On Saturday, March 14, 2015 at 1:24:03 PM UTC-4, Fred McKenzie wrote:
In article ,
Tom W3TDH wrote:

I was under the impression that the persons participating in any given QSO
could hear each other over the access point they were using. I had pictured
it as somewhat akin to the remote receivers on our club's analog FM repeater
in that the other users on the QSO would hear the conversation over the
repeaters output.

Tom-

The more you post, the more complicated it becomes!

What you describe sounds like a remote receiver for an existing
repeater, not a hot spot. The hot spot I have is a low power DVAP
operating on a simplex frequency. Yours might be equivalent, but using
a more powerful transmitter.

A hot spot does not connect to a repeater via RF. It connects via the
internet to another device. That device might be a D-STAR repeater, but
often it is a computer hosting a "reflector" that repeaters may also be
connected to.

If your hot spot is connected to the same reflector as the local
repeater, it would be possible for users to talk into the hot spot and
listen to the repeater output. But that would be a split frequency
setup for the radio.

As I said, go ahead and try what you had planned. It will work to some
extent, and will help you get your feet wet.

73,
Fred
K4DII

I'm not confused about how the hotspot connects to the repeater's reflector.. I would think that the words "somewhat akin" would have made it clear that I was talking about a functional similarity rather than physical one.

Part of the reason that I have never developed any enthusiasm for D-STAR is the reliance the system puts in Internet connections between various portions of that system. I see any radio system that depends on non radio pathways to function as inherently more frangible than one that is entirely RF based. That being said my club has made an investment in the build out of a D-STAR repeater and hot spot system which they are hoping will cover the whole county. All I am doing is trying to support that effort.

I didn't devise the approach being used but I know that it is already being used successfully at two other locations in our service area. Does it really matter how the hotspot interacts with the rest of the D-STAR network when what we are talking about here is how to use it on the same antenna as a Two Meter Radio Message Server Packet.

--
Tom Horne W3TDH

On Saturday, March 14, 2015 at 3:56:38 PM UTC-4, Jerry Stuckle wrote:
Tom,

Please see inlined...

On 3/14/2015 1:17 PM, Tom W3TDH wrote:

May I ask that you cool your jets a little. Please turn off the
afterburners and stick to the questions that I'm asking. I don't
want to be a focus of a flame war. I came here in the hope of
getting good information and the task of sorting out conflicting
advice is so much easier if I don't need to also filter out
gratuitous feuding.

If you followed this group before posting (always a good idea), you will
see that is pretty normal here. If you're going to post, you can expect
both good and bad advice. And some people (like Channel Jumper - who
probably isn't even a ham) are so far off with every post you can expect
a flame war.

But then that is true of almost every place on the Internet.

Your version of what is possible is attractive because it allows me
to do what I want to do to support my clubs D-STAR project and
provide a training resource for the ARES Hospital Emergency Net staff
to become competent with Winlink.

I realize that there are some Hams that despise Winlink and all other
automated store and forward systems. I will be doing everything I can
to avoid interference to other Amateurs but since we are using this to
support hospitals under emergency conditions I think that everyone can
just suck it up and bare with the emergency traffic and whatever
inconvenience it may generate. b


You are required by law to avoid interference. But you also need to
understand what constitutes emergency traffic to the FCC. For that to
occur, there must be an IMMEDIATE threat to life and/or property. An
example would be reporting an automobile accident, especially one
requiring immediate medical attention.

It does NOT include 99% of the traffic being passed during an emergency.
In the 19 years I've been a member of MoCo ARES/RACES (including the
Hospital Net), we have NEVER had emergency traffic passed during a
callout. Of course, I could also say that of most of the emergencies
I've been involved in in 47 years as a ham. The only times I can think
of that I've been involved in true emergency traffic during a callout
was when aiding search and rescue after tornadoes.

Just because it's a hospital net does not constitute emergency traffic.

So, while hams in the area will voluntarily yield the frequency, there
is no requirement for them to do so, and any interference would be a
violation.

Would you please advise if the third harmonic issue is likely to be
serious enough to require the use of a low pass filter between the
two meter transceiver and the Diplexer/Band Pass Filter when using
separate transmitters?


