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DIY Archer plans

TASEsq

Well Known Member
Patron
Has anyone built an archer antenna themselves? Shipping from the states is terrible at the moment.

Some specific questions:
1. Does the thickness of the sheet matter? I was thinking of mounting it on an angle riveted to the wingtip, and 0.025” seems pretty light weight and fragile (when the wingtip comes off).

2. I assume anything non conductive can be used an the insulator? (Like fibreglass or thin nylon etc?)

3. If I wanted it to be wider (wingspan wise) to reach to the outside of the wingtip fibreglass tip (this is on a -14) is it just a matter of scaling up all of the dimensions? (Including the size of the triangle and width of the strips?). Or does the triangle need to remain the same size and I can just extend the spanwise arm?

4. Am I correct that the shield of the coax needs to connect using brass hardware so it is grounded to the part attached to the wing rib? And the centre of the coax needs to connect to the small strip which is not electrically connected to anything?

Sorry if these are basic questions - all I really have to go on is the image on page 13-16.

Unfortunately I don’t have a lot of clues about antennae - I’ve read the aero electric connection but I’m more confused than enlightened.
 

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I built one exactly to this plan and am getting 80 m. range at 5,000'. Also used fiberglass for the small strip. .025" is fine. Easy peasy.

Michel
 
This is something that I have thought of doing for over 20-years. Since I knew Bob Archer and did not live far away from him, I purchased two of his nav antennae from him for $20 USD each. That was 30-years ago. The insulator material has been the part that I had the most concern over. My understanding is that it created a capacitance between the two pieces of metal and that was the secret to make the antenna work.

Good to know that fiberglass worked. May need to attempt to make my own for the RV-8 build. I did install two Archer antennae in my RV-6. One is used as an FM car radio antenna and the other for the SL-30 nav and glideslope. Typically can pick up a VOR 80 Nm at 5,000' just like Michel.
 
Hi Trent -

Some answers to your questions -

1. Material thickness does make a little difference in antenna performance. I used 0.025" and glued some foam to the outboard corners to protect them in the wingtip - works fine and should last a long time. You can also find some alternative mounting solutions on VAF.

2 If possible, use bakelite with the dimensions specified in the drawing. Although it does act as an insulator, it's actually there to be a capacitor that matches the antenna to your coax line and its dimensions are adjusted to do just that. If bakelite isn't available you can't use just any insulator, but fiberglass should work although you may need to adjust the thickness. This is more important if you plan to use the antenna for transmitting.

3. The total length of the antenna and the length of the individual "arm" sections are important and you shouldn't scale them - the antenna won't work as well. You may need to shorten the aft part of the "arm" to tune it for VHF.

4. You're correct about connecting the coax shield, doing that grounds it to the rib.

Do you know any ham radio operators? If you do, ask them if they have an antenna analyzer and can help you adjust the fiberglass thickness and antenna length. It's easier to do than it is to describe!

A couple of links that might help -

https://mightyrv.com/?p=4091 - my homebrew Archer antenna
http://www.vansairforce.net/articles/vorwingtipantenna/wingtip_vor_antenna.htm - instructions on rolling your own Archer antenna

HTH

Dave
 
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Using an Archer antenna for VOR/GS is overkill and unnecessarily complicated for the task. A capacitively coupled antenna is not necessary for receiving a signal. A simple homemade bent whip antenna attached to the wingtip rib can be made from a BNC bulkhead connector soldered to a piece of welding wire. Works great. $60 NanoVNA can be used to tune it.
 
My opinion

I believe for receive only, using bakelite, fiberglass or nylon should be adequate; the differences in their electric properties probably doesnt matter. But the thickness is what really matters. But as others have said, this is receive only, so things not as critical. i think the lengths are the most critical. JMHO.

