active antenna

[Frank Gentges KØBRA]

Fred,

Nice to hear from you.

At 01:44 AM 12/2/01 -0500, k2dx wrote:
>I wonder if anyone could offer some help with a receiving difficulty on 
>160 m. ( must seem like vhf to your group).
>
>
>In the CQ 160 ssb contest I have operated the past two years portable here 
>in South Jersey, from a salt marsh on Delaware Bay. Transmit is quite 
>good, using a helium filled weather balloon supporting a half wave 
>vertical. Receiving Europeans has been a problem . I think possibly it's 
>related to the large tx antenna, coupling to the rx ant. First year was a 
>beverage, last year an end fire array of delta loop shaped pennants 30 ft 
>high at apex. seperation to tx ant about 600 ft. Preamps ICE.
>
>Would your small active antenna possibly be less likely to hear reradiated 
>noise?

It hears what the local field is.  It can work over a long cable and be 
positioned to a quiet location easier than most other antennas.

You can use RG-6 which is cheap and you can use the F series connectors 
which are easy to attach.  I see partial reels of this at hamfests that are 
from the cable companies.  I think I would have built the project with F 
connectors between the power supply and the whip amplifier if I had it to 
do over.

>
>How robust is the transistor in regards to a nearby kw ?

It should do well (if you don't over do it).  Use an oscilloscope to check 
for clipping in the active amplifier output.  As long as that is not 
happening, you should get pretty good performance.  It should do 12 volts 
peak to peak without clipping.  Of course it will take a lot more without a 
permanent failure.  I still have more to learn about failure mode with JFETs.

>
>How would the transistor behave for weak signal work with the band being 
>"trashed" during the contest? Would a different transistor with greater 
>power handling be a better choice?

If the problem is just a lot of band occupancy, it should do quite 
well.  The transistor we chose is about the best you can do.

>
>Any thoughts on using two of these suitably phased in an end fire 
>configuration to obtain directivity?

Two or more of them should work well to form directional beams.  At 160 
meters you will need some decent spacing to get good beam forming.  With 
only two of them about all you will get is a figure eight pattern.  3 or 
more in a line broadside to Europe should combine into a decent pattern.  A 
computer simulation would be very helpful to work out the details.  Putting 
all this on top of a salt marsh where you have lots of space should get 
really interesting.

>
>I read with interest of your Nag's Head expedition. I go to Ocracoke 
>Island (south of Hatteras) and have operated mobile on the beach there. 
>Three years ago I used a kite supported 300 ft wire great results, not for 
>a contest.

We notice that when we operate on the beach, we hear a lot of stuff you 
don't hear inland.  For example, we hear AM broadcast stations out of New 
York City all during the day.  We have attributed this to surface wave 
propagation across the sea water.  I suspect some similar effects on 
transatlantic 160 meter propagation exist.

73,
Frank

>
>73, Fred   k2dx (kb2bf)
>
>

Frank Gentges KØBRA
<fgentges@mindspring.com>
LF web site at <http://www.amrad.org/projects/lf>