Re: "active antenna preamplifiers" in ham radio May 1986
Thank you, Martin.
73 Andrea IN3IWZ?
Il gio 20 mar 2025, 09:06 Martin - Southwest UK via <martin_ehrenfried= yahoo.com@groups.io> 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.
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Re: "active antenna preamplifiers" in ham radio May 1986
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.
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Re: "active antenna preamplifiers" in ham radio May 1986
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
--
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Re: File /AG5RT/LZ1AQ amplifier noise reduction.pdf uploaded
#file-notice
On Thu, Mar 20, 2025 at 12:28 AM, Paul V Birke wrote:
Maybe that is why the original East German design had a suitable inductor in the same place
East German???? To what are you referring?
As far as I am aware, the LZ1AQ loop amplifier is this one:
?
Dan - K3GMQ
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Re: File /AG5RT/LZ1AQ amplifier noise reduction.pdf uploaded
#file-notice
Maybe that is why the original East German design had a suitable inductor in the same place
Paul VE3PVB
On Wednesday, March 19, 2025 at 10:12:17 p.m. EDT, Group Notification <noreply@groups.io> wrote:
The following items have been added to the Files area of the loopantennas@groups.io group.
By: Mark Whittington AG5RT <mark-whittington@...>
Description:
LZ1AQ loop amplifier noise reduction
I ran an LTSPICE noise analysis of the original LZ1AQ circuit connected to a 3.3 uH loop. I also performed some bench measurements to verify the SPICE results. The analysis and measurements both indicate placing 47 uH inductors in series with the 51 Ohm input emitter bias resistors cuts input referred noise by 2 to 3 dB. This is a substantial reduction. Gain is little effected. Loop diameter can be reduced while maintaining the same input-referred noise level as the original setup.
The LTSPICE listings share this directory.
Mark
AG5RT
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File /AG5RT/LZ1AQ amplifier noise reduction.pdf uploaded
#file-notice
The following items have been added to the Files area of the loopantennas@groups.io group.
By: Mark Whittington AG5RT <mark-whittington@...>
Description:
LZ1AQ loop amplifier noise reduction
I ran an LTSPICE noise analysis of the original LZ1AQ circuit connected to a 3.3 uH loop. I also performed some bench measurements to verify the SPICE results. The analysis and measurements both indicate placing 47 uH inductors in series with the 51 Ohm input emitter bias resistors cuts input referred noise by 2 to 3 dB. This is a substantial reduction. Gain is little effected. Loop diameter can be reduced while maintaining the same input-referred noise level as the original setup.
The LTSPICE listings share this directory.
Mark
AG5RT
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After talking with Dave Evans, he noticed that my load resistance slider was at minimum and thought that my radials were too long.? He suggested that I raise and shorten them.? I raised them from on the ground to 18 inches high and shortened them to 15 feet.? That did it!? Thanks to Dave!??
I am satisfied with the antenna and will be able to do better with it after spending more time with it.
| FX |
QTH |
CALL |
DATE |
TIME |
AZ |
K9AY |
LOAD |
AZ |
LOOP |
COMMENTS |
| 363 |
NJ |
RNB |
3 19 |
1330 |
330 |
92-73=19 |
450 |
225 |
87-69-18 |
30 miles |
| 860 |
PA |
WWDB |
3 19 |
1330 |
310 |
90-68=22 |
300 |
000 |
80-65=15 |
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| 990 |
PHL |
WNTP |
3 19 |
1330 |
330 |
95-65=30 |
350 |
000 |
84-63=21 |
same tower locatiom |
| 1060 |
PHL |
KYW |
3 19 |
1330 |
320 |
95-60=35 |
350 |
000 |
78-60=17 |
same tower locatiom |
| 1150 |
DE |
WDEL |
3 19 |
1330 |
|
101-86=28 |
650 |
240 |
107-79=28 |
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| 1210 |
PHL |
WPHT |
3 19 |
1330 |
0 |
106-83=23 |
650 |
010 |
96-78=18 |
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| PERSEUS |
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END |
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Re: "active antenna preamplifiers" in ham radio May 1986
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
--
|
Re: "active antenna preamplifiers" in ham radio May 1986
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
|
Re: "active antenna preamplifiers" in ham radio May 1986
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
|
My 160m - 220m beverages are usually about 3dB better in s/n than the K9AY loop on 1.8 and 3.5MHz in their design directions, Thank you John. That is very impressive for the relatively small size. Thanks to the tips here in the group, I am very optimistic that I will be able to erect an AziLoop with the 13.8 metre circumference mentioned in the forthcoming manual - and that this antenna will serve me very well for mediumwave reception. 73 Christoph —
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Hi Christoph,
re. Loop and Beverage comparisons
My 160m - 220m beverages are usually about 3dB better in s/n than the K9AY loop on 1.8 and 3.5MHz in their design directions, as one would expect from the comparitive RDFs, but there are days and directions where the K9AY or conventional loop is as good, possibly because of steerable direction, nulling noise or favourable pattern. It appears to work comparitively well in disturbed conditions.
