How to Make a DAB Radio antenna

[Stewarth]

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.

 

[scotjimland]

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

 

[tonyidle]

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.

Broken Link Removed

 

[tonyidle]

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]

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.

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[Stewarth]

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.

Broken Link Removed

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

 

[Stewarth]

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.

 

[scotjimland]

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

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]

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 )

 

[tonyidle]

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.

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[bigbri5050]

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

 

[Shuismo]

Thanks for your thread appreciated your reply

 

[Magnus O.]

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.
[...]
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.

Don't ask me WHY it works, but I am stunned!!!
We had very bad reception in our car, or basically NO reception where we live (sometimes on highway I was able to pick something up). I tried three different aerials for my personal car DAB+ receiver:

• Glass aerial that came with the unit (Amazon product ASIN B07L12ZDST): sucks - no reception in the car unless you keep your hand near it all the time;
• Eightwood magnet roof antenna (Amazon product ASIN B077GTJ5GJ): fine in the car of my parents-in-law, but still no reception in our own car;
• Labgear LABDABO domestic roof antenna (Amazon product ASIN B00LFMW2O4): pretty serious piece, and had good hope it would work, but to make it work it would have to be vertical on a square bar That's a no go, but regardless: still bad reception!

After the Labgear aerial I was pretty much lost on what to try next.
And then this thread came around!

After reading the VERY IMPORTANT detail (fold back the braid shield, don't cut it off!!) of the quote here above, I had a working antenna in just a few minutes! I AM STUNNED but very happy . This self-made antenna of nothing more than a coaxial cable (and a piece of plastic tube to keep it straight) resulted in FULL RECEPTION where I had NO RECEPTION. This means: FINALLY we can receive our favorite DAB+ radio station in the area where we live, where DAB+ coverage is pretty weak.

Don't doubt if you're thinking of making this aerial. Just follow the quote above, and you'll have a working antenna. If not, then there's no hope I'm afraid - this is truely the best of all aerials I've tried.

 

[Magnus O.]

There's just one thing left and that is make the lady happy - my proof-of-concept is too ugly to make it on our car roof So I'll try to match it with a thinner piece of coaxial cable, and a thin black plastic tube.

 

[actu_8]

Works well! Couldn't get LBC on FM very well but clear as a bell with DAB. Thanks!

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[Paul3000]

I must say this is a very very interesting thread. I have trouble with DAB being a long way from a transmitter, however I find that a TV antenna amplifier most effective at producing a very good DAB+ signal. However, my problem is with DAB+ in the car. Again, using a 12 volt powered tv antenna amplifier I can get a good signal most times. However, will absolutely be giving this design of a passive antenna with choke a go to see what happens. (if you want to try the tv antenna amplifier idea get one that boosts both uhf and vhf. boost controls arent needed but are a bonus. I am using a cheap DAB+ radio, absolutely nothing special and with the antenna booster the sound is great. without it I get nothing at all. Paul Langley Australia

 

[Paul3000]

I use a tv antenna amplifier UHF VHF designed for motorhomes and caravans. btw. it runs on 12 volts.

 

[Paul3000]

this is the 12 volt antenna amplifier I use in the car and inside at home. It works well with DAB+ . However the idea of making the choked antenna is a very good one and tomorrow Ill have a go at making one. If nothing works for you, and you've run out of ideas, explore TV/FM/Dab antenna amplifiers locally. To make them compatible all you have to do is change the fitting to match the radio antenna input, or if none, use a small alligator clip on the radio's standard antenna, trying another clipped between an earth point on the radio and the 75 ohm outer braid of the coaxial cable (the headphone socket out perhaps) . It will probably still work ok without the earth connection.

 

[Paul3000]

