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
wrote:
> On 01/24/2013 03:52 PM, John Lofgren wro
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
cab
>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
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 wrote:
> On 1/23/13 9:45 PM, li...@lazygranch.com wrote:
>> I d
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 pattern,
precise time and frequency measurement
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 to the
> target. It is true for scanners a
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. ) Bu
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 the
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 fo
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
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 1
antenna pattern if it were not for the preamp.
-Original Message-
From: Jim Lux
Sender: time-nuts-boun...@febo.com
Date: Wed, 23 Jan 2013 06:07:49
To:
Reply-To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] "Better" gps antennas than a S
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.
< 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
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
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 misma
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
match.
On Mon, Jan 21, 2013 at 8:58 PM, 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
> than coax.
T
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.
___
tim
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 driven
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 t
On Mon, Jan 21, 2013 at 8:23 PM, 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 absorbing material
i
rtson
Sender: time-nuts-boun...@febo.com
Date: Mon, 21 Jan 2013 20:19:47
To: Discussion of precise time and frequency measurement
Reply-To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] "Better" gps antennas than a Symmetricom 58532A
On Mon, Jan 21,
4
To: Discussion of precise time and frequency measurement
Reply-To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] "Better" gps antennas than a Symmetricom 58532A
I'd say that if you have some extra money to spend, first spend it of
improving th
On Mon, Jan 21, 2013 at 6:59 PM, 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?
You are confusing "heliax" with "helix"
> 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 -- time-nuts@fe
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 fi
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
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 o
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 AeroAnt
Greetings:
I'm contemplating upgrading my GPS antenna. Does anyone have any suggestions
for an antenna that would be significantly better than a Symmetricom 58532A for
typical time nuts applications. (As a side note if I upgrade the antenna I
will also upgrade the feed line to LMR style cabl
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