USB/Bluetooth -> FM Transmitter for Car...

S

Sid 03

Guest
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

Any help is appreciated.
Thanks
 
C

Clifford Heath

Guest
On 24/1/22 2:47 am, Sid 03 wrote:
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

Not very far, if the one on our Subaru is anything to go by.
On a recent trip in the countryside (no local interference) we had to
revert to a wired connection to continue listening to the audiobook we
had on. Obviously on the highway there\'s a limit tolerance for fiddling
with radio tuning etc, so it might have just drifted outside the AFT
range of the FM channel we were on, but still, that\'s something to think
about.

If you wanted one for your house, I\'d look for a device sold for that
purpose, and failing that I\'d open it to attach a better antenna.

CH
 
J

Jan Panteltje

Guest
On a sunny day (Sun, 23 Jan 2022 07:47:11 -0800 (PST)) it happened Sid 03
<sidwelle@gmail.com> wrote in
<55aff9a0-ec42-4be7-b551-968502252c98n@googlegroups.com>:

I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for
music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with
?

No idea



Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

Any help is appreciated.
Thanks

I have one. works perfectly on the same floor to a big FM radio, not tried in other places in the house,
plays mp3 music from SDcard.
Payed about 9$ for it on ebay.

Your neighbors may receive the transmissions too, copyright?
 
D

David Brown

Guest
On 23/01/2022 16:47, Sid 03 wrote:
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

I think you\'ll find the answer varies, and is very unlikely to be well
specified. Clifford gave you a case where he had trouble within a car.
I on the other hand have experience listening happily to the
transmitter in another car when we were travelling together - mostly
reasonably closely, but certainly not bumper-to-bumper. I think there
would be no problem picking up the signal throughout the house when that
car was parked outside.
 
J

Jan Panteltje

Guest
Or you can make your own:
http://panteltje.com/panteltje/pic/fm_pic/

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2510209.m570.l1313&_nkw=BH1415F++FM+&_sacat=0
 
S

Sid 03

Guest
On Sunday, January 23, 2022 at 10:59:14 AM UTC-6, Jan Panteltje wrote:
Or you can make your own:
http://panteltje.com/panteltje/pic/fm_pic/

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2510209.m570.l1313&_nkw=BH1415F++FM+&_sacat=0

Nice links: When I get some time I will order one of the kits.
Thank you.
 
J

John Walliker

Guest
On Sunday, 23 January 2022 at 16:51:56 UTC, David Brown wrote:
On 23/01/2022 16:47, Sid 03 wrote:
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

I think you\'ll find the answer varies, and is very unlikely to be well
specified. Clifford gave you a case where he had trouble within a car.
I on the other hand have experience listening happily to the
transmitter in another car when we were travelling together - mostly
reasonably closely, but certainly not bumper-to-bumper. I think there
would be no problem picking up the signal throughout the house when that
car was parked outside.

The answer is actually very well specified, but many devices ignore the
standard. The maximum effective radiated power in the UK and the EU
is 50 nanoWatts when measured under specified conditions which include
ferrite absorbers at regular intervals on the power cable. This means that
without such ferrites, as for example in a car, the power radiated will be
significantly higher than 50nW because of radiation from the wiring harness.
This is just as well, because a genuine 50nW signal only gives a decent
signal to noise ratio at a range of up to a few metres. I designed such
a product a long time ago and was present in the test lab when the
measurements were made.

John
 
D

David Brown

Guest
On 24/01/2022 11:49, John Walliker wrote:
On Sunday, 23 January 2022 at 16:51:56 UTC, David Brown wrote:
On 23/01/2022 16:47, Sid 03 wrote:
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

I think you\'ll find the answer varies, and is very unlikely to be well
specified. Clifford gave you a case where he had trouble within a car.
I on the other hand have experience listening happily to the
transmitter in another car when we were travelling together - mostly
reasonably closely, but certainly not bumper-to-bumper. I think there
would be no problem picking up the signal throughout the house when that
car was parked outside.