Your diplexer should handle that well enough. What would be more of a
concern to me would be just the spurious radiation around the shack.
It's possible that could cause some desense, but I wouldn't expect it to
be significant.

--
Tom Horne W3TDH


Your sig separator is broken. It needs to be exactly
hyphen-hyphen-space-newline. You're missing the space.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry

All I was trying to do by saying that we plan to be careful about interference is to calm and reassure those that are pathologically afraid of Winlink.. I do realize that nothing short of a true SOS like being pinned under a fallen snag with a widfire approaching qualifies as an emergency in the eyes of the Friendly Candy Company (FCC). They have been known to confiscate radios and cancel the license of hams who invaded a public safety channel to ask for help with a person who was bleeding profusely from a scalp wound. As a trained EMT I know that scalp wounds are often scarier than they look but how a ham out mountain biking with friends was supposed to know that I have no idea. The actual reaction of the FCC to any given situation is just as predictable as the reaction of any other organization that is staffed by human beings.

Thanks for pointing out the the problem with my signature element. I appreciate the help.

--
Tom Horne W3TDH

On Wednesday, March 11, 2015 at 7:11:14 PM UTC-4, Brian Reay wrote:
Tom W3TDH wrote:
I am looking for recommendations for a dual band antenna that will serve
two separate radios. The reason that I want to use a single antenna is
that I have a limited number of mounting points for antennas. At present
it will be hard for SWMBO; as in Rumpole's spouse, She Who Must Be
Obeyed; to tolerate the use of both our home's gable ends and the chimney
being used to support antennas. I am planning to replace my Diamond X-30
with a triband vertical for Six, Two, and .7 Meters. The chimney will
then support a rotor aimed Two and .7 Meter beam. The second gable end
will support the Two meter / Seventy Centimeter dual band vertical that I
am asking for help in selecting.

One radio will be a two meter packet node which will be used as a Winlink
Radio Message Server. The other radio will be a UHF D-STAR hotspot. I
am willing to pay what is needed to to get the best antenna for this
application but I don't want to waste money ineffectively. So the two
meter radio will be in the 144 MHz portion of the band and I don't yet
actually know were the D-STAR hotspot will be run. I have a DCI filter
and diplexer to keep the two radios from actually knowing of each others
existence. Since a hotspot is not supposed to be a terribly wide area
installation I would imagine that I do not want an extremely high gain
antenna but I am perfectly open to be reeducated on that. The difficulty
is that I would guess that the Radio Message Server / Packet would
benefit from as much horizontal gain as can be achieved. I have a home
brewed collinear two meter J-Pole that has been a good performer on two
meters and presents a low SWR on 440 MHz. I have yet to master antenna
modeling but I would imagine; given all the warnings I have read on line;
that it has poor radiation pattern on UHF. Is it likely to be too poor a
performer for a hot spot on UHF?

I really am asking because I want to know. I am not looking for
encouragement to do something that will be ineffective. Thank you in
advance for any help you may be willing to offer.

--
Tom Horne W3TDH

Diamond do a number of other antennas similar to the x30, essentially
longer, with more gain. I would suggest you look at their website and pick
one to match you budget, acceptable profile, etc.

It may be worth investing in another tribander, you may just want the third
band in the future and it will save another negotiation with Senior
Management. Or you could take my approach and have an XYL who is licensed
;-)

73
Brian
G8OSN/W8OSN

Brian

Should I follow your suggestion I would need to also provide protection for the radio connected to the third band segment. Do you know of any reason why connecting two separate filters to the same feed line would not work.

Can I anticipate any ill affect from placing a coaxial Tee fitting across the output of one filter and connecting a jumper to the output of another filter in order to connect the transceivers to the multiband antenna? Would there be any additional concerns be raised if one of the two filters was the dual band model with separate connections for each of it's two bands on the end being used for input connections? What about if I make up the assembly using Three separate filters with Two of them connected to TEE fittings..

--
Tom Horne W3TDH

On 15/03/15 13:33, Jerry Stuckle wrote:
On 3/15/2015 5:50 AM, Brian Reay wrote:
Tom W3TDH wrote:


Would you please advise if the third harmonic issue is likely to be
serious enough to require the use of a low pass filter between the two
meter transceiver and the Diplexer/Band Pass Filter when using separate transmitters?


It depends on your tx.

