[eagle] Re: U-band receiver changes to reduce EMI and improve thermal regulation

Louis McFadin w5did at amsat.org
Sat Jun 30 14:18:12 PDT 2007


For a look at what is planned for the Eagle Power system, look at the  
presentation I prepared for Dayton this year. You can see it at  
"http://homepage.mac.com/w5did" Look in the w5did Eagle folder. The  
Max Solar Converter is a preliminary document annd not to be  
published but it describes the converter very well.


Lou McFadin
W5DID
w5did at mac.com


On Jun 30, 2007, at 7:05 AM, Juan Rivera wrote:

> John,
>
>
>
> For this particular application I think that approach might work,  
> but it forces others to make major concessions in terms of  
> utilization of space inside the enclosure to avoid CAN-Do radiated  
> EMI.  Regardless of what happens to the CAN-Do EMI it looks like  
> you better plan on some nasty DC power and filter the DC input  
> accordingly.
>
>
>
> I can see a small PCB attached to the CAN-Do 40-pin connector that  
> contains DC filtering, the receiver’s switching power supply, and  
> lands for the signal lines that need to go back to the receiver  
> (not all 40 conductors – just the ones we actually use.)  We’d  
> probably want to run those wires through to the other compartment  
> via feed-thru filters in the common bulkhead using a small wiring  
> harness, then another small harness on the other side to interface  
> to the receiver PCB.  An alternate approach might be to use a  
> smaller ribbon cable and connectors to move the actual signals and  
> power back to the receiver, but that adds weight and doesn’t allow  
> for filtering through the bulkhead unless we found an EMI ribbon  
> cable bulkhead connector.  I think I’d prefer the discrete wire  
> harness approach.  I think it’s lighter, more reliable, and  
> eliminates one set of connectors.
>
>
>
> Before proceeding with another revision I’d like to see an EMI  
> requirement spec and a practical way to generate the expected noisy  
> DC power.   This will also give the next group something to design  
> and test to.
>
>
>
> By the way, did you see my phase noise data?  I went back and  
> tested again using another spectrum analyzer while mine is getting  
> calibrated.  You’ll notice an interesting diversion between the  
> two.  As the saying goes, “A man with a watch always knows what  
> time it is.  A man with two watches can never be sure.”  I’ll run  
> that again when I get the calibrated spec. a. back from the shop.
>
>
>
> 73,
>
> Juan
>
>
>
> From: John B. Stephensen [mailto:kd6ozh at comcast.net]
> Sent: Friday, June 29, 2007 10:38 PM
> To: juan-rivera at sbcglobal.net; 'Louis McFadin'
> Cc: 'Dave Black (Work)'; 'Dave Black (Home)'; 'David Smith';  
> eagle at amsat.org; 'Samsonoff at Mac. Com'; 'Juan.Rivera (Work)'
> Subject: Re: U-band receiver changes to reduce EMI and improve  
> thermal regulation
>
>
>
> If the CAN-Do module can be placed in a shielded compartment with  
> multi-pole filters on all wires leaving the shielded area, we can  
> get at least 80 dB of attenuation for conducted interference and  
> the electric field component of radiated interference. Magnetic  
> shielding is harder as it requires iron or mu-metal so a  
> magnetically shielded inductor should be used in the CAN-DO module.
>
>
>
> Synchronizing the switchers to a frequency with no harmonics at  
> 10.5-10.9 MHz would help with radiated interference, but a shielded  
> inductor may be sufficient if it can be moved far enough from the  
> RF circuitry -- especially the PLLS and VCOs.
>
>
>
> If we have only two adjacent sides available for connectors, the  
> CAN-Do module and power supply circuitry could attach to the  
> existing connector bracket. The RF and IF connectors would then  
> exit along one long side of the box as far from the CAN bus  
> connector as possible.
>
>
>
> 73,
>
>
>
> John
>
> KD6OZH
>
> ----- Original Message -----
>
> From: Juan Rivera
>
> To: 'John B. Stephensen' ; 'Louis McFadin'
>
> Cc: 'Dave Black (Work)' ; 'Dave Black (Home)' ; 'David Smith' ;  
> eagle at amsat.org ; 'Samsonoff at Mac. Com' ; 'Juan.Rivera (Work)'
>
> Sent: Saturday, June 30, 2007 04:32 UTC
>
> Subject: RE: U-band receiver changes to reduce EMI and improve  
> thermal regulation
>
>
>
> Hi John,
>
>
>
> I had a chat or two with Bob Davis about chassis and I think you  
> can bring SMA connectors out one side and the CAN-Do out the end,  
> but nothing out the back.
>
>
>
> Given the amount of conducted 5 kHz noise I’m seeing, do you think  
