AN/GRC-7 antenna question

WRMorrison · Post by **WRMorrison** » Wed Sep 18, 2024 3:25 pm

If I'm reading SC-D-28624 correctly...

The image at the top left, the arrow pointing to the LR antenna (for the RT-70) states that items 17, 18, 19, 21 & 20 are needed for the -7. Is that for both antennas or just the LR? I would assume both antennas, because the frequencies ranges of both RTs and auxiliary Rx are so similar.

Also, when I look up the items, the -7 calls for:
(QTY1) Item #18 (MS-117A)
(QTY1) Item #20 (AB-22/GR)
(QTY2) Item #21 (AB-24/GR)

Items 17 (MS-116-A) & 19 (MS-118-A) are not used on the -7. So, that would mean 4 sections to each antenna assembly; correct? I'm thoroughly confused.

AB-24/GR has a small ball at the tip and does not accept another rod on top of it. If the -7 calls for 2 of these sections (-24), I would have to assume that one goes at the top of each antenna.

Do all successive (progressively smaller) sections screw inside its mating (lower) section? The -117 I have (longest of them all) is longer than the -22, but has the same size ends, so they don't attach to each other unless I slide one over the other (versus screwing them together).

The only way this makes sense to me (at this point) is that one antenna assembly consists of the (1) -117 and (1) -24, and the other antenna assembly consists of (1) -22 and (1) -24. That's the only way I see to make 2 antennas out of this pile of sticks.

-Rich

ETA: I edited the drawing for clarity and removed some items:

WRMorrison · Post by **WRMorrison** » Wed Sep 18, 2024 4:53 pm

Nevermind; mystery solved. RTFM...yeah, I know. Apparently though, I've read so much lately that it's all a bit of a blur.

-Rich

RonD2 · Post by **RonD2** » Wed Sep 18, 2024 4:58 pm

https://www.nf6x.net/wp/wp-content/uplo ... /grc-7.gif

WRMorrison · Post by **WRMorrison** » Wed Sep 18, 2024 4:58 pm

Now that that's figured out...

I'm assuming that it wouldn't hurt to put some copper anti-seize on the threaded connections after they've been cleaned and before they're put together?

-Rich

WRMorrison · Post by **WRMorrison** » Wed Sep 18, 2024 4:59 pm

Thanks Ron; I eventually came to the same conclusion.

-Rich

radtech · Post by **radtech** » Wed Sep 18, 2024 10:32 pm

The military uses dielectric grease.

RonD2 · Post by **RonD2** » Thu Sep 19, 2024 8:43 am

Unless you intend to leave your antenna assembled for super long periods of time (months, years), or are in a very harsh environment (ex: salt water and air) anti-seize or dielectric compound shouldn't be necessary.

While it wouldn't hurt anything, like any grease it captures dirt and displaces moisture --- and that doesn't make the joint "maintenance free".

The antenna should still be periodically disassembled, cleaned, and inspected.
If you don't use anti-seize or dielectric grease then that's one less thing to buy, clean off (and re-apply).

Whether or not you use anti-seize or dielectric grease, it's good to wrap the mated joints (after screwing them together) with a few turns of good quality electrical tape (or self-fusing rubber tape) to keep crud and water out of the joint.

These antenna elements are rather fragile, especially if tied down or slapping tree branches and the like.
Radio guys carried spare elements by the handfuls.

And they only need to be screwed together snug by hand (don't crank down on them hard). Known to split.

WRMorrison · Post by **WRMorrison** » Thu Sep 19, 2024 8:51 am

In that case I'll likely just keep using the copper anti seize. I've got enough of it to last 2 lifetimes, and it's a heck of a lot cheaper than my good coax tape. I don't mind cleaning it off and reapplying it if it means the joints will come apart easier. I had a heck of a time taking apart the antenna that was on it when I got it. Who knows how long it had been together or how it was tightened, but it was a bear.

-Rich