OT but related. Help with "whole house" fm xmitter antenna?

frascati

DTVUSA Jr. Member
#1
I've grown very fond of internet radio broadcasts while working in my basement shop. I listen on an HP mini plugged into a stereo. I'd like to be able to listen to the broadcasts over any handy fm radio while gardening, working in the garage, etc. I live on four acres in a lightly populated area and the xmitter I've chosen is well below the xmitting power threshold of the average that the hobbiest Christmas display enthusiast crowd utilizes to broadcast to passersby in their automobiles.

What I liked about this little unit was the dead simple plug and play usb connectivity and the dead simple GUI for adjusting frequency and range. And it was less than seven dollars with free ship! All information links are below.

Since there are so many very helpful members here (as I discovered while researching OTA antennas recently) I'm hoping I might get some advice on implementing a little 1/4 wave antenna with this little USB xmitter.

I ordered it and....

Arrived well packaged in bubble wrap three days ahead of estimate. Unit itself surprisingly well built with crimped metal clasps joining the halves of the case. Installed driver and plugged in unit. Selected an empty space on the dial of an fm radio, opened my last.fm scrobbler and typed in Steve Earle, and it worked just beautifully. Truly plug-n-play for the novice.

Slight ambient hum noticeable between songs that was eliminated simply by touching the metal side clasps with fingertips. Range sufficent for one large room.

I removed side clasps and split the case. 3.5 inch antenna wire was doubled over and bare end of it was simply tucked behind the metal side clip. Guess they were using the side clip as part of the antenna element. No solder. Must have been the source of the spotty ground and subsequent hum.

Ran xmitter as bare board with antenna wire extended and range improved to the other end of the house very clearly. No hum. Never owned a xmitter to compare but I"m pretty impressed.

Does not, however, reach the back yard or garage. That is my goal actually to have web broadcast music available while wrenching the motorcycles or gardening in the back, or sitting around the fire with a cheap radio. High fidelity is not a premium for me but the quality so far compared to actual stations on the dial is quite good.

So can anyone help me with a couple of antenna questions specific to this little unit?

Is a 1/4 wave ground plane antenna, built according to this calculator,
http://www.fmuser.com/uploadfile/201004/8/2349199801.png
inherently balanced and therefore SWR (which I have no means to measure) not a concern for me?


Are the tiny SMA connectors and associated tiny coax common to wifi applications compatible with FM frequencies? I'd like to use these connectors and coax to fab the antenna. And where is the best tap on the board for the ground elements? Right off of one of the solder pads of of the USB shield?

I've read that varying "skin effects" between different element choices can affect the length calculation. Copper, alum, steel.... different diameters of wire... insulated or bare....

Is this correct? It is supposedly sufficient to require adjustment of length by as much as an inch on a 30 inch element? I'm planning on using 3/32 steel tig welding filler rod for the elements on the antenna. Any advice here?


Ebay Link

USB2.0 FM Audio transmitter Wireless adapter | eBay

GUI
http://images52.fotki.com/v1551/photos/8/1799248/10530209/FM1-vi.gif

GUI
http://images15.fotki.com/v588/photos/8/1799248/10530209/FM2-vi.gif

Package Contents
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14265.jpg

Antenna was tucked under metal side clasp
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14268.jpg
Bare wire end was simply clasped behind the metal side clip. I noted during operation that
minor hum was eliminated simply by grounding the metal clip with my fingers.

Top of board
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14269.jpg

Bottom of board
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14270.jpg

Bottom closeup left
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14280.jpg

Bottom closeup right
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14279.jpg

Top closeup right
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14277.jpg

Top closeup left
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14275.jpg

Primary IC closeup
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14293.jpg

IC closeup
http://i802.photobucket.com/albums/yy303/svejkovat/SDC14291.jpg
 
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Fringe Reception

Super Moderator, Chief Content Editor
Staff member
#2
Frascati,

You have an interesting project. I am not familiar with current FCC rules regarding LP (low power) personal Broadcast Band (FM, in this case) rules but I bet you can find answers at FCC.gov

I ran a LP AM station about 40 years ago and we were legally restricted to 100 miliwatts input power and an antenna no longer than 10 feet in length. I also suggest you Google "Talking House" to see what Realtors use to promote homes using a "tape-loop" ... it would be pretty easy to change the input to any source you choose.