I've never required filters nor heard of their being required.

Remember, you would need to be listening on the 3rd Rx harmonic, or 'close'
to it for the rx to suffer and the harmonic should get several 10s of dB
down relative to tell 2m carrier.


Brian,

Yes, it will be several 10s of dB down - but that can still be
sufficient to be heard in (and potentially desense) a near-by receiver.
It doesn't take a lot of signal if it's within the receiver's passband.

But Tom's diplexer should handle this easily.


Well, I several of us often run full duplex 2m/70cm or even triplex
4m/2m/70cm nets locally and use a common 2m/70cm antenna without
problems- hence my comment that I've never experienced any issues.
(Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband
duplex while mobile with a common antenna and with dual antennas on the
roof of a SUV. True, I've not used the harmonic of the 2m frequency but
the desense was never an issue. While mobile and using the single
antenna, I relied on the internal duplexer of the radio. When using two
antennas, there was no filter or duplexer added.

If you think about it from a practical stand point, dual band radio with
the ability to operate full duplex cross band would be pretty useless if
it was an issue.

I'm simply relating my experiences of actually using 2m and 70cm on a
common antenna with a duplexer. If your experiences differ, fine.

On 15/03/15 15:42, Tom W3TDH wrote:
On Wednesday, March 11, 2015 at 7:11:14 PM UTC-4, Brian Reay wrote:
Tom W3TDH wrote:
I am looking for recommendations for a dual band antenna that will serve
two separate radios. The reason that I want to use a single antenna is
that I have a limited number of mounting points for antennas. At present
it will be hard for SWMBO; as in Rumpole's spouse, She Who Must Be
Obeyed; to tolerate the use of both our home's gable ends and the chimney
being used to support antennas. I am planning to replace my Diamond X-30
with a triband vertical for Six, Two, and .7 Meters. The chimney will
then support a rotor aimed Two and .7 Meter beam. The second gable end
will support the Two meter / Seventy Centimeter dual band vertical that I
am asking for help in selecting.

One radio will be a two meter packet node which will be used as a Winlink
Radio Message Server. The other radio will be a UHF D-STAR hotspot. I
am willing to pay what is needed to to get the best antenna for this
application but I don't want to waste money ineffectively. So the two
meter radio will be in the 144 MHz portion of the band and I don't yet
actually know were the D-STAR hotspot will be run. I have a DCI filter
and diplexer to keep the two radios from actually knowing of each others
existence. Since a hotspot is not supposed to be a terribly wide area
installation I would imagine that I do not want an extremely high gain
antenna but I am perfectly open to be reeducated on that. The difficulty
is that I would guess that the Radio Message Server / Packet would
benefit from as much horizontal gain as can be achieved. I have a home
brewed collinear two meter J-Pole that has been a good performer on two
meters and presents a low SWR on 440 MHz. I have yet to master antenna
modeling but I would imagine; given all the warnings I have read on line;
that it has poor radiation pattern on UHF. Is it likely to be too poor a
performer for a hot spot on UHF?

I really am asking because I want to know. I am not looking for
encouragement to do something that will be ineffective. Thank you in
advance for any help you may be willing to offer.

--
Tom Horne W3TDH

Diamond do a number of other antennas similar to the x30, essentially
longer, with more gain. I would suggest you look at their website and pick
one to match you budget, acceptable profile, etc.

It may be worth investing in another tribander, you may just want the third
band in the future and it will save another negotiation with Senior
Management. Or you could take my approach and have an XYL who is licensed
;-)

73
Brian
G8OSN/W8OSN

Brian

Should I follow your suggestion I would need to also provide protection for the radio connected to the third band segment. Do you know of any reason why connecting two separate filters to the same feed line would not work.

Can I anticipate any ill affect from placing a coaxial Tee fitting across the output of one filter and connecting a jumper to the output of another filter in order to connect the transceivers to the multiband antenna? Would there be any additional concerns be raised if one of the two filters was the dual band model with separate connections for each of it's two bands on the end being used for input connections? What about if I make up the assembly using Three separate filters with Two of them connected to TEE fittings.




It depends.

For example:

Some, duplexers are just an LPF and a HPF. Say your 2m filter is LPF and
your 70cm filter is HPF and your 3rd band is 220MHz (the one you wish to
Tee in).

