DAB workshop reception

I think Johnboy25 is correct that the impedence of that antenna connector is probably 300 ohms (Check the specification information in the radio manual.) It is very unlikely you will have the equipment to measure the impedence at 230 Mhz (DAB radio frequency.) The DC resistance will not be 300 ohms. To match it correctly to 75 ohm coax you should really use a balun transformer but it should work without but there will be some attenuation of the signal.

Les.

Yes I agree with your observation Les. I was referring to impedance as opposed to DC resistance.👍😀

.

Les,

I posted a link to the 'instructions' earlier ... they appear to be silent on such technicalities.

... Maybe there is a proper manual somewhere.

MichaelG.

Most likely given that the theoretical impedance of a folded dipole is around 292 ohms.

Andrew

300 ohm being the nominal impedance for a folded dipole - if you like to look at the theory a little more in depth take a look at

http://www.vias.org/radioanteng/radio_antenna_engineering_03_09.html

Ahh, I didn't realise that there was a Mick H involved in this thread (I must start to read all threads from the start),

so apologies for the confusion caused.

Nick.

No worries Nick, would have replied earlier but I bin listening to the radio!

Mick

If you have an internet connection in your shed the easiest way to get LBC would be: **LINK**

It's just one of 30,000 stations available on that site!

Russell.

Russell, works brilliantly indoors. Unfortunately no internet in shed.....as yet! Things may change.

Mick

being purely a mechanical engineer, I would agree, (on the basis of the picture) with the likelihood of the Antenna input being 300 ohm, and with the need to match the antenna and connecting cable impedance to that of the set, to maximise power transfer.

Radio hams usually opt for "as high as possible" for antenna positioning, and in alignment with the transmitter.

At 225MHz the elements of a yagi are going to be pretty short, (digital TV is around 240 / 250 MHz from memory,

So your radio antenna is going to be only a bit larger. A folded dipole is likely be even smaller, end to end.

The data already posted plus a bit of calculation should allow you make reasonable antenna, and position it for best reception.

Having said all this, I very rarely switch on the FM radio in my shop! Too busy metal mangling!

Howard

Only partially correct. They are run by Arqiva under contract to BBC. The BBC are still totally responsible for the transmission of their services both in quality and availability.
 

Digital TV is transmitted in Bands 4 and 5, channels 21-68, give or take some in the middle being hived off. The frequency is between about 480MHz and 900MHz and DAB is in Band 3 at about 225MHz, so quite a bit different.

There should be no problem in receiving TV and radio in Boston since it is only about 30 miles from the high power transmitter at Belmont which has a mast of 1265ft, line of sight and 30 miles away, providing there is nothing in the way. The problem is usually a poor aerial being used inside, instead of a decent aerial outside at a good height.

Edited By Clive India on 10/01/2016 17:05:18

Its been 30 odd years since dabbled with radio and aerials though easy to make.

I still use an early 2002 or 3 Roberts DAB Gemini 25 RD-25 discontinued around 12 years ago able to pick up, just checked 36 stations was 59 at one point. Ultra rarely get dropouts perhaps twice a year used daily with standard taped together busted aerial.
Around 2006 bought several Pure Dabs able to receive but not listen without 80% drop outs 6 stations.
Newer Roberts have two more received back then around 40 odd stations any where.
Took plunge in 2008 and bought a Cowan D2 DAB using ear phones as the aerial, again 59 stations even in the middle of no where. SN and Sensitivity better suited to DAB than nearly all other radios and you will be making an ill informed choice just picking something off the shelf from Asda that more than likely will be useless.

Same time pondered over an Alpine DAB in car via extra tuner box, I bottled out knowing would be useless when moving and an uncertainty over Signal to Noise Ratio and Sensitivity being ok.

One or two transmit above 128 kbps but not many more suited for tonal quality than stereo imagery but good enough when machines are running and I was a hifi freak up to 25 years ago, says something.

Noticed over 13 years more and more stations pulling out of VHF and DAB going internet only. Luckily have Ethernet hard wired in to workshop done 12 years ago, so when Roberts packs up, cant believe its still going I would go Internet route but what to get?

If you go internet keep an eye on the data rates and accumulated data usage unless you are on an unlimited tariff.

The proximity of the Belmont transmitter just adds to the frustration Clive. I would have thought that being so close it would blast out transmissions on a crystal set!

Mick

Mick,

For what it's worth ... Here is the Ofcom DAB Coverage Plan for Lincolnshire.

I still think the biggest problem is Sony's receiver [and the instructions!]

Have you tried another receiver in the same location ?

MichaelG.

Thanks for that Michael and I wish it were that simple. I have just bought a new car with an allegedly state of the art DAB radio and the problems are similar if not worse. It is a common complaint in this area. Having said that I think that the flimsy aerial connection to the Sony is a poor show.

Mick

Mick,

It does took like there are local area problems

It may be worth keeping an eye on this site.

MichaelG.

Michael, I think that that site and attached comments tell it all in a nutshell. Strangely, or even perversely the coverage map for 11D does not seem to cover Skegness.......but I went to Skegness yesterday and reception for LBC was perfect, cutting in at Wainfleet!  I was beginning to think that I might be the problem!

Mick

Edited By mick H on 11/01/2016 08:30:52

Mick,

Looking at this version of the map, I notice that you are almost equidistant from three major DAB transmitters. ... I am way out of my depth, now, but I suspect that a directional antenna would help a lot.

Multipath reception causes 'birdies' on FM, but Digital probably just fails !!

Hopefully, others can advise in detail.

MichaelG.

I understand your thinking Michael and the logic. However, DAB is not transmitted in the same way as FM.

It is much more resilient to multipath.

National DAB is transmitted on a single frequency network which is synchronised and therefore the problem you highlight is addressed.