sirio Performer 5000 swr problem

[RadioDaze2.0]

I have read that increasing power significantly when using a mag mount can make the capacitive coupling (not ideal as I gather) less possible to rely on. I hasten to add this being second hand, read information.

I have run 70W through a Sirio 4000, similar antenna and not seen SWR change greatly so maybe I am barking up the wrong tree. Maybe common mode current goes up significantly when you increase the power and it might negatively effecte the accuracy of your VSWR reading when the current on the cable is greater.

Maybe a MJF 1:1 isolator would would help if you run out of ideas/solutions. A handy thing to have around I have found. (MJF say you can put it at the radio end as well but maybe a bit bulky for true mobile) I bung it on every end fed antenna I use. Even though the UK price is a bit expensive compared to the US price I still prefer it than a coiled coaxial choke to reduce/eliminate CMC on coax.

http://www.mfjenterprises.com/Product.php?productid=MFJ-915

PS : Have you recently checked the integrity of the aluminium foil sticker under the protective rubber base sheath ?

 

[milocs]

ok yes the aluminum sticker and antenna are brand new just got it last week.. I'm outside right now I have removed everything and starting over checking grounds etc will post later on my findings and if any changes I'll be trying just with antenna and radio with variable power and built in meter then test with external meter to see any difference will post

 

[The DB]

As you add power to an antenna with a magnet mount, at some point that power will have enough voltage to arc over from the magnet to the metal in the vehicle underneath. Once this happens, the spot the arcing over happened will be weaker, and it will continue to happen even with less power.

The magnet mount and the metal it is magnetically attached to act like a capacitor. A capacitor has impedance, which is the AC/RF analogue to resistance. The impedance does not change simply because you add more power, unless you add enough power to induce arc over.

When it comes to magnets at CB frequencies, a 5 inch magnet is plenty adequate. It is large enough that the impedance is low enough that you won't notice the difference.

Luckily, magnet mounts are near enough the current node of the antenna that only a small portion of the voltage from the RF signal is present. If that wasn't the case, trying to run any more than a few watts through said magnet mounts would be a pointless endeavor. In most cases, said mounts can handle 100 watts, and I've seen a little more than that sometimes, but I've also seen less cause problems...

Unfortunately using a larger magnet, or even a three or even four magnet mount, won't increase the power handling capability of the magnet mount. It is still the same distance away from the metal it is magnetically attached to, and that distance is what determines weather the power you are running will induce arc-over. That isn't to say that there aren't benefits to using a larger magnet, or even tri/quad mount. They lower the impedance of the RF connection through said mount, and will generally have a better physical hold on the vehicle.


The DB

 

[milocs]

wow long day lol
took everything apart
1. ran positive and negative 8 gauge wires from battery
2. check battery has only one thick cable on negative post to chassis didn't see any to
engine will check near alternator tomorrow. if not just put one in just in case
3. relocated the sirio 5000 performer mag mount (New) a bit more to center of vehicle
4. connected Radio President lincoln directly to the wires from Battery
everthing should be fine right lol.....Results

I connected meter only to set watts.. set it at 4 watts dead key no mod removed meter calibrated radio and swr 1.2 on ch 1 and ch 40 sames as beginning...now
connected meter set watts at 30 deadkey removed meter recalibrated radio bam swr almost 2 ufffff once again stumped

did same tests only this time with the meter in line to verify radio results and they were either spot on or atleast almost the same

I just might remove everything and test this same setup on another vehicle and check
just wanna say thanks for all who posted and input thanks and 73's
oh and I'm not giving up just don't wanna keep nagging the same things will be paying attention to you guys thanks for your great forum

 

[camaro1]

do you have another radio to try? ,, could it be the radio is putting out some harmonic frequency that is being read by the meter when you turn up the power

 

[milocs]

do you have another radio to try? ,, could it be the radio is putting out some harmonic frequency that is being read by the meter when you turn up the power

yes it won't have variable power but I'll give it a try it's a stock 1gen president Grant

 

[M0GVZ]

I set my swr on ch1 and ch40
I get 1.2 lowest with 4 watts dead key no mod.. fine
as I add more watts say 35 watts
and recalibrate meter myself swr already almost 1.6 this is barefoot radio I add dx350 and dead key radio 1watt amp at about 60watt recalibrate and swr is off in the red 3 or 4 any ideas thanks

Yes. You are getting the perfect demonstration of having a lack of a decent RF ground. I'd bet a dollar that if you either cut the coax down to 9ft or put a patch lead on to the coax from the magmount so that the length of the coax was 27ft long that you'd see the SWR drop massively.

Even though I hate magmounts with a passion I would expect the Sirio mag to be good for the power you're using. There have been reports for the Sirio 145 magmount of the braid of the coax not being connected or becoming broken or disconnected at the magmount end of the cable, this certainly happens if you are in the habit of tugging on the coax when removing the magmount as there is no strain relief on the coax or anything to stop you twisting it. However there have been reports of the braid not being soldered on properly from new out of the box. If that was the case then the antenna system would try to use the coax as a RF ground. Altering the length of the coax and seeing the SWR change would be confirmation of that.

