What's new

DAB chat for the 7th Generation - beermat technology

Channel Hopper

Members
Messages
1,673
Reaction score
260
Location
KT8 Postcode
Car
Accord 7 Estate 2005
Following on from this thread in the 8th Gen section

http://typeaccord.co.uk/forum/topic/23404-dab-options/?p=243032

I thought it might be worth working on ideas to create an acceptable DAB reception system for the 7th Generation (I only have a Tourer to work on) without resorting to an aftermarket kit and all the potential pitfalls with drilling holes in roofs, sealing holes in roof, stripping/refitting upholstery , pulling new cables through blind compartments etc

The Tourer has two windows for the aerials, left for AM, MW/LW, and the right for FM.

Certainly from the following dimensions measured this morning the existing FM system does not lend itself well to adaption, though from my college training some thirty + years ago it might be worthwhile checking reception if the vehicle is in a strong signal area for the majority of its life and the owner really wants a DAB system running, regardless of the existing FM console.

I will split the posts into short ones for two reasons, to save people falling asleep and to ensure that what is in the create window does not disappear owing to an intermittent PSU fault which means shutdowns at irregular intervals.
 
In terms of the signals sent from transmitters dotted around the country, optimum reception relies on the following factors.

Distance - linked to the fundamental power of transmitter and, for these frequencies, the visible horizon that is determined by the curvature of the earth, roughly 30-50 miles depending on .......

Topography - what is between the listener and the transmitter, natural (landscape, ie hills, valleys, cliffs, expanses of water, forestation/woodland) and man-made (city landscape, buildings, building insulation/shielding, road tunnels or long gantries, interference from other similar or harmonic transmissions, and deliberate or incidental jamming.

Both the above have a height differential factor however this can be ignored to an extent. Reflection from temporary obstacles is similarly off the radar.
The receiving antenna collecting the best amount of good signal to that sent from the transmitter, on your vehicle or at home (though there are reasons why this is not always the case, but I'm not going to discuss these here).

Amplification - of the transmission once received in order to give the receiver's the optimum signal at the front end, tuner and demodulator. Optimum signal is based on resonance of the vehicle / home antenna, where the dimensions mimic the wavelength, either a full wave, or - for this discussion- a fraction of the measurement, a quarter wavelength.
Additionally the combining of other signals with the cabling of the vehicle / home that allows a reduction of the cable runs. This includes diplexing and the connections to each of the components, as well as the mechanical design inside the tuner circuitry that might be apparent for band switching, power delivery to external amplifiers or active filtering.

Polarisation of signal - In most cases FM is regarded as a horizontal polarised signal and DAB is vertically polarised. For optimum performance the receiveing aerial is best aligned to the same polarity (skew factor has an effect but not for this thread)

Orientation - Not so important for a vertically polarised signal, but for FM where the receiving aerial might be 90 degrees from the source, this will have an effect on lowering the incoming signal. The car windows are fixed and so travelling round a corner does have an effect on what is received.

Shielding. The junk one might carry in the boot of the car (or on the parcel shelf in a saloon does impact upon the reception characteristics. Aerials need clear space around their immediate vicinity to work at their best, I carry a lot of metal inside the boot space for my work, ladders included, and I do my best to keep them centralised.

Damage - The metal components on the window are subject to age, temperature changes, sunlight and physical effects, usually when equipment in the boot rubs against the material and breaks the contact but they can also be affected by cleaning, booth the effort and the chemical compounds used to clean glass surfaces.. These can be repaired with aftermarket metallic paint solutions but the change in the dimensions and the different metal used can cause chemical reactions leading to resistance and / or electrical potential. Ideally they shouldn't be touched in the first place and this thread ***umes they are in fair factory condition.
 
Measuring the individual elements in the two windows of the Tourer bring up the following dimensions for the parts that I can see (though it was dark outside when I checked, there may be more) - Dimensions in centimetres, horizontal (H) and Vertical (V)

Left side (AM reception)

Towards the Front

15.5 H
28.5 H
4.7 H
27.5 H
21.0 V

Centre line

22.5 V

at the Rear

24.5 H
9.0 V
6.0 H
15.0 V

Right Window (FM)

Towards the Front

36.0 H
30.0 H

Centre line

Main part of grid, no apparent individual aerial elements but the width of the array measures 71.0 cm to 73.0 cm increasing from top to bottom

Towards the rear

33.5 H
21.0 H
 
With the wavelengths of the two bands (FM - Band II and DAB - Band III) the minimum , centre and maximum wavelength are as follows (with quarter wavelength in brackets) . To first decimal place.

