We’ve done some rough modeling and it looks like 15-degrees for the cone’s slant angle is optimal. A 5-inch cone height yields a theoretical 9 dB increase at 10.7 GHz, but at the high end of the band, the simulation is only showing another 3 dB. The problem seems to be with placing the cone over the plastic LNB. That gap is throwing the pattern off at 11.7 GHz.
I might be fabricating a 15-degree cone next week, or just browse around for metal funnels.
If the LNB had no plastic case, then the performance would be even better. It’s kind of a pain to shuck the case–and can be dangerous if not careful (I’ve cut myself being lazy).
Since I have to rebuild my Ground Station (a loose dog ran over my LNB and tripod), I will try to replicate your design here. Losing the plastic case seemed like a no-brainer to me. I will be careful.
The case has two parts. The beige part is fairly easy to remove with a vise and screwdriver. The white cap is the trickier part. It’s a really tight friction fit.
I think it is important that the cone get’s protection from yellow jackets/birds/snow (and loose dogs), So some type of durable enclosure. I’m still thinking of ideas.
Haven’t tried it yet. but will. Dimensions: Length 8" long, large circular end 5" diameter,
small circular end 2.5" diameter. The MK1-PLL fits loose. Needs a bit of hot glue.
I would use heavy duty aluminium foil in inside or outside. Outside should be easier. The “cone” is from an old blender. Everyone should have one of these somewhere!
I though there might be a better design. SO you have a 5 inch high cone. What are the diameters at both ends? I have fabricated a test collapsible antenna cones with 8 x 4 x 2 inch. I want to make what you’re looking at for my portable terminal. Ken
@kenbarbi Can you show pictures of your collapsible version? The cone I am describing is 5" tall with a side length of 5.13". The narrow opening of the cone is about 2.3".
@ac8dg You mean just having the cone’s opening covered, right?
Yes cover the opening, my ideas would either a rf transparent plastic or as simple as fiberglass screening.
With ultraviolet safe materials (sun-proof)
@Syed, I think perhaps the question is, what would the wider opening calculate to at 15 degrees? I believe that figures out to be pretty close to 3.50" for a side measurement of 5.13"…
Just for fun, I tried to figure out a “typical” cup size for this cone, using truncated cone formula
top 3.5", bottom 2.3"
V=1/3 * (πh(a^2+ab+b^2))
V= 1/3⋅(π⋅5.13in(1.15in^2+1.15in⋅1.75in+1.75in^2))
In the last few days since Syed made changes, I am receiving SNRs about 5 dB higher on average. I say on average because I have not dipped below an SNR of -8dB as I used to do when I might have seen SNRs of -12 dB. Ken
Here are some pictures - - extended and collapsed. Not very pretty, but I got 2 dB improvement in SNR out of it as opposed to 4 dB with my 8x4x2 inch aluminum horn.
The problem I am having making a collapsible cone is one of mechanics to get the rings to slide apart correctly. This demo is just thin paper with aluminum foil glued on the inside.
Actually from my searching on the web, I think your size might work better - - see this chart on horn design - -
Your table from that vendor must use the same modeling as @Syed . For both the models labeled as ME and SYED, the angles of the sides are very similar . The “A” panels are about 11 degrees and the “B” panels are about 15 degrees. I can’t make a good correlation with the listed frequency bands, probably because they span such a huge range (10.0-15.0 and 12.4-18.0 is huge).
@Syed @ac8dg @Konrad_Roeder @kenbarbi
Syed’s measurements and Jim’s calculations correspond almost exactly to a 16-oz styrofoam cup I saw in a grocery store this morning. I think the difference in capacity from Jim’s calculation is only because the cup maker considers the cup full at about 7/8" down from the top. I built a paper angular “form” using a 15 degree angle and applying the measurements, then compared the form to various kinds of “picnic ware” that I saw. A person could possibly apply the aluminum tape or foil to the outside of one of these and use a lid made for that size cup to complete the radome. I haven’t tried this… yet.
It may also be possible to build such a cone from used “offset printing” masters, which are thin aluminum, ship it flat, then tab it together in the field. Still playing with ideas…
There is nothing to say that the cone has to be hollow. It could have internal supports that don’t affect the rf signal. This may keep it more durable.
Ken, I would have to get a large bow compass to correctly divide the arcs (I don’t possess one any more) for a proper rendering if I were to use paper or thin metal, so that each ring was larger than the previous one. I found some disposable16-oz soft drink cups of thin plastic at the local dollar store, that approximate the 15-degree cone’s size and shape, and would likely have to take two or three of them and mark the rings, and cut them out with aviation snips (this plastic is tough to cut with regular scissors, believe it or not!), then try to apply the aluminum tape or foil. It probably can be done, just pretty tedious. However, the plastic is already in the shape you need for the rings, it would just take a little experimenting to get them sized right so they would collapse properly. One could also possibly find a collapsible plastic cup (I had one for years when in the Boy Scouts, that lasted pretty well) and just adapt the bottom to fit the lnb and wrap it with foil… pretty fast and almost always would guarantee portability…
I am currently working with my idea of using the cut open cup for a pattern on a plastic sheet, with tabs for mounting, (similar to my aluminum 8" cone) then covering the cut out part with foil, making an overlap of about 1/2 inch that would have punched holes and a thin wire laced from top to bottom to lock the shape. The whole thing could lay flat and then rolled into shape when one needs to use it.
I just happened to find a stack of 16 oz styrofoam cups in the wife’s cabinet and decided to give one a try. A little aluminum duct tape did the trick. While it is a couple db’s less than my larger hardware cloth horn, it’s performance is totally acceptable.