If the Cut Off frequency of the HPF is such that is will allow too much
of the 220 MHz to pass to the 70cm radio, you could have an issue with
enough 220MHz reaching the 70cm radio to be an issue. Likewise of for
the 2m radio but with the LPF cut off.

You really need to know the performance of the filters you are using.

I don't know the unit you mentioned, I would suggest you study the data
sheet and see what its performance is at the frequency you plan to 'Tee'
in.

Ideally, build (or buy) a unit designed to work with three signals,
which you may be able to do using the unit you have when you know the
characteristics.

On 3/15/2015 11:54 AM, Brian Reay wrote:


Well, I several of us often run full duplex 2m/70cm or even triplex
4m/2m/70cm nets locally and use a common 2m/70cm antenna without
problems- hence my comment that I've never experienced any issues.
(Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband
duplex while mobile with a common antenna and with dual antennas on the
roof of a SUV. True, I've not used the harmonic of the 2m frequency but
the desense was never an issue. While mobile and using the single
antenna, I relied on the internal duplexer of the radio. When using two
antennas, there was no filter or duplexer added.

If you think about it from a practical stand point, dual band radio with
the ability to operate full duplex cross band would be pretty useless if
it was an issue.

I'm simply relating my experiences of actually using 2m and 70cm on a
common antenna with a duplexer. If your experiences differ, fine.





Brian,

Have you actually measured desense with good test equipment? If not,
you really don't know, do you?

I've run 2m/70cm crossband mobile also. However, I also haven't
measured the desense when trying to receive on the third harmonic. Have
you?

Additionally, when running crossband mobile, I've always gone from a
nearby handheld on 70cm to a 2m repeater. Never tried it the other way
around, and since the handheld is always (relatively) nearby, it always
has a strong signal into the mobile. So even if there were desense I
wouldn't see it.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 3/15/2015 11:25 AM, Tom W3TDH wrote:
On Saturday, March 14, 2015 at 3:56:38 PM UTC-4, Jerry Stuckle wrote:
Tom,

Please see inlined...

On 3/14/2015 1:17 PM, Tom W3TDH wrote:

May I ask that you cool your jets a little. Please turn off the
afterburners and stick to the questions that I'm asking. I don't
want to be a focus of a flame war. I came here in the hope of
getting good information and the task of sorting out conflicting
advice is so much easier if I don't need to also filter out
gratuitous feuding.

If you followed this group before posting (always a good idea), you will
see that is pretty normal here. If you're going to post, you can expect
both good and bad advice. And some people (like Channel Jumper - who
probably isn't even a ham) are so far off with every post you can expect
a flame war.

But then that is true of almost every place on the Internet.

Your version of what is possible is attractive because it allows me
to do what I want to do to support my clubs D-STAR project and
provide a training resource for the ARES Hospital Emergency Net staff
to become competent with Winlink.

I realize that there are some Hams that despise Winlink and all other
automated store and forward systems. I will be doing everything I can
to avoid interference to other Amateurs but since we are using this to
support hospitals under emergency conditions I think that everyone can
just suck it up and bare with the emergency traffic and whatever
inconvenience it may generate. b


You are required by law to avoid interference. But you also need to
understand what constitutes emergency traffic to the FCC. For that to
occur, there must be an IMMEDIATE threat to life and/or property. An
example would be reporting an automobile accident, especially one
requiring immediate medical attention.

It does NOT include 99% of the traffic being passed during an emergency.
In the 19 years I've been a member of MoCo ARES/RACES (including the
Hospital Net), we have NEVER had emergency traffic passed during a
callout. Of course, I could also say that of most of the emergencies
I've been involved in in 47 years as a ham. The only times I can think
of that I've been involved in true emergency traffic during a callout
was when aiding search and rescue after tornadoes.

Just because it's a hospital net does not constitute emergency traffic.

So, while hams in the area will voluntarily yield the frequency, there
is no requirement for them to do so, and any interference would be a
violation.

Would you please advise if the third harmonic issue is likely to be
serious enough to require the use of a low pass filter between the
two meter transceiver and the Diplexer/Band Pass Filter when using
separate transmitters?


