Re: LZ1AQ amp With 2SC3357
From the data sheets here are the absolute Max Voltages. As you can see the 2SC3357 has lower VCBO and VCEO:
?
????? 2SC5551??? 2SC3357
VCBO??? 40???????? 20
VCEO??? 30???????? 12
VEBO? ?? 2??? ? ??? 3
?
Measuring on an LZ1AQ amp with 2SC3357 operating at 12V, here are the max voltages over all four transistors:
?
???? Measured?? Margin
VCBO?? 5.5?????? 14.5
VCEO?? 6.2??????? 5.8
VEBO?? 0.743??? ? 2.257
?
?
So for the LZ1AQ design the 2SC3357 operates with plenty of margin.
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Mike M
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Re: LZ1AQ amp With 2SC3357
The?2SC3357 has a much lower voltage rating then the 2SC5551
?
Everett
In a message dated 2/7/2025 11:07:17 AM Central Standard Time, groups@... writes:
?
Thanks Fred. I was not aware of the history. The ones I have were sourced from DigiKey, so they are the EVVOSEMI parts. I also tested them in the Ikin Norton amp and they are equivalent to the 2SC5551 there as well. My hope was to find a suitable substitute that is still in production. The BFU590 seems to be one of the few still produced. I plan to test some in the future.
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Mike M
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Re: LZ1AQ amp With 2SC3357
Thanks Fred. I was not aware of the history. The ones I have were sourced from DigiKey, so they are the EVVOSEMI parts. I also tested them in the Ikin Norton amp and they are equivalent to the 2SC5551 there as well. My hope was to find a suitable substitute that is still in production. The BFU590 seems to be one of the few still produced. I plan to test some in the future.
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Mike M
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Re: LZ1AQ amp With 2SC3357
The 2SC3357 = NE85634 was a CATV RF Transistor manufactured by the japanese semiconductor giant RENESAS (merger of Mitsubishi & Hitachi & NEC) and later CEL (CA/USA - NEC partner). Production was discontinued in 2018. Unitronic (Taiwan)? too produced RF-transistors labeled as 2SC3357, obsolete too. The NE86534 (2S3357) were frequently used in Japanese Radio devices. Clifton Labs Jack Smith used it in his Norton Amplifiers.
?
The 2SC3357 offered since recently by Digikey are sourced from the the Hong-Kong based company EVVOSEMI. Althoug they carry the label 2SC3357, RF transistors from different manufacturers will very likely meet particular rated key values of parts offered as 2S3357, but they must not be identical in all parameters. It's worth to give'm a try.
?
regards, Fred
?
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Just compared 2SC5551 to 2SC3357 in an LZ1AQ amp. There is almost no difference in IP2/IP3 and frequency response. I was going to post to say the 2SC3357 are available, but looking at Digikey there are only 9 in stock. It says one week factory lead time and new product, so I assume they are still in production.
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Mike M
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Re: Deshibo GA-450 Loop Antenna Modification Question
Yes, these are very common connectors I see all the time.?
A standard 9-VDC "transistor" battery will supply roughly 400 to 500 (not the Chinese knockoffs) mAH of energy.? With that and knowing the current draw of your preamp, you can determine how long the 9-volter will last.
Dave - W?LEV
Hi Dave W0LEV
?
Thanks I didn't get a notification of your reply but just checked in and saw it and appreciate your time and comments especially regarding the aluminium tape which I have no experience of and would like to try.
?
Mr Everythingia (think I've got that YouTube name correct) did as you suggested and completely bypassed the DC converter. Surprisingly though he found a USB powered 9V battery performed admirably, with all the RFI gone.
?
I've pried off the bottom of the loop control box which came off fairly easily with mobile phone tools. Do you or does anyone else know if these are JST PH connectors?
?
?
It's so I'll buy a pack and try the 9V battery thing and might report back here my findings in case anyone is interested.
73 Adam?
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Re: Deshibo GA-450 Loop Antenna Modification Question
Hi Adam,
?
The retaining clip looks slightly different.
?
These could be a match, but without measuring them I can't be certain.
