Re: [time-nuts] GPS splitter
On Fri, Jun 16, 2017 at 8:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
And guess what? Satellite TV splitters work. They even have the answer to
"how much attenuation" printed right on the splitter and they come with F
type connecters you can use the recommended TV type antenna cable too.
You can buy them with DC blockers too. All this stuff is low cost because
it is mass produced by the billions
Yes, it's 75 ohm not 50 and the splitters a 2+ GHz but it works just fine
if your antenna has the right gain. The splitters don't high pass the
signal. Trimble actually recommends using the 75 Ohm TV cable and
supplies it with their kits.
Sometimes a GPS receiver will raise an "Antenna Alarm" if it does not see a
DC load but you can turn those off with a serial command
Chris Albertson
Redondo Beach, California
Hi,
Yes, I knew that, but wanted to play safe.
Funny how a quick hobbyist quick-and-dirty build was needed to get an
operator running. Ah well.
Cheers,
Magnus
On 06/17/2017 05:46 PM, Bob kb8tq wrote:
Hi
In some cases, you can get away with a 470 ohm resistor on the Tee and leave out the inductor. A lot depends on
the threshold of the detect circuit in the GPSDO. Since the signal is normally well amplified before it ever gets to the
splitter, adding a small amount of loss generally is not a big deal. Depending on this and that, you may see more
loss from the Tee than from the 470 ohm resistor :)
Bob
On Jun 17, 2017, at 10:12 AM, Magnus Danielson magnus@rubidium.dyndns.org wrote:
Hi,
At one time I had to design a DC-load since the GPSDO did not experience enough antenna current due to a different antenna being used. So, a BNC-T was quickly converted with a SMD inductor and resistor to add 150 Ohm of more load, and that helped the telecom operator to get their GPS out of "no GPS antenna" warning and actually accept the GPS satellites it was already detecting fine.
Cheers,
Magnus
On 06/17/2017 02:40 PM, Bob kb8tq wrote:
Hi
The DC block requirement depends a lot on the design of the GPSDO’s you
are using. With some GPSDO’s a 50 ohm load on the eighth port of a splitter
will do a pretty good job of “antenna detect” signaling. In the more general case
of “I didn’t design this beast” dc blocks and dc shunts to ground is the best approach.
This fairly quickly gets you headed in the direction of the HP / Symmetricom
splitters.
Bob
On Jun 16, 2017, at 11:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
If sharing an active GPS antenna, do you have to DC block all but one
receiver port to prevent multiple receivers trying to supply current to
the antenna?
On say a 26dB antenna (ignoring line loss, power divider insertion loss,
et al), what is the effective gain to each receiver? (Sorry, having a
senior moment)
Should ALL unused ports have 50 ohm +/- 0j terminators on them? I
assume so... Thus, it would be "better" to always use the divider with
the minimum required ports?
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
I would LIKE to share one PC-TEL 26dB GPS antenna mounted at the top of
my 38 foot horiz.loop mast right at the shack entrance, using
LMR-400-DB from antenna to Narda 2-way and thence to my current hacked
Nortel GPSDO and my soon to be complete RPi 2/3 w/ Adafruit Ultimate GPS
Hat NTP Server. On that mast, the antenna would have a near 360 degree
view of the sky completely unobstructed. (Eventually, I expect both of
those units to be replaced with commercial units).
I'm assuming that I DC block whichever unit is capable of providing the
LEAST current at 5VDC... I suspect the Nortel unit can supply more
current than the RPi, but that's not a guarantee... And I guess I could
block/turn off DC delivery on BOTH units and add a voltage adjustable,
current limiting DC injection unit into the line.
Thanks.
73,
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
On 6/16/2017 7:26 PM, Tim Lister wrote:
On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat w9gb@icloud.com wrote:
I have reached the point that I need a 4-port splitter for my GPS antenna (outdoor 5 volt). Any recommendations of models (HP/Symmertricom/Microsemi) to acquire OR to avoid??
