How to Make a DAB Radio antenna

Stewarth

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DAB isn't even CD quality. The bit sampling rate is too low. It could have been great, but the powers that be decided to lower the quality so that they could squeeze as many stations in as possible. Anyone who thinks that DAB is better than Band II FM has never listened to FM on a good quality receiver.
 
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scotjimland

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Anyone who thinks that DAB is better than Band II FM has never listened to FM on a good quality receiver.
I bow to your superior knowledge in this subject..

I only listen to them on my old car wireless
 
Aug 6, 2013
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It looks like a Bazooka antenna. I also can't see the reason for stripping the outer sheath from the bottom 9"
The sheath isn't stripped. An appropriate length of braid is stripped from larger diameter coax to form the lower leg. Here's one without the choke: a vertical dipole. The choke aims to prevent the feed coax influencing the transmission (or reception) pattern.

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Aug 6, 2013
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short wave

I've given up on digital.
Mainly I live in manchester and I have tried 3 differentDAB radios and finally bought a Roberts one which i was assured was one of the best.It has lots of nice features but is often "bubbly" even on bbc radio.If I tune into fm with same radio all channels are perfect.So I don't bother travelling with it.
Generally in the lake District reception is poor- usually Classicfm only with lots of interference.Is a short wave radio worth investigating?
Radio reception (FM or DAB) is patchy in parts of the Lake District. I've found DAB brilliant for travelling because of the instant and undetectable hand-off from one transmitter to the next. Poor reception of either FM or DAB is down to poor aerials. Mine is a dual band FM/DAB unit on the roof of the mh.
 

pappajohn

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DAB quality (when you get a good signal ) is excellent, far crisper and cleaner than FM ..
Maybe so Jim, but when you have one ear which only servers to hold your glasses on (no audio use whatsoever apart from tinnitus) and the other needs an aid to make any sound audible then all radios sound the same, it's only the transmitted rubbish which differs. Stereo can be a problem though.
 

Stewarth

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The sheath isn't stripped. An appropriate length of braid is stripped from larger diameter coax to form the lower leg. Here's one without the choke: a vertical dipole. The choke aims to prevent the feed coax influencing the transmission (or reception) pattern.

Tony, this isn't the same antenna design that the OP posted. This is an off-centre fed dipole where the lower element is shorter than than the upper due to the foreshortening effect of the feeder running through the centre of the element. The old Shakespeare Super Big Stick CB antenna used this design.

Stewart GM0GTU

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Stewarth

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It is mainly down to the coil at the bottom Brian.. That is a choke.. What you have made Jim is an end fed balanced 5/8 wave..
Dunno who came up with the design but the use of the coil, the 75 ohm coax and the fold back is very very clever indeed !
There's no mention of a "foldback" in the original post. We seem to have two different antenna designs now.
 
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scotjimland

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Not a single DAB station where we live.:Sad: We can and do transmit stuff all around the world and beyond, but not to Wales:RollEyes:
7 years on.. and and guess what.. still no DAB signal in that part of Wales.. just back from Cwmcuttan site near Llandovery , zilch.. not even an FM signal that didn't fade in and out ...

There's no mention of a "foldback" in the original post. We seem to have two different antenna designs now.
as for the how's and why's .. ? I honestly don't know.. all I do know is that it's still working.. 7 years on.
 

Jaws

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There's no mention of a "foldback" in the original post. We seem to have two different antenna designs now.
Errr.. yes there is.
The braid is folded back.

De G4VEL ( you may have come across the callsign in connection with a fairly successful range of HF mobile antennas I designed, produced and sold in the late 80's :) )

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Aug 6, 2013
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Tony, this isn't the same antenna design that the OP posted. This is an off-centre fed dipole where the lower element is shorter than than the upper due to the foreshortening effect of the feeder running through the centre of the element. The old Shakespeare Super Big Stick CB antenna used this design.

Stewart GM0GTU
I can't see any difference. The lower element capacitance will be greater when correctly tuned because of the greater diameter. The coax running through it should have no effect. The choke prevents RF from the lower element being influenced by the feed.
 
Oct 11, 2019
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While I agree with some comments on DAB radio I think it might be worth clarifying the construction method. I have just built this aerial and it has solved my DAB reception problems. There do seem to be some parts of construction missing from the various descriptions I have seen. Many people can't understand why you have to have the outer screen insulation stripped back and how this makes it work.

The key is to trim back 300mm of the outer plastic covering as described, but to leave the underlying screening copper intact. For ease of explanation I will call the point that you have stripped back to the 'centre point'. If you then push back on the copper screening from the stripped end it will bunch up around the inner conductor insulator. Push back further and it will go beyond the 'centre point' and form a reversed coaxial screen on the other side of the 'centre point' and will now lie flat on the outer sheath of the cable.

If you have done this correctly you will see that any induced currents will flow from the end of the inner conductor to the centre point while induced currents in the screen, now have to flow in the opposite direction to the centre point. Very clever! This is the key point to making the aerial work. In proper operation the induced radio signal is induced equally in both conductors. However the screen conductor is now in opposite phase to the inner conductor. this doubles the induced current and the gain of the aerial.

Tape up as in the article above and all will work well. I have put mine in a plastic tube. Don't forget to keep the whole thing pointing vertically, either upwards or downwards, as the signal is vertically oriented. It does not matter which way.

Have fun.
Bigbri5050
 
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Thanks for your thread appreciated your reply

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