73
John
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Hi Christoph,
Yes I need the (remote) preamp nearly all the time to get sufficient s/n over-ride not helped by feeder length of <200m.. Multi-joined RG6 most over 30 years old with loss about 4dB at 1.8MHz, loop R=10 ohms..
At VLF I find its conventional loop mode better and I did manage to hear the SAQ Xmas transmission on 17.2kHz.. Not as good as other larger antennas because of a 20kHz HPF.
A K9AY does not work as well at VLF. Modelling my loop gives a very low -69.5dBi at 300kHz, and only 5dB better if conventional earth used. Worse at 100kHz. Others may comment on what size (conventional?) loops are best for reception down on VLF frequencies and what sensitivities are needed, I would imagine it has been discussed on this forum before!
73
John
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However its remote steerability to 5deg azimuth and termination adjustment make it a very useful antenna like no other on the market. That's exactly how it is! Thank you, John, for the solid explanation. I am fascinated that despite the relatively small size of your AziLoop, you are often able to compare it with the Beverage and sometimes achieve similar results. Do you mostly work with the Azi's preamplifier here? 73 Christoph —
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Bill, My reply crossed with yours. Glad your results are better. My nulls in both loop and K9AY modes are very close to the bearing -180deg as expected, when f/b is optimised
73, John
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Hi Bill,
We have not heard further from you so I assume you have not improved your f/b.
I have been using my Aziloop in K9AY mode for a year now and always managed to get groundwave f/b ratios approaching or more than 30dB over the higher medium wave (1.0MHz) to 3.8MHz. My loop is similar size or slightly larger than yours - 20ft total diameter, apex 15ft high, bottom wire horizontal 4ft high. It is completely in the clear.
I have tried various radial systems, either 4x 12ft insulated radials lying on the ground or (now) 4 x 11ft radials 3ft high (1ft under the bottom wires) there is no earth connection apart from the radials, and I get similar results.
?
Possible reasons for poor f/b are:-
?- proximity of metal objects or other antennas, one might expect this worse on some frequencies and directions than others
?- lack of series resistor when using short radial system. Have you modelled your antenna and radial system? This resistor and the loop termination R are interdependent to some degree but both can be optimised
?- connecting both an elevated radial system and earth together
?- common mode affecting your coax feeder. (this affected VLF more on my antenna where the RG6 feeder length is 650ft ). (maybe larger loop size might help for MW-VLF)
?- lack of signal over-ride due poor output of antenna at VLF due to too small loop size or a fault. Have you checked you get in the region of 9 or 10dB noise over-ride when you connect the antenna? (you can do this by disabling the filter for the band you are listening on and LCU preamp, then measuring how much the noise drops on a clear frequency)
?- the K9AY pattern f/b varies with elevation angle the f/b is measured over. The back null can be optimised between about 45 degrees down to groundwave depending on how you connect the earth and type of earthing or radials.
?
Please note there is a difference in polar pattern between a K9AY tuned against conventional ground system (rod, buried radials etc.) and a K9AY tuned only against 4 short radials under the wires (either insulated or lying on the ground) with a series resistor.?
The conventional K9AY with ground rod etc. can have a relatively poor groundwave f/b 10-15dB with sharp null in the back lobe at about 45 degrees. Users of K9AYs say this higher null is an advantage when they can null steer using a vacrol to adjust the termination R.
The K9AY loop tuned against 4 short radials in series with a resistor usually between 100R and 560R depending on bottom heights and spacing has a pattern similar to a Flag or Pennant,? with high f/b on GW signals.
Try modelling them both.