Back to the magmount, undo the four screws on it and remove the top part and you will see a metal tag. Make sure the coax braid is soldered to that and that the braid itself hasn't got broken. In the image below you can see someone has used a hot glue gun to add some strain relief to the coax.

If its not that then the only other cause could be pinched coax. When you trap the coax in the door/trunk opening and pinch it, it flattens out the centre conductor insulator. That results in a far thinner spacing between the centre conductor and the braid. Because RF travels on the outside surface of the centre conductor and the inner surface of the braid, as you add more power the voltage increases and can get to a point where you start to get arcing between the centre core and the braid as the insulator isn't thick enough to prevent that anymore where the coax has been pinched.

 

[2RT307]

Did you ever try a low pass filter as Road Squawker suggested? I put one on my TS500 and it cured the high SWR. Indeed, it was harmonics.

You can find good, used filters on QTH.com. I see Drake or Johnson filters all the time for around 25 bucks, and they are usually good to 1kw.

73,
Brett

 

[222DBFL]

Also using better coax. I know, I know, it shouldn't matter, but I changed my coax out to lmr240 and used the PL145 mag mount with a sirio performer, radio was an optima mk3 and also had a magnaforce 350hd. It would do 250 watts on SSB easily and I never encountered vswr issues. Also used a magnum 257hp that was so finicky about bad vswr as well and never had an issue. Now I will say this, keeping it maintained is key to keeping it rifht as well. It will gather moisture under it. I had 6 magnets on the underside of where mine was mounted so I know it was held tight, and moisture woould still get in after a good rain. Under the rubber boot and between the rubber boot and magnet. I never really used the stock coax so I can't comment on it. But those antennas given a decent ground plane will tune pretty good. I've seen them at R=52, X=2, 1.0 swr cut for 27.405. So I know the antenna can be tuned. How old is this setup and have you cut anything off the whip? What kind of meter is being used to measure the vswr? Also like M0GVZ stated, try some different coax jumper lengths or longer coax with an added barrel connector. You might be able to change out the jumper from the radio to the amp to a longer one or shorter, depends on how long it is now. Also try moving the amp away from the radio a few feet if possible. Check all your coax jumper connections for s cold solder joint or a loose connection as well. Some things don't rare their ugly head until some power is applied. If you were to tell me you used an analyser on the antenna and it was cut for resonant freq and the best vswr you could obtain is 1.2:1, then I would say you have an impedance mismatch at the amp or radio. Like said, try different lengths of coax. 1/4 wave multiples. I know, I know, point a to b should in theory work fine, but sometimes you have to try different things. 1/4 wave multiples are easy but it may take an odd number as well. Like 4ft or 8ft and so on. At any rate. Hope you get it resolved. Would be nice if you could get your hands on an analyser to really see what is going on. Man do they make life easier when messing with antennas!! JMHO. Again. Hope you get it fixed. Good day.

 

[222DBFL]

That and adding a low pass filter. There are many that are available. The RF Limited DF3000 is $40 new. And they will handle some power. There are better ones I know, just throwing one out there that I use and know it works. Keeps the neighbors happy.

 

[milocs]

I'm in the process of ordering the low pass filter, the magnet mount I'd brand new will check the braid to make sure but I also just tried another antenna Magnet mount as well swr is flat when I added power same thing high swr almost 3 gonna check also the different lengths of coax
as stated. guys thanks

 

[milocs]

M0GVZ when I remove those four top screws I don't have to mess around with anything under the magnet foil wouldn't want to break it of will do if it'sa must thanks

 

[RadioDaze2.0]

I must be the only person to have actually broke one of the PL145's mag bases. I was in a field and let a tail gate up when camping and the base wedged against the roof and the whip parted company and bent that brass solder tag out and up from the side of the SO-239. I had to make an emergency repair using a tiny sized cable tie to tie the centre core to the pin. It worked with 15 Watts PEP, lol and I got on the net I was planning to in the West Country. Since I have put mini8 in there but I am not 100pct trusting of my repair.

I should buy a new base but tend to bung a silver rod up rather than use a mag mount as I don't work radio when actually driving.

Just a bit of useless information there.

Good luck sorting the problem out.

 

[milocs]

I must be the only person to have actually broke one of the PL145's mag bases. I was in a field and let a tail gate up when camping and the base wedged against the roof and the whip parted company and bent that brass solder tag out and up from the side of the SO-239. I had to make an emergency repair using a tiny sized cable tie to tie the centre core to the pin. It worked with 15 Watts PEP, lol and I got on the net I was planning to in the West Country. Since I have put mini8 in there but I am not 100pct trusting of my repair.

I should buy a new base but tend to bung a silver rod up rather than use a mag mount as I don't work radio when actually driving.

Just a bit of useless information there.

Good luck sorting the problem out.

it's new I've mounted and just removed it To move forward and hasn't been yanked

 

[222DBFL]

No you don't need to get to underside of magnet for anything. Pull the 4 screws keeping note which one has the brass insert for the coax shield. I don't think it's your antenna, or coax, but it doesn't hurt to check it.