FM - 88 - 108 MHz , centre frequency 98MHz, 340 / 280 / 310 (85.0 / 70.0 / 77.5 )

DAB/DAB+ - 175 - 230 MHz centre frequency 202.5 MHz , 170 / 130 / 150 (42.5 / 32.5 / 37.5 )
 
From the above posts it becomes clear that the right hand window for FM reception is unsuitable for use as a DAB antenna, since there are horizontal only polarity elements. Additionally the amount of space left within the surround in the vertical plane makes it difficult (though not impossible ) to add to the grid with a set of DAB friendly metal lines and couple this to the existing components via a diplexing combiner tuned to FM and DAB frequencies.

What is apparent from the left window for AM are the two vertical elements (21.0 and 22.5 cm), which could offer themselves to use at receiving DAB.

With these two suggestions in mind comes the idea of loading coils to allow the shorter dimension of the element to achive resonance at the correct frequency.
 
As a retired electronics engineer with 50 years experience, it's very nice to see the effort you have put into this post. May I ask what DAB receiver you are going to use?
 
And i thought Channel Hopper meant you liked to go to France often.

This is brilliant stuff, and I can actually follow it with my basic understanding of Physics.

Keen to see the result, as I have the radio on constantly in the house, yet resort to CD's in the car because I don't like anything on FM.
 
Laird chris said:
As a retired electronics engineer with 50 years experience, it's very nice to see the effort you have put into this post. May I ask what DAB receiver you are going to use?
I'm not going to use any DAB receiver as I do not believe in the hype surrounding the standard (I would prefer if this country went down the road with DVB-T2 Lite as technically it is superior and no need to install yet another set of transmitters), though for experimentation purposes I'm hoping to either test reception with what is already in the left window, or add one or two single element wires onto the glass with a loading coil, and then introduce the output signal into a portable DAB radio sitting here doing nothing.

I also have a NOS Woodstock Blaupunkt - somewhere in the house which was the one to fit into Honda ST series motorcycles a few years back, but I'm not sure if it is forward compatible with DAB+ services.
 
I don't want to get into a "willy waving" contest but I spent 20 years working in radio planning and optimisation in mobile phone networks (2G and 3G).

Those measurements don't really mean a thing tbh, from the brief look that I took, the FM antenna on the 7th gen appears to be 1/8 wavelength over a reflective plane.(which is why, in the other thread, I've been referring to it as a patch/mesh antenna).

From the circuit diagrams, without having seen the antennnas on the 8th gen, the latter seems to use diversity antennas to improve fading.

There is a lot of mystique about vertical and horizontal polarisation, because in mobile networks the base station 2G antennas initially used two receive antennas for space diversity, but then because they ran out of room on the towers and roof-tops, they switched to a single receive antenna that had two opposed slant systems for polarisation diversity.

Basically, there are two types of fading; slow fading (which is due to topology) and fast fading (which is due to multipath). The letter is the "enemy" of all non-LOS (line of sight) radio systems. Depending on the frequency, you get diffraction over edges, which is why you can receive over distance without having direct LOS (note that microwave links have to have LOS).

But diffraction (and reflection) cause multipath, which is phase-shifts and time delays at the receiver. It's only when you get a dominant signal (or path) that the fading is not apparent to the receiver.

Anyway, back to the antennas in the 7th gen Accord, they're junk, and on a first glance, the 7th gen does not have diversity whereas the 8th gen does. Note: with more work I can be sure whether I am right or wrong on that previous statement.

For DAB, I have seen stick-on "plate" antennas which would be perfectly good, but otherwise, there is nothing, absolutely nothing, better than an external shark-fin or a whip antenna.
 
And having a blue car, I can make it look like a legit shark too.....
 
CR-V has a shark-fin antenna ....Honda must have finally realised that patch/mesh antennas are cheap and nasty.
 
freddofrog said:
For DAB, I have seen stick-on "plate" antennas which would be perfectly good, but otherwise, there is nothing, absolutely nothing, better than an external shark-fin or a whip antenna.
Certainly a whip antenna should be the way to go, but car washes up and down the country would never forgive you.
 