?
?
Regards,
?
Martin.
?
On Tue, Feb 4, 2025 at 06:52 PM, Adam wrote:
Do you or does anyone else know if these are JST PH connectors?
|
Re: Deshibo GA-450 Loop Antenna Modification Question
Hi Dave W0LEV
?
Thanks I didn't get a notification of your reply but just checked in and saw it and appreciate your time and comments especially regarding the aluminium tape which I have no experience of and would like to try.
?
Mr Everythingia (think I've got that YouTube name correct) did as you suggested and completely bypassed the DC converter. Surprisingly though he found a USB powered 9V battery performed admirably, with all the RFI gone.
?
I've pried off the bottom of the loop control box which came off fairly easily with mobile phone tools. Do you or does anyone else know if these are JST PH connectors?
?
?
It's so I'll buy a pack and try the 9V battery thing and might report back here my findings in case anyone is interested.
73 Adam?
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Re: My PA0FRI active loop receiving antenna
I was talking about transistors in general, not specifically the BFU590. Although BJTs don't have protection diodes, they are often use active bias / current mirrors. The current mirror is another BJT with its collector and base tied together and the emitter connected to ground - which is effectively, a diode.
Hence, current decrease during oscillation is possible with both BJTs & FETs.
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Re: My PA0FRI active loop receiving antenna
This applies to FETs, either JFETs or MOSFETs.? Especially MOSFETs have ESD protective diodes.? BJTs generally do not.? Therefore, the noted decrease in current with oscillation likely applies to only FETs.? The '590 is a BJT.?
Dave - W?LEV
Moreover, I have encountered the opposite, where current decreases during instability. The oscillation cause negative polarity rectification in a connected diode (could be a ESD protection diode in the transistor or active bias circuit) which slightly decreases the current consumption.
The curious case when oscillation lowered the operating current :-)
?
The red trace is the stable condition when Idd = 75mA, while the black trace is the unstable condition when Idd = 50mA. The oscillation is ~300 MHz, and the 2nd & 3rd harmonics are shown on the graph.
?
The cause of this counterintuitive phenomenon is the strong oscillation was rectified by the active bias (which is identical to a negative polarity detector) and this generates a negative voltage which reduces the gate bias.
?
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Re: My PA0FRI active loop receiving antenna
Although CMRR is an issue, it's not always the overriding factor.
?
Noise is frequently introduced via a poor quality power supply, badly designed bias tee, ground loops, and poor screening of the feed line, and the amplifier CMRR performance is not going to significantly change the end result.
?
I'd suggest that it's always best to check for some of the more obvious issues first, by looking at the spectrum with the amplifier powered, but with the input shorted, and no loop connected, and then fixing those problems, before you move on to try and resolve any additional contribution due to poor CMRR.
?
Regards,
?
Martin
?
On Sun, Feb 2, 2025 at 05:49 AM, <biastee@...> wrote:
Two different paths for noise ingress, but one common parameter (CMRR) standing in their way?
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On Sun, Feb 2, 2025 at 12:35 AM, Mike M wrote:
So even though the 2SC3357 has a higher fT than the 2SC5551, it did not oscillate.
Thank you sharing your experiences, mike.
That fits to my observations, that a transistor with a higher fT is not automatically more prone to oscillation than a transistor with lower fT.? But they are able to oscillate at higher frequencies. Modern high fT RF-transistors of newer silicon-processes have normally lower junction capacitances, e.g. a lower feedback capacitance and a lower collector capacitance. These capacitors are components of a feedback network that forms,? together with external parasitic reactances, an oscillating device. The BFU590 in my experience ist not particularly critical in terms of parasitic oscillation.
?
regards
Fred
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Re: My PA0FRI active loop receiving antenna
On Sat, Feb 1, 2025 at 03:19 AM, Martin - Southwest UK wrote:
I think Fred's suggestion of an E-Field monopole simulation is still valid.
?
Although the coax may be longer providing a better ground path, the size of the loop providing the antenna element, and its value of equivalent capacitance remains the same.
?