As we recommended to me when I asked a similar question, the Narda
4372A-4 was a brand I had not heard of before and didn't come up in
'gps splitter' searches. I got one on ebay for $24 plus a bit extra
for DC blocks on the n-1 other ports and it seems to work well and it
was handy to have an SMA-based solution as most of the gps receivers
and the antenna pucks seem to use SMA. This meant I only needed 1 N to
SMA converter cable for an external antenna (which has yet to be
externalized...). I found it smaller in real life than it looks in a
lot of the pictures, about the size of a modern smartphone but about
double or more the thickness (the connectors are on the ends).
greg
Cheers,
Tim
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
+1 for satellite splitters as a low cost option. But as others have mentioned, you do need to use a little care. Some are 'DC isolated', but that can mean diode OR’ing for each port (all ports DC pass) and not a DC block. And they often don’t have the frequency response (many satellite splitters only say 1GHz or 1500MHz).
The Radio Shack 4 way splitter I started with was just such a device. One input, four outputs, DC pass on all ports with diode isolation. It worked OK, as long as all GPS were 5V antenna types. Adding a 12V receiver was suddenly a problem as my antenna is 5V, along with the other receivers.
The best satellite splitter choice (for me) was a DirecTV SWIM 4 way unit. It’s rated 2-2150, has DC pass on one port. So I could connect my somewhat deaf 12V receiver with an inline amp on one of the DC block ports, and a 5V unit on the DC pass port. Each receiver was happy. A picture of one is at <https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg> Easily found and cheap, 2, 4, or 8 port models exist.
BTW, putting each splitter on the network analyzer proved that the DirecTV unit had lower loss and better port to port isolation than the Radio Shack unit (no surprise really). I ran this way for quite a while until I uh… ran out of ports. I now have a GPS Networking 8 way with ‘proper’ DC block and load on each port which works well too.
Just as an aside, does anyone have any thoughts on the noise contribution of the diodes in the Radio Shack splitter (or similar)? It’s device dependent of course, but I wonder if it’s enough to be a ‘significant’ contributor.
Paul
On Jun 17, 2017, at 12:07 PM, Chris Albertson albertson.chris@gmail.com wrote:
On Fri, Jun 16, 2017 at 8:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
And guess what? Satellite TV splitters work. They even have the answer to
"how much attenuation" printed right on the splitter and they come with F
type connecters you can use the recommended TV type antenna cable too.
You can buy them with DC blockers too. All this stuff is low cost because
it is mass produced by the billions
Yes, it's 75 ohm not 50 and the splitters a 2+ GHz but it works just fine
if your antenna has the right gain. The splitters don't high pass the
signal. Trimble actually recommends using the 75 Ohm TV cable and
supplies it with their kits.
Sometimes a GPS receiver will raise an "Antenna Alarm" if it does not see a
DC load but you can turn those off with a serial command
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 6/17/2017 8:53 AM, Ben Hall wrote:
I've been toying with the idea of modifying one of the units to add
internal DC-blocking and resistors to ground for DC-load. For DC block,
seems like I could very carefully slice the trace on the board by the
SMA connector, bridging the gap with an SMA capacitor.
So I tried this today. Carefully put a gap in the traces using an Xacto
knife on all but one of the output ports and bridged them with 100pF NPO
SMD capacitors. I'll put it on the VNA at work tomorrow...but
measurements using my noise source and AirSpy SDR receiver plus the
SpectrumSpy software shows that it works with somewhere around 10dB of
loss which is very close to the loss of the unmodified unit. :)
So modifying a commercial unit is an option to consider.
thanks much and 73,
ben, kd5byb
Hi
One subtle advantage of the simple satellite splitters - F connector based DC blocks are dirt cheap ….
Bob
On Jun 18, 2017, at 4:06 PM, ziggy9+time-nuts@pumpkinbrook.com wrote:
+1 for satellite splitters as a low cost option. But as others have mentioned, you do need to use a little care. Some are 'DC isolated', but that can mean diode OR’ing for each port (all ports DC pass) and not a DC block. And they often don’t have the frequency response (many satellite splitters only say 1GHz or 1500MHz).
The Radio Shack 4 way splitter I started with was just such a device. One input, four outputs, DC pass on all ports with diode isolation. It worked OK, as long as all GPS were 5V antenna types. Adding a 12V receiver was suddenly a problem as my antenna is 5V, along with the other receivers.
The best satellite splitter choice (for me) was a DirecTV SWIM 4 way unit. It’s rated 2-2150, has DC pass on one port. So I could connect my somewhat deaf 12V receiver with an inline amp on one of the DC block ports, and a 5V unit on the DC pass port. Each receiver was happy. A picture of one is at <https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg https://images-na.ssl-images-amazon.com/images/I/41EWn-NoJlL.jpg> Easily found and cheap, 2, 4, or 8 port models exist.
