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Although the basic concepts and principles are sound, things have moved on over the 40+ years that have passed since the articles were published.
?
Regards,
?
Martin
?
On Fri, Mar 14, 2025 at 07:30 PM, crabtreejr wrote:
Ralph Burhans wrote an excellent series of antenna articles in Radio Electronics in 1983:
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If you want unbelievable nulls, that happen in about 5 seconds, buy a Perseus 22. You can also manually steer the signals with it to. If you are using verticals they need to be spaced about 200' apart. If you are using loops they need to be at least 55' apart.
?
I just finished building a Modified version of the AMRAD eProbe antenna which uses 4 2SK932 JFETs in parallel. I draws 50mA at 13.8VDC and works great. I am not able to hear WWBV much better than my loop and so far in testing it works well up to 30MHz. It is a lot more quiet then the loop on the VLF and LF frequencies.
?
Everett N4CY
In a message dated 3/14/2025 2:41:02 PM Central Daylight Time, martin_ehrenfried@... writes:
?
Although the basic concepts and principles are sound, things have moved on over the 40+ years that have passed since the articles were published.
?
Regards,
?
Martin
?
On Fri, Mar 14, 2025 at 07:30 PM, crabtreejr wrote:
Ralph Burhans wrote an excellent series of antenna articles in Radio Electronics in 1983:
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With my short E-field probes, I've never tried paralleling JFETS.? I need to try that someday with the J-310's.? I usually follow those with a simple emitter follower to establish 50-ohms for the coax.?
Dave - W?LEV
On Fri, Mar 14, 2025 at 8:19?PM Everett N4CY via <everettsharp= [email protected]> wrote:
If you want unbelievable nulls, that happen in about 5 seconds, buy a Perseus 22. You can also manually steer the signals with it to. If you are using verticals they need to be spaced about 200' apart. If you are using loops they need to be at least 55' apart.
?
I just finished building a Modified version of the AMRAD eProbe antenna which uses 4 2SK932 JFETs in parallel. I draws 50mA at 13.8VDC and works great. I am not able to hear WWBV much better than my loop and so far in testing it works well up to 30MHz. It is a lot more quiet then the loop on the VLF and LF frequencies.
?
Everett N4CY
In a message dated 3/14/2025 2:41:02 PM Central Daylight Time, martin_ehrenfried= [email protected] writes:
?
Although the basic concepts and principles are sound, things have moved on over the 40+ years that have passed since the articles were published.
?
Regards,
?
Martin
?
On Fri, Mar 14, 2025 at 07:30 PM, crabtreejr wrote:
Ralph Burhans wrote an excellent series of antenna articles in Radio Electronics in 1983:
|
Hi Martin
?
Have you tried the G4COL design with? transformer in the FET circuit?. Its simple and is supposed to have better large signal handling characteristics?
?
?
I have taken some snippets as pictures.
?
I was going to try it to see if it was superior to the Miniwhip design for broadcast band overload.
?
Its from a RSGB publication.
?
Henry
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Since the last email I read on this loop antenna group addressed an E-Field probe preamp and I've read a number of high-Z preamps on this group, I'll contribute in that thread: high-Z input preamps.
I've recently completed the 4-JFET preamp.? I'll include the schematic as an attachment to this email.? I've used four J-310 N-Channel JEFTs as the active devices instead of the noted devices (2SK932).? While the completed preamp isn't the epitome of neatness, it is proving to be a stellar performer for high-Z E-Field probes at LF and MF (depends on the ferrite material used in the chokes)!!? Just sitting on the bench and powered up with nothing but power leads connected, all the BCB stations are present and accounted for.? I should also add that with the exception of two AM stations, I am not in a strong-signal area.? Just holding a single finger within 1.5-inches of my input disc ceramic blocking capacitor increases the signals displayed on my spectrum analyzer by some 8 to 10 dB.? I'd recommend it to anyone considering the requirement for a high impedance input to a preamp!!
ADDITIONAL COMMENT:? The use of a CMC for the output and isolating DC from the RF should be adopted in many other preamps.? I will certainly use this trick in future builds that require power over coax (new acronym:? POC ?)).? This trick can also be used in the shack to do the same thing.? No need for a multi-component bias tee...
And, yes, the transformers/chokes are wound on 75 material ferrite.? Fortunately, I had a few.? Each has 20 bifilar turns on a 120-75 (1.2-inches OD of 75? material ferrite).?
Also note the output connector (I used BNCs) must be isolated from the main circuit ground plane.? The schematic clearly reflects this requirement.
One last note:? Once the proper bias current is established with the potentiometer, it can be removed, its value measured, and a fixed resistor of the same value can be installed in its place (I had to search a bit deep in my potentiometer collection to locate a 50k pot.).
Dave - W?LEV
Hi Martin
?
Have you tried the G4COL design with? transformer in the FET circuit?. Its simple and is supposed to have better large signal handling characteristics?
?
?
I have taken some snippets as pictures.
?
I was going to try it to see if it was superior to the Miniwhip design for broadcast band overload.
?
Its from a RSGB publication.