Seems that we're mostly all electronics engineers and/or physicists here! I ignored my technical skills and simply stuck a small vertical aerial in the bottom left corner of the windscreen for my DAB receiver. To be honest, reception is disappointing... but isn't that just DAB radio in the UK?
 
Jon_G said:
Seems that we're mostly all electronics engineers and/or physicists here! I ignored my technical skills and simply stuck a small vertical aerial in the bottom left corner of the windscreen for my DAB receiver. To be honest, reception is disappointing... but isn't that just DAB radio in the UK?
depends on several factors but you can get a loss of up to 6dB with an antenna inside the car (relative to mounting it outside the car).
 
I have found a pdf online which is a chapter from a book "New Trends and Developments in Automotive System Engineering" published 2011. The chapter is "Advancements in Automotive Antennas" link --> http://cdn.intechweb.org/pdfs/13369.pdf

Regarding Diversity reception it says
"Some automotive services use diversity to enhance the quality of the received signal. In non-line-of-site propagation environments such as the urban environment, reflections and shadows cast by buildings and other structures can cause fading in the signal strength in particular spatial locations or in given directions. In a diversity scheme two or more antennas are mounted in different locations or with different orientations on the vehicle. This provides two independent propagation paths for the signal. On an elementary level the diversity receiver switches between antennas to choose the one with the stronger signal. This provides a higher quality signal with fewer dropouts. Diversity is most commonly employed for FM radio reception purposes."


This table is a summary of the frequencies for services, and hence indicates the number of different antenna systems required

car_fequencies.jpg



This is from a section on Glass mounted AM/FM Antennas
"Glass mounted antennas provide no additional aerodynamic drag and create no wind noise which is a significant advantage over mast type designs. They also require no holes to be created in the vehicle body, which may lead to cheaper tooling for the metal work. Despite this, on-glass antennas tend to be more directional than mast antennas, which can lead to nulls in the reception at certain angles around the vehicle.
On-glass antennas were first located in the rear windscreen, and this remains a common position on sedans made today. Many SUV’s or station wagons use the rear quarter window in preference to the rear window. A variety of different shapes are used for the antennas, often forming grid or meandering geometries, with a shape that works well on one vehicle not necessarily performing well on other vehicles. No universal glass mounted antenna has yet been discovered. This is due to the effect of the vehicle body on the antenna’s impedance and radiation, which is significant for on-glass antennas."

This is from a section on Blade or Shark-fin antennas
"Many varieties of shark-fin antennas exist, having been popularised primarily by the European marques near the turn of the 21st century. Shark-fin antennas are commonly a collection of several antennas. Most designs consist of multiple narrowband antennas all located together under a single radome or housing. This housing is typically shaped like a blade or dorsal fin, and is usually located on the roof towards the rear of the vehicle"
(in my experience shark-fin antennas were originally developed for trains and some aircraft.)


The above supports what I have been saying in the other thread, which is
1. The mesh-on-glass FM antenna on the Accord was designed only for Band II, and it would not be simple to adapt for Band III.
2. Mesh-on-glass antennas are a cheaper factory installation than roof-mounted antennas.
3. The 8th gen Accord uses Diversity, whereas the 7th gen does not

If I decide to fit a DAB radio to my 7th gen, the most important part is the antenna, and IMO a decent shark-fin for Band III would be the most straightforward solution giving the best overall results in terms of reception, practicality in use, and aesthetics.
 
Yes, I have read about shark fin antennas on a BMW forum earlier (they think they invented them and the world should acknowledge it).

External would be the easy solution but with it comes the fixing and the spoilt lines, It might be that one section of the front roof rails could be converted to plastic with the aerial within, but then there is the question of the cable entry and internal run again
 
Whilst this thread is in the main on a DAB solution, the reason why some look for alternatives is down to the poor FM response which could still do with resolving in the seventh (and 8th) gen cars.

Some other potential causes , which should be ***essed/eliminated are as follows.
 
LOL that's funny about BMW owners, and if you read the pdf, an example shown is an E46, so it's possible that BMW were the "early adopters" of the factory-fitted shark-fin antenna. Note that CR-V has shark-fin.

I accept that fitting a shark-fin (fitted towards the rear) would require a bit of skill, but the end result would be the best overall.
 
Channel Hopper said:
Whilst this thread is in the main on a DAB solution, the reason why some look for alternatives is down to the poor FM response which could still do with resolving in the seventh (and 8th) gen cars.

