|
All:
Conditions were not ideal, but we did get some RBN reports. While it's far too soon to say much, it appears the mag loop gives up about 1-2dB over the EFHW, which is up about 60' or so. VE8JY in Alberta heard us, but looking at their antenna system, they can probably still hear Jimmy Hoffa's last conversation. Also, we did get some rain during the test period which forced us to stop for a while. We tried to protect the cap, but were not totally successful. We are going to try again after we iron out some hiccups that showed up during the test. We also need to put it in a protective case.
About the design. The feed loop is rotatable (by hand right now), but we do not think it's worth the effort to motorize it. The software driving the cap via a stepper motor works pretty well, but we think we can refine it somewhat. We are about 50' away from the ML and the control aspects seem to work just fine. Why the 4-loop construction? Because we wanted to be able to fit the loop in the truck of a car without killing the efficiency. True, it's not an Alex loop, but we didn't intend it to be. On the other hand, it's going to be cheaper than most portable antennas and it can handle considerably more power than most. We have more tests in mind down the road, but we are encouraged by the results.
To all of you who tried to give us a listen today, Al and I very much appreciate your efforts on our behalf.
Jack, W8TEE
On Thursday, May 30, 2019, 1:18:40 PM EDT, Jack Purdum <jjpurdum@...> wrote:
All:
Today we began testing Al's new mag loop (ML) design, shown here:
It's a 40-30-20M "luggable" loop. It's about 3' in diameter, breaks down so it fits in a car, and we can get almost 1.1:1.0 on all three bands with our remote controller. (Peter Parker might use it on the beach down under, but most of us won't use it as a walkable antenna.) We ran some tests today and did see RBN reports so we know it radiates. However, it's not waterproof yet and the rains moved in...again. We plan on testing later today starting at 3PM EST on 7.050MHz. We will be transmitting on two antennas: 1) the ML and 2) an EFHW in an attempt to get some meaningful comparisons. We expect to run about 20W of power. We will alternate between the two, but you won't know which is which. After about 45 minutes and it the weather holds, we will move up to 14.080MHz to repeat the tests.
If you have time around then, use the RBN to report what you're hearing. We'd really appreciate it!
Jack, W8TEE Al, AC8GY
|
Looks like a great job of pipe bending. Terry - KB8AMZ Brimfield Twp, OH USA EN91hd Linux User# 412308, Ubuntu User# 34905,?PCARS#78, NAQCC#6668, QRP-ARCI#8855, SKCC#14195
On Thu, May 30, 2019 at 4:54 PM Jack Purdum via Groups.Io <jjpurdum= [email protected]> wrote:
All:
Conditions were not ideal, but we did get some RBN reports. While it's far too soon to say much, it appears the mag loop gives up about 1-2dB over the EFHW, which is up about 60' or so. VE8JY in Alberta heard us, but looking at their antenna system, they can probably still hear Jimmy Hoffa's last conversation. Also, we did get some rain during the test period which forced us to stop for a while. We tried to protect the cap, but were not totally successful. We are going to try again after we iron out some hiccups that showed up during the test. We also need to put it in a protective case.
About the design. The feed loop is rotatable (by hand right now), but we do not think it's worth the effort to motorize it. The software driving the cap via a stepper motor works pretty well, but we think we can refine it somewhat. We are about 50' away from the ML and the control aspects seem to work just fine. Why the 4-loop construction? Because we wanted to be able to fit the loop in the truck of a car without killing the efficiency. True, it's not an Alex loop, but we didn't intend it to be. On the other hand, it's going to be cheaper than most portable antennas and it can handle considerably more power than most. We have more tests in mind down the road, but we are encouraged by the results.
To all of you who tried to give us a listen today, Al and I very much appreciate your efforts on our behalf.
Jack, W8TEE
On Thursday, May 30, 2019, 1:18:40 PM EDT, Jack Purdum < jjpurdum@...> wrote:
All:
Today we began testing Al's new mag loop (ML) design, shown here:
It's a 40-30-20M "luggable" loop. It's about 3' in diameter, breaks down so it fits in a car, and we can get almost 1.1:1.0 on all three bands with our remote controller. (Peter Parker might use it on the beach down under, but most of us won't use it as a walkable antenna.) We ran some tests today and did see RBN reports so we know it radiates. However, it's not waterproof yet and the rains moved in...again. We plan on testing later today starting at 3PM EST on 7.050MHz. We will be transmitting on two antennas: 1) the ML and 2) an EFHW in an attempt to get some meaningful comparisons. We expect to run about 20W of power. We will alternate between the two, but you won't know which is which. After about 45 minutes and it the weather holds, we will move up to 14.080MHz to repeat the tests.
