NVIS and VHF?
 

On 5/24/2011 4:23 PM, 'Captain' Kirk DeHaan wrote:

I have heard from a club member that the repeater is weak and it has
been overrun by one on the coast! He is much farther away than me and in
a much less desirable location, signal wise.

I have been out of HAM radio for about 15 years so am having to relearn
quite a lot. Had a brain injury, doh!, so lot's of what I knew went bye
bye. Lot's of holes in the memory. I will find out about the repeater
during the next club meeting. Specs and all.


Sounds great, Kirk. I'll bet they will fix you up right away.

Hang in there.

Cheers,
John

NVIS and VHF?
 

On Tue, 24 May 2011 14:23:20 -0700, 'Captain' Kirk DeHaan
wrote:

I have heard from a club member that the repeater is weak and it has
been overrun by one on the coast! He is much farther away than me and
in a much less desirable location, signal wise.

Ok. Might be a sick repeater. That would explain quite a bit.

I have been out of HAM radio for about 15 years so am having to relearn
quite a lot. Had a brain injury, doh!, so lot's of what I knew went bye
bye. Lot's of holes in the memory.

I have a slight idea of what's that's like. I had a triple bypass
operation in 2002. They're not sure what happened but the result is
that my memory around that time is like Swiss cheese. It's a mix of
things that happened that I don't remember, and things I remember that
never happened. Fortunately, things got better after about a year for
me. Hopefully, you'll do as well. Also, my neighbor had a brain
tumor removed. She's fine, but has the same scrambled memory problem.

I gave up ham radio from about 1975 to 1992. I was working designing
radios and working in commercial 2way. The last thing I needed was
ham radio after hours. Welcome back.

I will find out about the repeater
during the next club meeting. Specs and all.

Good idea. I assumed that you had already done that. If the specs on
the repeater (tx power, feed line losses, antenna gain, antenna
height, lat-long) were known on the repeater, I can calculate the
signal strength you should expect at your end.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

NVIS and VHF?
 

On 5/24/2011 4:43 PM, Dave Platt wrote:
In ,
John wrote:

All of this leads me to think that something else is wrong. I can hit a
repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft
tower. My antenna (half wave end-fed dipole) is on a 20 ft mast.

I wonder whether he might have his antenna sitting in a particularly
deep multipath cancellation null.

I help run a repeater located about 4 miles from my house, which is up
at about 80' AGL on a hospital roof. There's an office building
blocking direct line-of-sight path from my house to the repeater.

For a few weeks, several years ago, I found myself unable to
successfully open up the repeater using my base station, even while
transmitting 50 watts of power from a good-quality commercial 2-meter
antenna located a few feet above my roofline. Had no trouble with any
other repeater in the area, or with simplex operations. The
feedline/antenna system measured out just fine... no reflected power
worth speaking about.

I moved the antenna mast about 2' to one side, and was then able to
open up the repeater full-quieting with 100 milliwatts.

All I can figure is that there must have been a *very* deep multipath
cancellation effect playing out... maybe interference between a
edge-diffraction path involving the office building, and reflections
from nearby trees. Moving the antenna a fraction of a wavelength
changed the path lengths enough to eliminate the cancellation (or
reduce it by a large factor).


That is always a possibility, Dave. I have seen similar situations and I
am not surprised at your findings. It is one reason I suggested moving
his antenna, even slightly.

His latest post may also indicate that there is a repeater problem. So,
I hope he posts his findings after his meeting with his club.

Cheers,
John

NVIS and VHF?
 

On 5/24/2011 2:54 PM, Dave Platt wrote:


I'm using 75' of
professionally assembled RG8X which is required to get from the radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


The results are all over the map. A piece of Cable TV cable might not
be a bad choice, if you can scrounge one. The 75 ohms probably isn't a
big deal.

At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB

NVIS and VHF?
 

On 5/24/2011 6:11 PM, Jim Lux wrote:
On 5/24/2011 2:54 PM, Dave Platt wrote:


I'm using 75' of
professionally assembled RG8X which is required to get from the radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


The results are all over the map. A piece of Cable TV cable might not be
a bad choice, if you can scrounge one. The 75 ohms probably isn't a big
deal.

At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has 9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php

Cheers,
John

NVIS and VHF?
 

"John KD5YI" wrote in message
...

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has
9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php

Cheers,
John


John you need to see where you went wrong. The numbers Jim listed are
either correct or very close. I did not bother to do the calculations, but
looking at a 100 foot chart, the numbers are very close and no where near
the numbers you have.

I thought you may have looked at the web page and missed it defauls to
meters, but that does not seem to be the case to me.

NVIS and VHF?
 

