcha with the Archer installation as well, particularly for creating interference transmitting as I see it.

Most com antennas are well grounded at the base. Further, the feed is shielded by the ac skin. The antenna is outside, the feed is inside, so it is not exposed to the antenna EM field and will not have significant RF voltage on the shield. All is good.

With the Archer install, that natural isolation is not present. There are 2 potential features which need to be addressed to prevent swamping the cabin area with EMI.

It should be understood that the coax feed just may be a better transmission line externally than internally. First, the shield is much bigger and more conductive than the center wire. Second, it is operating within a metallic structure with mostly a low loss air dielectric. So, any voltage on the shield at the antenna location will be pretty much what will be present in the cabin area 15 feet away.

The first mechanism that will induce voltage/current on the shield, is proximity to the antenna. The second is the more direct voltage divider effect of a poor shield ground. An example is a recent posting of a "proper" grounded coax to an Archer antenna. The workmanship was flawless, but the ground wire was about 3 " long. A 3 inch wire has a inductance of about 5 nH which is about 4 ohms at 120 MHZ. A 10 watt transmitter produces roughly 20 volts at 1/2 amp. The result is a solid 2 volts on the shield to be conveyed efficiently to the cabin area. A similar level might be expected on the shield from a feed lurking near the antenna.

So...., my suggestion to reduce some of this badness.

Add a BNC bulkhead/feedtrough fitting on the end rib. The rib along with the fitting applied will strip any voltage from the coax shield and isolate the cable run.


The image below may explain what could cause a lot of gremlins




PoorGrd1.png



BTW, a good quality coax single shield is rated about -80db, a double shield about 100db. In the case of the single shield and a 10 watt transmitter, 2mv(0.002V) outside the shield is about it, several orders of magnitude less that the 2 volts of conducted EMI above.

Ron
 
When I first built my plane, I installed a Bob Archer antenna for both VOR and COM. Both antennas worked OK for a couple of years then all of a sudden my VM-1000 engine instrument and GPS started behaving strangely and the COM was not consistent causing the controllers sometimes unable to hear my transmissions. I could not find anything wrong but decided to replace the Bob Archer COM antenna on the wingtip with a bent COM antenna on the belly right under the passenger seat in my RV-4. Immediately everything fixed itself and my range at least doubled with better voice reception and never had trouble with the fuselage blocking reception again. I really did not notice any substantial decrease in speeds but even if I did, I would trade for the superior communications and no gremlins.

I still have the old RG-58 coax cable that was used successfully for decades in certified airplanes but notice that my ILS slope reception is sometimes week when I am more than about 7 miles from the FAF. I should try RG-400 to see if I can improve reception but have been to lazy to change it out. Has anyone else had this problem?

Cheers
 
I don't want to discourage the use of the archer antenna, particularly on the nav side by what I've posted, Dale. I hate hair sticking out on aircraft, probably more than most. Using a BNC feedthough on the end rib should reduce EMI well below the point of it not being a problem. That problem solvable.

However, the big problem using an Archer for a com antenna is still there. Polarity. A/C communication now a days are vertical polarized. FAA ground facilities used to use a kind or twisted turnstile antenna that was OK for any polarization, but I think that has mostly gone away. It is very difficult challenge to launch a vertically polarized 120 MHz signal from an object only 6 inches thick. Canting the antenna to get some vertical current as Bob Turner suggested could help, but not as much as the geometry would indicate. Much of the vertical current will be cancelled by the opposite vertical current induced in the structure, leaving very little radiated.

Re RG400 vs RG58, I see little performance advantage to the RG400 - a db or so. It is more heat tolerant, though. And if you are trapped in a space capsule with 100% oxygen, it won't make as much toxic fumes if it burns, and other advantages which may not be important to gen aviation.

I always liked the luxury, pre-GPS, of picking up the GS 40 or 50 miles out, hitting top of decent and riding it down. To do this, the GS has to be working very well. In my opinion, the surest bet would be a separate GS antenna. There are several posts on making a separate GS antenna, which isn't a big deal. Further, I have simulated the archer antenna for quite a while now, and though I don't know how accurate my model is, it does not do GS freqs too well. I know Bob Turner has said that antennas usually work pretty well on 3rd harmonic freqs, which is correct, but the Archer has a built-in matching network which can diminish this - so maybe not the best for GS distance, though many are happy with the Archer as a source for the GS.