I tried making the antenna as per the instructions, however in my location, which is a fringe area for TV, FM and Dab, and I received no stations at all, whether using my antenna amplifier or not. Perhaps if were roof mounted on the house it would work. In the course of experiments, and resultant rummaging around in the shed, I found an old el cheapo Dab+ radio the size of my palm. Forgot I had it. I extended its antenna, and did a scan and picked up 50 stations just standing in the backyard. I took it inside and it still worked just off its little antenna. I thought well this the most sensitive one I have (I have a Bauhn, a Bush, and a DGTec). I began to wonder why a $30 radio direct from China with no brand would be better at picking up stations than the other brand name products (in Australia the well respected Dab radio brands are rare like Pure, Roberts etc and too expensive for me, plus my favourite station, SBS Chill, is available on TV.) Its only the desire for a decent dab radio in the vehicle that is causing me to experiment really. the next step is try the el cheapo Chinese radio in the car. To that end I opened it up and soldered in wires so I can attach the car antenna to it. It has a rechargeable battery and 5 volt power socket. I imagine the difference between different radios in the Integrated circuits used. I doubt many radio manufacturers make their own chips. So Ive begun trying to research which the best Dab ICs are. So far Ive found this: Broken Link Removed (2009) and https://www.stereo.net.au/forums/topic/220111-best-dab-receiever-reception/ Now, it is quite possible that very good ICs, when they are replaced by later ones, enter the market at a cheap price. And such things bought wholesale in bulk might be very cheap indeed, just right for budget electronics companies to take advantage of. Its not always the case that the brand name on the finished product is the most important component of an electronics devices. Its the spec of the integrated circuits etc that matter. So the whole thing really is "suck it and see". I have no doubt though that if I could a Pure or a Roberts radio, I would not tend to experiment. Maybe Im a cheap skate or just a curious fellow. So the final thing for me to found out is - what, at the current time, is the "best" IC Dab+ module and which companies use it and are there some surprising radios out there that have the current best ICs in them at bargain prices? I dont know, Yet.

 

[Paul3000]

Now this is interesting. Prior to today's research, which stems from the antenna guide at the top of this thread, I'd never heard of this mob: <Broken link removed>
"Frontier Silicon is the world’s leading provider of chips, modules and software for digital radios. Customers include Sony, Philips, Panasonic, Pure, Roberts, Grundig and several major retailer own-brands. Since it was founded in 2001, Frontier has shipped over 30 million digital radio solutions worldwide. " "In 2015, Frontier Silicon introduced its 4th generation Kino 4 chip. This chip delivers significant cost and power consumption savings. Now in mass production as part of the Verona 2 module.(<Broken link removed>" So I guess that means I need to find out which radios have the Verona 2 module in them. This is turning into as much fun as finding the best Class D amplifier module containing the Texas Instruments TPA3255 chip. Of course even the best ICs, when surrounded by cheap supporting components, are not the best. And that is part of the fun too.

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[Paul3000]

Last one. The Verona 2 Dab+ module : <Broken link removed> "
Verona 2 is Frontier Silicon’s latest DAB/DAB+/FM custom digital radio module, designed to enable Digital Tick compliant products, using the new, highly integrated Kino 4 digital radio System on a Chip (SoC).
Designed to provide a high-performance, low-cost solution to a wide range of digital radio products, Verona 2 can be configured in master-mode for stand-alone portable, clock or (with a third party Bluetooth™ module) Bluetooth capable radios and slave-mode for audio systems with a host MCU. Capable of supporting a full colour display and Slideshow technology. Slideshow allows colourful displays to run alongside the station’s audio to provide extra information, such as, track details, web information, weather maps or traffic updates.

In addition to enabling reduced system cost, Verona 2 introduces a host of state-of-the-art technologies to optimise power consumption, RF and audio performance. "

• Colour display support with Slideshow technology
• Customisable feature-set via the latest DAB SDK
• Innovative system for minimising self-interference
• On-chip audio DAC
• Sensitivity optimised antenna configurations
• Band II/III and option for L-Band
• DAB/DAB+ sensitivity to -100 dBm (typical)
• FM sensitivity to -108 dBm (typical)
• Works with third party Bluetooth™ module
• Power consumption typical 100mW/Stand-by 1mW
• Option for fully digital audio signal path with internal EQ
• Memory:
  • Integrated for DAB/DAB+/FM
  • Built-in flash - size dependent on application
• Battery charge control on platform
• Temperature range:
  • Operation: 0 to +70°C
  • Storage: -40 to +85°C end quote how much does this module cost I wonder?

 

[rico1]

£££££££££

Change to DAB. Close down FM and sell off the frequencies to highest bidder.

That's what I saw somewhere.

Jaws

Hi
I don’t own a motorhome, though I have often thought it would be fun. However, I am no longer allowed to drive, so am DABbling with ham radio instead.

I am intrigued by the aerial described on this thread. It works excellently, but yours is IMHO the best description which hints at how. If I can find out, I plan to make some for other VHF/UHF bands.

I have done some investigating into 5/8 end-fed and baluns, but this post is simply to find out if you are willing to continue a more technical discussion (off-forum if necessary).

Hope to hear from you or any Ham who can help.

Tks

R