Your diplexer should handle that well enough. What would be more of a
concern to me would be just the spurious radiation around the shack.
It's possible that could cause some desense, but I wouldn't expect it to
be significant.

--
Tom Horne W3TDH


Your sig separator is broken. It needs to be exactly
hyphen-hyphen-space-newline. You're missing the space.


Jerry

All I was trying to do by saying that we plan to be careful about interference is to calm and reassure those that are pathologically afraid of Winlink. I do realize that nothing short of a true SOS like being pinned under a fallen snag with a widfire approaching qualifies as an emergency in the eyes of the Friendly Candy Company (FCC). They have been known to confiscate radios and cancel the license of hams who invaded a public safety channel to ask for help with a person who was bleeding profusely from a scalp wound. As a trained EMT I know that scalp wounds are often scarier than they look but how a ham out mountain biking with friends was supposed to know that I have no idea. The actual reaction of the FCC to any given situation is just as predictable as the reaction of any other organization that is staffed by human beings.

Thanks for pointing out the the problem with my signature element. I appreciate the help.


Tom,

From your previous statement:

"I will be doing everything I can to avoid interference to other
Amateurs but since we are using this to support hospitals under
emergency conditions I think that everyone can just suck it up and bare
with the emergency traffic and whatever inconvenience it may generate."

I'm just pointing out that by law you are REQUIRED to avoid
interference. Also, your traffic is almost NEVER emergency traffic, and
any interference you cause will be illegal. Other hams do NOT have to
"suck it up" just because you're calling it a "hospital net". If you
cause interference, you are liable - unless it is a true emergency.

And yes, I was part of the local hospital net before you ever got your
license. I manned Suburban Hospital. Of course, we had an 800MHz
channel at the time, not ham. But the hams were the operators of the
system.

BTW - I also was an EMT - and probably have worked more runs than you've
ever dreamed. I know how bloody a scalp wound can be. But I also know
it can be a symptom of a much more serious injury such as a skull
fracture (BTDT). To a non-trained person, this would be emergency
traffic. As an EMT, I would never consider such a wound to NOT be
emergency traffic when reported by a non-trained person. Neither would
any of the other EMS people I have known over the years.

And I'd like to see the details of the "hams who invaded a public safety
channel to ask for help with a person who was bleeding profusely from a
scalp wound". I suspect there is much more to it than you are
reporting. References?

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On 15/03/15 16:40, Jerry Stuckle wrote:
On 3/15/2015 11:54 AM, Brian Reay wrote:


Well, I several of us often run full duplex 2m/70cm or even triplex
4m/2m/70cm nets locally and use a common 2m/70cm antenna without
problems- hence my comment that I've never experienced any issues.
(Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband
duplex while mobile with a common antenna and with dual antennas on the
roof of a SUV. True, I've not used the harmonic of the 2m frequency but
the desense was never an issue. While mobile and using the single
antenna, I relied on the internal duplexer of the radio. When using two
antennas, there was no filter or duplexer added.

If you think about it from a practical stand point, dual band radio with
the ability to operate full duplex cross band would be pretty useless if
it was an issue.

I'm simply relating my experiences of actually using 2m and 70cm on a
common antenna with a duplexer. If your experiences differ, fine.





Brian,

Have you actually measured desense with good test equipment? If not,
you really don't know, do you?

I've run 2m/70cm crossband mobile also. However, I also haven't
measured the desense when trying to receive on the third harmonic. Have
you?

Additionally, when running crossband mobile, I've always gone from a
nearby handheld on 70cm to a 2m repeater. Never tried it the other way
around, and since the handheld is always (relatively) nearby, it always
has a strong signal into the mobile. So even if there were desense I
wouldn't see it.


I haven't measured the desense, I was relating practical experience as I
said. In the circumstances, they are probably more relevant in my
opinion*. Tom is free to take which ever advice he decides is relevant.

* The desense would have a number of variables, including the tx power
(which may vary), tx and rx frequency (also variable). Plus the impact
of the dense on the receive performance is almost impossible to predict
in terms of who/what you could receive- by which I mean you could
generate a raft of numbers for loss of system sensitivity but how do you
translate that into practical link budgets, other than for known
stations? It would be virtually useless for a random contact.



