why is SMA cable so expensive?

I have a D-link ANT24-0700 2.4GHz Omni-Directional 7dBi indoor
antenna. It has a 6ft. cable that I want to add an extension to so I
have more area to move it for a better signal. I checked various
websites for prices of SMA cables and found even a short cable isn't
cheap. For example http://www.smacables.com/ wants $21 for a 10ft.
cable.

Also, I was told by one website's tech support that adding more cable
length will cause signal loss. Why is SMA cable expensive and will
more length really degrade the signal to a significant degree? Thanks.

sillyputty <(E-Mail Removed)> hath wroth:

>I have a D-link ANT24-0700 2.4GHz Omni-Directional 7dBi indoor
>antenna. It has a 6ft. cable that I want to add an extension to so I
>have more area to move it for a better signal.

<http://www.dlink.com/products/?pid=416>

Hmmm... There's a bit of subterfuge in the specs. The antenna gain
is 7dBi. However doesn't include the 1.5meters of RG-316 coax, which
has a loss of about 1.1dB/meter or -1.65dB loss. What you really have
is a 5.35dBi gain antenna.

>I checked various
>websites for prices of SMA cables and found even a short cable isn't
>cheap. For example http://www.smacables.com/ wants $21 for a 10ft.
>cable.

Yeah, that's about right search for:
"RP-SMA extension"
to find other vendors and suppliers. Be sure to check eBay.

>Also, I was told by one website's tech support that adding more cable
>length will cause signal loss.

Yep. So do the connectors. Do the math:
type Insulation dB/meter loss at 2.4GHz
RG174 PE 1.20
RG316 PTFE 1.10
LMR195 Foam 0.56

If you add 3 meters of extension cable, the ADDED loss would be:
type loss final antenna gain
dB in dBi
RG174 3.6 1.75
RG316 3.3 2.05
LMR195 1.68 3.67
Now you know why coax cables on external antenna are so short.

>Why is SMA cable expensive

LG316 cable in bulk costs about $0.50/ft. RF Industries RP-SMA
connectors are about $5/ea. So, you have a parts cost of about $15
per pigtail. I'm not sure how much to add for labor because building
pigtails is really tedious and time consuming with all the cable end
preparation and crimping. Add a few dollars for sweep testing the
final assembly.

>will
>more length really degrade the signal to a significant degree? Thanks.

Do the math. 6dB is equal to half the range. 3dB is equal to 0.7
times the range. You're starting with a 7dBi antenna. I've added the
1.65dB loss that DLink conveniently ignored, and the approximately 2dB
loss that you proposed to add, for a total of of 3.7dB coax loss.
That's about a 0.78 times decrease in range. Not too horrible a loss.
The improved location of the antenna will also be a benefit. I would
say it won't hurt to add 3 meters more coax.

Incidentally, I'm not a big fan of omni antennas for improving range
and performance. Look into directional antennas for far more gain.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thanks for the info! Gonna try a DIY directional antenna.
--
"Your estimated wait time is 8 minutes; your actual wait time may
vary." MS tech support

sillyputty <(E-Mail Removed)> wrote:
> I have a D-link ANT24-0700 2.4GHz Omni-Directional 7dBi indoor
> antenna. It has a 6ft. cable that I want to add an extension to so I
> have more area to move it for a better signal.

You could add a free reflector instead of a cable. Maybe instead of the
7db antenna.

http://www.freeantennas.com EZ-12, printed on photo paper for thick stock,
with aluminum foil glued to the sail, provides a substantial boost in
signal. http://www.rahul.net/dold/clarence/EZ12-windsurfer.jpg
http://www.rahul.net/dold/clarence/w...fer-dining.JPG The signal with
the reflector is not only 13dB stronger, it's more stable.

--
Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5

On Aug 9, 5:00 am, d...@92.usenet.us.com wrote:

> You could add a free reflector instead of a cable. Maybe instead of the
> 7db antenna.
>
> http://www.freeantennas.comEZ-12, printed on photo paper for thick stock,
> with aluminum foil glued to the sail, provides a substantial boost in
> signal. http://www.rahul.net/dold/clarence/E...-dining.JPGThe signal with
> the reflector is not only 13dB stronger, it's more stable.

