[Kenwood] Re: [HFpack] Maldol experiments (40 meter coil)

[doc]

What about a belt-mounted aluminum plate to which the F6a clips, 
then a longer antenna would be mounted on the aluminum plate and 
a short sma-bnc jumper cable runs from the F6a to a bnc connector 
on the plate.

This way one gets a better ground plane and a larger antenna 
yet the F6a is still quickly removed with a twist of a bnc.  (The 
larger antenna could be concealed under a shirt or jacket.) 

Anyone out there have time to give it a try?  Up to my eyeballs 
here at the moment! 

73, doc KD4E 

> I own a Kenwood TH-F6A HT with wideband receiver. It's a good 
> receiver, too, but practically useless handheld on HF due to not 
> tolerating a capacitive antenna like the VR500 and similar receivers.
> 
> I picked up a 40 meter Maldol to see if this would help. Boy does it 
> ever! I figured I could collapse the whip to tune it higher in 
> frequency. I can get useful 40 meter, 30 meter and 20 meter reception 
> (and the shortwave bands in this range) on the TH-F6. This antenna is 
> a bit heavy for the SMA adapter, however.
> 
> That was the good news.
> 
> The BAD news is, I tested the Maldol antenna on an Autek RF-1 and an 
> MFJ-259. I did most of the tests with the MFJ. 
> 
> While there is a good SWR at some point, the resonant SWR swiftly 
> departs from good as the whip is collapsed (in the 20 meter range I 
> was looking at 160 ohms resistive and 190 ohms reactive).
> 
> Worse, the 1:1 SWR lowest resonant frequency is about 8.8 MHz.  I get 
> 2:1 SWR from about 8.5 MHz to 9.1 MHz. The antenna appears to have a 
> coil resonance that extends the 3:1 SWR so it JUST covers the 40 
> meter band, 3:1 or better from about 7 to 9.3 MHz. This resonance is 
> present with the whip removed (though then not much help).
> 
> I attached a short loop of wire to the tip of the antenna, and this 
> did lower resonance, the main one, from 8.8 to about 8.3, and the 2:1 
> SWR range then did include 40 meters.  As a final and very rough 
> experiment, I hung about 2 feet of wire from the tip of the Maldol's 
> whip and saw the primary resonance had shifted, with near 1:1 SWR, to 
> BELOW the 40 meter band. This leads me to think that this antenna 
> needs a whip perhaps a foot longer. 
> 
> This was with no counterpoise, and the MFJ 259 handheld. The Autek  
> RF-1 gave worse results, probably because its small size and plastic 
> cabinet did not couple well enough to my hands to allow resonance to 
> occur. In this case, the MJF-259 more closely approximates the size 
> and capacitance of an FT-817.
> 
> Results with a counterpoise (from an old B&W portable antenna) were 
> so confusing that I need to set up a more controlled experiment. They 
> were NOT better. The counterpoise resonance appears to dominate the  
> system, which may be good news for fixed-portable operation, but it 
> looks not so good for walkabout. Since my 817 is hor-de-blown-finals 
> I can't give an evaluation using it, but I'll keep experimenting.
> 
> Cortland