The answer is actually very well specified, but many devices ignore the
standard. The maximum effective radiated power in the UK and the EU
is 50 nanoWatts when measured under specified conditions which include
ferrite absorbers at regular intervals on the power cable. This means that
without such ferrites, as for example in a car, the power radiated will be
significantly higher than 50nW because of radiation from the wiring harness.
This is just as well, because a genuine 50nW signal only gives a decent
signal to noise ratio at a range of up to a few metres. I designed such
a product a long time ago and was present in the test lab when the
measurements were made.

I meant \"not specified\" in terms of documentation on the devices - as
you say, not all devices will follow the rules and standards. But it is
interesting to know what the standard says, even if it is ignored in
practice!
 
S

Sid 03

Guest
On Monday, January 24, 2022 at 10:49:58 AM UTC-6, David Brown wrote:
On 24/01/2022 11:49, John Walliker wrote:
On Sunday, 23 January 2022 at 16:51:56 UTC, David Brown wrote:
On 23/01/2022 16:47, Sid 03 wrote:
I see a lot of these small transmitters that plug into the cig\' lighter for power and accept USB and Bluetooth as a source for music to re-transmit to your car radio via FM.

Easy to find dozens on Amazon and other sites, but one spec that I don\'t see on any of them is how much power they transmit with ?
Can I use one in the house and transmit to all the FM radios in the house ?
I am looking for an effective radius ?

I think you\'ll find the answer varies, and is very unlikely to be well
specified. Clifford gave you a case where he had trouble within a car.
I on the other hand have experience listening happily to the
transmitter in another car when we were travelling together - mostly
reasonably closely, but certainly not bumper-to-bumper. I think there
would be no problem picking up the signal throughout the house when that
car was parked outside.

The answer is actually very well specified, but many devices ignore the
standard. The maximum effective radiated power in the UK and the EU
is 50 nanoWatts when measured under specified conditions which include
ferrite absorbers at regular intervals on the power cable. This means that
without such ferrites, as for example in a car, the power radiated will be
significantly higher than 50nW because of radiation from the wiring harness.
This is just as well, because a genuine 50nW signal only gives a decent
signal to noise ratio at a range of up to a few metres. I designed such
a product a long time ago and was present in the test lab when the
measurements were made.

I meant \"not specified\" in terms of documentation on the devices - as
you say, not all devices will follow the rules and standards. But it is
interesting to know what the standard says, even if it is ignored in
practice!

Jan, looking at all those projects from the link(s) that you posted, most talk about minimum frequency drift.
I thought that crystal controlled radios did not experience frequency drift, or at least negligible drift ?

Thanks
 
J

Jan Panteltje

Guest
On a sunny day (Mon, 7 Feb 2022 19:41:57 -0800 (PST)) it happened Sid 03
<sidwelle@gmail.com> wrote in
<9bdd5c05-255b-4802-8178-4edf9df28c9dn@googlegroups.com>:

Jan, looking at all those projects from the link(s) that you posted, most talk about minimum frequency drift.
I thought that crystal controlled radios did not experience frequency drift, or at least negligible drift ?

Yes crystal controlled, in this case phase locked loop should have negligible frequency drift
for an _FM_ modulated radio transmitter,

As long as the loop is locked that is.

But if you have a 2.4 GHz transmitter locked to a 10 MHz crystal
then the 10 MHz is multiplied by 2400 / 10 = 240, and so is its error.

If the 10 MHz now drifts 10 Hz (1 part per million, so 1 ppm) then the 2.4 GHz will drift 2400 Hz.
If the modulation type was SSB then a 2400 Hz shift will be totally out of audio range!
So a solution in a case like that (QO100 ham satellite) is to lock the 10 MHz crystal to for example
a 10 MHz Rubidium frequency source that has a much lower drift than 10 Hz.
Or use some other precision 10 MHz source.
 

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