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Combemartian
#1 Posted : 04 August 2018 10:22:47(UTC)
Combemartian

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Hi everyone, the FM radio reception in my 95 mk1 Eunos import is pretty poor.

I know the radio itself is okay as it used to be in my mk2 before I traded it in, and the reception was fine in that. It's a Sony unit about 6 years old.

So far I have remove and cleaned the ( electric ) aerial, checked for a good earth connection at the aerial base, connected a separate earth wire from a solid ground point to the radio, run a new coaxial cable between the aerial and the radio using good quality cable. I used 75 ohm cable, as I had a drum of it to hand. I believe in an ideal world I should have used 100 ohm but I didn't have any to hand and I don't believe it would make that much difference in this application. I have even tried fitting an aerial booster amp from a Mazda 3 but the reception is still poor. I don't think it's interference from the engine/alternator as there is no rpm related background noise. Reception is fine in strong signal areas but as I drive along the AF function struggles and often drops out completely. I had thought of fitting a longer manual aerial but would rather keep original if possible.

Do any other Eunos owners suffer from poor reception?  Can anyone think of anything else I could try to improve things?

Many thanks as always.

Dave.

1998 mk2 racing bronze. Died RIP
2000 mk2 silver gone but not forgotten.
2011 mk3.5 metropolitan grey
1995 mk1 chaste white
RichardFX
#2 Posted : 04 August 2018 16:38:53(UTC)
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Originally Posted by: Combemartian Go to Quoted Post

Hi everyone, the FM radio reception in my 95 mk1 Eunos import is pretty poor.

I know the radio itself is okay as it used to be in my mk2 before I traded it in, and the reception was fine in that. It's a Sony unit about 6 years old.

So far I have remove and cleaned the ( electric ) aerial, checked for a good earth connection at the aerial base, connected a separate earth wire from a solid ground point to the radio, run a new coaxial cable between the aerial and the radio using good quality cable. I used 75 ohm cable, as I had a drum of it to hand. I believe in an ideal world I should have used 100 ohm but I didn't have any to hand and I don't believe it would make that much difference in this application. I have even tried fitting an aerial booster amp from a Mazda 3 but the reception is still poor. I don't think it's interference from the engine/alternator as there is no rpm related background noise. Reception is fine in strong signal areas but as I drive along the AF function struggles and often drops out completely. I had thought of fitting a longer manual aerial but would rather keep original if possible.

Do any other Eunos owners suffer from poor reception?  Can anyone think of anything else I could try to improve things?

Many thanks as always.

Dave.

Hmm, if you have used a different characteristic impedance cable from that intended by aerial and receiver, then it is quite probable that the FM is compromised. Cable impedance mismatch is less of a problem for long wave or medium wave where the signal wavelength is significantly longer than the cable, but with the FM you might just be tuned out!  You might be able to trim it in again by adjusting the cable length...

 

The correct cable is RG62 or RG62/U both with Z = 93 Ohms.  This is hard to find in economic quantities.  The radio will have a matching circuit on its input, and the aerial will be tuned to suit.

If the impedances of terminations and cable all match (key word) then the signal cannot bounce at any mismatch points and travels on through quite happily. 

 

An old story from work during the 1970s in the old analogue colour TV days. One of the educational tricks we used to play on trainees was to put a drum of 50 Ohm video cable into the usual 75 Ohm system, and then give them a training exercise to equalise the approx 100metre 'long line'.  This was actually impossible because of the nature of the notches in the different frequencies of the video.  If they were keen they would keep on struggling while we went to tea.  When we returned, just in time to send them off before the tea bar closed, we would then swap the drum for one with the correct 75 Ohm cable, set all the equaliser controls to the usual points and when he came back with his paper cuppa burning his hand we had 'fixed it' in just a couple of minutes whereas he might have wasted an hour.  Then we pointed out the different drum, and a few other tricks one can do with tuned lengths of cable on a colour system.