On 5/24/2011 8:08 PM, Ralph Mowery wrote:
"John wrote in message
...

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has
9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php

Cheers,
John


John you need to see where you went wrong. The numbers Jim listed are
either correct or very close. I did not bother to do the calculations, but
looking at a 100 foot chart, the numbers are very close and no where near
the numbers you have.

I thought you may have looked at the web page and missed it defauls to
meters, but that does not seem to be the case to me.

You are correct, Ralph, and I apologize to the group for my error. I did
indeed put meters rather than feet into the calculator.

Again, my apologies, and thanks, Ralph, for correcting me.

Cheers,
John

NVIS and VHF?
 

Dave Platt said the following on 5/24/2011 2:54 PM:
In ,
'Captain' Kirk wrote:

All of this leads me to think that something else is wrong. I can hit a
repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft
tower. My antenna (half wave end-fed dipole) is on a 20 ft mast.

There may well be something wrong with the antenna. I don't have an SWR
meter handy but will try and borrow one from a club member. The J-pole
was beat around quite a bit over the years but since the radio has a
limiting circuit if the SWR is too far out of whack I am assuming it is
fairly close. It will transmit of full power.

One of the things to know about the American Legion J-pole (and most
vaguely-similar J-poles) is that it has no feedline or mount-point
isolation to speak of. The outside of the feedline coax, and any pipe
or tower or other metal to which you strap the antenna, become part of
the antenna's ground system, and can radiate a significant amount of
RF. This can interact with the RF coming from the main radiator, and
significantly alter the antenna's pattern... it no longer behaves like
an idealized half-wave vertical radiator.

In most installations this doesn't seem to matter all that much... but
it's possible that you've got some sort of weird interaction (feedline
emissions, reflections from the ground or nearby metal, etc.) which is
creating a null in the antenna's pattern in just the wrong direction.
If this is an issue (not all that likely but perhaps possible) you
could insulate the antenna from the mounting mask, and install a choke
(e.g. a few ferrite cores) on the feedline just below the antenna.

It is mounted on an angle bracket about 12" from a mast 20' above my
metal roof. The mast is isolated from roof but is not yet grounded.


Also, the American Legion J-poles are subject to a couple of forms of
mechanical/electrical failure after a few years. The plastic
insulator which spaces apart the radiator and matching arm can degrade
(UV from sunlight is the main offendor, I believe) and crack, allowing
the two arms to change spacing. More subtly, the connection between
the two arms and the metal base can degrade... it's aluminum-to-
aluminum using a set-screw, and the connection can loosen and corrode.

My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I
measured the spacing at the base and got it as close as possible.

I will check out the other connections. There is obvious aluminum oxide
on the assembly so it is very possible it is down between the parts.

I'll get up on my steep metal roof after the rains stop. :-)


It might be worth checking the spacer (replace if necessary), and
checking and tuning up the set-screw connections (squirt with Liquid
Wrench if necessary, loosen and remove, take out the rods, clean the
ends of the rods and the mounting holes in the place, dab with NoAlOx
or a similar corrosion-blocker, reassemble and tighten).

I'm using 75' of
professionally assembled RG8X which is required to get from the radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


Thanks for the suggestions.

--
'Captain' Kirk DeHaan
N6SXR

"Beam me up Scotty, there's no intelligent life here"

NVIS and VHF?
 

On 5/24/2011 5:17 PM, John KD5YI wrote:
On 5/24/2011 6:11 PM, Jim Lux wrote:
On 5/24/2011 2:54 PM, Dave Platt wrote:


I'm using 75' of
professionally assembled RG8X which is required to get from the
radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


The results are all over the map. A piece of Cable TV cable might not be
a bad choice, if you can scrounge one. The 75 ohms probably isn't a big
deal.

At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has 9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php


That's what I used..
Sure you got feet and not meters?

B9219, 75ft, 146 MHz = 1.811dB

NVIS and VHF?
 

On 5/25/2011 3:51 PM, Jim Lux wrote:
On 5/24/2011 5:17 PM, John KD5YI wrote:
On 5/24/2011 6:11 PM, Jim Lux wrote:
On 5/24/2011 2:54 PM, Dave Platt wrote:


I'm using 75' of
professionally assembled RG8X which is required to get from the
radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


The results are all over the map. A piece of Cable TV cable might not be
a bad choice, if you can scrounge one. The 75 ohms probably isn't a big
deal.

At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has 9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php


That's what I used..
Sure you got feet and not meters?

B9219, 75ft, 146 MHz = 1.811dB

Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology
to him. I see that I should also analogize to you for my mistake.

Thanks to you both.

John