I just went ahead and bought mine, because it was one less thing I had to make. (and I prefer not to play with arcy sparky stuff, this hobby is suppose to be fun)
 
I’ve made many of these antennas. I do modify them to take advantage of the entire wingtip width by lengthening the arm that extends out into the wingtip as much as possible, then shortening the arm that runs aft to bring the antenna back into resonance. I typically use fiberglass for the Gamma match capacitor.

Some thoughts:
- I recommend moving the antenna aft on the rib to get it further away from the NAV/Strobes.
- I recommend not running NAV/Strobe or LL wire on the back of the antenna as suggested in the Archer instructions.
- Changing dimension as I describe moves the arm further away from the rib. For such quarter wave antennas most “work” is done by the first third of length from the feed point. The rest of the antenna brings it into resonance. Making this arm longer helps antenna performance. But keep the Gamma match “triangle” dimensions constant.
- I mount the antenna onto a piece of 0.032” angle and that angle is attached to the end rib with a couple of screws. The wingtip then just goes over the antenna.

Regardless if you buy or make this antenna, you need to turn it, both for resonance frequency (the overall length) and for impedance matching to the coax (the Gamma match). The Gamma match is adjusted by increasing/decreasing the insulator overlapping conductor or by increasing/decreasing the insulator thickness. None of this can be done without an antenna analyzer. If you don’t have a ham in the area to help, go in with you local EAA chapter members to buy one as a shared tool. It is a very good tool to check out any antenna install. Here is a standard one:
https://www.dxengineering.com/parts/mfj-259d

Carl
83-E65357-0601-482-D-A6-A0-0-C7-D57595-C53.jpg
 
Trent
#4 Do NOT use brass hardware. Brass and aluminum create a battery. You would be asking for corrosion problems. Best to use Cad plated steel hardware. [No, stainless steel hardware is not better, corrosion wise]

Charlie
 
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Hi All,

Thanks for all the help.

I will see if i can borrow an analyser. It looks fairly straight forward:
https://youtu.be/aBtYlL-OLoE

Do I have to analyse it with the full run of coax to the panel? Or would it be ok to get it resonating properly at say 113mhz using just the coax from the antenna to the wing root? (As the fuselage doesn’t exist yet )

To summarise everyone’s suggestions:
1. Ground a piece of angle to the wing rib with screws / nutplates (I have some j channel like Carl used - great idea)
2. Keep the gamma match triangle dimensions the same (5”) as well as the thickness of the insulator material.
3. Extend the spanwise arm to help it reach the outer parts of the wingtip and reduce the length of the chord wise arm.
4. Use steel hardware to connect the shield to the ground side and nylon (with any type of nuts I assume) on the capacitor.
5. Use an analyser to tune.

A question - say I was going for 113 but the analyser showed it resonating at 120mhz. Which way would you go with the chord wise arm? Shorter or longer? Similarly, if the impedance was say 55ohms would you make the insulator shorter or longer?

@carl - is yours in a rv14? If so, would you know the dimensions of the 2 arms you used and also the length of the insulator by any chance?
 
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Trent.

I made wingtip antennas for RV-8A, 8, 10 and a 14. The dimensions are whatever I could get out into the wingtip.

If you end up with the resonant frequency too high, you trailing element is too short. I suggest starting with it a little long and trim to the desired frequency (in the middle of the VOR band, around 113mhz).

This is an iterative process. Trim the trailing element to get close, then tune the gamma match to get the lowest SWR on the analyzer. Repeat as needed. This typically takes just a few minutes.

You can have a pigtail on the antenna to connect to the analyzer to do this or do it at the end of the coax run. The reading will be a little different but way in the grass for what we need.

One note - I add a piece of piece of 3/8" split nylon conduit on the outboard edge of the trailing element as something to keep the antenna from rubbing against the inside of the wingtip. I attach with small zip ties into small holes in the aluminum. A few dabs of RTV would work just as well.

