Thoughts on this please.....

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SOTS 87 7
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Thoughts on this please.....

Post by SOTS 87 7 » Tue Sep 03, 2019 10:55 am

I came across this on eBay, seems quite expensive but well made.
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Albert H
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Re: Thoughts on this please.....

Post by Albert H » Tue Sep 03, 2019 11:58 am

The length of the phasing loop doesn't look quite right - perhaps it's the perspective.

You do know that you can make a J-pole yourself for <£10 with materials from B&Q or most other DIY stores? I used to make them out of copper plumbing pipe, with a cut-up thick plastic chopping board used for the spacers between elements.

I had a test set-up in my garden that let me put the aerial under test about 3m up in the air and well away from the house, shed and any trees. I had a clean little 1 Watt transmitter that was matched accurately to 50Ω and had a built-in SWR bridge. The test transmitter could be tuned anywhere in the band and allowed very accurate adjustment of the aerial before it went to site!

Incidentally - look up the "copper cactus" aerial. It's really easy to make and has useful gain.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

XXL
who u callin ne guy bruv
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Re: Thoughts on this please.....

Post by XXL » Tue Sep 03, 2019 5:11 pm

I know exactly who made that.

SOTS 87 7
no manz can test innit
no manz can test innit
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Re: Thoughts on this please.....

Post by SOTS 87 7 » Wed Sep 04, 2019 9:16 pm

Exactly Albert, The rather odd length of coax threw me a bit. yes, I've made one or two J poles before for 2 meters etc, and had some fantastic results. Can't say I've ever known about a "coax balun" ever fitted to one.
Go on Mr.XXL Who makes them? I will say they look nicely constructed.

RF-Head
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Re: Thoughts on this please.....

Post by RF-Head » Wed Sep 04, 2019 11:13 pm

please NO names

SOTS 87 7
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Re: Thoughts on this please.....

Post by SOTS 87 7 » Tue Sep 10, 2019 5:30 pm

Absolutely not.

XXL
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who u callin ne guy bruv
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Re: Thoughts on this please.....

Post by XXL » Wed Sep 11, 2019 11:21 am

I won’t say who made them but they are fucking awesome. A regular pirate unmatched dipole compared to this is no comparison. I’d rather buy that than a more powerful rig tbh.

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thewisepranker
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Re: Thoughts on this please.....

Post by thewisepranker » Wed Sep 11, 2019 12:38 pm

An unmatched dipole is lousy when compared to pretty much anything.

Albert H
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Re: Thoughts on this please.....

Post by Albert H » Fri Sep 13, 2019 10:13 am

The cheapest power amplifier is a well-matched antenna (and feed system). Also, don't waste your expensive power in inappropriate (PL259 / SO239) connectors. You can lose a significant amount of power just heating up those crappy connectors!

It's even better if you can use an antenna with gain - a dipole (when correctly matched) radiates a Watt for an input Watt. A dipole is convenient and cheap, but can easily be bettered at little cost. A stacked dipole shapes your coverage and gives gain very cheaply (if you get the dimensions and matching right), and a quad stack works even better. Professional installations always use aerials with gain (and shaped coverage), or if they're British and afflicted with the insane desire to transmit "circular" polarisation, they use lossy aerials. It should be noted that "circular" polarisation doesn't actually do anything to mitigate multipath distortion (it actually worsens it) and most listeners will be using vertical aerials!

I always used vertical aerials up blocks (except for link receive!) - the ⅜, ⅝ and ⅞-wave aerials all provide very useful gain and don't look obvious from the ground. The J-pole generally matches better than a dipole, and is (effectively) an end-fed half-wave. It shouldn't really give gain over a dipole, but because it's easy to match correctly, doesn't require a balun and puts the power where you want it, it's a great choice for clandestine broadcasting and always works better than a dipole.

Back in the 80s, a certain well-known engineer was astonished to see how little power we could get useful coverage with. I put a little rig (about 80 Watts as I recall) up a block on Sydenham Hill and got better coverage than his 400 Watts into a stacked dipole on Church Road Crystal Palace. The field strength difference over most of Central London was the difference between us being able to run good-sounding stereo and his signal being too noisy to do that except close to his site. Our aerial was too tall (just) - even when broken down - to fit in the lift, so we pulled it up the side of the building with a rope! Gotts thought that the signal was coming from Peckham because it was so strong there!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

XXL
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Re: Thoughts on this please.....

Post by XXL » Sun Sep 15, 2019 1:19 am

What connectors would you recommend Albert ? They all seem pretty lousy tbh.

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