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Author Topic: Can't hear my net.  (Read 18179 times)

W9ADY

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Can't hear my net.
« on: May 07, 2015, 08:32:45 AM »

I have been off the air for a couple years but am trying to get back on now.  I was able to log into my MARS net since back in March but haven't been able to make any contact since.

When I was active before I was using a Cobra dipole antenna.  It worked ok but it was really hard to stretch out on my lot.  My house is in the middle of a pie shaped lot with power lines diagonal over the back yard.  There are two trees about 70 feet apart, but a wire between the two runs directly over the chimney of the house.  Thats how I had the antenna before, with the extra wire and the ladder feed line strung out haphazardly in the trees.

When I started up again I was getting very week signals and the tuner was working overtime.  I took the antenna down and found the ladder line insulation badly frayed in a couple places from rubbing on branches.  I did make my one contact with this antenna though and I could hear a couple other stations, but very weakly.

I replaced it with a CHA 250B mounted off my chimney.  It seems to work fine in the HAM bands and the tuner barely activates to tune to my MARS frequencies but I have yet to hear anyone on the net.  A couple times I've heard some station but not well enough to identify them.

I'm not sure if the problem is that I'm using a vertical or that the propagation is just really bad.  When I did hear the net there were just a couple stations so I don't know if the problem is just that the couple stations are in the wrong locations.

I'm open to any suggestions.
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WD8DBY

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RE: Can't hear my net.
« Reply #1 on: May 08, 2015, 05:51:21 AM »

When you make contacts on the amateur bands, how distant are the stations you contact?  Using a dipole for your previous antenna, you were probably making MARS contacts using NVIS (freqs below 10 megs and stations no more than 200-300 miles distant).  When you switched to a vertical, you are no longer using NVIS, so MARS stations within that 200-300 mile radius of you will be very hard receive.  Try tuning to nets in other regions (more distant from you), try checking into the J0G national net, or try making a call to the Fort Huachuca gateway station.  Good luck!

v/r

Paul

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N1EN

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RE: Can't hear my net.
« Reply #2 on: May 08, 2015, 04:06:18 PM »

I'm not sure if the problem is that I'm using a vertical or that the propagation is just really bad.  When I did hear the net there were just a couple stations so I don't know if the problem is just that the couple stations are in the wrong locations.

I think you're going to find using that antenna on a state MARS net challenging.

While I haven't used one myself, I note that it is advertised as being a 23 foot "broadband" vertical requiring no radials.  The physics of antennas is such that you're always finding the best compromise among size, bandwidth, and efficiency.  If you have a small, broadband antenna...it's not going to be very efficient.

Aggravating that is that verticals generally have low angles of radiation, which is good for DX.  But for local communications, you need high angle radiation, the kind you'd expect to get with a dipole or some loops.

I know folks who check into MARS nets on verticals, or mobile (even near 160m!), or QRP, so I wouldn't necessarily say that the antenna is a lost cause...but it will probably be challenging.

You might try listening to the AFD cross band test activities Saturday morning, or seeing which AFD broadcasts you can hear in the evening to get a better feel for the pattern of your antenna.

Other possible explanations are the change to summertime propagation (e.g. 80m probably starts dropping out for you around 9am this time of year, but it be fine at 8pm), or perhaps a change in the timing of the nets.  You might consider checking with your state director to see if there's been a change to the net plan that  you weren't aware of.
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WB6BYU

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RE: Can't hear my net.
« Reply #3 on: May 10, 2015, 01:08:08 PM »

What frequency range are you using?  What distance to the NCS?

The CHA-250 is not particularly efficient (sometimes referred to as a "dummy load on
a stick") and a vertical is not ideal for NVIS working (the typical propagation mode for
contacts out to 200 miles on HF.  Because there can be a fair amount of radiation from
the coax, you can try running the coax horizontally across the roof to optimize high angle
radiation.

Another possibility is that the conditions have changed in the last couple of months and
the ionosphere no longer supports the required path on your net frequency.  (Make sure
they didn't make a seasonal frequency shift.)  For such short-range nets the frequency
needs to be below the "critical frequency" at the time but not so low that D-layer
absorption is excessive.

A quick test would be to put up a temporary dipole or loop, even if near the ground,
and see if you can hear them: that will tell you whether the problem is propagation
or your antenna.

You can also check the propagation forecasts for the path using online tools from the
Australian Ionospheric Prediction Service (www.ips.gov.au/HF_Systems/7/1) or
VOACAP Online (www VOACAP.com/prediction.html).

W9ADY

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RE: Can't hear my net.
« Reply #4 on: May 12, 2015, 07:03:48 AM »

Thanks for some things to look into.  I talked to another MARS member last night and he's not been able to check in recently using a wire, so propagation must be part of the issue.  I'm at the extreme north end of Illinois and some of the stations are central and south so I'm hoping the vertical will work on that path.

How do I find the AFD broadcasts.  Its the first I've heard of those. What are they?
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N1EN

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RE: Can't hear my net.
« Reply #5 on: May 12, 2015, 07:24:37 AM »

The Armed Forces Day crossband test is an annual event, in which military (mostly MARS) stations work amateur stations cross-band.

Included during the test is the broadcast of a message from the Secretary of Defense by multiple stations, in multiple modes.

It was this past weekend, and it could have served as one way to test your antenna away from the amateur bands...but frankly, propagation this weekend was lousy.
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WI9MJ

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RE: Can't hear my net.
« Reply #6 on: May 12, 2015, 03:34:52 PM »

I'll second the propagation issue. Regional comms are primarily NVIS, and 2 crucial things to know are the FoF2 frequency, which is the highest freq that signals will bounce back from the F layer, and the D-Region absorption rate. There have been several times in the past 2 weeks when the 1db absorption frequency was above the FoF2 freq.
Makes for some challenging operating conditions.
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VA2PBJ

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RE: Can't hear my net.
« Reply #7 on: May 13, 2015, 05:51:17 AM »

I recently built a cobra and when I first put it up I had the same problem that you described.....it was kinda deaf....but tuned well. A long story being short...the ladder line I was using was coming too close to my metal sided house and the window it was going through in the basement had metal around the glass. The fix was simple; put a coax (as short as possible) to the edge of the house and use a 4:1 current baln at that edge. The antenna was performing in no time.
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Peter

KA0HCP

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RE: Can't hear my net.
« Reply #8 on: May 13, 2015, 11:27:44 AM »

-The qualities (ahem) of the CH250 have been mentioned above.

It is always best to have a selection of antennas, particularly having both vertical and horizontal polarizations.

I would suggest adding a [horizontal] loop antenna to your antenna farm.  Make it full wave for your lowest frequency if possible.  If not, run it at the perimeter of your yard.  A lightning arrestor at the shack entrance with a DC ground will drain static, making for significantly reducing noise.

The predominant high takeoff angle will favor NVIS (regional) comms needed for your MARS nets and will null [low angle] local/household EMI better than a dipole.

good luck, and welcome back!

[edited]
« Last Edit: May 13, 2015, 11:39:37 AM by KB4QAA »
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.

VE6FGN

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RE: Can't hear my net.
« Reply #9 on: February 18, 2016, 11:53:06 AM »

I've had good luck using a G5RV on CFARS frequencies. Needs a good tuner, but I can work near and far.
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W3JKS

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RE: Can't hear my net.
« Reply #10 on: February 18, 2016, 05:53:32 PM »

Whenever I read about someone using that particular Comet vertical, my mind flashes back to that old QST article about making contacts with an incandescent light bulb on the end of the feedline.   ::)

john W3JKS
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