3D of an Archer model which might be of interest..

Archer1.png


I would like to mention for those with some background in electronics, there is a great antenna tool available on Ebay, etc called a NanoVNA. I bought a Vector Network Analyzer a few year ago for the better part of a grand. But these handy little rascals are only ~50 dollars. You'll need some BNC adapters as well - and maybe some good reading glasses:). More to say. Too much thread drift.

Ron
 
Certainly the Dynon box is not immune to very much EMI in older versions, and I agree, the most direct solution may be to upgraded it. Ron
FWIW: This issue happens to the older Dynon box with every antenna on the market, not just the Archer antennas. Play with the antenna all you want but the ONLY solution, is to fix the actual problem which is the DYNON box. Dynon has done an excellent job to make sure this doesn't happen with the upgrade. Everything else said here, although correct, won't fix this particular issue.

:cool:
 
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BNC feedthrough connector

Using a BNC feedthough on the end rib should reduce EMI well below the point of it not being a problem. That problem solvable.

Ron

Thanks Ron, that was really helpful. To my surprise, I thought a BNC feedthrough connector would be a fairly simple cure but there seems to be a huge price variance. I may be looking at the wrong connector or not understanding how they work? but one such connector is

https://www.idealvac.com/Electrical-Coaxial-Feedthrough/pp/P108034

and another is

https://www.ebay.com/itm/5-pkg-King...632532?hash=item46aaf10394:g:VRsAAOSwfbxebti7

I must be missing something? thanks for your help

Dale
 
There have also been reports of significant 'shadowing' (not sure if that is a technical term) supposedly from the proximity of the antenna to the metal wing. The Archer COM antenna installed in a composite aircraft that allows vertical orientation would most likely be a good performer.

I have an Archer nav and com antenna in my Lancair. The nav antenna works well. The com antenna is in the fuselage bonded to the inside behind the baggage area. As a result I see shadowing in the direction of aircraft travel - the pilot and motor blocks the signal. Compared to the Red tail antenna from Delta pop aviation that was on our RV, the Archer antenna is marginally acceptable.


the COM was not consistent causing the controllers sometimes unable to hear my transmissions. I could not find anything wrong but decided to replace the Bob Archer COM antenna on the wingtip with a bent COM antenna on the belly right under the passenger seat in my RV-4. Immediately everything fixed itself and my range at least doubled with better voice reception and never had trouble with the fuselage blocking reception again. I really did not notice any substantial decrease in speeds but even if I did, I would trade for the superior communications and no gremlins.

This is consistent with my experience, and expect would be the same for the OP.
 
I have an Archer nav and com antenna in my Lancair. The nav antenna works well. The com antenna is in the fuselage bonded to the inside behind the baggage area. As a result I see shadowing in the direction of aircraft travel - the pilot and motor blocks the signal. Compared to the Red tail antenna from Delta pop aviation that was on our RV, the Archer antenna is marginally acceptable.
.

I have no personal experience with composite aircraft but if building one I think the only place I would locate an Archer COM antenna is in the vertical stab. But there isn't any operational reason not to use a good whip antenna unless the aircraft is designed for racing.
 
I have no personal experience with composite aircraft but if building one I think the only place I would locate an Archer COM antenna is in the vertical stab. But there isn't any operational reason not to use a good whip antenna unless the aircraft is designed for racing.

I have a whip in the vertical stab. It isn't great either; believe that is due at least in part to insufficient ground plane. At one point it suffered poor transmit range and turned out to be due to internal cable damage secondary to cable bouncing in turbulence right at antenna connector as result of a poorly secured cable.
 
I have no personal experience with composite aircraft but if building one I think the only place I would locate an Archer COM antenna is in the vertical stab. But there isn't any operational reason not to use a good whip antenna unless the aircraft is designed for racing.

I have a whip in the vertical stab. It isn't great either; believe that is due at least in part to insufficient ground plane. At one point it suffered poor transmit range and turned out to be due to internal cable damage secondary to cable bouncing in turbulence right at antenna connector as result of a poorly secured cable.

I was referring to an external whip antenna.

Yes, providing a good ground plane for a COM antenna in the vertical stab would be problematic. Maybe extend wire ground plane radials into the horiz stab? Makes an external whip look simple. :)
 
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