BTW, putting each splitter on the network analyzer proved that the DirecTV unit had lower loss and better port to port isolation than the Radio Shack unit (no surprise really). I ran this way for quite a while until I uh… ran out of ports. I now have a GPS Networking 8 way with ‘proper’ DC block and load on each port which works well too.
Just as an aside, does anyone have any thoughts on the noise contribution of the diodes in the Radio Shack splitter (or similar)? It’s device dependent of course, but I wonder if it’s enough to be a ‘significant’ contributor.
Paul
On Jun 17, 2017, at 12:07 PM, Chris Albertson albertson.chris@gmail.com wrote:
On Fri, Jun 16, 2017 at 8:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
And guess what? Satellite TV splitters work. They even have the answer to
"how much attenuation" printed right on the splitter and they come with F
type connecters you can use the recommended TV type antenna cable too.
You can buy them with DC blockers too. All this stuff is low cost because
it is mass produced by the billions
Yes, it's 75 ohm not 50 and the splitters a 2+ GHz but it works just fine
if your antenna has the right gain. The splitters don't high pass the
signal. Trimble actually recommends using the 75 Ohm TV cable and
supplies it with their kits.
Sometimes a GPS receiver will raise an "Antenna Alarm" if it does not see a
DC load but you can turn those off with a serial command
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
FWIW the one I chose (V26-102LED is specified to 2.4GHz and has a real DC block on one port and DC pass on the other. They also do up to 8 way versions.
http://vision-products.co.uk/matv-splitters-taps/
At an overall cost of about USD3 or so!!!
Dave
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of ziggy9+time-nuts@pumpkinbrook.com
Sent: 18 June 2017 21:07
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] GPS splitter
+1 for satellite splitters as a low cost option. But as others have mentioned, you do need to use a little care.
Hi Magnus - what sort of inductor value did you use? 68nH or so?
Dave
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Magnus Danielson
Sent: 17 June 2017 15:12
To: time-nuts@febo.com
Cc: magnus@rubidium.se
Subject: Re: [time-nuts] GPS splitter
Hi,
At one time I had to design a DC-load since the GPSDO did not experience enough antenna current due to a different antenna being used. So, a BNC-T was quickly converted with a SMD inductor and resistor to add 150 Ohm of more load, and that helped the telecom operator to get their GPS out of "no GPS antenna" warning and actually accept the GPS satellites it was already detecting fine.
Cheers,
Magnus
On 06/17/2017 02:40 PM, Bob kb8tq wrote:
Hi
The DC block requirement depends a lot on the design of the GPSDO’s
you are using. With some GPSDO’s a 50 ohm load on the eighth port of a
splitter will do a pretty good job of “antenna detect” signaling. In
the more general case of “I didn’t design this beast” dc blocks and dc shunts to ground is the best approach.
This fairly quickly gets you headed in the direction of the HP /
Symmetricom splitters.
Bob
On Jun 16, 2017, at 11:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
If sharing an active GPS antenna, do you have to DC block all but one
receiver port to prevent multiple receivers trying to supply current
to the antenna?
On say a 26dB antenna (ignoring line loss, power divider insertion
loss, et al), what is the effective gain to each receiver? (Sorry,
having a senior moment)
Should ALL unused ports have 50 ohm +/- 0j terminators on them? I
assume so... Thus, it would be "better" to always use the divider
with the minimum required ports?
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
I would LIKE to share one PC-TEL 26dB GPS antenna mounted at the top
of my 38 foot horiz.loop mast right at the shack entrance, using
LMR-400-DB from antenna to Narda 2-way and thence to my current
hacked Nortel GPSDO and my soon to be complete RPi 2/3 w/ Adafruit
Ultimate GPS Hat NTP Server. On that mast, the antenna would have a
near 360 degree view of the sky completely unobstructed.
(Eventually, I expect both of those units to be replaced with commercial units).
I'm assuming that I DC block whichever unit is capable of providing
the LEAST current at 5VDC... I suspect the Nortel unit can supply
more current than the RPi, but that's not a guarantee... And I guess
I could block/turn off DC delivery on BOTH units and add a voltage
adjustable, current limiting DC injection unit into the line.
Thanks.
