[R-390] Coaxial extremes!

Fri, 15 Nov 2002 09:17:27 -0600

Hi Jon and group,

                Concerning the SMA connectors...my documentation indicates
the closest crimp connector to the sizes you have mentioned are for RG-58.
I think the standard is to measure the outer diameter of the the crimp
sleeve or ferrule...which is listed as .213 for use with RG-58.  Thats an RF
Industries part number....the AIM Electronics part which is more common at
electronics parts stores is .210 for RG-58...so both are very close to the
ID measurement you listed.  My guess is that they are for RG-58.  Sounds
like your best bet would be to put the SMA connectors you have on the best
quality RG-58 you can find and put some crimp on Type N male connectors for
RG-58 on the other end and use a couple Type N female Bulkhead feedthroughs
for mounting in your weatherproof  box.  The Bulkhead feedthroughs are
available with O rings mounted to seal the opening made through the box.
Works real nice.  The added loss incurred from using these instead of a
crimp on N female bulkhead is negligable at the frequencies you are working
and it allows you to change the equipment or cables in the box without
having to disturb the connection through the box once you have it sealed.

1 5/8 foam connectors are expensive as you have found.....besides that the
feedline will need to be attached to the tower in a way that will support
it's weight...cable ties won't get it!  You need to use a hoisting grip
attached to the tower at the top to support some of the weight and probably
hose clamps at 15 or 20 foot intervals with maybe some cable ties in
between.  It is usually installed using round member adapters and butterfly
or snap in hangers down one tower leg if the tower is not already punched
for snap in hangers.  But all that gets expensive for Amateur work so hose
clamps to the tower leg would work fine.

The connectors are upwards of $200+ each for N female, which is probably
what you will want. A low loss Type N M-M jumper is usually used at the top
and bottom ends to connect to the antenna and equipment.

I will look around and see what I can find for connectors.....

You know of course that for HF frequencies....1 5/8" feedline is way
overkill....you don't gain much over using 1/2" foam hardline for example.
1/2" has .357 db loss per 100' whereas 1 5/8" has .109 db loss per 100' both
at 30 mhz.  Less than a quarter of a db per 100', you could not tell the
difference on the air...but the cost to implement is much higher with the 1
5/8".  Connectors for 1/2" can be picked up easily for $10-$12 each.
Hanging it is easy as well.  But...I am sure your decision is based on the
fact that you already have the 1 5/8" cable, which by the way, weighs nearly
125 lb all by itself...so hopefully it's not going on a light weight Rohn
25G tower.    Of course at frequencies of 450 mhz and up all this
changes....1/2" becomes more lossy and the 1 5/8" begins to shine!

Cecil Acuff....
WB5VCE

----- Original Message -----
From: Jon & Valerie Oldenburg <[email protected]>
To: <[email protected]>
Sent: Thursday, November 14, 2002 10:50 PM
Subject: [R-390] Coaxial extremes!

I've been finaly assembling an amplified receive antenna project here. I
have obtained a broad band amplifier with a coverage of  5-mhz to 1500-mhz,
which uses SMA connectors. I will be mounting the amp in a weather proof
feed with 1/2 inch hard-line to the steel box on the mast of the antenna.
The box will be provided with "n" chassis mount jacks. The big question is
on the SMA connectors to the amp. The connectors I have obtained appear to
be of a crimp-on type, with a knurled shield crimp area having a diameter of
.168 (OD) inch, and a crimp sleeve provided to fit over it of .197( ID).
The box for this installation is rather small and since the coax runs are
only 2 or 3  inches I was going to use RG-174.  The crimp/ contact area
seems  wrong, but the center conductor -ok,  maybe RG-58 is required?  On
the other extreme-( he-he !!! ) I just obtained a brand new 150' roll of
Andrew LDF7-50A  Hard-line. Will be using this as the feed line on my tower
project in Townsend WI. If any one has a line on reasonable priced "N"
female fittings for this 1 5/8" foam dialectric cable I'd appreciate the
tip.  Thanks in advance & 73's Jon AB9ah

"If everything seems under control, you're just not going fast enough."
 - Mario Andretti

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