Carl
 
108-137mhz

Carl, does that cover the VOR/LOC range? Or all the aviation bands [Com, Nav, GPS, ELT, etc] ? I ask, because Bob suggested getting your EAA Chapter to buy an analyzer. I need to know what specs the analyzer needs to check all aviation antennas. Sorry I didn't specify that the first time.

Charlie
 
Carl, does that cover the VOR/LOC range? Or all the aviation bands [Com, Nav, GPS, ELT, etc] ? I ask, because Bob suggested getting your EAA Chapter to buy an analyzer. I need to know what specs the analyzer needs to check all aviation antennas. Sorry I didn't specify that the first time.

Charlie

All the VHF bands, and HF if you do that in your plane.

The one I listed will do everything you need. Note, this is an antenna analyzer, not an SWR bridge.
https://www.dxengineering.com/parts/mfj-259d

For this NAV antenna the VOR/LOC band is 108-118mhz.

Carl
 
This is an iterative process. Trim the trailing element to get close, then tune the gamma match to get the lowest SWR on the analyzer. Repeat as needed. This typically takes just a few minutes.

Thanks Carl,

I’m definitely going to give this a go if I can get my hands on an analyser.

I’ll extend the spanwise arm into the wingtip as far as I can, and I’ll make the chordwise arm long. I’ll trim it short to get it close to 113 using the analyser.

I see on spruce 2.0:1 is listed as the SWR for a purchased antenna. If mine was higher than this, would I shorten the Bakelite? Is it worth making this also a little longer at the start?
 
SNIP

I see on spruce 2.0:1 is listed as the SWR for a purchased antenna. If mine was higher than this, would I shorten the Bakelite? Is it worth making this also a little longer at the start?

After the antenna length is about right, adjust the Gamma match for lowest SWR on the analyzer. You can experiment by just loosening the screw holding the Bakelite between the two pieces of aluminum as this simulates a thicker insulator (less capacitance). You can also experiment with changing the aluminum pieces of the capacitor sandwich (shorter is less capacitance, longer is more)

All this is ~$1 of material. Play around with it.

Carl
 
Interesting.

So the Bakelite length is not really that important? It’s the length of the aluminium piece on top?

Thank you for your advice.
 
Does the long arm need to be parallel to the ground plane arm? (The most outboard arm running fore/aft parallel to the rib?)
 
Does the long arm need to be parallel to the ground plane arm? (The most outboard arm running fore/aft parallel to the rib?)

The ‘ground plane arm’ should be electrically connected (screws, rivets) to the end rib, which is the ‘ground plane’. By your description the outboard arm is parallel to the ground plane already. Whether the ‘arm’ is tilted up or down on the rib doesn’t matter.
 
The ‘ground plane arm’ should be electrically connected (screws, rivets) to the end rib, which is the ‘ground plane’. By your description the outboard arm is parallel to the ground plane already. Whether the ‘arm’ is tilted up or down on the rib doesn’t matter.

Thanks - I guess what I meant was: from a top view (horizontal antenna), does the outboard most radiating arm need to be parallel to the end rib, or can it follow the contour of the fibreglass tip (which gets wider as it moves aft)?

Hard to describe sorry! You can see what I mean by the shape of the cardboard template I’ve been working on.
 

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Thanks - I guess what I meant was: from a top view (horizontal antenna), does the outboard most radiating arm need to be parallel to the end rib, or can it follow the contour of the fibreglass tip (which gets wider as it moves aft)?

Hard to describe sorry! You can see what I mean by the shape of the cardboard template I’ve been working on.

My Archer antennae are on the TOP of the old style fiberglass wingtip and work extremely well. What I see in your photo will work just as well. It does not matter if it were along the bottom, middle, or top of the wing. A few degrees up or down makes little difference. Extending out from the last outboard rib and grounded / connected to the airframe rib or skin will work. My installation uses nutplates riveted to the fiberglass that is connected to the sheetmetal airplane with screws that hold the wingtip on.
 