I made a 'windsurfer' reflector and did a few initials tests (turned
it in different directions), but really couldn't tell if it made a
difference, though I did pick up a couple signals I hadn't before. My
question is the reflector is 4.5" inches high and my antenna is 11".
Can I make a longer reflector to match the length of my antenna or
does it have to be a certain size?

sillyputty <(E-Mail Removed)> wrote:
> I made a 'windsurfer' reflector and did a few initials tests (turned
> it in different directions), but really couldn't tell if it made a
> difference, though I did pick up a couple signals I hadn't before. My
> question is the reflector is 4.5" inches high and my antenna is 11".
> Can I make a longer reflector to match the length of my antenna or
> does it have to be a certain size?

I would say that you need to cover all of the antenna. Some portion of the
assembly near the base might not be an active part of the antenna, but
covering less than half of your antenna is probably not good at all.

The parabolic reflectors scale in size. If you simply enlarge the
template, your curve will be larger, and the focal point of the parabola
will be farther out, scaled up on the drawing of the support part.

In the "original" part of the www.freeantennas.com web site, there is a
separate template for a 5/8 wave whip, instead of the common dipole. I
don't know if your large antenna is still a dipole. There are some
pictures, and a link to a bunch more, at the bottom of the page.

--
Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5

On Aug 10, 10:56 am, d...@92.usenet.us.com wrote:

> I would say that you need to cover all of the antenna. Some portion of the
> assembly near the base might not be an active part of the antenna, but
> covering less than half of your antenna is probably not good at all.
>
> The parabolic reflectors scale in size. If you simply enlarge the
> template, your curve will be larger, and the focal point of the parabola
> will be farther out, scaled up on the drawing of the support part.
>
> In the "original" part of thewww.freeantennas.comweb site, there is a
> separate template for a 5/8 wave whip, instead of the common dipole. I
> don't know if your large antenna is still a dipole. There are some
> pictures, and a link to a bunch more, at the bottom of the page.

Ok, thanks. I assume changing the size and curve of the reflector
moves the focal point, and the focal point should be where the antenna
is? Also, some designs use metal mesh. Is there any difference between
metal mesh and tin foil?

On Aug 10, 4:53 pm, sillyputty <karmictara...@2die4.com> wrote:
> Also, some designs use metal mesh. Is there any difference between
> metal mesh and tin foil?

As long as the distance of the wires in the mesh is less than a
quarter wavelength, then no significant difference.

But, lets say you have a 36" wide by 28" tall GRID antenna that looks
like a BBQ grill, it will have a 29 dB gain where a smaller 24" full
metal dish will have about the same gain.

When you get into the four and six foot dishes, the mesh/grid doesn't
appear to be as strong. Another reason is ice build up on a grid
antenna. For good measure, I keep my four foots dishes waxed to that
ice slides off, but this isn't really a concern for most people as a
four foot dish will retail for about $1,500.

I really hate using Google Groups, but appears my ISP isn't
downloading the alt.internet.wireless anymore.

On Aug 10, 12:56 pm, d...@92.usenet.us.com wrote:
> The parabolic reflectors scale in size. If you simply enlarge the
> template, your curve will be larger, and the focal point of the parabola
> will be farther out, scaled up on the drawing of the support part.

Just a thought, one could take a hard rubber beach ball and cut it
half, then cover the inside with aluminum foil. It would be more
forgiving in feed horn placement (just aim the whole dish for best
signal).

sillyputty <(E-Mail Removed)> wrote:
> Ok, thanks. I assume changing the size and curve of the reflector
> moves the focal point, and the focal point should be where the antenna
> is? Also, some designs use metal mesh. Is there any difference between
> metal mesh and tin foil?

Resizing the template gives a larger curve, and the focal point, as noted
on the enlarged printed template, is moved out, so it is in the correct
spot for the larger curve.

Mesh and solid are the same, as long as the mesh is small enough for the
frequency that you are working with. The freeantennas page suggests a 1/4"
mesh. The mesh should be closer than 1/10 of a wavelength, or almost 1/2"
for 802.11b.

Noted on the www.freeantennas.com home page, at the bottom,
"Undoubtedly the best implementation of the Parabolic Template Design I've
seen so far." http://www.nodomainname.co.uk/parabolic/parabolic.htm
Is a fine mesh parabolic.

--
Clarence A Dold - Hidden Valley Lake, CA, USA GPS: 38.8,-122.5