?
Henry
|
Dave,
I used 36 turns of #32 bifilar turns on a FT75-50 toroid for the 4 JFETs amp. I designed a new board that has a common mode choke on the back side of?the board, which uses a FT84-75 toroid wound with 18 turns of RG178.
On Wednesday, March 19, 2025, 1:01 PM, W0LEV via groups.io <davearea51a@...> wrote: Since the last email I read on this loop antenna group addressed an E-Field probe preamp and I've read a number of high-Z preamps on this group, I'll contribute in that thread: high-Z input preamps.
I've recently completed the 4-JFET preamp.? I'll include the schematic as an attachment to this email.? I've used four J-310 N-Channel JEFTs as the active devices instead of the noted devices (2SK932).? While the completed preamp isn't the epitome of neatness, it is proving to be a stellar performer for high-Z E-Field probes at LF and MF (depends on the ferrite material used in the chokes)!!? Just sitting on the bench and powered up with nothing but power leads connected, all the BCB stations are present and accounted for.? I should also add that with the exception of two AM stations, I am not in a strong-signal area.? Just holding a single finger within 1.5-inches of my input disc ceramic blocking capacitor increases the signals displayed on my spectrum analyzer by some 8 to 10 dB.? I'd recommend it to anyone considering the requirement for a high impedance input to a preamp!!
ADDITIONAL COMMENT:? The use of a CMC for the output and isolating DC from the RF should be adopted in many other preamps.? I will certainly use this trick in future builds that require power over coax (new acronym:? POC ?)).? This trick can also be used in the shack to do the same thing.? No need for a multi-component bias tee...
And, yes, the transformers/chokes are wound on 75 material ferrite.? Fortunately, I had a few.? Each has 20 bifilar turns on a 120-75 (1.2-inches OD of 75? material ferrite).?
Also note the output connector (I used BNCs) must be isolated from the main circuit ground plane.? The schematic clearly reflects this requirement.
One last note:? Once the proper bias current is established with the potentiometer, it can be removed, its value measured, and a fixed resistor of the same value can be installed in its place (I had to search a bit deep in my potentiometer collection to locate a 50k pot.).
Dave - W?LEV Hi Martin
?
Have you tried the G4COL design with? transformer in the FET circuit?. Its simple and is supposed to have better large signal handling characteristics?
?
?
I have taken some snippets as pictures.
?
I was going to try it to see if it was superior to the Miniwhip design for broadcast band overload.
?
Its from a RSGB publication.
?
Henry
--
|
Hi Dave
It seems that the attachment has been removed from your email.
Thanks for all your contributes!
73 Andrea IN3IWZ?
Since the last email I read on this loop antenna group addressed an E-Field probe preamp and I've read a number of high-Z preamps on this group, I'll contribute in that thread: high-Z input preamps.
I've recently completed the 4-JFET preamp.? I'll include the schematic as an attachment to this email.? I've used four J-310 N-Channel JEFTs as the active devices instead of the noted devices (2SK932).? While the completed preamp isn't the epitome of neatness, it is proving to be a stellar performer for high-Z E-Field probes at LF and MF (depends on the ferrite material used in the chokes)!!? Just sitting on the bench and powered up with nothing but power leads connected, all the BCB stations are present and accounted for.? I should also add that with the exception of two AM stations, I am not in a strong-signal area.? Just holding a single finger within 1.5-inches of my input disc ceramic blocking capacitor increases the signals displayed on my spectrum analyzer by some 8 to 10 dB.? I'd recommend it to anyone considering the requirement for a high impedance input to a preamp!!
ADDITIONAL COMMENT:? The use of a CMC for the output and isolating DC from the RF should be adopted in many other preamps.? I will certainly use this trick in future builds that require power over coax (new acronym:? POC ?)).? This trick can also be used in the shack to do the same thing.? No need for a multi-component bias tee...
And, yes, the transformers/chokes are wound on 75 material ferrite.? Fortunately, I had a few.? Each has 20 bifilar turns on a 120-75 (1.2-inches OD of 75? material ferrite).?
Also note the output connector (I used BNCs) must be isolated from the main circuit ground plane.? The schematic clearly reflects this requirement.
One last note:? Once the proper bias current is established with the potentiometer, it can be removed, its value measured, and a fixed resistor of the same value can be installed in its place (I had to search a bit deep in my potentiometer collection to locate a 50k pot.).
Dave - W?LEV
Hi Martin
?
Have you tried the G4COL design with? transformer in the FET circuit?. Its simple and is supposed to have better large signal handling characteristics?
?
?
I have taken some snippets as pictures.
?
I was going to try it to see if it was superior to the Miniwhip design for broadcast band overload.
?
Its from a RSGB publication.
?
Henry
--
|
Yes, that's the default setting in this group, attachments are removed.
?
Dave, can you add it in the files section please.
?
Regards,
?
Martin
?
?
?
On Thu, Mar 20, 2025 at 06:47 AM, Andrea Dalbagno wrote:
It seems that the attachment has been removed from your email.
|
Thank you, Martin.
