In-line Coax Connectors + db loss

[Rayjk110]

Hello. At my present house set-up, I run a 4.5db VHF/ 7.2db UHF omni-fiberglass antenna at about 10' above roof-top. (35-40' from ground) Coax used is CommScope (E82833) at about 20-25' length.

My main question is....

I have a PL-259 female-female adaptor so I can run a short length of RG-58 (less than 1') to the back of my CDM1250 (VHF) so I do not over-strain the coaxial connector on the rear. About how much loss is usually seen with adaptors like this? I have a mini-UHF to PL-259 adapter on the back of the radio, but it's a solid metal piece, so I don't think that's loosing much right there....

I also have about a 6' length of Andrew Heliax that is about a hair thicker than RG-58 (like super-mini heliax) that I was thinking about running from the antenna to the main coax (obviously cut to something shorter - either this or a short jumper of RG8) with another PL-259 adapter in place so that I do not have to dis-assemble the lower part of the antenna to get the coax out (goes into about a 5" length of pipe to the bottom of the antenna) should I need to do maintenance.


If all the said stuff is in place, about how much do you think the loss would be?

Thanks
Ray

[FF/EMT/KC2NFB]

im not sure of the loss on the connectors your using. the cable your using i believe is equivalent to rg58 a/u. the loss of that cable is around 4 db at 440 MHZ at 40 feet and using pl259 connectors doesnt help. at the freq's your using you should be using something a little more robust both on the coax and the connectors. in my opinion i feel rg58 and pl259 connectors have no place above 30 MHZ. i would run some LMR 400 with N connectors.

[Rayjk110]

The main coax that I use (CommScope) is just barely thinner than RG8.....It's double sheilded with a 10AWG conductor, and kinda hard to bend and manage. I'd think it's better than rg58 stuff. A group of hams around here (whom I got it from) use upwards of 100' of this stuff, and swear it's better than 9913 lmr400 etc. All these guys are tower climbers/installers, so they get coax alot.

[FF/EMT/KC2NFB]

ok im sorry, i tried looking up the part # you listed above and all i got was rg58a/u equiv. ok i believe your using the commscope equiv. of lmr 400. ok thats good stuff my apologies.

well as i said before i would stay away from pl259's. at higher freq's espeacialy 440MHZ they have terrible loss.

on the commscope cable you will have around 1 db loss at 440MHZ at 40 feet. so if you were using a 100W transmitter at the antenna you wil have around 78w.

[440roadrunner]

at higher freq's espeacialy 440MHZ they have terrible loss.

I'm not sure I agree with that statement, but I guess it depends on your definition of "terrible."

The thing is, there ARE some "terrible" connectors, and adaptors. A few years ago, Radio Sh.. got somewhat of a reputation by marketing, for example, 90 elbows and other adaptors that had SPRINGS in series with the center conductor. These of course, barely worked at 30 mhz, much less VHF/UHF.

Here's just one of the thousands of pages on the subject, which you can find easily on the 'ol net:


http://www.qsl.net/vk3jeg/pl259tst.html


In this particular case, using whatever brand he used for these tests, he says, in part, and speaking of a PL-259:

"At 144.5 MHz and 146.3 MHz the Insertion Loss runs around 0.2 dB, increasing to around 1 dB at 432 MHz"


I certainly don't call that "terrible" for the average consumer base or repeater setup. There are many, many systems still yet, out there, that have ALL UHF connectors (PL-259) on the transmitter/ receiver, the interconnects on the duplexer, and the antenna. DB products, and others, have made (and I guess still do) many, many antennas with UHF instead of N connectors.

The QUALITY and BRAND of the connectors is probably a lot more important that the specific type.


Also, you might want to take a second look at your Commscope cable. I didn't spend a lot of time looking for that E82833 as you call it:


http://dominoportal.commscope.com/CommS ... .1.1#3.1.1

[Rayjk110]

This is the full length of writing on the cable that appears in intervals:

COMMSCOPE NETWORK CABLE E82833 10 AWG SHEILDED 125 C (UL) TYPE CL2P HNS # 1010809 REV C MADE IN USA 3568 FT.

[FF/EMT/KC2NFB]

i did a search on commscopes web site for that number (e82833) nothing comes up. there good rg8 type network coax has a loss of 3.45 @400MHZ @ 100 feet.

as far as the above mentioned tech article it clearly states that pl 259 so239 connectors are not recomended for uhf dispite the name they were given.

look at the results of all three tests the N connector bearly moves and is a far superior connector.

for the general conumer i guess they would not care. but most of us want to get every thing we can out of our equipment. so why not use the best. good coax and good connectors realy dont cost that much when your talking about RG 8 type coax.

[440roadrunner]

pl 259 so239 connectors are not recomended for uhf dispite the name they were given

The reason that a "UHF" connector is called a UHF connector, is that at the time these were invented, the frequencies that they were intended for WAS UHF. In other words, the "frequency breaks" for UHF was amended some years ago.


I've forgotten the details, but here's at least one hit or two:

"The UHF connector is a pre-World War II threaded RF connector design, from an era when UHF referred to frequencies over 30 MHz."

http://en.wikipedia.org/wiki/UHF_connector


Somewhere, someplace, I saw a "horses mouth" document (Amphenol?) that had the dirt.

[va3wxm]

I always thought UHF meant "union high frequency"?

Ideally you should use N for anything above 200 MHz. The traditional PL connector does not have a constant impedance whereas the N (and BNC) does.

[FF/EMT/KC2NFB]

i understand when and what the UHF connector was used for. but for people that are new to the realm of radio and are not in the know you can understand how they can be misled by its name.