Conducted interference, and ground loops via the feed coax are different factors, which require separate analysis.
Two different paths for noise ingress, but one common parameter (CMRR) standing in their way?
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Re: My PA0FRI active loop receiving antenna
On Fri, Jan 31, 2025 at 07:07 PM, <biastee@...> wrote:
Moreover, I have encountered the opposite, where current decreases during instability. The oscillation cause negative polarity rectification in a connected diode (could be a ESD protection diode in the transistor or active bias circuit) which slightly decreases the current consumption.
The curious case when oscillation lowered the operating current :-)
?
The red trace is the stable condition when Idd = 75mA, while the black trace is the unstable condition when Idd = 50mA. The oscillation is ~300 MHz, and the 2nd & 3rd harmonics are shown on the graph.
?
The cause of this counterintuitive phenomenon is the strong oscillation was rectified by the active bias (which is identical to a negative polarity detector) and this generates a negative voltage which reduces the gate bias.
/g/loopantennas/photo/300438/3881635
?
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Thank you Mike for sharing this data point!
I have added 1206 inductor footprints on the PCB now.
My design files are open at the following?link:
Cheers, Dhiru
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Re: loop material question
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With the recent talk about oscillation I thought I would share a recent debug. Summary: have multiple ferrite bead types on hand.
?
I made a PCB for the Ikin Norton Amp:
?
?
It is a 2-layer PCB with ground fills. I built one using 2SC3357 transistors and it worked. I built a second using 2SC5551 and it oscillated at 660MHz. It also did not amplify. I checked and double checked the transformers but could find no difference between the two boards, but then I found the amplification problem: one end of the T1 primary was soldered but had not melted the enamel on the wire so it was not actually connected. But it still oscillated. The ferrite beads I used are Laird MI1206K310R, which are about 41 ohms at 1GHz. I tried replacing them with 68 ohm resistors but no change. I tried replacing the 10pF caps with 39pF, still no change. I then put the 10pF caps back and put Laird LI1206H121R-10 ferrite beads in and it tamed the oscillations. The new ferrite beads are around 135 ohms at 1GHz, so that is what it took.
?
So don't be afraid to use high fT transistors, but make sure you have a ferrite bead in the design as well as a variety of ferrites to test.
?
I just looked at the data sheets. The ZTX327 used in the original has an fT of 800MHz, the 2SC3357 is 6.5GHz and the 2SC5551 is 3.5GHz.
?
So even though the 2SC3357 has a higher fT than the 2SC5551, it did not oscillate.
?
--
===================================================================
Mike M
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Re: My PA0FRI active loop receiving antenna
For what it's worth, we have found that Vcc to an antenna-mounted preamp (or in our case, the varactor control tuning bias) must be ultra clean. SMPS have no place there. A a GOOD SMPS will have upwards of 100+ uV of switchcing noise and at least 30uV of hash ... very typical. As suggested, at this point in a receiving system, where we deal with uV incoming signals, sub-millivolt noise on the Vcc is mandatory, otherwise all the concern about transistor type selection, shielding, etc, is for nothing. As suggested, a decent linear supply with a regulator reduction of at least 4-6 volts (18 to 12, for example), with bypass caps on both, in and out, legs, like .001uF and followed by a cap-input pi-filter resonated to something down to 2-digit Hz will give you almost battery-pure DC to feed the preamp (something like 10uH and 10uF) It's not only the conductive line level noise that ruins the S/N factor, but also the radiated junk RF that is transmitted from the SMPS to the antenna. With strong signals the difference probably won't be noticed. We built some proof-of-play systems for AM b'casters who deal with double digit uV and would never know the difference, but if you need to recover those 1 uV, or less, signals then add the few extra components for Vcc noise levels that usually run about 1/3uV or less. It will help you sleep at night knowing you put your best effort into your LP.
