[MRCA] NVIS antenna tests

[B. Smith]

When conducting  short haul communication tests  it is very difficult to 
differentiate between a NVIS bounce and the "trickle groundwave" that is 
always present regardless of  obstacles. Switching of antennas of course is 
a great idea  for detecting either but an efficient swithching network has 
to be utilized and each line carefully matched prior to the switch  so that 
tuning  "touch up" is not requried when accomplishing your "A or B" testing.

breck k4che


Meet Communications Readiness Bulletin II


| Rob,
|
| I agree that the dipole we use is probably a good vertical radiator, but 
we
| could actually have a better one to compare against.   From the reading I
| have done the experts say the NVIS antenna should be .15 to .2 wavelengths
| high.  Other sources say .05 wavelength to enjoy some gain reduction but
| overall s/n improvement.  The antenna I put up is approx. .25 wavelength
| high, but I would like to have second antenna, a lower NVIS dipole at the
| Gilbert base with maybe three parallel interconnected counterpoise wires
| under the antenna.   That way we could switch from the higher dipole to 
the
| lower with counterpoise and see if there was any difference.  The only
| problem lies in having two tuners matched to the GRC-19 such that the 
power
| level from the transmitter is the same into both antennas.
|
| I may have some suitable wire around here for a counterpoise for at least
| one of the NVIS antennas.
|
| Dale
|
|
| The   ----- Original Message ----- 
| From: "Rob Flory" <robandpj at earthlink.net>
| To: "Military Radio Collectors Association" <mrca at mailman.qth.net>
| Sent: Friday, August 31, 2007 10:44 AM
| Subject: Re: [MRCA] MRCA Meet Communications Readiness Bulletin II
|
|
| > The dipole that we always set up at base is a perfectly good NVIS 
antenna.
| >
| > RF
| >
| > -----Original Message-----
| >>From: Radio Station KW1I <kw1i at earthlink.net>
| >>Sent: Aug 31, 2007 10:20 AM
| >>To: Military Radio Collectors Association <mrca at mailman.qth.net>
| >>Subject: [MRCA] MRCA Meet Communications Readiness Bulletin II
| >>
| >>MRCA Meet Communications Readiness Bulletin II
| >>
| >>On the Friday afternoon (Sept. 21) group field exercise to Big Pocono
| >>there
| >>will be an opportunity to test Near Vertical Incidence Skywave 
propogation
| >>over the 19 mile path between the field site and base at the Gilbert
| >>Fairgrounds.  The access road to the top of the overlook point is on the
| >>far
| >>side of the mountain.  Setting up a NVIS antenna equipped station near 
the
| >>bottom of the access road would present a significant communications
| >>challenge back to base with the bulk of the mountain shadowing normal
| >>antenna take off angles.
| >>
| >>I propose that one team on the way up the mountain separate from the
| >>convoy
| >>and set up a short way up the mountain's access road.  The team should 
be
| >>equipped with VHF set for coordination through stations on top of Big
| >>Pocono
| >>back to Gilbert. This team will be in place when the main communications
| >>convoy reaches the top, sets up and commences tests.  Upon completion of
| >>NVIS testing the station at the bottom of Big Pocono can pack up and 
join
| >>the main body on the mountain top.
| >>
| >>This experiment will require two NVIS antenna set ups.  One remote and 
one
| >>at the Gilbert base.  The simplest and probably the most effective 75m
| >>NVIS
| >>antenna is a low dipole 15-20 ft off the ground, with typical sag in the
| >>middle and with at least one counterpoise wire running under the antenna
| >>attached to the HF rig ground.   Two end support masts should be 
planned,
| >>though it is likely a tree can be used for support at one end.
| >>
| >>VOLUNTEERS NEEDED:
| >>
| >>1.  A 2-3 person comm team to set up and man the remote Big Pocono NVIS
| >>test
| >>station.
| >>
| >>2.  One of more Individuals who can provide NVIS antenna kits, one for 
the
| >>base at Gilbert, one to be erected at the Big Pocono remote NVIS
| >>experiment
| >>site.
| >>
| >>Commenters and volunteers send mail to kw1i at earthlink.net.
| >>
| >>Complete MRCA Meet information at http://www.mrca.ar88.net/
| >>
| >>
| >>
| >>
| >>
| >>
| >>_______________________________________________
| >>MRCA mailing list
| >>MRCA at mailman.qth.net
| >>http://mailman.qth.net/mailman/listinfo/mrca
| >
| > _______________________________________________
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| >
| >
| > -- 
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| >
|
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