Compact DAB/FM aerial

[ericmark]

I have made many aerials from simple J using 300Ω ribbon to Yargi beam and HB9CV but in all cases they were for a single band.

I only worked on VHF for many years and when I went to UHF I bought ready made aerials with traps built in so they would work with both bands.

Although I was transmitting as well as receiving you are trying to do something similar, but big difference is getting it wrong will not reflect signal into the set and blow the output stage.

To receive both means the aerial will need a trap so it is seen as to different lengths for the two bands. However since it would seem one is horizontal and the other vertical can't really see how that will work!

The other method is to use a band pass filter to combine and split signals from different bands.

However radio theroy does not always work. I have used a long wire to transmit VHF never mind receive it shouldn't have worked but it did.

Personally can't see the point in DAB it's just a waste of band plan everything is transmitted else where on free view, satellite and internet I use a free to air box the only down side is the display only give a number and I have to connect to TV to find what each number is but once tuned I have far more to choose from than ever I will get with DAB.

OK you have the set clearly the better the aerial the longer the range but as already said start with a paper clip and work up to what works for you.

May be you can design your own cross di-pole aerial for omni-directional vertical is the way to go for one to one horizontal is the way I was surprised to hear VHF is horizontal as in the main I use a car radio with vertical aerial however I have noted aerials built into windscreens which are horizontal however I would have thought signal strength would alter as you turned every corner?

I think DAB was designed for cars but it's been rather a failure in Wales at least can't even get good FM coverage never mind DAB how long it will continue before it is abandoned I don't know I think it will go the way of many more inventions like 8 track, and Betamax they may have been better than cassette and VHS but too expensive and failed.

 

[theprinceofdarkness]

you can always dangle your aerial DOWNWARDS, the signal strength will be lower, but it should be less visible.
Frank

 

[plugwash]

However radio theroy does not always work. I have used a long wire to transmit VHF never mind receive it shouldn't have worked but it did.

Things to consider

1:If you have enough signal strength even a cr*p antenna will work. Antennas may have terrible performance outside their intended band but that does not mean they won't work at all.
2: antenna location is just as important if not more so than antenna design. A cr*p antenna on the roof will be much better than an ideal antenna inside a steel box.

 

[winston1]

I was surprised to hear VHF is horizontal as in the main I use a car radio with vertical aerial however I have noted aerials built into windscreens which are horizontal however I would have thought signal strength would alter as you turned every corner?

It isn't. VHF FM uses mixed polarisation. Some small local stations are vertical only. It used to be horizontal many years ago but the vertical component was added for portable/car use.
I fail to understand why horizontal halos are installed these days when a vertical dipole gives more gain.

 

[Lucid]

Personally can't see the point in DAB it's just a waste of band plan everything is transmitted else where on free view, satellite and internet I use a free to air box the only down side is the display only give a number and I have to connect to TV to find what each number is but once tuned I have far more to choose from than ever I will get with DAB.

When you can walk/jog/cycle and receive satellite transmissions or DVTB-T/T2 on the move then let me know. Ditto with internet. 3G might be reasonably widespread, but there are still areas where FM/DAB reaches but 3G does not.

As much as I dislike DAB for sound quality and for commercial reasons, there is a practical need for it in certain circumstances. DAB might be my last choice at home. But it does have applications on the move; albeit somewhat limited to walking pace only.

I think DAB was designed for cars

I have a somewhat more cynical view. IMO, DAB was designed to allow the Government of the day to sell off juicy chunks of the broadcast spectrum. It's pure and simple commercialism. More channels, less space. Money, money, money and two fingers up to the public and to quality.

... how long it (DAB) will continue before it is abandoned I don't know I think it will go the way of many more inventions like 8 track, and Betamax they may have been better than cassette and VHS but too expensive and failed.

Neither 8 track nor Betamax used the Government owned broadcast spectrum. That's the big difference.

The Treasury won't allow DAB to die because the prize at the end from selling off bits of the broadcast spectrum is just too lucrative. "The government is committed to turning off the FM radio signal" BroadcastNow article The article was readable direct off a web search. But I guess it comes up with the subscription page once the address is stored in cache. Here's a couple of additional extracts:

The government is committed to turning off the FM radio signal, but there will be no analogue switch-off until digital listening reaches 50%. At the moment that would likely miss the 2015 target date. Nevertheless, the benefits of DAB have been compared to the switch from AM to FM as the preferred medium: digital radio offers greater choice to the listener with better reception and superior sound quality.

