Hi Bill and the list.
I just want to let you know I might ramble a little, but here are some of
my thoughts. I want to mention first where you can find some cable on the
Internet; the results of a little test I did using this type of large cable
(unfortunately mine is bigger even than this); and a word about velocity
factor. I hope this isn't going to bore too many of you too much. I am
just sort of an amateur myself when it comes to radios and radio parts.
I do all my coax shopping over the Internet at a place called "RF Parts" in
Southern California, if I remember correctly. They do have a $25.00
minimum order, but that isn't usually so difficult once you figure out your
cable length, connectors, etc. I just did a search for "rg-189 7/8" 50 ohm
coax" once I entered the site and got the following;
https://www.rfparts.com/catalogsearch/result/?q=rg-189+7%2F8%22+50+ohm+coax
I then did a search for "lmr 900 50 ohm coax" and got quite a few pages of
hits. It may even be the same list of my last last search. Not sure. When
I did the second search, I had to click on "p. 4" on my machine at the
bottom of the screen to get to the right area which display the higher end
LMR cables. I clicked on the LMR 900 DB (direct burial, or weather proof)
at: https://www.rfparts.com/lmr900db.html. You have to order this quite a
bit in advance, but I'd rather do it over any other non-weather protected
coax.
I had a project where I was using frequencies around 33 CM and needed a run
from my 900 MHz yagi antenna to the radio. At such high frequencies, big
cable like this is *extremely* important. I hooked the yagi up to my radio
using a 1 M run of LMR 400. It sounded as clear as a bell. I had people
located 50 miles away from me, where the repeater is. No problem. They
said I didn't even have a trace of "popcorn" (a type of static unique to
those higher frequencies).
That was great, but I didn't want to leave the yagi on the entertainment
center forever, so I take it out through a "pass through" through the
window and get it out to the antenna. I tried to use only DB because I
would rather it have all the protection it can get over the years against
the elements. LMR 900 DB was the best type of coax (but most expensive).
I used N connectors, so as not to get as much loss (ni Europe VHF and up
use N connectors). Anyway, (sorry to make a short response long -- just
wanted to write it all out in case anyone might benefit from what I've done
(or haven't done) right. I connected a LMR 400 run-off wire from the LMR
900 to the radio to be able to fit it through the pass-through, as well as
to make the coax malleable enough by the time it got to the radio that it
wouldn't break the connector off every time I moved the radio. And with
all of these even STILL, I had some popcorn My run was only around 8 M of
cable and still I was losing a *lot* of signal. .
Using the VF (velocity factor), calculate the proper length of the cable.
This is explained in the Extra ARRL manual, about 2/3 of the way through
the book. Whenever I've done this, I always get 1:1 SWR or extremely
close, At high frequencies, it makes it even more critical. You should
check with someone who knows about the subject, if necessary.
I'll show you a piece of my bill here, which I paid to RF Parts. Note
especially the "large" N connectors to fit onto the large LMR 900 cable.
They're $68 each to buy them and I think it looks like it was $25 per for
labor. Not having worked with cable that big before, I left it to them to
work out. Then there was the cable, which was around a little over
$18/meter. Wow! Shipping's another 18 and there you have it: $350 for an
8 M legnth of coax!
ItemSkuQtySubtotal
*LMR900DB 0.870 Dia, Low Loss Coax, Direct Buriel* LMR900DB 24 $142.80
*EZ900NMC-2 Type-N Male Clamp Connector, LMR900DB* EZ900NMC-2 2 $135.90
*LABOR-XLARGE* LABOR-XLARGE 2 $50.00
Subtotal $328.70
Shipping & Handling $18.00
*Grand Total (Excl.Tax)* *$346.70*
Tax $0.00
*Grand Total (Incl.Tax)* *$346.70*
Shon R. Edwards, MA, AG (Czech Republic)
Amateur call: K6QT
1039 N 2575 W
Layton, UT, 84041-7709
USA
Home phone: (801) 444-3445
E-mail: sre.1966@gmail.com
or
Shon Edwards
715 Strawberry Creek Private Rd.
Bedford, WY 83112
Cell: (307) 248-2104
On Sun, Jan 1, 2017 at 1:48 AM, Jim Brown <jim@audiosystemsgroup.com> wrote:
> Hi Bill,
>
> Remember that RG numbers are no longer specs for cable, merely generic
> descriptors. Remember also that below UHF, attenuation is all copper loss,
> so if you can get physical dimensions and construction details, you can get
> pretty close to its loss by comparing to another cable with the same
> dimensions and construction.
>
> Google found this on the first try. Center is solid copper, 0.25-in,
> shield is double silver-covered copper. Dielectric is 0.632-in.
>
> http://www.awcwire.com/productspec.aspx?id=rg189-coaxial-cable
>
> http://catalog.standard-wire.com/Asset/RG-Attenuation.pdf lists
> attenuation for a bunch of RG numbers, and I saw a note in my searches that
> 189 has been replaced by 389. RG389 is listed here as 0.8 dB at 100 MHz.
>
> 73, Jim K9YC
>
>
> On Sat,12/31/2016 10:55 PM, Fuqua, Bill L wrote:
>
>> Does anyone have the attenuation vs frequency specs for RG189 cable?
>> I can't seem to find it anywhere. It is 7/8" 50 Ohms and that is about
>> all I
>> have found.
>> 73
>> Bill wa4lav
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