This is what I mean by “not parallel”
 

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Well, didn’t take me too long to get it built tonight.

I left the top plate of the capacitor and the trailing arm long to trim them to size once I can find someone with an antenna analyser.

Apart from some nutplates to add to the last rib was a fun little project.
 

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Spent 3 hours with a very hospitable gentleman from my local HAM radio club today. After a bit of an antenna theory lesson (at least 10% even stuck) we moved on analysing the antenna.

I had to do it attached to the wing in the cradle so we moved the assembly away from the walls as best we could into the centre of the room. Initially it was resonating at 88Mhz and we ended up trimming off about 12”. I had left it waaay long and we knew we would need to trim it. In the end it came out right at 28.5” long - same as the plans indicated.

We got it resonating at 111Mhz (we think when removed from the room “ground plane” it will resonate a bit higher, but if it doesn’t 111 is a good number for the ILS). The SWR was approx 1.5 at this frequency.

At the 2 SWR line we get a bandwidth from 108-118MHz - spot on I think.

I didn’t have to trim the capacitor plate at all - which was weird because I made it slightly longer. I did use fibreglass not Bakelite tho, and it was 0.040 not 0.032 as per the plans, so maybe we fluked it. He did another test and showed the impedance was almost exactly 50ohms.

Anyway it’s all in theory - will be years before I fly it. But it was a great exercise anyway! Learned stacks - but still don’t understand how the gamma match capacitor works #pureeffinmagic.
 

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Here is the plot of the analysis - if anyone knows what the second graph means please elaborate! :)

https://drive.google.com/file/d/1h5q8FDgk_dK6kqbzoAPvIboYRyvMmJ9I/view?usp=drivesdk
OK, elaboration follows: ;-)

The instrument your Ham friend used looks like a somewhat upscale NanoVNA, good device for this application.

The three traces of the 2nd plot look like impedance, resistance, reactance.
Impedance is the vector sum of the reactance(not good) and resistance(good).

This is the basic info from which VSWR is calculated. This resistance BTW is not ohmic resistance but rather the effect of RF power radiated to or from the antenna. (Antennas are completely reciprocal.)
Edit add:
The lower trace in the 2nd plot I believe, is the reactance and from what I see it is capacitive (-ohms) across the band, so increasing the series capacitance will tend to reduce that reactance and drop the VSWR a tad. Sounds backward, I know, but increasing the amount of series capacitance will lower the cap reactance. Antenna length is also in there, so 2 variables.

The glass composite wingtip when installed will cause some dielectric loading of the antenna which may tend to lower the tuning a bit. I wonder if some one has already measured for any significant effect? In any case, your numbers are good to go. Any improvement from your less than 2.0 VSWR would be hard to detect.
Good work,

Ron
 
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I’ll add a simple bit too. The reason your ‘too long’ capacitor needed no adjustment is because it was also 20% ‘too thick’ (spacing between plates). Increasing spacing decreases capacitance, increasing plate area increases it. You lucked out!
 
I’ll add a simple bit too. The reason your ‘too long’ capacitor needed no adjustment is because it was also 20% ‘too thick’ (spacing between plates). Increasing spacing decreases capacitance, increasing plate area increases it. You lucked out!

Sounds like i did!!

Better to be lucky than good.

When we were seeing 1.5-2 on the VSWR we were surprised - but it made it an easy task.

OK, elaboration follows: ;-)
Thank you!

Up in the very top right corner i noticed a tiny R X [Z] - the green is the X, which is reactance - you were right. All a bit of a mystery to me how the capacitor works - a little bit of magic i think.

Shame it will be a few years before i can try the antenna out but it was a fun project - learnt a lot about antennas.
 
All a bit of a mystery to me how the capacitor works - a little bit of magic i think.
.

The function of the capacitor is to change the relative phase between the current and voltage, to match the phase difference found in the standing waves in the antenna.
 
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