If you have time around then, use the RBN to report what you're hearing. We'd really appreciate it!
Jack, W8TEE Al, AC8GY
|
Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
|
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
Il 31/mag/2019 01:52, "Kees T" < windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
|
Loop efficiency is dependent on size versus frequency.? There are many articles
on-line that discuss this.
_._
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
|
We are also trying to assess other factors, too, such as a counterpoise and its affect on performance. We may find that these "other factors" play no significant role in the antenna's performance. Still, learning that something doesn't matter is as helpful as learning what does matter.
Jack, W8TEE
On Friday, May 31, 2019, 1:38:51 PM EDT, Arv Evans <arvid.evans@...> wrote:
Loop efficiency is dependent on size versus frequency.? There are many articles
on-line that discuss this.
_._
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
|
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See:
| Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
Jack, W8TEE
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote:
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
Il 31/mag/2019 01:52, "Kees T" < windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
|
NEC4 will tell you all of that without building a thing¡ ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Friday, May 31, 2019 12:45 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? We are also trying to assess other factors, too, such as a counterpoise and its affect on performance. We may find that these "other factors" play no significant role in the antenna's performance. Still, learning that something doesn't matter is as helpful as learning what does matter. On Friday, May 31, 2019, 1:38:51 PM EDT, Arv Evans <arvid.evans@...> wrote: Loop efficiency is dependent on size versus frequency.? There are many articles on-line that discuss this. ? As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
-- ¡_. _._
|
Yep¡ that¡¯s true¡ for ideal calculations. ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Friday, May 31, 2019 12:51 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
-- ¡_. _._
|
If you have an alternative model, we'd be interested in knowing about it. We are in the process of finding out which tests make sense and which are really little more than intellectual smoke. Truthfully, we may never know the difference.
Jack, W8TEE
On Friday, May 31, 2019, 1:53:26 PM EDT, MadRadioModder <madradiomodder@...> wrote:
Yep¡ that¡¯s true¡ for ideal calculations. ? ?
From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Friday, May 31, 2019 12:51 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing ? Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
--
¡_. _._
|
Well the good old standby is using a field strength meter around the compass at various distances from the antenna for transmit.? I guess you can do the same thing with a point source on receive.? Forget the on the air ¡°Hows my antenna sound¡± approach¡ it¡¯s useless because it¡¯s inconsistent.? ? Again you can¡¯t do better than NEC4 modelling.? I always start with it.? ??With your background, you should be able to get an academic version for Al to use..? ?
? ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Friday, May 31, 2019 12:56 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? If you have an alternative model, we'd be interested in knowing about it. We are in the process of finding out which tests make sense and which are really little more than intellectual smoke. Truthfully, we may never know the difference. Yep¡ that¡¯s true¡ for ideal calculations. ? ? ? Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
-- ¡_. _._
|
Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io < jjpurdum@...> wrote:
toggle quoted message
Show quoted text
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See:
Jack, W8TEE
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos < and2oosiz2@...> wrote:
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
|
Right now, like most figures, those are the modeled values. We plan on doing our own field tests when we have the second version built.
Jack, W8TEE
On Friday, May 31, 2019, 3:14:07 PM EDT, Gordon Gibby <ggibby@...> wrote:
Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io < jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See:
Jack, W8TEE
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos < and2oosiz2@...> wrote:
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be?
|
Here you can calculate it for yourself.? Arv posted this: ?
? The math is in the other links Arv forwarded¡ ? ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Gordon Gibby
Sent: Friday, May 31, 2019 2:14 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
-- ¡_. _._
|
Interesting.? ?Thanks for forwarding the link.? ?i ran the default look (which is of reasonable size) and it was a small db down at 20 meters and 20 db down at 80 meters....? ??
?
A ton of the people I work with all the time in local clubs are always excited by antennas that are "quiet receivers."? ?Of course, the easiest way to get a very quiet receiving antenna is to use a 50 ohm resistor.? ?(dummy load).? ?Very quiet -- down into
the thermal noise!? ? But not terribly good for transmitting!? ?
All antennas are compromises and one uses what one has to, but I'm interested in emergency work, so efficiency for transmitter work is important to me.? ?Might be very different for someone working with FT8!
Thanks -- I learned something! (As usual on this site)
Gordon
toggle quoted message
Show quoted text
Here you can calculate it for yourself.? Arv posted this:
?