Another one was to swap the red and green inputs of an RGB monitor fed from a test signal generator, scramble the shadow-mask with a brief pass of the degaussing coil, then bring in the trainee to degauss and converge and colour balance the monitor with the Cross-hatch and Colour Bars test patterns - impossible, but some came close!  Again the tea break trick.  And again the deceit was revealed, as yet another example to always check for 'finger trouble' before diving in to fix the equipment.

And just before I retired I was bitten by one of my designs which had a serial digital input (SDI) video stream running at 1.5GHz via an SMB connector.  We could not figure out where about 70% of the signal was being lost until I put a TDR (Time Domain Reflectometer) on the input, and discovered that where the signal passed through the ground plane of the printed circuit board the characteristic impedance dropped from 75 down to something near 25 and then was back to 75 on the tracks.  It turned out that the footprint of the connector (pattern supplied by the connector manufacturer) was wrong, I recalculated the size of the ground ring-hole and all was well, except the expensive board needed to go to issue 2.

 

 

2008 Niseko NC 2.0
2016 Mazda3 SE-L Nav 2.0
Combemartian
#3 Posted : 04 August 2018 20:33:18(UTC)
Combemartian

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Hi Richard, thanks for the comprehensive reply. I don't think the 75 ohm cable I fitted is an issue as I only fitted it to try and eliminate a possible failure of the original as its quite thin and I thought it may have been damaged at some point. Reception is the same with both the original and the new one I fitted. I think I've got a manual aerial in the garage somewhere so I might put that in just to see.
I just wondered if any othe mk1 Eunos owners also had bad fm reception.
Thanks.
D
1998 mk2 racing bronze. Died RIP
2000 mk2 silver gone but not forgotten.
2011 mk3.5 metropolitan grey
1995 mk1 chaste white
missfire
#4 Posted : 04 August 2018 20:52:59(UTC)
missfire

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Buy yourself a cheap retractable aerial ,and plug into the rear of the radio directly.Not through your extn lead.This will prove if the radio is ok.
RichardFX
#5 Posted : 04 August 2018 21:23:06(UTC)
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Missfire has the right idea.  Eliminate the unknowns.

Car radios are renowned for their excellent sensitivity, hence why so many workshops use them with just a bit of wire hanging out the back!

2008 Niseko NC 2.0
2016 Mazda3 SE-L Nav 2.0
drturbo
#6 Posted : 09 August 2018 21:25:22(UTC)
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Our 96 UK 1.8iS has an electric aerial and the reception is lousy, the only station it'll get is Radio 1!!

I don't think its any worse if I unplug at the aerial end so seems the aerial is doing bugger all..

If I get some time I'll try and investigate it further..

Mark

Doctorates in several areas, car related, electrical, guitar amps, lawn mowers, tractors..... oh, and turbo's. Just not Windows 10!

1991 NA Eunos 1.6, Classic red
1996 NA 1.8iS, Brilliant Black
2016 Mazda 3 2.0 Sport Black, Soul Red
2011 Suzuki Alto SZ4, Silky Silver
charcoal
#7 Posted : 10 August 2018 16:10:12(UTC)
charcoal

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Hi All

Owner of a mk3 Venture for a month fm radio reception, no problem.

Am, and LW rubbish. spoke to various dealers, they reply that's as good as it gets.

Spoke to Mazda customer services, very nice people, useless with information.

Help/suggestions very welcome Cheers

drturbo
#8 Posted : 12 August 2018 17:09:37(UTC)
drturbo

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Just in case it helps anyone, I've just found the culprit to the poor reception in our 1.8.

Turned out it was the cheap little adaptor that converts from the old school aerial plug to the new ISO one. I just used a 3 foot length of wire and pushed it directly into aerial connector on the head unit... perfect reception. Then took the wire away and held the center of the cars aerial plug against the head units center pin and again, perfect reception.

Now temporarily fixed until I find a decent adaptor.....

Mark

Doctorates in several areas, car related, electrical, guitar amps, lawn mowers, tractors..... oh, and turbo's. Just not Windows 10!

1991 NA Eunos 1.6, Classic red
1996 NA 1.8iS, Brilliant Black
2016 Mazda 3 2.0 Sport Black, Soul Red
2011 Suzuki Alto SZ4, Silky Silver
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