> you can filter it out?  Don’t forget, I’m feeding the receiver with  
> bypassed clean DC from the bench supply at the moment.  The CAN-Do  
> switched DC is nasty.
>
>
>
> In your next version why not raise the switching frequency up and  
> get it out of the passband completely?  What do you think of  
> Howard’s idea of synching the switching supplies?
>
>
>
> Juan
>
>
>
> From: John B. Stephensen [mailto:kd6ozh at comcast.net]
> Sent: Friday, June 29, 2007 9:24 PM
> To: Louis McFadin; juan-rivera at sbcglobal.net
> Cc: Dave Black (Work); Dave Black (Home); David Smith;  
> eagle at amsat.org; Samsonoff at Mac. Com; Juan.Rivera (Work)
> Subject: U-band receiver changes to reduce EMI and improve thermal  
> regulation
>
>
>
> For the next version of the 70 cm receiver, I'm thinking of an  
> arrangement where the CAN bus exits out of the opposite side of the  
> module from the RF and IF. Does this create any problems in the  
> wiring harness?
>
>
>
> The CAN-DO module would be mounted on a small PCB containing most  
> of the power supply circuitry. This PCB would contain the switcher  
> that generates 7 VDC for the receiver and some of the linear  
> regulators. It would be mounted at one end of the module and be  
> heat-sinked.
>
>
>
> The RF circuitry would be mounted on a separate PCB at the other  
> end of the module. This allows all RF and IF coax connectors to  
> mount on this PCB and attach directly to the connector mounting  
> bracket. It also eliminates the flying lead for the frequency  
> reference input. The power dissipation would be limited so that it  
> doesn't need to be heat-sinked. This protects the SAW filters from  
> rapid temperature excursions and keeps them above -30 C at all times.
>
>
>
> The two PCBs would be connected with a cable carrying DC power and  
> the signals being monitored. Each PCB would have filtering for  
> power and the signals being monitored by the IHU. The interconnect  
> cable would travel through a common-mode choke using high- 
> permiability ferrite.
>
>
>
> If necessary for thermal reasons, the RF amplifier and first mixer  
> would go on a third PCB with a heat sink. LO and IF would connect  
> to the second PCB via 2 coax cables. Once the new requirements  
> document is approved, the power dissipation can be calculated for  
> each of the 3 PCBs and a thermal analysis would determine whether 2  
> or 3 PCBs are needed and how far apart they should be.
>
>
>
> Unless more problems are found during testing of the current  
> version of the receiver, the circuitry would be same as now, except  
> that an MCU is added to initialize the PLLs and the second mixer  
> and second IF amplifiers are changed to devices that dissipate less  
> power in line with the new requirements document. Bob has expressed  
> some interest in Peregrine PLLs that can have the frequency hard  
> wired so they could be inserted instead of adding the MCU.
>
>
>
> 73,
>
>
>
> John
>
> KD6OZH
>
> ----- Original Message -----
>
> From: Louis McFadin
>
> To: juan-rivera at sbcglobal.net
>
> Cc: Dave Black (Work) ; Dave Black (Home) ; David Smith ;  
> eagle at amsat.org ; Samsonoff at Mac. Com ; Juan.Rivera (Work)
>
> Sent: Saturday, June 30, 2007 02:36 UTC
>
> Subject: [eagle] Re: CAN-Do EMI - Let's Get Going on This!
>
>
>
> Juan,
>
> Why not think out of the box, Put the Can Do module outside the  
> box, perhaps on top of the module.
>
> I think that is a more likely solution  than re building the Can-do  
> module.
>
>
>
> Lou McFadin
> W5DID
> w5did at mac.com
>
>
>
>
> On Jun 29, 2007, at 10:25 PM, Juan Rivera wrote:
>
>
>
> Bdale,
>
>
>
> I'm sorry to pick on you, but you seem like a good guy to complain  
> to...
>
>
>
> I seem to be having a problem stimulating a discussion.  After  
> saying that I
>
> though the CAN-Do power supply needed to be completely scrapped and  
> replaced
>
> with one running at around 1 MHz I expected to be buried in email,  
> but I've
>
> only received one message referring to this so far, and it wasn't from
>
> anyone working on CAN-Do.
>
>
>
> The CAN-Do module is unique in that it is going to be an integral  
> component
>
> INSIDE of every payload, so any deficiencies it may have are going  
> to have a
>
> large impact.
>
>
>
> Let me restate my finding so far:
>
>
>
> There are 4 categories of EMI and the CAN-Do module / 70 cm Receiver
>
> combination is experiencing all four.  They break down into  
> radiated and
>
> conducted emissions and susceptibility, and they are generally  
> referred to
>
