[Amps] Coax specs

Mon Jan 2 15:52:03 EST 2017

  Thanks for all the replies, I am not shopping but have some RG189 on a reel with connectors in my garage and looking at how I may make use of it.
I may use it for VHF and UHF applications on my tower in the future.
Thanks again.
tnx es 73
Bill wa4lav
________________________________________
From: Shon Edwards [sre.1966 at gmail.com]
Sent: Monday, January 02, 2017 10:17 AM
To: Fuqua, Bill L
Cc: Amplifier Reflector
Subject: Re: [Amps] Coax specs

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!

Item    Sku     Qty     Subtotal
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<tel:(801)%20444-3445>
E-mail:  sre.1966 at gmail.com<mailto:sre.1966 at gmail.com>

or

Shon Edwards
715 Strawberry Creek Private Rd.
Bedford, WY 83112
Cell:  (307) 248-2104<tel:(307)%20248-2104>

On Sun, Jan 1, 2017 at 1:48 AM, Jim Brown <jim at audiosystemsgroup.com<mailto:jim at 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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