Some other potential causes , which should be ***essed/eliminated are as follows.
8th gen uses Diversity so reception is unlikely to be an issue, and anyway, commercial FM stations will switch over to DAB in the UK over the next decade.
 
HID lighting, and the circuitry behind it.
LED lighting solutions, interior should be easy enough to identify/isolate, but how
many have checked if previous owners might have installed bulbs outside ?
Window darkening - what is contained in the fabric that is now stuck on the inside, right up against the antennas on the rear windows ?
Resprays , is there overspill of metallic paint on the window surround that might be affecting the standard reception characteristic? ?
 
Channel Hopper said:
HID lighting, and the circuitry behind it.
LED lighting solutions, interior should be easy enough to identify/isolate, but how
many have checked if previous owners might have installed bulbs outside ?
Window darkening - what is contained in the fabric that is now stuck on the inside, right up against the antennas on the rear windows ?
Resprays , is there overspill of metallic paint on the window surround that might be affecting the standard reception characteristic? ?
more reasons to fit a shark-fin and DAB radio

note that Norway is going to switch off Band II by the end of this year

the current trajectory for adoption of DAB suggests that critical mass may be reached in the UK in 2018

http://www.bbc.co.uk/news/technology-38529435
 
freddofrog said:
8th gen uses Diversity so reception is unlikely to be an issue, and anyway, commercial FM stations will switch over to DAB in the UK over the next decade.
As mentioned earlier, I'm not a fan of DAB at all, and I suspect FM lovers will have their cake and eat it for some time yet. Longer than a decade as well in many parts of the world since DAB is being considered/confirmed as non viable in a number of countries.
 
Channel Hopper said:
As mentioned earlier, I'm not a fan of DAB at all, and I suspect FM lovers will have their cake and eat it for some time yet. Longer than a decade as well in many parts of the world since DAB is being considered/confirmed as non viable in a number of countries.
well maybe so, but we live in the UK and as that BBC article suggests, critical mass may be reached sooner than you think. Once that happens, there will be a snow-ball effect until only BBC stations remain on Band II


edit: btw my quota of giving "likes" has been reached yet again :angry:
 
I forgot more than I now have in my brain on phased arrays, but there is a 'wavelength x 3 ' rule that should be observed with diversity solutions , the minimum distance between the elements that is not being observed in the vehicle dimensions. Additionally some sources mention a three aerial solution is the correct way diversity should be implemented otherwise it is little better than a single element, insofar as orientation effects of the vehicle relative to the transmitter.
 
Channel Hopper said:
I forgot more than I now have in my brain on phased arrays, but there is a 'wavelength x 3 ' rule that should be observed with diversity solutions , the minimum distance between the elements that is not being observed in the vehicle dimensions. Additionally some sources mention a three aerial solution is the correct way diversity should be implemented otherwise it is little better than a single element, insofar as orientation effects of the vehicle relative to the transmitter.
well it depends on other factors, that rule does not have to be strictly applied. In mobile base-stations, and as in that pdf in #15 (it's a good read) polarisation diversity is a practical solution where space is limited.

Anyway, my next concern, is finding a non-Honda DAB radio. I'm getting interested in doing this, dependent on cost.

A DAB receiver would only have to have an output that goes into an aux input on the Premium unit.
 
Norway still has time to renew the FM licence, and I believe the frequencies are potentially going to remain active for emergency messages to be relayed via the RDS of FM radios (or even a forced override of the radio station itself, when near the scene of an accident.

Trials of this are ongoing in Scandinavia as of two months ago, Ill have a quick read when I have time.
 
I'm using an iPad touch ATM which does not easily allow quotes in replies so forgive me if some responses are not entirely logical or in keeping with your posts.
 
^ you're up to speed ok

RDS is a good point, but surely that too would move to DAB ? Apparently 66% of Norwegians are concerned that their government is going to switch FM off. Strange in a socialist country like that.


Got to go, and I'll have to come back in a few hours when my quota for giving "likes" has got a few spare again ;)
 
With regards to splicing in a DAB system to the existing speakers, I did mention my tests would be with a standalone radio from the house with external aerial socket. I'm unlikely to change what is already in the Tourer as it is the best sound system I've had in a vehicle for some 20 years, possibly on par with that in a top of the range CX saloon.
 
I'm fairly sure there's an aux input at the back ....somewhere.

I was not that keen on the CX at the time, but now it doesn't look too bad ;)


btw, stick a motorbike whip antenna onto the DAB that you have, it'll work better
 
Top