On 01/24/2013 03:52 PM, John Lofgren wrote:
Should I make it a habbit of TDRing my GPS antennas, receivers and
splitters?
Cheers,
Magnus
I think that question ties into some of the other responses to the original
post. The value of doing the TDR measurement would probably depend on your
Hi
The other nice thing about TDR's is that the units come out in units of time.
If you are working on a timing system, there's much less opportunity to goof
things up by a conversion error.
Bob
On Jan 25, 2013, at 6:37 PM, Magnus Danielson mag...@rubidium.dyndns.org
wrote:
On 01/24/2013
Hi
In a receive only application, match at either end of the cable is rarely high
on the list. You can sweep the input of a lot of classic receivers and find
some interesting VSWR plots.
Bob
On Jan 24, 2013, at 12:51 AM, Jim Lux jim...@earthlink.net wrote:
On 1/23/13 9:45 PM,
Should I make it a habbit of TDRing my GPS antennas, receivers and
splitters?
Cheers,
Magnus
I think that question ties into some of the other responses to the original
post. The value of doing the TDR measurement would probably depend on your
cable lengths and how likely you think it is
mspencer12...@yahoo.ca said:
This URL goes into some of the issues involved in using 75 ohm coax in a gps
system. I do acknowledge that several GPS manufacturers have promoted the
use of 75 ohm coax so some of the conclusions might be arguable..
If the coax is short, the loss due to
On 1/23/13 12:41 AM, Hal Murray wrote:
mspencer12...@yahoo.ca said:
This URL goes into some of the issues involved in using 75 ohm coax in a gps
system. I do acknowledge that several GPS manufacturers have promoted the
use of 75 ohm coax so some of the conclusions might be arguable..
If the
snip
And it's not clear that there's actually loss due to mismatch. Most
antennas/preamps/receivers don't have exactly 50 ohm impedances. 75/50
is only 1.5:1, and there's an awful lot of antennas and receivers out
there that only claim 2:1 VSWR. The usual spec for the antenna is
1.5:1,
Fat fingers. Replace test with rest.
snip
And it's not clear that there's actually loss due to mismatch. Most
antennas/preamps/receivers don't have exactly 50 ohm impedances. 75/50
is only 1.5:1, and there's an awful lot of antennas and receivers out
there that only claim 2:1 VSWR. The
: [time-nuts] Better gps antennas than a Symmetricom 58532A
On 1/23/13 12:41 AM, Hal Murray wrote:
mspencer12...@yahoo.ca said:
This URL goes into some of the issues involved in using 75 ohm coax in a gps
system. I do acknowledge that several GPS manufacturers have promoted the
use of 75 ohm
The Thunderbolt book suggests using RG6 (75 ohm) up to some given
length and then other cable like RG8if the length is longer. I can't
look it up right now. They claim the rg6 is very good because of the
double shield. Trimble claims the 75 v. 50 mismatch is trivial.
On Wed, Jan 23, 2013 at
On 01/23/2013 03:59 PM, John Lofgren wrote:
snip
And it's not clear that there's actually loss due to mismatch. Most
antennas/preamps/receivers don't have exactly 50 ohm impedances. 75/50
is only 1.5:1, and there's an awful lot of antennas and receivers out
there that only claim 2:1 VSWR.
Just a few comments on the cable and VSWR business.
The short version is that unless the run is longer than 100 Ft any antenna with
a preamp gain of more than 30 dB will probably do and the VSWR business does
not matter at all unless it is truly terrible.
For example the loss due to mismatch
On 1/23/13 7:26 AM, li...@lazygranch.com wrote:
For a single frequency use like GPS, the impedance should be close to the
target. It is true for scanners and such, 50 ohms is quite nominal. (This
notion of DC to daylight and maintaining 50 ohms is fantasy. ) But for a GPS,
you know exactly
On 1/23/13 8:50 PM, Jim Lux wrote:
On 1/23/13 7:26 AM, li...@lazygranch.com wrote:
For a single frequency use like GPS, the impedance should be close to
the target. It is true for scanners and such, 50 ohms is quite
nominal. (This notion of DC to daylight and maintaining 50 ohms is
fantasy. )
-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Better gps antennas than a Symmetricom 58532A
On 1/23/13 7:26 AM, li...@lazygranch.com wrote:
For a single frequency use like GPS, the impedance should be close
On 1/23/13 9:45 PM, li...@lazygranch.com wrote:
I doubt the impedance would be designed so nobody gets a right match. Anyway,
the geometric mean, which is how you would do such a compromise is 61.24 ohms.
