This Any good ?

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piratefm
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This Any good ?

Post by piratefm » Mon Dec 11, 2017 9:44 am

Would this be any good for a low power station?

Look at this on eBay

FM UK RADIO BROADCAST BAND 88-108Mhz DIPOLE ROD AERIAL ANTENNA pirate interest?

https://rover.ebay.com/rover/0/0/0?mpre ... 2844183799

doc retro
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Re: This Any good ?

Post by doc retro » Mon Dec 11, 2017 3:11 pm

id build your own if its going to be for long term use my opinion only .but they not a silly price if you wanted to try one

Banus_radio
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Re: This Any good ?

Post by Banus_radio » Mon Dec 11, 2017 11:03 pm

NO - DO NOT USE ONE TO BROADCAST!

Look in the centre piece, it has a pcb with stripline on it. The swr will be horrific when running a few watts through it and it will burn out at higher powers.

stevemay
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Re: This Any good ?

Post by stevemay » Mon Dec 11, 2017 11:27 pm

Banus_radio wrote:
Mon Dec 11, 2017 11:03 pm
NO - DO NOT USE ONE TO BROADCAST!

Look in the centre piece, it has a pcb with stripline on it. The swr will be horrific when running a few watts through it and it will burn out at higher powers.
Confirmed these melt on 150w! Pay the extra few quid and get a proper one from cresent radio on ebay or there shop in wood green

s2000
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Re: This Any good ?

Post by s2000 » Tue Dec 12, 2017 3:33 pm

It looks to me like a receive antenna as I remember seeing one of those exact striplines inside a tv aerial centre cap I once fitted for someone. I am just wondering what purpose it serves? As far as I know, a half wave dipole in free space has an impedance of 73 ohms, making it ideal for use with 75 ohm coax. So I would of thought it'd work ok without the stripline and the coax connected straight to the terminals?

I would imagine you could use the aerial for broadcasting if you took out the pcb and connected the coax to the elements directly with a decent balun to stop feedline radiating. I wouldn't use much power with it though lol

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Re: This Any good ?

Post by yellowbeard » Tue Dec 12, 2017 4:35 pm

A couple of things on this, he is not stating impedance or power handling - that info would be on the outside of the box that he is not showing. The mounting bracket on the end looks like it would interfere with mounting it on a mast with a Shelley clamp too, so I reckon it is a receive antenna like s2000 says. When you add in the postage it becomes a little expensive for something you are probably going to have to modify to use. Personally I would make a slim jim like this one: It'd be cheaper and better. :tup

Code: Select all

https://www.scribd.com/document/8511637/Slim-jJm-Omnidirectional-Aerial-Construction-Details

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Re: This Any good ?

Post by piratefm » Tue Dec 12, 2017 8:05 pm

https://sigmaeurocomm.co.uk/product/fm- ... -500-watt/

Anyone used these before? I was gonna by a “broadband” dipole from Broadcast Warehouse. Thoughts

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Re: This Any good ?

Post by Banus_radio » Tue Dec 12, 2017 11:51 pm

https://www.ebay.co.uk/itm/FM-Broadcast ... SwCL9ZqW5V

These are the best, very very rugged.

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Re: This Any good ?

Post by Banus_radio » Tue Dec 12, 2017 11:52 pm

piratefm wrote:
Tue Dec 12, 2017 8:05 pm
https://sigmaeurocomm.co.uk/product/fm- ... -500-watt/

Anyone used these before? I was gonna by a “broadband” dipole from Broadcast Warehouse. Thoughts
Flimsey shit!

The link I posted above, you cant go wrong, supplied with tuning chart and boom arm is 90cm long

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Re: This Any good ?

Post by nrgkits.nz » Wed Dec 13, 2017 2:34 am

I never buy antennas, I always build my own. Go down to your local hardware store and pickup a couple aluminium or copper pipes approx 20mm diameter and build a jpole or end fed NRG halfwave. I've just finished mounting a jpole up on my roof and it performs much better than a dipole - there's plenty of websites with details on measurements etc... I cut my pipes a couple cm longer than required and once assembled cut bits off the end and adjusted the feedpoint to get best SWR - I got it down to 1.1, but this needs to be done away from metallic objects and up off the ground. Use a ferrite clamp on the coax at the feedpoint or bundle a few turns of coax and tie it together to form a choke - this will stop the coax shield radiating and improve the SWR.

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Re: This Any good ?

Post by McDonalds » Wed Dec 13, 2017 11:45 am

So I have just bought this
https://www.superyagi.com/FM_88_to_108_ ... 78057.aspx
I want to know will it work right away for 87.5 FM or will it need tuning?
and how do you do that as have only used retuned dipoles.

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Re: This Any good ?

Post by Albert H » Thu Dec 14, 2017 12:28 am

s2000 wrote:
Tue Dec 12, 2017 3:33 pm
As far as I know, a half wave dipole in free space has an impedance of 73 ohms, making it ideal for use with 75 ohm coax.
You're right. Unfortunately, coaxial cable provides an unbalanced feed, and a dipole antenna is balanced. There are various ways of making the conversion from unbalanced to balanced - the easiest and least critical is the Pawsey Stub. Other methods include the use of lengths of coax as delay lines to change the phase at one of the feed points.

Incidentally - I always used brown 75Ω TV coax for link receive aerial leads. This made it easier to identify the cables during a hurried rooftop install, as the mains leads were usually white insulation, and the RF output was black coated fat coax. My link receive aerials were usually Band IV TV aerials ("Group A"), which never look out of place on a rooftop. The link transmit aerial was usually a TV Yagi too, and the link rig would be matched into 75Ω. The TV-type aerial connectors were remarkably low loss, available everywhere and cheap as chips!

The TV aerials I used for links had stripline balun networks inside the terminal box in the middle of the active element. These were fine up to about 5 Watts of RF. I never needed anywhere near that much - I linked 22 miles in one instance, using just 150mW out of the link rig!
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FM King
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Re: This Any good ?

Post by FM King » Mon Dec 18, 2017 6:27 pm

McDonalds wrote:
Wed Dec 13, 2017 11:45 am
So I have just bought this
https://www.superyagi.com/FM_88_to_108_ ... 78057.aspx
I want to know will it work right away for 87.5 FM or will it need tuning?
and how do you do that as have only used retuned dipoles.
If you message them maybe they could preset it for you.

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Re: This Any good ?

Post by Albert H » Tue Dec 19, 2017 12:22 am

£59? I'm in the wrong game!

You could build yourself a nice j-pole for less than a tenner!
"Why is my rig humming?"
"Because it doesn't know the words!"
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McDonalds
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Re: This Any good ?

Post by McDonalds » Thu Dec 21, 2017 5:03 pm

FM King wrote:
Mon Dec 18, 2017 6:27 pm
McDonalds wrote:
Wed Dec 13, 2017 11:45 am
So I have just bought this
https://www.superyagi.com/FM_88_to_108_ ... 78057.aspx
I want to know will it work right away for 87.5 FM or will it need tuning?
and how do you do that as have only used retuned dipoles.
If you message them maybe they could preset it for you.
after testing it seems best around 95.0 to 96.0 right now.

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