[aprssig] Re: How Much Antenna for PCSAT?

gerheim at cox.net gerheim at cox.net
Wed Aug 15 07:22:21 CDT 2007

Thanks.  I'm going to google the maldol antenna asap.  BTW, the OEM antenna also will +not+ poke out your eye.  (Its only other endearing feature!)  

---- "Stephen H. Smith" <wa8lmf2 at aol.com> wrote: 
> gerheim at cox.net wrote:
> > I've been trying to hit PCSAT with a D7.  Apparently, the rubber duckie isn't enough wire.  Will a telescoping whip do any better?  
> >
> > KB9GVR has been having some success.  
> >
> > My goal is to send it an APRS packet from a moving motorcycle, so big antennas are out of the question.  I almost managed it back in January.  
> >
> >
> >   
> If you are referring to the OEM duckie that came with the TH-D7, it is 
> little more than a badly-shielded dummy load.  You need something that 
> is electrically a half-wave design that doesn't depend on a ground plane 
> as a 1/4-wave whip (even full-sized) does.  The problem is that the D7 
> is simply too small physically to be a significant ground plane (i.e. 
> counterpoise) to most whips.
> I have used a dual-band Maldol replacement whip for the TH-D7 (can't 
> remember the model number) with great success. This whip is made of 
> thin, flexible piano wire (non-telescoping) about 20" long . The base 
> and matching transformer is terminated in an SMA connector for direct 
> connection to the D7 without the clumsy SMA-to-BNC adapters many people 
> use.  The base of the fitting is flared out so that it contacts an area 
> on the top panel of the D7 that is about 2 and a half times the radius 
> of the SMA socket alone which drastically reduces stress and twisting on 
> the lightweight SMA socket on the radio.     This whip radiates about 
> 10-15 dB more RF than the OEM duck (actually measured on an IFR-1500's 
> spectrum analyzer). 
> If you are trying to use this for satellite modes, you need to hold the 
> radio horizontal and at right-angles to the satellite track so that the 
> dipole-type radiation pattern (max is at right-angles to the whip)  will 
> extend from one horizon to overhead and then down to the other horizon.
> --
> Stephen H. Smith    wa8lmf (at) aol.com
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-Al Gerheim

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