[R-390] Coaxial extremes!

Fri, 15 Nov 2002 23:24:09 -0600

Hello Cecil & the Group: I have had my gut feelings that the SMA connectors
where for RG-58, so I will change to that. I am familiar with the
installation requirements for 1 5/8 heliax, working as a municipal
construction inspector, I have over seen a couple of cell tower
installations with  lets say a greater than normal amount of time & interest
allocated. The tower  for this project is  a Rohn HDBX-48 ( 48' self
supporting tower  rated @ 16sq ft load).
The antenna plan is stacked KMA log periodics, the lower one a  20 - 10
meter
unit, the upper a 50-1300mhz unit. Will  top mount a 440 antenna for a GE
Mastr repeater, and have a side mount for a 2 meter fm Quad. I am still
considering  between using a remote antenna switch or getting some 7/8
hard-line for the H.F. antenna. I think it will be real interseting to get a
R-390A on a directional antenna instead of a long wire! Thanks for your help
& 73's Jon AB9AH
----- Original Message -----

> 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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