Sirio SU 375 - 480 PL tuning advice

This Sirio is for PMR 446. I thought it would be in separate parts as you need to cut the bottom and top for SWR. 
It is in fact one piece including the centre spring.
So my thought of buying replacement steel rod if cut wrong is out the window.

I don't have an SWR meter and they are expensive for these I'm also thinking it would be a nightmare to do since you have to cut both ends ???

Anyway, looking at the supplied chart I've worked it out roughly (going up a mil or two to be safe) to 
474mm top section from 508mm (34mm)
70mm  btm section from 160mm (90mm)

sirioantenne.it
https://www.sirioantenne.it › ...PDF
SU 375-480 PL - Sirio Antenne 

Chart link on knights.
https://www.kcb.co.uk/contents/en-uk/p2037_Sirio_SU_375-480PL__(375-480mHz).html


I'd like some opinions please before I go and butcher it especially if someone else has done one of these aerials. 

Thanks.

I've not done one myself, but have a look at this video



Hope this helps or gives you confidence to start hacking

Haha, thanks Razz, I may have spoken to him already. Pretty sure I have the breaker shouting hello

I should give him a shout out to swr mine

So I calculated 474mm top length and he slightly longer at 481mm.
And I, 70mm btm length, he quite a bit longer 102mm.
But he did say the chart recommended more to cut off.
So I'll be happy to trim it down to his measurements.
Thanks very much for that video mate.
Much appreciated.

I've not tuned up an antenna properly for that band. If I was to tune up a twig on a mag mount I would do it outside on the car. I did skip through the vid, so he might of done that, but he was showing measurements inside on the bench where they would surely be a little different?

SangueG wrote:

I've not tuned up an antenna properly for that band. If I was to tune up a twig on a mag mount I would do it outside on the car. I did skip through the vid, so he might of done that, but he was showing measurements inside on the bench where they would surely be a little different?

He did do it on the car. He put a black and white notice up "ten years later" which I laughed at, but I did wonder. 

Someone mentioned it in the comments and he confirmed he kept cutting 3mm at a time and had to keep going back and to

Also I was thinking Ray (Razz)
Your advice on the other thread
("SO239 to 3/8" adaptor and then fit a 3/8" whip adaptor")

If this antenna does end up toast. At least I have the base connection and considering the antenna was only £14.95 and the two connections probably around £11, I'll only lose around £4 and will just stick a 17cm bike spoke/coat hanger in

Ps
I just know I'm going to end up buying a
UHF/VHF SWR meter

Sharpshooter wrote:

Haha, thanks Razz, I may have spoken to him already. Pretty sure I have the breaker shouting hello

I should give him a shout out to swr mine

So I calculated 474mm top length and he slightly longer at 481mm.
And I, 70mm btm length, he quite a bit longer 102mm.
But he did say the chart recommended more to cut off.
So I'll be happy to trim it down to his measurements.
Thanks very much for that video mate.
Much appreciated.

I was a bit surprised that Ken's video was the only 1 I could find about this antenna on YouTube 

Different measurements has got me wondering if the size of vehicle could effect the measurements of the antenna? Something like a classic Mini needs a bigger antenna and a stretch limo a smaller antenna or visa versa, I don't know?

Sharpshooter wrote:

Also I was thinking Ray (Razz)
Your advice on the other thread
("SO239 to 3/8" adaptor and then fit a 3/8" whip adaptor")

If this antenna does end up toast. At least I have the base connection and considering the antenna was only £14.95 and the two connections probably around £11, I'll only lose around £4 and will just stick a 17cm bike spoke/coat hanger in

Ps
I just know I'm going to end up buying a
UHF/VHF SWR meter

I'm hoping the antenna works out

But if it does go wrong, as you say, you can cut down the longer whip and use the base connector. 
When the SWR meter comes you might get bitten by recycling and repurposing bug and start making things like this for out door radio. . . . . .



or this



Enjoy you radio

I was wondering myself if the vehicle or magmount might make a difference too.
And also how little info there is on that antenna.
But it's a nice little twig so hopefully it works out .

I was looking at the home brew twigs on delboy's blog and elsewhere.

Yes I need a swr meter.
I've already gone well over budget so what the hell, might as well buy some more bits while I'm at it

I'm certainly enjoying it up to now.
Especially with all the advice.

Cheers.

Sharpshooter wrote:

I was wondering myself if the vehicle or magmount might make a difference too.
And also how little info there is on that antenna.
But it's a nice little twig so hopefully it works out   .

I was looking at the home brew twigs on delboy's blog and elsewhere.

Yes I need a swr meter.
I've already gone well over budget so what the hell,  might as well buy some more bits while I'm at it

I'm certainly enjoying it up to now.
Especially with all the advice.