Really?... Better sound quality??? This is part of the misinformation being peddled by the Government and its supporters for the switch to Digital.

The facts are that DAB has the potential to sound as good as average FM in the UK. But many stati0ons don't achieve even that mediocre standard. Those cited as sounding good are Radio 3 because it uses very high bit rates compared to other stations, and BBC Radios 1, 2, 4, 6 Music and 1 Xtra because they use a more efficient encoding algoriothm to get more from the meagre bit rate they're allocated. Everyone else peers in to the beggar's bowl.

Public reaction has ranged from embrace to indifference and outright resistance; digital listening currently stands at 31.3%.

Digital Radio UK has gone to great effort to get the ball rolling, with a national campaign to boost public awareness. Now with government backing, the switchover will no doubt prove a success.

"success"... that's an interesting word, isn't it. "Yes, the operation to transplant the heart was a success. Unfortunately the patient died."

Look at the charm offensive - sorry, "public awareness campaign" - with the D Love puppet

In truth the Government wants to sell the UK the idea of DAB and is relying on public apathy or confusion to obscure what is basically state endorsed robbery.

FM may get a stay of execution due to public apathy. But sooner or later the bean counters will work out a way of manipulating the figures so that they can justify the decision to switch off FM. The biggest outcry will come from car drivers. How many vehicles have DAB-capable radios fitted and, as your example shows, do they work as well as FM?

 

[ericmark]

I did an experiment I worked in Suffolk but lived in North Wales so set up the radio (FT290R with hard wired MM linear) with aerial switch and 7/8 whip and a halo and arranged with another ham to test them on my way home.

He was using rather a good horizontally polarised beam we were some where near 144.600 Mhz using single side band.

As the distance increased so the difference started to be noticed with the halo working better than the 7/8 whip around Cambridge another amateur joined us and I lost contact with the guy from Ipswich however as I continued on my journey around Huntingdon the Ipswich amateur came back in this time the 7/8 whip was out preforming the halo which was unexpected.

After this we repeated the experiment a few times and it does seem as distance increases the polarisation has less effect. As to with commercial FM or DAB the distance is enough to matter is another thing we were only using 30W over 70 miles with very flat countryside.

Having said that Moel-y-parc has an amateur radio repeater on the mast GB3MP which uses the same frequency as the Ipswich repeater and I have talked from Cambridge to Cefn-y-bedd just outside Wrexham using the Ipswich repeater until some one keyed the Moel-y-parc one when I had not bothered to re-tune. Because I knew the guy I was talking to I know it was that distance on again 30 Watt FM.

Clearly Isotropic Propagation too close for Sporadic E but it would seem the same weather conditions also caused loss of TV signal for Ipswich area as the aerial for TV was above the inversion. This was made worse still because the Dutch transmitter was below the inversion degrading any signal which did get through.

TV is in a way easy we know where the transmitter is and can aim an aerial at it but radio is broadcast from many different locations so the aerial needs to be omni-directional since a halo has a minus gain and a 7/8 whip has a plus gain it would be crazy to use horizontal for broad cast radio except for some very special cases.

With microwave I know circular polarisation is used not sure why? But with TV the polarisation is more to help rejection than receiving with repeaters vertical and main horizontal but again you need to know where the station is. The problem with digital is you can't hear or see interference from analogue stations it either works or it does not work there are no ghost images to warn you what is happening.

I know a friend used cross polarisation with TV on a rotator so he could swing aerial to receive Welsh or English but I found two aerials worked far better because they had a better rejection of unwanted signals.

Personally I think DAB is pointless as for a fixed station all is also broadcast on freeview and satellite and for a mobile station it drops out too much.

 

[ericmark]

Only just seen the reply the website requires a subscription so not a clue what it says.

Yes we can reduce the band width with Ham it was 25 now dropped to 12.5 in some regions down to 5 I think commercial is far higher around the 100 mark and if you have ever tried side band clearly no good for music unless into Pinky and Perky.

I did try packet for a while and I see how the baud rate can be increased to allow more information to travel on the same frequency but even packet was still FM. (Or AM on HF).

But as yet there is not even FM coverage along the roads of Wales in fact the mobile phone is often the only way to listen to radio the multi mast with the phone auto changing between the cells seems to be the only way in Wales.

I do see how a system similar to mobile phones could replace the FM broadcast but as far as DAB goes it just plain and simply does not work.