- Posts
My fellow radio scientists,
My fellow radio scientists,
Radio Joe here, I have a question that I can’t find an answer for so I am turning to the great knowledge base of the part 15 broadcasters. For a background, I have many years experience working with radio electronics, but I admit, I will never know it all nor do I think I do.I have always wanted to use some of my car radios in my home thinking of the great reception I can get and also put some of them to use and have some fun with them.
The radios I have are not old car radios, nor is aftermarket, the present one Chrysler radios from 2006. This is a CD, Cassette and AM/FM type.I know in the past for AM there was an antenna trimmer on car radios, I know all about antenna trimmers for AM and adjusting them always did the trick for peaking out the antenna for top performance. It never affected FM performance nor was it suppose to.
On the “newer” factory car radios (and after market) there seems to be no antenna trimmer to be found. Service information is hard to get and I don’t even know where to find service info on these radios. It used to be Howard Sams covered them now there is nothing. Anyone know of a source of factory service manuals for OEM car radios?Anyway I would like to know exactly what the deal is on the AM antenna trimmer, do new radios have them or is the antenna match electronically made inside the radio through the electronics, or does the manufacture just ball park the antenna match knowing the length of connection cable and antenna for their cars or do you just get what they give you.
I never had a problem with performance when the radio is installed in the vehicle, but on the bench a piece of 30 inch wire doesn’t cut it.Most of the time when tuned to FM ( using a 30 inch piece of wire ) things work out as far as good reception, but it still isn’t as good as when the radio is installed in the vehicle.
I know the body of the car is essential for ground plane and I’m assuming that is part of the problem when the radio is on the work bench and reception is poor.Another question for my good scholars on the part 15 board is: Just what kind of antenna system will work with car radios which are located in the house? When used in the home, there are problems with electrical interference you don’t get driving down the road unless near noisy power lines etc. When using just a piece of 30 inch wire up in the ceiling there are noise problems, so do I make a ground plane antenna outside and feed with coax and if so, will the long coax upset the tuning of the front end of the radio to reduce sensitivity? I know if the coax impedance is correct that length of the coax shouldn’t be a factor except for signal loss, but it seems from my experience performance always degrades when using any kind of antenna except when the radio is in the car and I use the car antenna.
And no, I don’t care to park my car in my basement ha ha, ok with that said if anyone knows answers to my questions based on actual experience and fact, not just ideas, please let me know about how modern day car radios handle the antenna trimmer, and if you have had a successful car radio installation in your home let me know what you used for the antenna.
I have had good luck also by using an antenna tuner prior to going into the radio, the antenna tuner was a simple loopstick which tuned the antenna but that was a work around and I would like to do things properly.
Hope someone out there has some answers, I did searches on the web and found all kinds of old wives tales types of answers about my questions but none which were not based on facts. Well, Id like to write more… but I have broadcasting to do !
Thanks Guys !Radio Joe
Total posts : 45366Well to start, these new radios are not even made in this country. They are imported, just like 90 percent of the rest of the vehicle is, and assembled here by automation.
Also vehicle radios work by using the metal of the vehicle (what little metal is there anyway) for a ground plane. The antennas are embedded in the windshield. Combined, it forms a roving ground plane type antenna system.
Another thing to consider, and you referenced to it, is that in vehicles you do not hear noises unless driving under power lines or close to them. The vehicle radio your setting up in the basement, well your pretty darn close to noise sources.
Here is an experiment you can try. Power the radio from a battery source and tune to the noise. Then kill all the power at your house at the breaker box (primary breaker), and watch how fast that noise dumps down to next to nothing.
There are a lot of inductive loads these days on the power grid, much more than ever before with these power saver light bulbs, dimmers, LCD and Plasma TV’s and other electronics running off switching power supplies, all of which induce tons and tons of garbage onto the power wiring in and around your home..all contributing to the heavy increase in noise, on all bands.
Even filtering the power source connected to the radio wont help much because the other wiring in the home still has the induced noises on them and the radio is simply picking up that noise. Possibly putting chokes on all the electrical wiring might help, but then there are the other homes nearby with the same induced noises on their wiring.
Try running an outdoor antenna system as far away from overhead power lines or underground power lines if you know where they are, and that will probably help a great deal.
It’s a noisy world out there!
