DIY FM antenna, can it be better than radioshack junk? - Page 6 - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th June 2005, 02:45 AM   #51
diyAudio Member
 
Join Date: Apr 2003
Location: Portland,Oregon
Blog Entries: 4
Send a message via AIM to DigitalJunkie
I don't recall the exact dimensions of my J-pole,but there's info all over the net on how to build one..
One trick I used,was to drill a hole in each of the copper pipe caps that go on top (to keep rain out,etc) and solder a nut on the inside of them,then I cut a couple short (3-inch?) pieces of "all-thread",and screwed then into the endcap+nut,and put a nut on the top to lock them inplace..
This way you can fine-tune the length of the J-pole..
(Mine was actually intended to be used with a small transmitter,but it works just as well on a reciever.)

I shot it with a coat of grey spray-primer,and it blends in with the grey house nicely,It's right outside my window,and you'd hardly notice.

It's matched for 50 ohms,but works quite well on the 75ohm input of the reciever. Got a run of RG-8 going to it..
  Reply With Quote
Old 13th September 2005, 09:05 PM   #52
diyAudio Member
 
Join Date: Dec 2003
Location: Montreal
WBTZ is quite far from Montreal, the antenna is situated in Plattsburgh, 80KMs away. They use directional antennas, instead of non-directional like most others.

You might also want to know that the antenna is 550m higher than sea level.

More info:
http://www.fcc.gov/fcc-bin/fmq?list=0&facid=52807

I have one antenna able to receive that channel perfectly; A RadioShack Active Directional FM/VHF/UHF rabbit ear antenna. It's the only active antenna I have. All others have separated signal amps. There's a strange thing with 99.9 is that if your antenna is incorrectly placed is that you receive all the powerful channels between 90and 100MHz :94.3, 95.1, 96.9 and 99.5. Also, in my case, my CDP produces so much interference that I hear the line out of my CDP in the tuner.

The only thing is that if you listen TV with the same antenna, TVA reception will suck. Doesn't matter, it's a sensationalism channel with only poor content.

You might also want to mod your tuner's IF section:
http://www.amfmdx.net/fmdx/mods.html
and Google. the link I provided is not the best I found.
  Reply With Quote
Old 23rd September 2005, 09:19 PM   #53
diyAudio Member
 
Join Date: Aug 2004
Location: Illinois
Antenna design is mostly a matter of mathematics. You can't fool Mother Nature. Antenna elements must be able to resonate to certain frequencies. Any element (or 1/4 wave stubs placed end to end to be a 1/2 wave antenna) is only good for a limited frequency range (fatter element is better) so to get the entire FM band one needs 3-4 separate elements. Or, you could design an antenna just for the desired transmitter's frequency.

Then, consider if its signal is vertically or horizontally polarized or has some sort of a circular polarization. This would relate to how the elements are positioned.

Next shun amplified antennas. If there is no signal you can't amplify it and most modern FM tuners are extremely sensitive to the slightest hint of a signal.

Next, find the room's "hot spot" for the desired FM station. The elements should be placed at right angles to the station but moving the antenna fore and aft or left or right even a few inches can make a big difference and the directional position may not always follow logic. I currently am using TV rabbit ears with each 1/2 extended out 26" and the antenna is nested in a ceiling fixture lamp shade. That particular spot is the best spot in the entire room for some reason and I am getting quite regular good reception of an 89.9mhz station located 98 miles away up a river valley (no high hills in the way).

Also, be aware of tropospheric bending or ducting. Depending on atmospheric conditions you may get excellent reception with a coat hanger dangled from a window and at other times even the best of outdoor antennas may not provide a useable signal.

An indoor antenna is a vexsome thing and can consume a lot of time fiddling with it as the signal strength is so low in amplitude and it gets jumbled from object reflections. Multipath distortion will always be a big factor and can cause reception distortion. And, the room will definitely have a hot spot for each station.

BTW, Radio Shack antennas are not junk. If I were you I would buy their yagi FM antenna and try positioning it around the room to find the best spot and then figure out how to make it appear as a work of modern art or a mobile dangling from the ceiling.
  Reply With Quote
Old 1st November 2011, 10:44 PM   #54
diyAudio Member
 
Join Date: Sep 2005
Quote:
Originally Posted by jackinnj View Post
EDIT: this design is a log-periodic array -- has nice bandwidth although the gain is somewhat lumpy:

Click the image to open in full size.

here's an EDIT implementation used by a ham radio operator on 432MHz which can be repurposed for FM -- this design will give around 8.5 dB of gain with a front-back ratio of 22 to 28dB:

Click the image to open in full size.

they used copper tape for the elements and affixed them to a piece of foamcore.

for a 100MHz antenna (98Mhz to 102MHz) the element spacings are as follows:
D1 = 0.259m
D2 = 0.248
D3 = 0.238
D4 = 0.228
D5 = 0.218
D6 = 0.209
D7 = 0.200

the length of the elements are:
L1 = 1.561m
L2 = 1.495
L3 = 1.432
L4 = 1.371
L5 = 1.313
L6 = 1.258
L7 = 1.204
L8 = 1.154

I realise that this is a truly ancient thread, but the photos in this post have really interested me. I haven't been able to find any examples/instructions for a log periodic antenna which looks anything like this anywhere else, so if anybody has any more information, I'd be very grateful. I am intending to build a directional FM antenna, and I liked the idea of making a thin yagi to put on my ceiling, and then I saw this. Looks great, but the lengths mentioned seem to indicated that it will actually have to be enormous for FM. Is this right, or are the numbers wrong? Also, I can't see from the photos, but how/where does the feed cable attach?

