Loco Antennas - Does Anybody Make a "Top Hat"?

[C855B]

Shapeways or otherwise. I was firsthand familiar with these when working in a Santa Fe radio shop since they were a very big user of the style. UP also used them for Locotrol.

Unfortunately the 1:1 version I had in a junk box was misplaced during a move 30 years ago, so I have nothing other than photos to base my own modeling on. They need to be cast or 3D modeled since a "simple" piece of tubing won't capture the bottom rim detail.

[Spades]

Do you have a picture of the antenna?  Is it not on the BLMA detail set? https://www.lombardhobby.com/Locomotive-Antenna-Stands-4-styles-p/blma92.htm

[C855B]

The BLMA fret is mostly antenna platforms, along with four each of two versions of a specific antenna type. Here's what I'm after:



The "top hat" antenna is that black cylinder-looking affair in the middle of the platform. While the casual observer may think, "Oh, I see - it looks like a top hat," that's not what it gets its name from. Internally it has a phenolic stick with a coil on it with a plate on the top, and these plates are called "hats". The cylinder thingie is just a fiberglass radome trying to keep the rain out, which I know from hard, hard experience doesn't do the job all that well.

The antenna representations on the BLMA fret are a design known as an Excaliber, and the two versions are VHF and UHF. That's not what I'm looking for, as the Excaliber design came out in the late '70s.

Anyway, I knew about the BLMA antenna platform detail set, and had checked them out for my project (UP's Locotrol-equipped SD45s circa 1970). Unfortunately none are close, so I'll have to scratch my own. In the end I may sketch the antenna for Shapeways output from memory with dimensional help from the few online pictures available.

[C855B]

Here's Detail Associates' rendition of the top hat antenna in HO. Photo brazenly stolen from an eBay listing:



Maybe I should spend the buck or so on the HO part for dimensions reference.

[Ed Kapuscinski]

That looks like a very easy thing to draw up in something like Tinkercad, if you want to DIY.

[C855B]

No problem with a CAD app, I use TurboCAD. There's a slight taper to the radome, and aside from getting the basic dimensions right I have to reach deep into faded (...or suppressed!...) memory how many bolts held the dome to the baseplate, four of which were through holes for installation. IIRC it was 12, but it may have been 8, which in retrospect would explain why they had a tendency to pucker the gasket and leak.

This is also a case of "knowing too much". I guess we all have our little focus/experience areas, mine happens to be RR radio $#!+.

[Lemosteam]

... I have to reach deep into faded (...or suppressed!...) memory how many bolts held the dome to the baseplate...

Unless those bolts are 3/4" or larger, they won't even be printable (0.004" in N  Scale).  I have a hard time getting 3/4 rivets to print right, much less a hex head bolt.  SW has feature size limits that won't prevent a pert from printing but many times will be indistinguishable.

[C855B]

Yeah, good point. They were 9/16 or 5/8". I'll draw 'em anyway and maybe the resulting amorphous bump will convey the idea.

[John]

Kind of looks like a truck pin

[C855B]

Well, almost. Here's a few minutes of fooling around:



I'll build-up a sprue in a few minutes and send 'er in.

[C855B]

Found another picture from above, this one on an S-2:



Cropped from an rrpicturearchives.net contribution. Unexpected reassurance I didn't get the bottom rim too thick. The semi-circle sticking out from the cab roof below the antenna is sort of an antenna-platform-lite, completing what is technically known as a "ground plane". Seeing that I've sort of committed to detailing the roof, I guess that beacon at the front (a unique style) is now on the to-do list. [...sigh...]

[Spades]

You could try shrink casting the HO parts, This is from a post I made to Brian Banna some time ago.

 https://www.therailwire.net/forum/index.php?topic=29171.msg312038#msg312038.  I used this method on some Athearn HO SP specific details with mixed results.  Cannon Co is not interested in producing n scale so this may be the only way to fab some parts.

[peteski]

Wow, IMO there is some serious overthinking going on here.
 I also think that those bolts will likely not be missed if not modeled.  Shrinking H0 version?  Why?  This item is a very simple shape which can easily be made by chucking a piece of styrene or arylic rod in a Dremel and shape it using needle files.  Hey, to simulate the bolts one could simply make small dimples in the collar, using a sharp scribe, to give indication that something is there.

If multiples are needed then use that handmade piece as a master, make a simple RTV open mold and cast more using urethane resin.  3-d printing will also work, but the antenna will have rough surface which might need some smoothing.

[C855B]

I'm happy with the Shapeways output for these, the proportions seem to be right. Of course you can only see the blobs where I drew the bolts under a microscope, but on a model they'd be obliterated by paint anyway.

I've been incredibly busy since receiving them, so they're not on any models yet. But soon.

[lajmdlr]

Here's a can antenna on a Santa Fe round roof CF7. Looks like it has a "mini" ground plane under it.