RFB
Total posts : 45366Being indoors is a major factor in steep signal loss compared to the outside.
Yes, having an outdoor antenna is probably the main way of achieving near “in car” performance.
Total posts : 45366In the good old days the antenna trimmer was many times located behind one of the control knobs. To gain access the concentric knobs were removed.
I used a 30 something inch vertical whip when I had an indoor car radio and it worked well.
Neil
Total posts : 45366What kinds of power supply work well for auto radios in the house?
Total posts : 45366When I think about it, that radio was on all
the time when my Dad and I drove around
in that increasing rusting old blue wreak. That
53 Olds had seen it’s best days in it’s first
five years. Then after that, it started to get
to be a pretty flaky car.But the car RADIO was the thing.
Listening to it, there were many firsts for me.
It was the first time I heard anything close to Hi Fi.
I had never heard the bass instruments, in music
before. But one day around 1960, I did, on my
Dad’s car radio.I was the first time I heard radio drama.
It was the first time I heard NBC Radio’s Monitor, and
the wonderful Monitor Beacon. And on multiple
NBC network radio stations. It was the first time I
realized that there were lots of radio stations, not
just a few.It was also the first time I ever heard a radio station sign
off. WRYM, RHYME RADIO, 840, 1 kW day only, In
Newington, Connecticut. Probably about 1962. I heard
the word kilocycles for the first time. And 1000 watts.
What did that mean? It started to get my 8 year old
mind going.And of course, that radio had to have a vibrator, to help
bring the voltage up for the vacuum tubes. That was cool,
too.Moving forward to 2012.
I still ride around with my Dad in the car. He will be
83 in August and (knock on wood real real hard) he is still
doing pretty well. Now, he picks me up at home to
take me to job number 2 (the day job). I always tune in
DOGGRADIO 2’s FM on 90.9 MHz.It’s always the same. When sitting in the driveway, I ask
him if I can tune in my station. We always tells me to
do whatever I want. I tune into 90.9, and usually it’s
really old big band music. He always says that it sounds
great. Then we pull out of the driveway. We travel up
a hill a couple of hundred feet, and then the signal is
gone. I always say to him something like, “Crud, I wish
my FM signal could go further.” Then he laughs like he
doesn’t quite understand.A few minutes later, I’m at wonderful job number 2,
the SuperMarket.My Dad is a great guy. A graduate of Annapolis, class
of ’52. He was a Navy pilot. He used to land planes
on aircraft carriers. (Although that wasn’t his main
thing.) He actually met Jim Lovell, of Apollo 8 and
13 fame. He doesn’t know him very well, but they
ate together at a class reunion years ago. My dad said
Jim Lovell was a really nice guy.And so it goes.
Best wishes,
Bruce, DOGGRADIO STUDIO 2
Total posts : 45366A car antenna has a length of shielded cable running from the radio to the antenna element (whip or windshield wire). The coax is NOT a transmission line. It serves only to shield the inner wire from noise inside the car. Because the coax shield surrounds the antenna wire, it is behaves as a capacitor to ground in parallel with the small antenna element capacitance. The capacitance of the coax is typically 20-25pf per foot, and the shielded part of the overall antenna assembly is typically about 3 ft. So the capacitance to ground due to the coax is in the neighborhood of 60-75 pf.
The older car radios had a semi-hidden trimmer to compensate for the coax capacitance. I don’t know how modern car radios do the compensation, but the fact remains that the antenna still has that pesky added capacitance due to the coax.
To use a car radio indoors, either you should use a complete car radio antenna assembly with the coax, or you can use a wire with a trimmer capacitor to ground at the car radio antenna input. A trimmer with a max capacitance of about 100 pf seems appropriate. Adjust the trimmer for max signal. This will also allow compensation for varying lengths of your antenna. The longer your antenna wire, the lower the setting of the trimmer. The end result is that your are simulating the behavior of a real car antenna assembly.
Total posts : 45366Very good tip for an indoor antenna and will help increase sensitivity.
Unfortunately it will also increase the sensitivity to the surrounding noise from the home wiring and other electrical devices.
Only way to get away from that is to put up an outdoor antenna so that you simulate the condition of the vehicle radio away from noise sources. Since we do not need to worry about ignition noise, which is what the coax shield and B+ filter inductor does in a vehicle, the performance should be even better on the car radio set up indoors with an outdoor antenna.
