From: Jeff Seale
Organization: Insight Broadband
Newsgroups: rec.radio.shortwave
Date: Sat, 08 May 2004 21:16:15 GMT
Subject: MARS?

Arthur Harris wrote:

"Greg" wrote:

Is anyone hearing MARS activity (the military affiliates, not the planet)?
I never hear anything on the freq's I have.


I hear the MARS nets most often between 4.0 and 4.1 MHz mornings and
evenings.

Art N2AH



The last MARS net I heard was on 4003 kHz at about 8:00 EDT.

Jeff Seale
Louisville, KY

There was already activity on that freq when I tuned in around 7:45 EDT.

Also, I have heard the special Armed Forces Day traffic on 13985, 13996, and
14467 USA earlier and 14467 is still active.

Greg

Greg wrote:

There was already activity on that freq when I tuned in around 7:45 EDT.

Also, I have heard the special Armed Forces Day traffic on 13985, 13996, and
14467 USA earlier and 14467 is still active.

Greg


That's cool, I don't do too much daytime/morning listening though except
on the weekends when I don't have to work. The earliest you'll find me
hitting the radio is about 3:00 PM EDT.

Jeff Seale
Louisville, KY

On Sun, 09 May 2004 02:31:59 GMT, Jeff Seale
wrote:

Greg wrote:

There was already activity on that freq when I tuned in around 7:45 EDT.

Also, I have heard the special Armed Forces Day traffic on 13985, 13996, and
14467 USA earlier and 14467 is still active.

Greg


That's cool, I don't do too much daytime/morning listening though except
on the weekends when I don't have to work. The earliest you'll find me
hitting the radio is about 3:00 PM EDT.

Jeff Seale
Louisville, KY

I've been wondering: If a shortwave transmitter was put on Mars could
I pick it up - at night I mean? Would I need an external antenna?
BTW - I tune down.

"Bill Everhart" wrote in message
...


I've been wondering: If a shortwave transmitter was put on Mars could
I pick it up - at night I mean?

Probably. The ionosphere would refract the received signals, but I think it
would still come in if it hit the ionosphere at a the correct angle. If the
signals were directly overhead, absorbtion would be the main problem.

There's a couple of small bands in SW allocated to radio astronomy. One is
around 13MHz and the other is around 26MHz.

Would I need an external antenna?

Only if the signal from Mars is weak when it gets to Earth. As long as this
is hypothetical, let's give the Martians a terawatt transmitter and a
steerable parabolic dish a mile across. In the real world, radio astronomy
needs good antennas.


BTW - I tune down.

Never up?

Frank Dresser

"Bill Everhart" wrote:
I've been wondering: If a shortwave transmitter was put on Mars could
I pick it up - at night I mean? Would I need an external antenna?

Interesting question. When Mars is at its closest point to Earth, it's still
about 35 million miles away. Only a tiny portion of the transmitted power
would arrive on Earth (the rest would "miss" us and go out into space in all
directions).

The "free space path loss" between Earth and Mars at 15 MHz would be 211 dB.
That's a HUGE loss. At UHF and microwave frequencies the path loss is even
greater, BUT the use of very high gain dish antennas both on Earth and Mars,
as well a low noise figure receivers, makes communication possible. At HF,
antenna gain of more than about 10 dB is hard to obtain. And the
atmosphereic noise at HF is a killer for weak signal reception.

Plus, you'd have to be listening at a time when your side of the Earth was
facing "their" side of Mars, and the E and F layers of the ionosphere were
NOT refracting signals.

BTW - I tune down.

Huh?

Art N2AH

In article ,
"Arthur Harris" wrote:

snip

The "free space path loss" between Earth and Mars at 15 MHz would be 211 dB.
That's a HUGE loss. At UHF and microwave frequencies the path loss is even
greater, BUT the use of very high gain dish antennas both on Earth and Mars,
as well a low noise figure receivers, makes communication possible. At HF,
antenna gain of more than about 10 dB is hard to obtain. And the
atmosphereic noise at HF is a killer for weak signal reception.

snip

How did you calculate this loss? I'm assuming you mean the 211 dB to be
an absorptive loss? Maybe you are considering the antenna on Mars to be
a point source off a 180 degree ground plane so the loss figure is power
distributed over a half sphere with the Earth - Mars distance?

--
Telamon
Ventura, California

"Telamon" wrote"
"Arthur Harris" wrote:

The "free space path loss" between Earth and Mars at 15 MHz would be 211
dB.
That's a HUGE loss. At UHF and microwave frequencies the path loss is
even
greater, BUT the use of very high gain dish antennas both on Earth and
Mars,
as well a low noise figure receivers, makes communication possible. At
HF,
antenna gain of more than about 10 dB is hard to obtain. And the
atmosphereic noise at HF is a killer for weak signal reception.

snip

How did you calculate this loss? I'm assuming you mean the 211 dB to be
an absorptive loss? Maybe you are considering the antenna on Mars to be
a point source off a 180 degree ground plane so the loss figure is power
distributed over a half sphere with the Earth - Mars distance?

The Free Space Path Loss Equation is:

Path Loss (dB) = 36.6 + 20 Log F + 20 Log D

Where F is freq in MHz and D is distance in miles. This assumes isotropic
antennas as both ends. The "path loss" represents the portion of the
transmitted signal that is NOT captured by the receiving antenna. It does
not include absorptive losses (which should be negligible in free space).

Some will argue that this is not a true dissipative loss, and that is
correct. But by knowing the "path loss" you can determine your needs as to
transmit power, receiver sensitivity, and antenna gain in order to assure
successful communication.

Art N2AH

Arthur Harris wrote:


The Free Space Path Loss Equation is:

Path Loss (dB) = 36.6 + 20 Log F + 20 Log D

Where F is freq in MHz and D is distance in miles. This assumes isotropic
antennas as both ends. The "path loss" represents the portion of the
transmitted signal that is NOT captured by the receiving antenna. It does
not include absorptive losses (which should be negligible in free space).

Some will argue that this is not a true dissipative loss, and that is
correct. But by knowing the "path loss" you can determine your needs as to
transmit power, receiver sensitivity, and antenna gain in order to assure
successful communication.

The key here is a theorem that shows that the "capture area" of a
perfectly efficient isotropic antenna is (wavelength)^2/(4 Pi).

-jpd

for all of you who were speaking about what times you listen, here is what
happened to me when I was real young. I heard an advertisement on a shortwave
station for a program I wanted to hear, but at the time, I didn't understand 24
hour time since I had never heard of it before.

However, when I asked about it, either my uncle or my grandpa (maybe both)
explained it to me. and I then understood it.

But I STILL missed the program when I tuned in at the time said to hear it.

I didn't find out until later that the reason why I missed it is even though I
understood 24 hour time, I wasn't aware of different time zones in different
parts of the world.

The time given was in GMT and I was tuning in according to Eastern Time instead
of GMT.

On 09 May 2004 21:56:47 GMT, (Mediaguy500)
wrote:

for all of you who were speaking about what times you listen, here is what
happened to me when I was real young. I heard an advertisement on a shortwave
station for a program I wanted to hear, but at the time, I didn't understand 24
hour time since I had never heard of it before.

However, when I asked about it, either my uncle or my grandpa (maybe both)
explained it to me. and I then understood it.

But I STILL missed the program when I tuned in at the time said to hear it.

I didn't find out until later that the reason why I missed it is even though I
understood 24 hour time, I wasn't aware of different time zones in different
parts of the world.

The time given was in GMT and I was tuning in according to Eastern Time instead
of GMT.


It really all boils down to this. If you were on Mars you could still
tune in the BBC.