?
The math is in the other links Arv forwarded¡
?
?
?
?
Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See:
|
Fw: [JackAl] W8TEE Mag Loop Testing
|
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote:
As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would
the efficiency be?
?
Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto:
Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
--
¡_. _._
|
This isn¡¯t much of a compromise for an antenna: ? 
? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Gordon Gibby
Sent: Friday, May 31, 2019 4:55 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? Interesting.? ?Thanks for forwarding the link.? ?i ran the default look (which is of reasonable size) and it was a small db down at 20 meters and 20 db down at 80 meters....? ?? ? A ton of the people I work with all the time in local clubs are always excited by antennas that are "quiet receivers."? ?Of course, the easiest way to get a very quiet receiving antenna is to use a 50 ohm resistor.? ?(dummy load).? ?Very quiet -- down into the thermal noise!? ? But not terribly good for transmitting!? ? ? All antennas are compromises and one uses what one has to, but I'm interested in emergency work, so efficiency for transmitter work is important to me.? ?Might be very different for someone working with FT8! ? Thanks -- I learned something! (As usual on this site) Gordon ?
Here you can calculate it for yourself.? Arv posted this: ?
? The math is in the other links Arv forwarded¡ ? ? ? ? Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
--
¡_. _._
-- ¡_. _._
|
Is it portable?
Jack, W8TEE
On Friday, May 31, 2019, 6:06:08 PM EDT, MadRadioModder <madradiomodder@...> wrote:
This isn¡¯t much of a compromise for an antenna: ? 
? ?
From: [email protected] [mailto:[email protected]] On Behalf Of Gordon Gibby
Sent: Friday, May 31, 2019 4:55 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing ? Interesting.? ?Thanks for forwarding the link.? ?i ran the default look (which is of reasonable size) and it was a small db down at 20 meters and 20 db down at 80 meters....? ?? ? A ton of the people I work with all the time in local clubs are always excited by antennas that are "quiet receivers."? ?Of course, the easiest way to get a very quiet receiving antenna is to use a 50 ohm resistor.? ?(dummy load).? ?Very quiet -- down into the thermal noise!? ? But not terribly good for transmitting!? ? ? All antennas are compromises and one uses what one has to, but I'm interested in emergency work, so efficiency for transmitter work is important to me.? ?Might be very different for someone working with FT8! ? Thanks -- I learned something! (As usual on this site) Gordon ?
Here you can calculate it for yourself.? Arv posted this: ?
? The math is in the other links Arv forwarded¡ ? ? ? ? Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
--
¡_. _._
--
¡_. _._
|
Better clean your trunk out for this one¡ ? ?
toggle quoted message
Show quoted text
From: [email protected] [mailto:[email protected]] On Behalf Of Jack Purdum via Groups.Io
Sent: Friday, May 31, 2019 5:23 PM
To: [email protected]
Subject: Re: [BITX20] Preliminary results -- W8TEE/AC8GY Mag Loop Testing? This isn¡¯t much of a compromise for an antenna: ? 
? ? ? Interesting.? ?Thanks for forwarding the link.? ?i ran the default look (which is of reasonable size) and it was a small db down at 20 meters and 20 db down at 80 meters....? ?? ? A ton of the people I work with all the time in local clubs are always excited by antennas that are "quiet receivers."? ?Of course, the easiest way to get a very quiet receiving antenna is to use a 50 ohm resistor.? ?(dummy load).? ?Very quiet -- down into the thermal noise!? ? But not terribly good for transmitting!? ? ? All antennas are compromises and one uses what one has to, but I'm interested in emergency work, so efficiency for transmitter work is important to me.? ?Might be very different for someone working with FT8! ? Thanks -- I learned something! (As usual on this site) Gordon ?
Here you can calculate it for yourself.? Arv posted this: ?
? The math is in the other links Arv forwarded¡ ? ? ? ? Hmmmm. ?I didn¡¯t see any math to explain the quoted efficiencies of 40 or 90%......??
On May 31, 2019, at 13:51, Jack Purdum via Groups.Io <jjpurdum@...> wrote:
Not true. Our loop is 40% efficient on 40M and 90% on 20M. See: | Fw: [JackAl] W8TEE Mag Loop Testing |
|
|
On Friday, May 31, 2019, 12:30:24 PM EDT, iz oos <and2oosiz2@...> wrote: As far as I have understood, loops have poor efficiency (something like 10%, ie - 10db), although they might have rx advantages. Did you software modeled it first? What would the efficiency be? ? Il 31/mag/2019 01:52, "Kees T" <windy10605@...> ha scritto: Jack,
How do we figure out which reflector to follow for info on the ML Testing since it's on several. Guess this is the largest "member count" reflector, but might not be the best one.
