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Today's Topics:
1. Antenna problems (Peter Krengel)
2. Re: Antenna problems (Mark J. Blair)
3. Re: Antenna problems (David Bobbett)
4. Re: Phase noise measurement (was - no subject) ([email protected])
----------------------------------------------------------------------
Message: 1
Date: Sun, 22 Aug 2010 04:15:26 +0200
From: "Peter Krengel" <[email protected]>
Subject: [time-nuts] Antenna problems
To: <[email protected]>
Message-ID: <8a8fa241387e4bdba95d68da228a4...@xpserver>
Content-Type: text/plain; charset="iso-8859-1"
Hi group,
Warren found out that the signals TB gets out of my small ceramic typ
antenna are too weak. They are too noisy.
So I had a look for a good antenna and found some commercial typs called
choke-ring antenna. As they are really expensive is there any DIY solution
avaliable?
I have a lathe so its possibly to machine rings if I get the dimensions...
Thanks a lot making me a "nut" ;)
regards
Peter, DG4EK
------------------------------
Message: 2
Date: Sat, 21 Aug 2010 19:35:37 -0700
From: "Mark J. Blair" <[email protected]>
Subject: Re: [time-nuts] Antenna problems
To: Discussion of precise time and frequency measurement
<[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Aug 21, 2010, at 7:15 PM, Peter Krengel wrote:
Warren found out that the signals TB gets out of my small ceramic typ
antenna are too weak. They are too noisy.
So I had a look for a good antenna and found some commercial typs called
choke-ring antenna. As they are really expensive is there any DIY
solution
avaliable?
I think that the TBolt wants a fair amount of gain up at the antenna,
based on the signal levels it reported from the roof antenna feed at work
(we're in the GPS industry) compared to what I normally see from our
"normal" GPS receivers. Mine is installed at home with a Lucent/Alcatel
+26dB antenna which I believe was primarily intended for use at cellular
base stations, and my TBolt sees nice, strong signals from it with about
9m of feedline. These antennas are all over eBay, both used and unused,
and with or without the pole mount. The TBolt will power them with its +5V
bias. An eBay search for "lucent gps antenna" should turn up a few
antennas and several mounts at the moment.
There are probably many other antennas that will work fine. I'd suggest
looking around for active GPS antennas meant for outdoor fixed
installations (they'll generally have a somewhat pointy radome to keep
snow, birds, etc. from accumulating on them), powered by +5VDC, and with
at least 20dB of gain. Used ones can be cheap.
--
Mark J. Blair, NF6X <[email protected]>
Web page: http://www.nf6x.net/
GnuPG public key available from my web page.
------------------------------
Message: 3
Date: Sun, 22 Aug 2010 09:58:59 +0100
From: David Bobbett <[email protected]>
Subject: Re: [time-nuts] Antenna problems
To: Discussion of precise time and frequency measurement
<[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Mark is absolutely right about this Peter, the Tbolt receiver is
'deaf' by modern standards. In fact I seem to remember the Tbolt
documentation specifically mentions the use of a +26dB aerial. I use a
+16dB Lucent unit on top of the TV pole here in Central England and
although there is enough signal, the mapping feature of Lady Heather
shows that I am operating about 10dB below the expected signal level.
I'll be buying a +26dB aerial very shortly so that I can upgrade the
installation when it next gets serviced.
You can get them from eBay for less than 30 Euros, they are purpose
designed for use outside and I have never had any problem buying from
China. I bought all my Tbolt gear from 'fluke.l' without a hitch and
would recommend him.
David
On 22/08/2010 03:35, Mark J. Blair wrote:
On Aug 21, 2010, at 7:15 PM, Peter Krengel wrote:
Warren found out that the signals TB gets out of my small ceramic typ
antenna are too weak. They are too noisy.
So I had a look for a good antenna and found some commercial typs called
choke-ring antenna. As they are really expensive is there any DIY
solution
avaliable?
I think that the TBolt wants a fair amount of gain up at the antenna,
based on the signal levels it reported from the roof antenna feed at work
(we're in the GPS industry) compared to what I normally see from our
"normal" GPS receivers. Mine is installed at home with a Lucent/Alcatel
+26dB antenna which I believe was primarily intended for use at cellular
base stations, and my TBolt sees nice, strong signals from it with about
9m of feedline. These antennas are all over eBay, both used and unused,
and with or without the pole mount. The TBolt will power them with its
+5V bias. An eBay search for "lucent gps antenna" should turn up a few
antennas and several mounts at the moment.
There are probably many other antennas that will work fine. I'd suggest
looking around for active GPS antennas meant for outdoor fixed
installations (they'll generally have a somewhat pointy radome to keep
snow, birds, etc. from accumulating on them), powered by +5VDC, and with
at least 20dB of gain. Used ones can be cheap.
------------------------------
Message: 4
Date: Sun, 22 Aug 2010 13:23:10 +0200 (CEST)
From: [email protected]
Subject: Re: [time-nuts] Phase noise measurement (was - no subject)
To: [email protected]
Message-ID:
<19147149.1282476190211.javamail.ngm...@webmail18.arcor-online.net>
Content-Type: text/plain; charset=ISO-8859-1
> NXP BF862, available from digi-key.
>
Don't these devices have relatively high flicker noise?
1/f corner is well below 100 Hz. Look at the noise voltage plots of
that audio guy I cited.
My results for the BF862 were the same shape, absolutely somewhat worse
in amplitude because I wanted a differential input and less FETs in
parallel.
Most of my BF862 had abt. 12 mA IDss, btw.
The input capacitance is relatively noncritical in this application
(phase noise measurement) since it is shunted by the much larger output
capacitance of the low pass filter at the mixer IF port.
The 300 pF Cin of a single IF3602 could seriously detune the input low
pass
and the 200 pF feedback capacitance in a stage with substantial voltage
gain would destroy the bandwidth unless cascoding is provided.
I think, I'll test some Analog Devices ADA9848-2 in parallel. It's hard to
beat
that combination of noise, 1/f, bandwidth, offset stability and price.
Such a preamp can be used as an add-on to a scope or FFT-Analyzer, too,
to characterize power supplies, references or oscillator bias circuits.
It's fun to enter 60 dB probe gain into a scope channel menu
and still see usable traces with uV/div scale factors.
( with a low pass, of course)
There are noise nuts, too! ;-)
Gerhard
> One heroic effort for audio is here:
> http://www.diy-audio-engineering.org/index.php?board=2.0 HPS5.1
------------------------------
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End of time-nuts Digest, Vol 73, Issue 95
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