Many thanks for any ideas!
  Reply With Quote
Old 2nd November 2011, 12:07 AM   #55
diyAudio Member
 
Speedskater's Avatar
 
Join Date: Sep 2002
Location: Lakewood, Ohio
For a huge amount of information on FM antennas see:

88108 MHz
__________________
Kevin
  Reply With Quote
Old 2nd November 2011, 12:44 AM   #56
hags is offline hags  United States
diyAudio Member
 
Join Date: Nov 2004
Location: Chain o' Lakes
Quote:
Originally Posted by fishwinker View Post
I realise that this is a truly ancient thread, but the photos in this post have really interested me. I haven't been able to find any examples/instructions for a log periodic antenna which looks anything like this anywhere else, so if anybody has any more information, I'd be very grateful. I am intending to build a directional FM antenna, and I liked the idea of making a thin yagi to put on my ceiling, and then I saw this. Looks great, but the lengths mentioned seem to indicated that it will actually have to be enormous for FM. Is this right, or are the numbers wrong? Also, I can't see from the photos, but how/where does the feed cable attach?

Many thanks for any ideas!
Build a Yagi for FM, especially for a first project. IMO, nothing can touch a well built, purpose designed yagi for FM. Anything you build based on a good design is going to be light years ahead of and outperform anything you can buy or in the past.

You can see mine on the 88–108 MHz website. I built the 10' yagi for 88-92MHz.

I'm picking up 50/100 watt high school stations 20, 30 and 40 miles away, along with higher powered stations from over 180 miles away. I haven't even started to do any serious DX work with it.

I'm going to build either the Korner 19.3 for which I've just received the MMANA-GAL files for from Peter Korner or a LFA designed specifically for FM by Free Yagi Antenna Designs for Ham Radio. Justin, (G0KSC) owns InnoVAntenna in addition to the G0SKC website. He and his designs are cutting edge, he uses the latest technology and, how's this for a shock, actually builds his designs.
__________________
"Some lures are designed to catch fish, others are designed to catch fisherman."

Last edited by hags; 2nd November 2011 at 12:52 AM.
  Reply With Quote
Old 2nd November 2011, 01:19 PM   #57
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
The figures given for the FM log periodic are probably right. It will be large. For a given gain a log periodic will be much larger than a Yagi, but will have greater bandwidth. It is not possible to have a really good indoor FM antenna, as any decent VHF antenna has to have dimensions commensurate with at least half a wavelength: 1.5m.

The J-pole has a big disadvantage for indoor use: it is long (3/4 wavelength) and consists essentially of an end-fed half-wave dipole with a matching section. This makes it very sensitive to surrounding objects, which is exactly the opposite of what you want indoors.

The folded dipole is about the best you can do indoors. It has fairly wide bandwidth, so it is less affected by nearby objects. Note that for good bandwidth don't build it with 300 ohm cable. Instead, cut it out of a roll of aluminium kitchen foil. However, if you do use 300 ohm cable you need to be aware that you can't just shorten it by the velocity factor as this only applies to the internal transmission line mode, not the external dipole mode. If you don't understand what I mean here, then you should simply copy a published design and hope that the designer does understand.
  Reply With Quote
Old 2nd November 2011, 01:41 PM   #58
stoc005 is offline stoc005  United States
diyAudio Member
 
stoc005's Avatar
 
Join Date: Feb 2007
Location: Midwest in the USA
Wideband Vertical Omni

A vertical polarized omni for FM in the US (88-108). The only thing better would be a circular polarized one.
  Reply With Quote
Old 2nd November 2011, 02:04 PM   #59
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
That looks good. It is a skeleton version of the wideband biconical antenna. I did something similar, but much smaller, for indoor reception of UHF digital TV.
  Reply With Quote
Old 2nd November 2011, 02:18 PM   #60
diyAudio Member
 
Join Date: Jan 2008
Location: Carp
My understanding is that in North America FM radio is horizontal polarization. If one cannot install an outdoor antenna perhaps one on the ceiling that is painted the same colour as the ceiling will help hide it, or an atic if possible.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
My DIY UcD amp from the junk box acid_k2 Class D 38 3rd September 2012 05:01 PM
What to do with RadioShack 40-1041? Spasticteapot Full Range 0 14th October 2006 08:14 PM
Radioshack special GC Dustin Haug Chip Amps 16 15th February 2004 03:22 PM
Dr.Bose and Radioshack.. Bose(o) Multi-Way 7 1st January 2003 06:43 PM
WTB: Radioshack RS 40-1354A psarin Swap Meet 1 5th April 2002 07:31 PM


New To Site? Need Help?

All times are GMT. The time now is 03:34 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2