> by a two-letter designation - RE, RS, CE, and CS.
>
>
>
> RE and RS go together - the CAN-Do module's switching power supply  
> inductor
>
> radiates the 5 kHz switching noise out the back directly towards the
>
> receiver (RE.)  The Receiver's VCO's are both very sensitive to EMI  
> and are
>
> impacted by the CAN-Do module if they are within 4-1/2 inches of the
>
> inductor (RS.)  I've had to move the CAN-Do module off of the  
> receiver PCB
>
> and interconnect it with a ribbon cable to deal with this problem.   
> The good
>
> news is that I am fairly confident that It can be fixed by going to a
>
> two-compartment chassis, with a bulkhead separating the CAN-Do  
> module from
>
> the analog Receiver to provide shielding.  The bad news is that I  
> think this
>
> means we need a milled module chassis.
>
>
>
> CE and CS also go together, and this is the real problem I see  
> since you
>
> can't fix conducted EMI with a shielded enclosure.  It requires  
> filtering.
>
> The CAN-Do module is trashing the DC input from the power source  
> and also
>
> feeding noisy power to the Receiver.  The outgoing noise is the bigger
>
> concern because it will add to the CS problems for everything  
> connected to
>
> the power source.  In the other direction, the switched power from the
>
> CAN-Do module shows up in the IF output as 5 kHz spurs.  Moving the  
> CAN-Do
>
> module physically away from the Receiver only dealt with the RE/RS  
> issue.  I
>
> had to bypass the CAN-Do module and run clean power directly from  
> the lab
>
> bench supply to deal with the CE/CS problem.  This means that there  
> is no
>
> current monitoring and no power control.
>
>
>
> The 5 kHz switching frequency is bad for two reasons - it makes  
> filtering
>
> this noise a much larger problem than it needs to be, and the  
> impact is more
>
> severe since it is putting spurs all over the passband of the IF at  
> 5 kHz
>
> intervals.
>
>
>
> If you sit back and think about the impact of a dozen noisy power  
> supplies
>
> all feeding EMI back to the common power source where they all mix  
> together
>
> and make their way back to each payload, it starts to look nasty.   
> All these
>
> supplies will be drifting around and beating with each other to  
> produce sum
>
> and difference noise on the power bus.  5 kHz noise is hard enough  
> to get
>
> rid of but what if there are difference components at a few hundred  
> Hz?  How
>
> can you design a filter when you won't know what to expect until  
> you hook
>
> everything up and turn it on?  And by then you're out of time.
>
>
>
> I'm not making this stuff up.  People I know have run into this exact
>
> problem before and the result was very bad.
>
>
>
> A while ago Howard Long made a suggestion that I think has great  
> potential.
>
> Here's what he had to say:
>
>
>
> ...in the original SDX PSU design I had in San Francisco last year  
> is an
>
> SMPS using the LM2672 device. These can be fitted with an AC  
> coupled SYNC
>
> signal to override the internal default SMPS frequency. I selected  
> 375kHz
>
> for my unit (6MHz divided by 16) to ensure its harmonics were  
> outside the
>
> 10.7MHz IF passband. If the external SYNC fails the internal SMPS  
> oscillator
>
> takes over.
>
>
>
> My Suggestions:
>
>
>
> 1) Revise the CAN-Do module to move the switching frequency up as  
> far as
>
> possible to move spurs out of the passband of sensitive analog  
> circuitry,
>
> and to ease the burden on EMI filtering.
>
> 2) The power and grounds must be filtered in both directions to  
> minimize CE
>
> back to the power source and to the payload.
>
> 3) The switching inductor should be a shielded to reduce RE inside the
>
> module chassis.
>
> 4) A power supply capable of synching to a master oscillator should be
>
> strongly considered.
>
>
>
> This topic needs to be elevated to the top of the queue.  The EMI
>
> environment surrounding the CAN-Do module impacts the design of the  
> next
>
> revision of the 70 cm Receiver, and also directly impacts the chassis
>
> design.  What do we need to do to get going on this?
>
>
>
> 73,
>
>
>
> Juan - WA6HTP
>
>
>
>
>
>
>
>
>
>
>
> _______________________________________________
>
> Via the Eagle mailing list courtesy of AMSAT-NA
>
> Eagle at amsat.org
>
> http://amsat.org/mailman/listinfo/eagle
>
>
>
> _______________________________________________
> Via the Eagle mailing list courtesy of AMSAT-NA
> Eagle at amsat.org
> http://amsat.org/mailman/listinfo/eagle
>
>

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