Cheers.

I'm looking forward to hear about the results and your views on the twig

What's going to be you next project, repurposing a old tv aerial to a PMR beam?

Glad your enjoying the radio 

73 for now

Ray

Razz229 wrote:

Sharpshooter wrote:

I was wondering myself if the vehicle or magmount might make a difference too.
And also how little info there is on that antenna.
But it's a nice little twig so hopefully it works out   .

I was looking at the home brew twigs on delboy's blog and elsewhere.

Yes I need a swr meter.
I've already gone well over budget so what the hell,  might as well buy some more bits while I'm at it

I'm certainly enjoying it up to now.
Especially with all the advice.

Cheers.

I'm looking forward to hear about the results and your views on the twig

What's going to be you next project, repurposing a old tv aerial to a PMR beam?

Glad your enjoying the radio 

73 for now

Ray

Well today is "Baofeng, sheds and home brew juicy IPA day" 

I've been sorting my three sheds out.
Everything is everywhere so I'm trying to sort them into.
A - scooters bikes and tools shed.
B - home brew, radio control cars, drones .
C - miscellaneous

I brought a Baofeng, hung it up and put it on radio 2 fm listening to the rolling stones night. 
I've learned that whatever frequency your on it will revert back to any transmission.
In this case some kids chatting on PMR channel lol.

And I have found some things I forgot I have, and some I didn't know I had

Sat on the reclaimed chair, drinking home brew and listening to radio slowed my progress but gave me time to ponder .


Yes Ray, I probably will spend more money and time setting up a home base and building antennas

Sharpshooter wrote:

I was wondering myself if the vehicle or magmount might make a difference too.

Only where you mount it and if the coax gets pinched where it comes into the car. On those frequencies even the smallest roof is more than a good RF ground. The only problem you'll have is if you mount it lower down so there's vertical(ish) metal near it which will detune it and if the coax gets pinched or crushed. The impedance of the coax is defined by the ratio of the outer diameter of the centre conductor and the inner diameter of the outer braid so when you pinch or crush the coax that ratio alters which alters the impedance of the coax which affects the SWR. It can even put it well into the red which you'd get with a dead short even if you measure no short with a multimeter.

Northern Crusader wrote:

Sharpshooter wrote:

I was wondering myself if the vehicle or magmount might make a difference too.

Only where you mount it and if the coax gets pinched where it comes into the car. On those frequencies even the smallest roof is more than a good RF ground. The only problem you'll have is if you mount it lower down so there's vertical(ish) metal near it which will detune it and if the coax gets pinched or crushed. The impedance of the coax is defined by the ratio of the outer diameter of the centre conductor and the inner diameter of the outer braid so when you pinch or crush the coax that ratio alters which alters the impedance of the coax which affects the SWR. It can even put it well into the red which you'd get with a dead short even if you measure no short with a multimeter.

I made sure it doesn't get pinched. Cable goes through the top of rear hatch where there is a good gap.
Magmount is virtually centre of the roof.
 The reading on the built in swr on the 9900 is I think around 1.2 and 1.4.
I haven't altered the sirio 4000 from purchase.
I've bought a swr/power meter for a second opinion though.
And I'll probably buy one for UHF.
But this sirio looks a nightmare since you have to cut both ends.

My thoughts are to cut it to the size Ken did in the video Razz posted, which is longer than the chart suggests. And try and contact Ken to ask him if he will check mine, and service a manor kestrel

Or just buy a swr meter, which I probably will eventually but like to spread the cost out

Cheers

Sharpshooter wrote:

Razz229 wrote:

Sharpshooter wrote:

I was wondering myself if the vehicle or magmount might make a difference too.
And also how little info there is on that antenna.
But it's a nice little twig so hopefully it works out   .

I was looking at the home brew twigs on delboy's blog and elsewhere.

Yes I need a swr meter.
I've already gone well over budget so what the hell,  might as well buy some more bits while I'm at it

I'm certainly enjoying it up to now.
Especially with all the advice.

Cheers.

I'm looking forward to hear about the results and your views on the twig

What's going to be you next project, repurposing a old tv aerial to a PMR beam?

Glad your enjoying the radio 

73 for now

Ray

I brought a Baofeng, hung it up and put it on radio 2 fm listening to the rolling stones night. 
I've learned that whatever frequency your on it will revert back to any transmission.
In this case some kids chatting on PMR channel lol.

Yes Ray, I probably will spend more money and time setting up a home base and building antennas

I sometimes use my UV5R when I'm working late. I can listen to BBC Radio 2 or the local D & B pirate station when it's on and Gatwick Ground which can be interesting listening.

I've been there spending money. SWR meter, beam, brackets, extra battery for the UV5R and other bits and bobs