73 Andrea IN3IWZ?
Il gio 20 mar 2025, 09:06 Martin - Southwest UK via <martin_ehrenfried= [email protected]> ha scritto: Yes, that's the default setting in this group, attachments are removed.
?
Dave, can you add it in the files section please.
?
Regards,
?
Martin
?
?
?
On Thu, Mar 20, 2025 at 06:47 AM, Andrea Dalbagno wrote:
It seems that the attachment has been removed from your email.
|
Hi Henry,
?
I just quickly built one up.
?
The gain seems quite low and the IMD performance isn't that good. Current draw is about 10mA, which is quite low.
?
I need to experiment to see if I can further optimise the circuit, but it's not looking too promising.
?
When folks state things like "good strong signal handling" without providing any figures, or other parameters as evidence, it's difficult to know if a circuit is performing as expected.
?
Regards,
?
Martin
?
?
On Wed, Mar 19, 2025 at 02:30 AM, <tardivat@...> wrote:
Have you tried the G4COL design with? transformer in the FET circuit?
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Has the 4 FET input High Z amp schematic been posted to the files section, if so under what heading?
??????????????????? Thanks, Mikek
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Mike,
?
I just uploaded it.
?
Everett N4CY
In a message dated 3/20/2025 10:44:13 AM Central Daylight Time, amdx@... writes:
?
Has the 4 FET input High Z amp schematic been posted to the files section, if so under what heading?
??????????????????? Thanks, Mikek
|
So we can not do attachments OR embedded graphics in the body of an email??? A picture is worth 1k words.? But I understand the cost when archived in storage.? These days, storage is the least expensive of digital options.? But I still understand.?
Today I will be attempting to make a frequency sweep of my unit.? I'll wait to upload to the files until that is complete. ?
Dave - W?LEV
On Thu, Mar 20, 2025 at 8:06?AM Martin - Southwest UK via <martin_ehrenfried= [email protected]> wrote:
Yes, that's the default setting in this group, attachments are removed.
?
Dave, can you add it in the files section please.
?
Regards,
?
Martin
?
?
?
On Thu, Mar 20, 2025 at 06:47 AM, Andrea Dalbagno wrote:
It seems that the attachment has been removed from your email.
|
Hi Dave,
?
The free versions of IO groups, have limitations on storage. These limitations depend on the T&C's of when the group was established, the older groups have more free storage than younger groups. It was offered as an incentive to early adopters.
?
If folks include images or files in the body of their posts, it automatically gets included and stored, which counts towards the overall limit.
?
IO also reduces the resolution of images included in posts, but not when uploaded to images, and any messages that include previous posts with files or images can end up being copied multiple times.
?
By getting folks to deliberately upload to the files and photos area, only items that are likely to be of long term use get to be stored, and the more trivial items are excluded.
?
I hope this helps provide a bit of the background as to why the rules on various groups sometimes differ.
?
Regards,
?
Martin
?
On Thu, Mar 20, 2025 at 04:12 PM, W0LEV wrote:
So we can not do attachments OR embedded graphics in the body of an email???
|
Hi Everett,
?
I think if you do this, you will have to spell out that a separate "ground" reference for the antenna and PCB needs to be provided, as the coax performs this function by default in most other designs.
?
I know it seems obvious, but many end users don't understand this significant point.
?
Regards,
?
Martin
?
?
On Wed, Mar 19, 2025 at 06:24 PM, Everett N4CY wrote:
I designed a new board that has a common mode choke on the back side of?the board,
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Hi Everett,
?
Incidentally, note that in your schematic, one of the input diodes, seems to have the wrong polarity.
?
Personally, I'd bias them to ensure decent IMD performance, but maybe you have already measured this using a high Z source and considered it to be OK ?
?
Regards,
?
Martin
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Show quoted text
So we can not do attachments OR embedded graphics in the body of an email??? A picture is worth 1k words.? But I understand the cost when archived in storage.? These days, storage is the least expensive of digital options.? But I still understand.?
Today I will be attempting to make a frequency sweep of my unit.? I'll wait to upload to the files until that is complete. ?
Dave - W?LEV
On Thu, Mar 20, 2025 at 8:06?AM Martin - Southwest UK via <martin_ehrenfried= [email protected]> wrote: Yes, that's the default setting in this group, attachments are removed.
?
Dave, can you add it in the files section please.
?
Regards,
?
Martin
?
?
?
On Thu, Mar 20, 2025 at 06:47 AM, Andrea Dalbagno wrote:
It seems that the attachment has been removed from your email.
--
|
Thanks Martin, I will correct it.
On Thursday, March 20, 2025, 11:45 AM, Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote: Hi Everett,
?
I think if you do this, you will have to spell out that a separate "ground" reference for the antenna and PCB needs to be provided, as the coax performs this function by default in most other designs.
?
I know it seems obvious, but many end users don't understand this significant point.
?
Regards,
?
Martin
?
?
On Wed, Mar 19, 2025 at 06:24 PM, Everett N4CY wrote:
I designed a new board that has a common mode choke on the back side of?the board,
|
Everett N4CY