Experiment and find what works. That’s the neat thing about the hobby..discovery!
RFB
Total posts : 45366Carl asked what kind of power supply would work. No one’s answered him yet.
Carl, you would need a well regulated power supply. Now, in my experience, there’s regulated and then there’s REGULATED. The cheap ones from Radio shack and other places that claim that they’re regulated often introduce hum into the equation – I once had a ‘regulated’ Pyramid power supply and it was worse than a good standard wall wart branded by ICOM.
If I were going to do this (and I have done, many, many years ago when I was a teenager and couldn’t afford a high end, sensitive radio), I would do some research first and be prepared to try a few out. You don’t need a power supply that delivers more than a few amps, but they need to be ‘quality’ amps.
Total posts : 453661 120VAC to 15VAC 2A power transformer.
1 full bridge rectifier
1 3000Mf 25VDC cap
1 7812 regulator
1 200Mf 25VDC capTo add: Be careful of which car radio type you use. A lot of these newer radios have part of their circuitry in another module buried in the dash, behind the kick panel or even back in the trunk where the power amp is. No worry if it’s an aftermarket deck or older deck, but most stock stuff these days are modular and will not function since part of their guts are located elsewhere besides where the front panel controls are.
RFB
Total posts : 45366You can use a salvaged PC power supply or buy a new one for less than $30. Search the web for ATX power supply or ATX12V power supply. The lowest wattage rating seems to be 250W which is way more than needed.
The +12V output of ATX12V supplies is rated at anywhere form 8 to 15 amps and is well regulated per the Intel standard document. Higher power (more expensive) supplies have more than one +12V output, each rated at about 15 amps. You certainly don’t need all that power, but if you have one, you can use it.
Total posts : 45366you could build something like this to get your antenna outdoors and away from internal household noise
http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=SM100
Total posts : 45366PC power supplies are switching power supplies and do have multiple outputs, except for the minus 5 and 3 volt rails, all of the voltage rails are merely the same output points with more than one wire. In other words, it’s like having 10 wires off the same + connection point. Just open one up and see.
Sometimes the 12V rails will have up to 10 wires, the 5v rail up to 5 or more, and the 3v rail, same thing.
It does not mean there are 10 sections of individual 12 volt generating supplies, or 5v or 3v.
And they do put out good current. Problem is..they are noisy as hell. I don’t mean fan noise..I mean electrical switching noise.
This is why inside the computer, and you can see for yourself, simply look at the mother board and all those parallel connected capacitors in several rows, as well as the inductors to filter out that switching noise on the DC side.
The AC side is no more filtered than with a couple of bypass caps and the two AC wires wrapped around a ferrite core a few times, then on to the power supply board. There may be an inductor on the power supply board as well. Not a whole lot of filtering but some.
Still your going to run into problems with the sensitive receiver, the indoor antenna and adding more noise source with all the rest of the noise sources already present…what are you gaining there except adding more noise to pick up on the sensitive radio already picking up noise??
Use a linear supply.
RFB
Total posts : 45366PhilB’s mention of using a computer power supply made some brain chemistry click up stairs in the vicinity of the hair-do…..
I have a CB transceiver that a trucker friend gave me when he installed a newer one, and I’ve always thought I’d build a power supply and have CB ready to go (I live 1-block from a major highway).
Then, yesterday when I was hunting for my scope, which I haven’t used since the mid 90s, I noticed a computer power supply politely being forgotten down on a shelf.
Yup.
Total posts : 45366Ya well I would filter that thing to the nth degree like they do in the computers they are designed to operate in the first place. There is a reason why those mother boards have all those filtering electrolytic caps in parallel along with the plentiful inductors to boot.
It isn’t for a beauty contest or for the ohh ahh factor.
And one thing that was not mentioned about those PC power supplies. The more current they have to produce, the harder the switching (on time) they hit, in turn the more pulse noise produced, both on the supply side, AC side AND EMF side of things.
That is why they are in a metal case. Doh!
Don’t take my word for it…try it and find out! Heh.
Or perhaps another prospective might convince you all that I’m not talking out my arse here…
Switching Power Supply..as noted by a HAM
Fell better now?
RFB
- You must be logged in to reply to this topic.