Both modes are only single loops so you cant expect miracles, some days it compares with my beverages, others it is down a few dB as you might expect from the comparitive RDFs of a K9AY and beverage. However its remote steerability to 5deg azimuth and termination adjustment make it a very useful antenna like no other on the market.
Good luck
73
John
?
PS I hate to buy also and up until now have made all my own RX antennas but cannot possibly replicate Dave GW4GTE's years of development and computer skills designing a desktop DF antenna providing remote site capability and desktop application. Unfortunately it is more expensive now reflecting dealer mark up and support costs.
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Here is a list of stations that I used to further check my AZIloop.? I used my trusty Perseus and got better results than from the Apache.? I believe the AZI loop is working ok. I believe low nulls are caused by my SAL and tower being close by.? I will experiment with longer and higher (1 to 2 feet off the ground) and see if that helps the null.
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AZI
LOOP NULLS |
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| FX |
QTH |
CALL |
AZ |
DATE |
EST |
AZI NULL |
LOOP NULL |
| 1060 |
PHL |
KYW |
0 |
03 15 25 |
1000 |
96-82=14 |
100-83=17 |
| 1090 |
BALT |
WBAL |
235 |
03 15 25 |
1000 |
93-79=14 |
90-80=10 |
| 1120 |
MD |
WUST |
270 |
03 15 25? |
1000 |
106-87=19 |
100-87=13 |
| 1150 |
DE |
WDEL |
355 |
03 15 25 |
1000 |
99-80=19 |
103-81=22 |
| 1210 |
PHL |
WPHT |
350 |
03 15 25 |
1000 |
90-76=14 |
98-78=20 |
| 990 |
PHL |
WNTP |
0 |
03 15 25 |
1000 |
90-76=14 |
98-78=20 |
| 980 |
DC |
WTEM |
270 |
03 15 25 |
1000 |
103-88=15 |
107-87=20 |
| 950 |
PHL |
WKDN |
0 |
3 15 25 |
1000 |
80-65=15 |
85-63=22 |
| 880 |
NY |
WCBS |
10 |
3 15 25 |
1000 |
95-87=8 |
103-87=16 |
| 860 |
PA |
WWDB |
0 |
3 15 25 |
1000 |
92-75=17 |
93-74=19 |
| 830 |
PA |
WEEU |
0 |
3 15 25 |
1000 |
98-80=18 |
108-78=30 |
| 770 |
NY |
WABC |
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3 15 25 |
1000 |
91-83=7 |
97-80=17 |
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Receiver -? |
Perseus |
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73,? Bill, WA2DVU Cape May, NJ
On Friday, March 14, 2025 at 02:48:22 PM EDT, Simon via groups.io <ohhellnotagain@...> wrote:
Hi Dave.. totally agree..when comes to antennas I hate to buy!!
However, not all feel the need to do so, or have the time? to do.
(Dave you are on rsgb technical, you have no doubt? seen my thread on short marconi T for 160m and the quest? to improve, so on same page. (Getting better btw, vk’s on ft8 now.))
The “ standard? loop” has short falls .. bi directional being one..(hence the k9ay/? azi- loop.)? Ie yes ( standard loop) stunning null, but not much use if ( example) dx is north and qrm ( from local station) is south.
Simon g0zen
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I don't doubt.? But I'm retired and have the time.? However, the scourge of retirement:? Have the time but don't have the $$$.
Dave - W?LEV On Fri, Mar 14, 2025 at 7:54?PM Martin - Southwest UK via <martin_ehrenfried= yahoo.com@groups.io> wrote:
As a constructor, I'd also agree, however in this case I'd be tempted to buy.
?
If you price up how much time, effort and cost, that would be required to develop and build your own version, with comparable features, including the software and remote control functions, I suspect you would be close to the price Dave is charging. I have no affiliation with Dave, but the more I learn about its capabilities, and how well thought out the design and implementation has been, the more impressed I become.
?
If I was more interested in operating, rather than constructing, then I'd definitely buy.
?
Regards,
?
Martin
?
On Fri, Mar 14, 2025 at 06:48 PM, Simon wrote:
totally agree..when comes to antennas I hate to buy!!
However, not all feel the need to do so, or have the time to do.
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Re: "active antenna preamplifiers" in ham radio May 1986
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= aol.com@groups.io> 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= yahoo.com@groups.io 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:
|
Re: "active antenna preamplifiers" in ham radio May 1986
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:
|
Bill Riches
Everett N4CY
Christoph Ratzer