Jim
 

frascati

DTVUSA Jr. Member
#3
Thank you. Can you recommend a forum that might entertain some of these questions with me?
I posted this at eham.net and was pretty largely ignored. It's a pretty active forum too. Not sure if they see it as a newbie overreaching and risking pirate behavior or what. Like I mentioned, this project is well below the typical xmit power that many hundreds of christmas light display enthusiasts (there are actually a few active boards for this hobby) are implementing. Probably below the typical realtor "talking house" unit you mention as well.

Frustratingly, I did join Light-O-Rama Forums and posted this question there. It was immediately flagged as spam, topic closed, and I was put on notice via PM by the admins. The post was, word for word, exactly as you see it above. They presumed that I had a commercial interest in the unit. ??????? Reading that post over again I think that would require quite an overactive imagination to presume such. Anyway.

So any other place you can recommend to ask this? I hesitate to join half a dozen electronics forums since the mileage varies so much.

Thanks for your input.
 
G

Guest

Guest
#4
I checked out the "talking house" transmiters. They are probably no more sophisticate than the USB dongle I am playing with. And they are on the average of four to twenty times the price. Nor are they PC compatible with GUI control. Most notably, all that I saw on ebay are AM. Fidelity is not paramount for these, simply voice for home descriptions.
 
G

Guest

Guest
#5
Guess this is just too unorthodox a question since I'm hooking directly to the antenna with the xmitter. I may be just overthinking this.

I connected the xmitter directly to a one inch stub of flat twin lead on a fully extended pair of rabbit ears, hung vertically from a rafter with a 10ft USB cable dangling down to my laptop. I was able to get full fidelity great reception out to the corners of my four acre lot before it started to drop off. Perfect quality stereo out to the firepit, the garage, the workshop, and all rooms in the house from the HP mini sitting in a corner of my workshop. I'm pretty happy. 7 dollar xmitter from ebay, PC controllable with GUI, 2 dollar monoprice usb extension, one dollar rabbit ears from Goodwill. I'm really happy with it.
 

Jim1348

DTVUSA Member
#6
OT But Related. Help With "Whole House" FM Transmitter Antenna?

I did something similar several years ago and I continue to do this today. I t started with the intercom system. It was probably installed in 1978 when my home was built. I did not own it then. It has a 4 position switch AM FM AUX and PHONO or something similar. I decided to run a cable from my computer and pipe audio through the intercom. As I though about this more I decided to buy a used Panaxis ACC-100 transmitter that originally had been in a health club to broadcast TV audio. I added length to the device and I can receive this is my barn about 150 feet away. I do have an old VHF antenna pointed right at the house where the transmitter is located. Also, I use an HD radio, which I find to be more sensitive than most analog FM radios.

Another device that I added in the basement was a 4 position switch so that I can easily select the input to the transmitter. My "default" is TV audio from a digital to analog converter box. The second most common input is the internet radio. The third (least) selected is audio from the computer.

You could go on the forums for Ramsey Electronics. It has been quite some time, but they used to be pretty helpful to people that like to tinker with electronic projects. The most important thing to keep in mind is don't give up because this is a great thing for any home. I ended up going with 87.9 mHz and I love being able to hear that transmitter around my hobby farm.
 
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G

Guest

Guest
#7
Stopped by my mom's house yesterday. I had my laptop out in the car and got a little inspired. She's 87 and really fond of musical memories. I brought the laptop on, inserted the xmitter, opened last.fm and typed in tommy dorsey. I had her tune her beloved monster of a magnavox console that takes up 1/6 of den. She was astonished. Song after song as if she was listening back as a child. She kept asking for more like doris day, don cornell, everly brothers, sinatra, ozzie nelson and orchestra, etc etc. It takes a lot to impress her with technology anymore. What fun.
 
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