Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: VHF/UHF FM vs. Car Audio FM  (Read 638 times)
AF4YA
Member

Posts: 44


WWW

Ignore
« on: March 31, 2001, 09:00:05 PM »

I'm sure many of you have encountered the FM radio stations cutting out when you key up a 2 meter rig with moderate power. Are there any antenna filters that one could use on the FM radio antenna to block out the front end overload?

Thanks,
Nick
AF4YA
Logged
WB2WIK
Member

Posts: 20540




Ignore
« Reply #1 on: April 02, 2001, 03:46:44 PM »

I'd recommend a simple 1/4-wave stub tuned to 2m and placed in parallel with the FM radio input jack.  Two problems with this, or also what you asked for (a bandpass filter to separate FM BCB from 2m): (1) The connectors used in the car BCB radios are usually "Motorola" type, not the UHF or BNC type normally used by hams; you might have trouble working out a "Tee" connector.  However, using a BNC "Tee" connector, with BNC-to-Motorola type adapters where required, should work.  (2) Even worse, auto radio antenna coaxial cable is neither 50 Ohm nor 75 Ohm, it's normally specialized, high-impedance cable which actually measures about 140 Ohms impedance.  You can't find it on the market, and it doesn't have an "RG" number.  However, one way to get this cable is to buy a replacement AM radio whip antenna on the aftermarket, throw away the whip, and use the cable it comes with (I've done this).

Then, make a 1/4-wave stub out of that cable.  It should be about 16-1/4" long and have its end "open" (that is, the far end of the stub is not shorted or connected to anything).

I've done it -- it works.

73 de Steve WB2WIK/6
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!