Bob, N1KPR AmComm
-
- Youtube: N1KPR
- Youtube: Ham Radio Doctor
Engineering, where enigma meets paradox
On Saturday, February 1, 2025 at 01:56:01 PM EST, W0LEV via groups.io <davearea51a@...> wrote:
I've forgotten about the small ferrite bead.? You can also pass both the emitter and collector (insulated from eachother) through the same bead.? This acts as a common mode choke and forces equal currents to be drawn by both elements of the BJT.? THis is also a good oscillation quencher.
Dave - W?LEV ?
I use a Siglent SSA 3021X SA for checking for oscillation. Reading that
eevblog thread certainly would lead you to believe the BFU590 is hard to
tame and readily prone to oscillation, yet as I've shown in my ugly
build there is no oscillation at all for this particular configuration,
at least using the QX version of the transistor. And putting a -61
material small ferrite bead in the collector lead will generally stop
oscillation, in my experience.
Steve AA7U
On 1/31/2025 10:46 AM, Dhiru Kholia via wrote:
> Thanks for all the tips, info and help!
>
> I have access to TinySA Ultra but I believe monitoring my power supply
> for unexpected current consumption might work better to detect
> oscillations.
>
> I was reading the following page earlier today:
>
>
>
> ...
>
> I am attaching the PCB files to this email to aid the review process.
>
> The complete set of files is open at the following link:
>
>
>
> Cheers,
> Dhiru
>
>
>
>
>
|
Re: My PA0FRI active loop receiving antenna
I've forgotten about the small ferrite bead.? You can also pass both the emitter and collector (insulated from eachother) through the same bead.? This acts as a common mode choke and forces equal currents to be drawn by both elements of the BJT.? THis is also a good oscillation quencher.
Dave - W?LEV ?
I use a Siglent SSA 3021X SA for checking for oscillation. Reading that
eevblog thread certainly would lead you to believe the BFU590 is hard to
tame and readily prone to oscillation, yet as I've shown in my ugly
build there is no oscillation at all for this particular configuration,
at least using the QX version of the transistor. And putting a -61
material small ferrite bead in the collector lead will generally stop
oscillation, in my experience.
Steve AA7U
On 1/31/2025 10:46 AM, Dhiru Kholia via wrote:
> Thanks for all the tips, info and help!
>
> I have access to TinySA Ultra but I believe monitoring my power supply
> for unexpected current consumption might work better to detect
> oscillations.
>
> I was reading the following page earlier today:
>
>
>
> ...
>
> I am attaching the PCB files to this email to aid the review process.
>
> The complete set of files is open at the following link:
>
>
>
> Cheers,
> Dhiru
>
>
>
>
>
|
Re: Deshibo GA-450 Loop Antenna Modification Question
Just a couple of ideas:
SHIELDING:? It's not a perfect shielding material, but will illustrate if good shielding would improve things.? At any hardware store, you can buy wide "decorative" shiney aluminum tape.? While the adhesive is not conductive, if you overlap enough, there will be enough capacitive coupling between applications to enable a "reasonable" degree of shielding.? It's inexpensive and at least worth a try.?
BEST CASE:? Get rid of that switcher!!!? In the design of the overall antenna, there should have been absolutely no excuse to install a switcher that close to the receiving element - the loop.? That amounts to engineering WORST PRACTICES!!!? Build yourself a good linear supply with a transformer (surplus), a bridge rectifier (surplus), filter capacitor (surplus), and a 3-terminal regulator (surplus).? You could even build it into the existing plastic enclosure.
Dave - W?LEV
Hi Martin
?
Good to hear from you and thanks for the reply. I agree about the shielding from the DC converter and if I had the skills I may possibly try to attempt it myself. Another alternative is to look out for another used one at a very good price to experiment with modifying, keeping this one intact. I have to say my expectations were very low and I was expecting it just to be awfully noisy and pretty much unusable but I have been pleasantly surprised. Interesting about the tuned loop story. With so much RFI around I would have thought that was a bad decision on their behalf. I thought us radio enthusiasts loved nothing better than a bit of tinkering with electronic equipment! Although my friend at the radio club jokedthat we don't call it "tinkering" we call it "technical assessment"!!
73 Adam?
?
?
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Everett N4CY
Adam
Superlite
Bob, N1KPR