73
Brian

On 3/15/2015 4:47 PM, Brian Reay wrote:
On 15/03/15 16:40, Jerry Stuckle wrote:
On 3/15/2015 11:54 AM, Brian Reay wrote:


Well, I several of us often run full duplex 2m/70cm or even triplex
4m/2m/70cm nets locally and use a common 2m/70cm antenna without
problems- hence my comment that I've never experienced any issues.
(Being in the UK, we have access to 4m.) I've even run 2m/70cm crossband
duplex while mobile with a common antenna and with dual antennas on the
roof of a SUV. True, I've not used the harmonic of the 2m frequency but
the desense was never an issue. While mobile and using the single
antenna, I relied on the internal duplexer of the radio. When using two
antennas, there was no filter or duplexer added.

If you think about it from a practical stand point, dual band radio with
the ability to operate full duplex cross band would be pretty useless if
it was an issue.

I'm simply relating my experiences of actually using 2m and 70cm on a
common antenna with a duplexer. If your experiences differ, fine.





Brian,

Have you actually measured desense with good test equipment? If not,
you really don't know, do you?

I've run 2m/70cm crossband mobile also. However, I also haven't
measured the desense when trying to receive on the third harmonic. Have
you?

Additionally, when running crossband mobile, I've always gone from a
nearby handheld on 70cm to a 2m repeater. Never tried it the other way
around, and since the handheld is always (relatively) nearby, it always
has a strong signal into the mobile. So even if there were desense I
wouldn't see it.


I haven't measured the desense, I was relating practical experience as I
said. In the circumstances, they are probably more relevant in my
opinion*. Tom is free to take which ever advice he decides is relevant.


So you really don't know if you have any desense or not. You just
haven't noticed any. That does not mean it's not there.

* The desense would have a number of variables, including the tx power
(which may vary), tx and rx frequency (also variable). Plus the impact
of the dense on the receive performance is almost impossible to predict
in terms of who/what you could receive- by which I mean you could
generate a raft of numbers for loss of system sensitivity but how do you
translate that into practical link budgets, other than for known
stations? It would be virtually useless for a random contact.



73
Brian


Actually, knowing the characteristics of the transmitter and receiver,
as well as the characteristics of whatever filters are used, it's
possible to quite accurately determine desense. That allows you to
predict with pretty good accuracy how much signal it would take to
attain a certain signal level (i.e. 12db SINAD) in the receiver. But
that's the important part of ANY system.

And it's impossible to predict the results of ANY random contact without
knowing the details of the other station. But then that's true on any
frequency with any mode.

Something I did a fair amount of back in the mid 70's when I worked for
a worked for a 2-way shop and planned UHF repeater systems. I doubt
it's changed any today.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On Sunday, March 15, 2015 at 12:36:28 PM UTC-4, Brian Reay wrote:

It depends.

For example:

Some, duplexers are just an LPF and a HPF. Say your 2m filter is LPF and
your 70cm filter is HPF and your 3rd band is 220MHz (the one you wish to
Tee in).

If the Cut Off frequency of the HPF is such that is will allow too much
of the 220 MHz to pass to the 70cm radio, you could have an issue with
enough 220MHz reaching the 70cm radio to be an issue. Likewise of for
the 2m radio but with the LPF cut off.

You really need to know the performance of the filters you are using.

I don't know the unit you mentioned, I would suggest you study the data
sheet and see what its performance is at the frequency you plan to 'Tee'
in.

Ideally, build (or buy) a unit designed to work with three signals,
which you may be able to do using the unit you have when you know the
characteristics.

Brian

I was specifically referring to the Digital Communications Incorporated band pass filters that I had identified earlier in the thread. I have in hand a DCI-146-444-DX-DB I was thinking of adding a DCI-223.5-3H for 125 Centimeter band for the 146/220/446 tri-band antenna. That would give me three separate input ports to attach the three separate transceivers to.

On the 6,2,& 0.7 Meter multi-band antenna I would buy a DCI-146-444-DB and a DCI-6M-53 MHz-2-4p. That way I could connect a dual band 146/446 Mhz radio to the dual band filter and the Six Meter Transceiver to the Six Meter band pass filter inlet.

The spec sheets for all of these filters can be seen at the manufacturers web site at
http://www.dci.ca/?Section=Products&SubSection=Amateur.

--
Tom Horne W3TDH