Coax Losses

fatboymsport

a good link

http://www.ocarc.ca/coax.htm

makes you think??

213 is junk above 30mhz.

PauloMN

Very useful link, thanks for that. Never would have thought that the losses could be so high for my RG213 that I have feeding my co-linear, in particular at 70cms.

:o:o I also have a short length of RG58 between my handheld and the SWR meter which REALLY must go. :o:o I'm probably doing well if I get half a watt of RF up to the antenna all told!!!!

Also suprised at how the losses vary so much based on frequency - you can have long lengths of RG213 at HF with very little loss, but at UHF it's insane how much is lost.

Note to self: carry out all that antenna work I've been meaning to carry out for years now!

I wonder is there a UK version of that little app anywhere? I don't recognise a lot of the coax brands listed, I guess they are US brands.

watty

fatboymsport wrote: »

a good link

http://www.ocarc.ca/coax.htm

makes you think??

213 is junk above 30mhz.

Depends on the distance.

I have my 2m PA & preamp on brackets of pole on gable end. Then the longer part of cable is low power TX and preamped RX, so the RG213 losses mean I use 5W drive instead of 3W drive to get full PA power.

I use that link all the time

Compare RG174 and RG213 for 25m cable run at 900MHz!

For longer runs of UHF I use LMR400. The RG213 is OK for short runs UHF, medium at 2M and longer runs at 6m.

On 100kHz to 30MHz I use RG58 unless it's very long run or more than 100W.

fatboymsport

here is another look look at the bottom of this page not as detailed as the last one.

http://whwestlake.110mb.com/

and yes its a shame the first link doesnt do w103 and ecoflex its all US stuff that we cant get over here.

watty

I've used 75Ohm CT125 instead of 50Ohm RG213 as a compromise for my Discone. Certinally lots better than RG58 (RG59 is 75 Ohm equivalent).

The SWR difference for TX is not that significant using 75R rather than 50R actually.

fatboymsport

i wouldn't use 75 ohm on any 50 ohm system as it is a mismatch and as for rg58 apart from a 12" patch lead i wouldnt let it near a radio.

watty

The reflected power on 75 Ohm resistor on a 50Ohm radio is only about 4% reflected power, Even 1:1.5 is not a high SWR.

In real life on VHF
Discone may not be exactly 50 + 0j Ohms
Radio may not be exactly 50 + 0j Ohms
CT125 might not be exactly 75 + 0j Ohms

I get 1.1 to 1.2 SWR on 50MHz to 440MHz 50 Ohms source on Discone via CT125 75Ohm cable.
At 28MHz and 1.3GHz bands it is 1.5 to 1.8
Why is it better than 1.5:1 ever? Because only the transmission line is a nominal 75. The Discone is a Nominal 50 Ohm.

If it was an HF aerial on 1.8Mhz to 30MHz, you'd be happy

I use RG58, RG8, RG213 and LMR400 on other feeds and systems. The discone is not important enough to warrent the extra cost as the CT125 was a wasted off cut.

I'd really hate to use RG213 or LM400 for my Mobile Whips.
Watson 770 dual band 2m/70cm
Spring base trucker style 10m/11m
Comet 10m/6m monster on triple magnet base.

My Military set (Syncal30) will tune either 10m whip from 1.8Mhz to 29MHz.
My elecraft T1 ATU on FT817 tunes the 6m/10m Comet whip to 40m OK and poor SWR giving 1/2 power on 80m.

I tried a 21' telescopic mast on rear bumper and it gave good SWR on the elecraft tuner on 80m and allowed TX at 1/2 power on 160m, but the extra hassle not worth it as most mobile QSO on 20m and above as even the Syncal's 20W is a bit low for a short whip at 40m/80m/160m
You'd be a very dedicated QRP op to do 40m/80m/160m on the FT817's 5W to 2.5W depending on SWR on a short whip (21' is very short for 80m never mind 160m!).


Indeed don't use 75 Ohm gear on 50 Ohm systems without an SWR meter and without good reason. But blanket statements without qualification simply make the hobby into black box mystery. It's about Experimenting.

Unless you are installing a commercial system.

les45

I am not sure if it is still available but I was very fortunate to aquire about 15 30 mt runs of LDF450 AND 750 with various plugs and connectors , a bitch to work with but well worth the effort , the guy in question had the contract for replacing all the Garda Towers for O2 when they did the deal, you were basically buying the feeders off the old towers , I also bought a tower from him which I split into a 60 ft and a 40ft , price for the whole lot was € 800.00 Euro , I ill try and dig up a old phone number for him.

John EI9HW

fatboymsport

if you are talking to him ask him has he any more towers ?????

fatboymsport

anyway back on topic im sure 75 ohms works well for you not my cup of tea i would rather order any wait for the right cable than make do with the the wrong but thats just me.

les45

It would seem that the gentleman in question is no longer in the tower business , or he has changed his mobile number .:(

John

fatboymsport

i hear of more people getting towers "right" but i never seen to be able to find one

ah well im sure there is some out there some where thanks for trying anyway John.

BTW heard you on 80 the other night you were doing well into the states wish i had an antenna for 80 there seems to be an awful lot of people on 80m dx at the mo and most seem to have 4 squares
no matter what time of the day or night there isnt a spare Freq in the Dx window.

experimenter

:eek: Antennas - Feeder - Radio :eek:

For VHF/UHF, Heliax is the way to go...don't forget about your connectors, N types etc.. in the ideal world for VHF/UHF, a separate cable run for tx and rx would be best, most if not all the EME guys go that route!!!

Westflex is fine for 50/70Mhz..

HF, well I have no real interest in HF but I use 120Mtr of wire fed with 10Mtrs of 450ohm twin feeder to a SGC tuner, with a 4Mtr run of RG213 to the radio. Works perfect from 160M to 6M.

Who needs the DX window for USA, use CW or PSK at the lower end, work USA easy...

watty

A 90ft tower with heliax would be nice OK.

Sam Radford

fatboymsport wrote: »

213 is junk above 30mhz.

No, it's fine above 30 milliHerz. It doesn't go bad till 30 MegaHerz (MHz).

watty

It's usefull even at 900MHz if it isn't too long a feed.