I suspect that it's more like.. the mfr builds a prototype that has the
right
On 1/21/13 10:59 PM, Chuck Forsberg WA7KGX N2469R wrote:
RG-6 used for satellite TV has much lower loss than RG-58,
and is much cheaper and easier to work with than Heliax or LMR400.
And has a foil shield (if not multiples) with 100% coverage.
___
On Mon, Jan 21, 2013 at 8:58 PM, li...@lazygranch.com wrote:
It is possible that the noise figure of the preamp is better than that of
the gps. This is especially true if the GPS predates SiGe parts being
common place.
I never ran any heliax, but isn't the idea also that it will last longer
Re the RG-6 cable suggestion, I agree it's probably a better choice than RG-58
for a longer cable run.
The downsides I see are:
It's impedance is 75 ohms not 50 ohms so in a 50 ohm system the actual loss is
going to be a bit higher than the data sheets indicate due to the impedance mis
Mark wrote:
Does anyone have any suggestions for an antenna that would be
significantly better than a Symmetricom 58532A for typical time nuts
applications. Immunity to other transmitters is also a
consideration for me, and this may push me towards staying with the 58532A.
I use an
I'd say that if you have some extra money to spend, first spend it of
improving the antenna's location. Unless it already is on top of a tall
mast with a clear view of the horizon and far from any radio reflectors.
The Heliax will only do good if the length of the run is long.
Another good use
albertson.ch...@gmail.com said:
The Heliax will only do good if the length of the run is long.
I don't understand that. What does the type of antenna have to do with the
length of the run?
Do Heliax antennas have a couple of dB gain over other antennas? I can fix
attenuation in coax with
Hal Murray wrote:
albertson.ch...@gmail.com said:
The Heliax will only do good if the length of the run is long.
I don't understand that. What does the type of antenna have to do with the
length of the run?
Do Heliax antennas have a couple of dB gain over other antennas? I can
Heliax is a type/brand of coax not an antenna.
Ahh. Thanks. Everything makes sense now.
I was thinking of Helix from Jim's recent comments rather than Heliax.
--
These are my opinions. I hate spam.
___
time-nuts mailing list --
On Mon, Jan 21, 2013 at 6:59 PM, Hal Murray hmur...@megapathdsl.net wrote:
albertson.ch...@gmail.com said:
The Heliax will only do good if the length of the run is long.
I don't understand that. What does the type of antenna have to do with the
length of the run?
You are confusing
Jan 2013 09:20:44
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Better gps antennas than a Symmetricom 58532A
I'd say that if you have some extra money
albertson.ch...@gmail.com
Sender: time-nuts-boun...@febo.com
Date: Mon, 21 Jan 2013 20:19:47
To: Discussion of precise time and frequency measurementtime-nuts@febo.com
Reply-To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Subject: Re: [time-nuts] Better gps antennas
On Mon, Jan 21, 2013 at 8:23 PM, li...@lazygranch.com wrote:
There was a thread on RF absorbing material a few months ago to get rid of
reflections.. That might be a way to spend spme money. I'd like to see
before and after results.
If you have a very good location for the antenna then RF
Thanks all for the comments and suggestions.
Re my contemplated cable choice, my interest in using Heliax is primarily
driven by shielding and to a lesser extent phase stability considerations. (I
also happen to have some 1/2 Heliax and LMR400 on hand.) I'm currently using
approx 70 feet of
RG-6 used for satellite TV has much lower loss than RG-58,
and is much cheaper and easier to work with than Heliax or LMR400.
On 01/21/2013 10:27 PM, Mark Spencer wrote:
Thanks all for the comments and suggestions.
Re my contemplated cable choice, my interest in using Heliax is primarily
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