73 Kees K5BCQ
--
¡_. _._
-- ¡_. _._
|
The factors in loop efficiency is:
Radiation resistance, usually calculated as a Wheeler measurement would require an arena sized room.
Typical values are in the range of hundred of milliohms to very low ohms.? For less than 1/10 wave
less than .4 ohms.? The only way to increase the Rr (radiation resistance) is increase the loop diameter.
at above .1 wavelength the loop will not exhibit constant or near constant current and most of the
small loop equations look better than it will be.
AC resistance of conductors.? Typical values are in 10s to 100s of milliohms.
More surface, skin effect is the know adversary here.? With greater surface there
are edge crowding effects and phase of inside (id of the loop) vs OD of the loop.
this shows up when loops use very fat conductors causing enough of a differential
between ID and OD and adds a new loss factor, cancellation of currents.
ESR of the capacitor.? ?10s of milliohmms.? This adds to the total AC resistance
of the loop.
Coupling and matching system and its losses. varies with coupling and type.
Loop coupling to loops generally has a K of less than 1, this adds loss.
Direct connections suffer from the very large transformation, usually
capacitor based is better than inductor or transformer is preferred for
lower losses, high Q caps are costly (vacuum if high voltages).
Generally loops, specifically small loops are high loss compared to radiation resistance.
That does not include environmental losses however small they may be.? Also height
above ground usually 1 to 2 loop diameters is a minimum.
Multiturn loops are not more efficient, usually less so due to cancellation of fields.
In some case the offset is required for less tuning capacitance.
The greatest trade is bandwidth, the higher the effective Q the lower the bandwidth.
At 160M the bandwidth is often so narrow for high Q [low loss] loops sideband clipping?
and high IMD from the transmitter as the swr across 2khz changes enough to load pull
the amplifier.? The positive side is offending signals on the RX out of the tuned bandwidth
of the loop are attenuated.? Loop Q tends to decrease with increasing frequency due to?
Skin resistance and combined factors with a small offset due to increased size relative
to frequency.
Allison
|
The antenna calculator barfed out. Didnt anyone have better luck with the online loop calculator? - f
On Sat 1 Jun, 2019, 3:56 AM ajparent1/KB1GMX, < kb1gmx@...> wrote: The factors in loop efficiency is:
Radiation resistance, usually calculated as a Wheeler measurement would require an arena sized room.
Typical values are in the range of hundred of milliohms to very low ohms.? For less than 1/10 wave
less than .4 ohms.? The only way to increase the Rr (radiation resistance) is increase the loop diameter.
at above .1 wavelength the loop will not exhibit constant or near constant current and most of the
small loop equations look better than it will be.
AC resistance of conductors.? Typical values are in 10s to 100s of milliohms.
More surface, skin effect is the know adversary here.? With greater surface there
are edge crowding effects and phase of inside (id of the loop) vs OD of the loop.
this shows up when loops use very fat conductors causing enough of a differential
between ID and OD and adds a new loss factor, cancellation of currents.
ESR of the capacitor.? ?10s of milliohmms.? This adds to the total AC resistance
of the loop.
Coupling and matching system and its losses. varies with coupling and type.
Loop coupling to loops generally has a K of less than 1, this adds loss.
Direct connections suffer from the very large transformation, usually
capacitor based is better than inductor or transformer is preferred for
lower losses, high Q caps are costly (vacuum if high voltages).
Generally loops, specifically small loops are high loss compared to radiation resistance.
That does not include environmental losses however small they may be.? Also height
above ground usually 1 to 2 loop diameters is a minimum.
Multiturn loops are not more efficient, usually less so due to cancellation of fields.
In some case the offset is required for less tuning capacitance.
The greatest trade is bandwidth, the higher the effective Q the lower the bandwidth.
At 160M the bandwidth is often so narrow for high Q [low loss] loops sideband clipping?
and high IMD from the transmitter as the swr across 2khz changes enough to load pull
the amplifier.? The positive side is offending signals on the RX out of the tuned bandwidth
of the loop are attenuated.? Loop Q tends to decrease with increasing frequency due to?
Skin resistance and combined factors with a small offset due to increased size relative
to frequency.
Allison
|
Terry Morris
MadRadioModder