Sirio 5000 PL & Sirio 145 ML swr test

General Mobile CB antenna advice and troubleshooting

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Mon Feb 25, 2013 9:53 pm

hello :D

today I tested the Sirio PL 5000 and the Sirio 145 ML for swr values, and I came to some results that I want to share with you.

the setup is:

roof mount, SO239 fitting / chassis grounded
5.5 meters of Ecoflex low loss 50 ohm coax
Avanti Kappa II unit
car: Honda Civic hatchback MY 2004

first I measured the SWR at the radio side and the results where:

with the Sirio Performer PL 5000 the SWR was 1.1 all the way and all the power (with this rig you can select the output power from 4 to 60 W).

with the Sirio 145 ML the result where arround 1.3 @ all chanells and 1.5 @ arround 50W.

so, we all know that this medot of measuring the SWR is wrong and to obtain the real SWR values we need to measure at the antenna side. I wonder why the internet is full results obtained with the above metod. I conected the swr meter at the antenna side and surprise....

on the ML 145 the SWR values where 1.1 on CH1 and 1 on CH40 at 50W :shock:
(previous , on the radio side the value where 1.3 - 1.5 across the band)

on the PL 5000 the values where 1.8 on CH 40 and 1.5 on CH 1
(previous, on the radio side the value was arround 1.1 across the band)

it's obvious that the values are so much different. in the first measuring metod the coax lenght was acting like a 50 ohm dummy load (please correct me if i'm wrong) with 1.1 swr on the PL 5000....

I had to cut arround 20 mm from the whip to bring the swr arround 1.5 with the PL 5000, but I can't obtain values under this number.

the radio and the setup works fine, but I want to share this results and perhaps have some opinions on this :D

many thanks
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Tue Feb 26, 2013 3:49 pm

if i get 1.5 on an antenna then it will do seems to work a lot better than one at 1:1 for some reason never figured it out

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Tue May 07, 2013 11:12 am

good results & thanks for sharing tomi i used to use a Sirio 145 ML good working antennas & it never let me down as i used to get a good range of 26 miles :wink:
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Thu Mar 30, 2017 6:50 pm

I have a sirio 145ml antenna and a thunderpole t1000 rig.
Iv tried to swr the antenna in, on ch1 its 1.1 and ch40 its 1.3
I cant even hear anyone on the rig as i just get static bursts all the time. Iv not cut the antenna but moved it up and down with the 2 grub screws to try and tune it in!
Help!! This is my first rig.
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Mon Jul 03, 2017 8:24 am

Thanks for posting your results tomi.
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Wed Jul 12, 2017 11:41 pm

The sirio 5000 has a much larger bandwidth than the 145ML
If your running extra power I would advise you don't use mag mounts,as the grounding is not as good compared to a drilled in antenna and a proper DC grounded antenna connection to cars body is best.
Years in the commercial pmr business taught me this!

You can get erroneous results due to RF flowing back on the shield of cable,wont go into technicalities.
Mag Mounts use loose coupling,or worse the braid of coax cable to find a earth connection,generally at 4 watts this isn't an issue.
At 50w+ it will in some cases cause issues with VSWR readings an can cause you some funny effects with VSWR.

Sometimes this can be resolve with a braid strap from magmount or radio body to a earthing point on vehicle or a RF choke balun,but best is drilled,or next best is snail mount\boot mount with earthing grub screws into body of vehicle

Always VSWR cb antenna without RF power amp in line first,sometimes these amps cause mismatches on IN & OUT generally because lack of Lowpass filters on output of RF amplifier or poor matching on input of amplifier depending on brand and quality.
I would always recommend legal or not if using RF amplifiers always use a good quality Low Pass Filter on amplifier to keep it RF clean.

A neat trick-if using a mag mount with a SO239 socket on it and not sure antenna is ok or magmount at fault\cables ,place a PL259 50 ohm dummy load and screw into the SO239 mag mount,place on car roof and then check on VSWR meter across all bands.
IF there's any variations,either its poor ground or cable\magnmount cable contions faulty,yes I had centre pin just fall of coax on magmount and was barely making contact to centre pin of SO239,it can happen.
That will check your mag mounts good.
For double check,use a digital volt meter set on ohms and check continuity of both centre and braid connection back to PL259 plug if in any doubt and short circuits between braid and centre on coax.

If antenna new out of packet and adjust on magmount the length maybe different to a drilled mount due to better grounding.
If antenna Second hand and was used on a drill mounted set up and your putting onto a mag mount setup,beware the whip maybe now too short to get a good VSWR match,Ive seen this also in the field too!

If VSWR is as high as 2:0 on band edges don't worry it wont hurt your cb to cause serious damage,just a tiny reduction in RF power.
Most magmount antennas should cover at least 120 channels generally speaking,unless very short less than a foot or so.

I have a ML125,while not a bad antenna the siro 4000/5000 works the best due to longer whip to radiate signal.
The sirio mag mount can sometime loose its solder connection in the mag mount base,this is a common problem I have come across in fault finding CB radio installs.

MY fav is a tri-mag mount or drilled ball mounted,big pig spring and 9Ft quarter wave,I cannot fault it for range and bandwidth,not practicable for all but rule of thumb longer the better & higher the better on CB band as it has very close properties to VHF Low-band line of sight with less mobile flutter involved.

Hope you resolve your problems!

All the best 73's

Rob WT-27
South Wales
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