Why will this Sirio so called "Performer" 5000 PL not tune?

I have a decent enough SWR across all blocks with an old stinger type antenna.   With a modulator the needle barely moves on 27/81 but goes a bit too high on lower mid block, it needs a longer whip really.   However these antennas are behaving as I would expect and so I have no doubts about the PL145 mag mount.

Enter the Sirio "Performer".   The best I can get is 1.7 across a narrow range of frequencies.   It goes up to to nearly two 2 on lower mid and the same at the top.    Sky high on the  start of 10 metres, sky high if I go down onto 26 mhz.   All I read about this antenna is how wonderful it is and how it has one of the best band coverage for a mobile antenna;  not for me   Lengthening it or shortening it just moves the 200Khz or so where it goes down to 1.7.    I've blown  the Mosfets on my 6900N trying to tune this bloody antenna, fortunately the replacements are dirt cheap and I have some already from the last SWR nightmare I endured.  Does anyone know what the hell is going on here?       This antenna promised me the world and has thus far given only frustration and bewilderment!

I may be getting somewhere....   I opened up the magmount to inspect the insides and discovered that there is a particular screw which connects the shield with the earthing point, ergo, the top of the mount has to be screwed down in the right position.   I know i have looked inside it before so it is highly possible that I screwed it back together without the "earth screw" in the right hole.   Now outside the flat in a built up areaI am seeing more sensible SWR readings.   As low as 1.5 on upper block.  I think the whip is pulled out to it's fullest.  I did trim it earlier today in desperation, a replacement whip may be required to get better readings on midblock.    Also, where I have been testing and shutting the cable in the door the cable is quite badly squished....  SO...  When my RG8X coax which I have ordered arrives and I install it to the mag mount, and test it in an open space, I may well start getting some acceptable results.   Fingers crossed.

That's common on them.
When i got my 2 i sorted them out and put silicone grease in there before i even put them near a radio.

Hi Chris,

Isn't everything 'radio' fun!

Flipping frustrating too.


Glad to see you slowly getting somewhere with it all and learning stuff as you go along.

You can all too easily fall into an obsession with SWR and resonance though and a trap many of us have fallen into. A SWR of 1:1 or 100% efficiency is obviously an impossible task for any antenna. Anyone obtaining a so called 1:1 is usually due to misgivings in their SWR meter readings as the detector diode in them falls into it's non-linear region. Even a fancy 'digital display' meter may still rely on that basic diode detector circuitry and give us inaccurate readings.

As such, most meters are only giving an accurate reading much higher up often in the 1.5 region which for all intent and purposes is good enough. In fact a SWR of 1.9 means you are operating at 96% efficiency which is really good!
(Most 'Hams' are happy with a SWR of 2 or less and even a SWR of 3 means you are operating at 75% which for a temporary or field operation setup is good enough and doesn't tend to blow your finals.)

The things that do tend to blow finals are high impedance or open connections and more often than not short circuits. Easily done when you're playing around with antenna setups.

As for antenna bandwidth the manufacturers and retailers usually aren't much help. All too often an antenna is advertised as being able to operate in the 26 - 30MHz region when what they actually mean is it can be tuned somewhere along that range, not actually cover all of it. It's quite a big ask anyway and all often down to the design of the impedance matching circuitry for the antenna, (matching coils and capacitors often used in 5/8ths or shorter loaded antennas).

If you get a SWR of less than 2 across the whole range then you've really done quite well, as mentioned 1.9 = 96% efficiency.

With all of this you soon begin to appreciate the antenna 'system' aspect of it all. Everything is important from the connector on the back of the radio, through the coax or feedline, the connections to the antenna and finally the antenna itself.....

...coax being 'pinched' in the door certainly won't help matters.


Anyway, I hope my 'waffling' is of some help, it is provided as helpfully as it can be.


Enjoy yourself, continue with experimenting/learning and try not to blow too many finals.

All the best,
Victor

well done, looks like you stuck with it an solved your problems, I drove trucks for many years and never swr once, just lucky I think now. Victor is spot on as usual, a dummy  load will give perfect swr but no contacts. Get it about right and see what the signal reports are.
good luck
mark 26ct3433

but did you have your high swr switched on as it will stop you blowng the out puts i use the 800 performer and use the 4000 hp and the 5000 turbo both sirio antennas but use the tri mag and never moves even at 100+ mph

stephen Gunrunner wrote:

but did you have your high swr switched on as it will stop you blowng the out puts i use the 800 performer and use the 4000 hp and the 5000 turbo both sirio antennas but use the tri mag and never moves even at 100+ mph

Yes, but I set the threshold on it pretty high as it is a royal PITA on SSB with amp in tow.   You pause speaking for a split second and you get cut off with high swr warning.   It's no problem for me to replace the mosfets.  I did the job before on my other radio and they are like £2.50 for two!   At that price I won't even bother trying to work out which ones are knackered, I'll just do all three.

Very happy camper here!   Having correctly reseated the 145 mount with the ground lug in the correct position, my RG8x arrived today, so I replaced my squished 58 with this vastly superior coax.   I will never touch RG58 again having seen the superior quality of this stuff.    Anyhow, readings became more consistent , very low at the bottom of mid block and up to 2 top of UK 40.   After much tedious trimming (must have taken about 10 cm off in total, I now have just under 1.4 at top of UK40 and about 1.2 bottom midblock..   I'll leave it at this as it will give me a bit of room to play on 26 mhz.   Coax is now routed in via rear light unit and grommet ( no shutting in doors ).

I think this was a classic case of confirmation bias.   Because I had another antenna which was working OK, I dismissed the idea of there being anything wrong with the mount or coax.  I have gone from hating this antenna to loving it!   Hopefully my other antennas will tune better too. 

26uk81 wrote:

 Also, where I have been testing and shutting the cable in the door the cable is quite badly squished....  SO...  When my RG8X coax which I have ordered arrives and I install it to the mag mount, and test it in an open space, I may well start getting some acceptable results.   Fingers crossed.

I've warned about this repeatedly on here and every other board I'm on, it's the biggest issue when using mag mounts. 

The impedance of the coax is determined by the spacing between the outside of the inner conductor and the inside of the outer braid. If you pinch that you alter the coax impedance and that will affect the SWR. 

If you've pinched the coax it's scrap, even if you test it with a multimeter and it shows no shorts. You can end up with SWR so high purely from the coax being pinched that's high enough to blow the outputs on a CB yet when you test it with a DC multimeter it appears to be OK.