73,
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
On 6/16/2017 7:26 PM, Tim Lister wrote:
On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat w9gb@icloud.com wrote:
I have reached the point that I need a 4-port splitter for my GPS antenna (outdoor 5 volt). Any recommendations of models (HP/Symmertricom/Microsemi) to acquire OR to avoid??
As we recommended to me when I asked a similar question, the Narda
4372A-4 was a brand I had not heard of before and didn't come up in
'gps splitter' searches. I got one on ebay for $24 plus a bit extra
for DC blocks on the n-1 other ports and it seems to work well and
it was handy to have an SMA-based solution as most of the gps
receivers and the antenna pucks seem to use SMA. This meant I only
needed 1 N to SMA converter cable for an external antenna (which has
yet to be externalized...). I found it smaller in real life than it
looks in a lot of the pictures, about the size of a modern
smartphone but about double or more the thickness (the connectors are on the ends).
greg
Cheers,
Tim
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
HI
The typical answer is: The largest one I could that 1) Would handle the short circuit current expected and
2) was self resonant at or above 1.6 GHz.
Bob
On Jun 21, 2017, at 2:12 PM, David C. Partridge david.partridge@perdrix.co.uk wrote:
Hi Magnus - what sort of inductor value did you use? 68nH or so?
Dave
-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of Magnus Danielson
Sent: 17 June 2017 15:12
To: time-nuts@febo.com
Cc: magnus@rubidium.se
Subject: Re: [time-nuts] GPS splitter
Hi,
At one time I had to design a DC-load since the GPSDO did not experience enough antenna current due to a different antenna being used. So, a BNC-T was quickly converted with a SMD inductor and resistor to add 150 Ohm of more load, and that helped the telecom operator to get their GPS out of "no GPS antenna" warning and actually accept the GPS satellites it was already detecting fine.
Cheers,
Magnus
On 06/17/2017 02:40 PM, Bob kb8tq wrote:
Hi
The DC block requirement depends a lot on the design of the GPSDO’s
you are using. With some GPSDO’s a 50 ohm load on the eighth port of a
splitter will do a pretty good job of “antenna detect” signaling. In
the more general case of “I didn’t design this beast” dc blocks and dc shunts to ground is the best approach.
This fairly quickly gets you headed in the direction of the HP /
Symmetricom splitters.
Bob
On Jun 16, 2017, at 11:54 PM, Clay Autery cautery@montac.com wrote:
This brings up some interesting questions:
If sharing an active GPS antenna, do you have to DC block all but one
receiver port to prevent multiple receivers trying to supply current
to the antenna?
On say a 26dB antenna (ignoring line loss, power divider insertion
loss, et al), what is the effective gain to each receiver? (Sorry,
having a senior moment)
Should ALL unused ports have 50 ohm +/- 0j terminators on them? I
assume so... Thus, it would be "better" to always use the divider
with the minimum required ports?
I am assuming since this is a receive only situation, it will follow
approximately the same rules of physics that dealing with satellite
antenna installations.
I would LIKE to share one PC-TEL 26dB GPS antenna mounted at the top
of my 38 foot horiz.loop mast right at the shack entrance, using
LMR-400-DB from antenna to Narda 2-way and thence to my current
hacked Nortel GPSDO and my soon to be complete RPi 2/3 w/ Adafruit
Ultimate GPS Hat NTP Server. On that mast, the antenna would have a
near 360 degree view of the sky completely unobstructed.
(Eventually, I expect both of those units to be replaced with commercial units).
I'm assuming that I DC block whichever unit is capable of providing
the LEAST current at 5VDC... I suspect the Nortel unit can supply
more current than the RPi, but that's not a guarantee... And I guess
I could block/turn off DC delivery on BOTH units and add a voltage
adjustable, current limiting DC injection unit into the line.
Thanks.
73,
Clay Autery, KY5G
MONTAC Enterprises
(318) 518-1389
On 6/16/2017 7:26 PM, Tim Lister wrote:
On Fri, Jun 16, 2017 at 4:40 PM, Gregory Beat w9gb@icloud.com wrote:
I have reached the point that I need a 4-port splitter for my GPS antenna (outdoor 5 volt). Any recommendations of models (HP/Symmertricom/Microsemi) to acquire OR to avoid??
As we recommended to me when I asked a similar question, the Narda
4372A-4 was a brand I had not heard of before and didn't come up in
'gps splitter' searches. I got one on ebay for $24 plus a bit extra
for DC blocks on the n-1 other ports and it seems to work well and
it was handy to have an SMA-based solution as most of the gps
receivers and the antenna pucks seem to use SMA. This meant I only
needed 1 N to SMA converter cable for an external antenna (which has
yet to be externalized...). I found it smaller in real life than it
looks in a lot of the pictures, about the size of a modern
smartphone but about double or more the thickness (the connectors are on the ends).
greg
Cheers,
Tim
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On Wed, 21 Jun 2017 15:03:54 -0400
Bob kb8tq kb8tq@n1k.org wrote:
The typical answer is: The largest one I could that 1) Would handle the short circuit current expected and
2) was self resonant at or above 1.6 GHz.
I found out, by experiment, that any "large enough" inductance is ok.
A simple "a few dozen windings of AWG30, air core and a tiny bit of
epoxy to keep the windings apart, yet stable" does the trick quite well.
At least it does for the bias-T I used it in. As a rule of thumb,
at the frequency you are using it, the inductor should have an
impedance much larger then the 50Ohm. And for 1.5GHz you get there
pretty quickly. E.g. 20-30 windings on 3mm spread to a length of 20mm
give you something in the order of 150 to 350nH, which translates
to 1k5 to 3k5 impedance at 1.5GHz.
I recommend reading [1] and [2] for the design of bias-T's
(there are probably better sources, but these are those
that I stumbled upon, some time ago)
Attila Kinali
[1] "Design of Bias Tees for a Pulsed-Bias, Pulsed-RF Test System
using Accurate Component Models", by Baylis, Dunleavy, Clausen, 2006
http://www.microwavejournal.com/articles/3912-design-of-bias-tees-for-a-pulsed-bias-pulsed-rf-test-system-using-accurate-component-models?v=preview
[2] "Wideband Bias Tee". by Johnson, 2008
http://wb9jps.com/Gary_Johnson/Bias_Tee_files/Bias_Tee_Design_V2R.pdf
--
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering. -- The Doctor
Hi
Hitting the inductance required is relatively easy. Doing so and not hitting self resonance is a bit more tricky.
Even a zero ohm reactance likely will work ok (in series with a 150 ohm resistor). It’s tough to know
what you have done without a network analyzer. It is even possible that your resistor has enough stray C
to mess things up. Of course it might also have enough stray L to get you back in business.
A somewhat less critical approach is to use ferrite beads on both sides of the resistor. They generally are a
bit less critical (= more likely to do what the data sheet claims). The trick there is to find some that are set up
to work at L band …. they aren’t common in my junk box.
Bob
On Jun 21, 2017, at 4:16 PM, Attila Kinali attila@kinali.ch wrote:
On Wed, 21 Jun 2017 15:03:54 -0400
Bob kb8tq kb8tq@n1k.org wrote:
The typical answer is: The largest one I could that 1) Would handle the short circuit current expected and
2) was self resonant at or above 1.6 GHz.
I found out, by experiment, that any "large enough" inductance is ok.
A simple "a few dozen windings of AWG30, air core and a tiny bit of
epoxy to keep the windings apart, yet stable" does the trick quite well.
At least it does for the bias-T I used it in. As a rule of thumb,
at the frequency you are using it, the inductor should have an
impedance much larger then the 50Ohm. And for 1.5GHz you get there
pretty quickly. E.g. 20-30 windings on 3mm spread to a length of 20mm
give you something in the order of 150 to 350nH, which translates
to 1k5 to 3k5 impedance at 1.5GHz.
I recommend reading [1] and [2] for the design of bias-T's
(there are probably better sources, but these are those
that I stumbled upon, some time ago)
Attila Kinali
[1] "Design of Bias Tees for a Pulsed-Bias, Pulsed-RF Test System
using Accurate Component Models", by Baylis, Dunleavy, Clausen, 2006
http://www.microwavejournal.com/articles/3912-design-of-bias-tees-for-a-pulsed-bias-pulsed-rf-test-system-using-accurate-component-models?v=preview
[2] "Wideband Bias Tee". by Johnson, 2008
http://wb9jps.com/Gary_Johnson/Bias_Tee_files/Bias_Tee_Design_V2R.pdf
--
You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering. -- The Doctor
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.