[hfsig] hfsig Digest, Vol 40, Issue 3

Sun Mar 24 12:29:56 EDT 2019

I want one of the ant analyzer kits. If you come up with the kit, I'll provide addy, K5KBV, EDSent from my Samsung Galaxy smartphone.
-------- Original message --------From: hfsig-request at lists.tapr.org Date: 3/24/19  11:00 AM  (GMT-06:00) To: hfsig at lists.tapr.org Subject: hfsig Digest, Vol 40, Issue 3 Send hfsig mailing list submissions to	hfsig at lists.tapr.orgTo subscribe or unsubscribe via the World Wide Web, visit	http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.orgor, via email, send a message with subject or body 'help' to	hfsig-request at lists.tapr.orgYou can reach the person managing the list at	hfsig-owner at lists.tapr.orgWhen replying, please edit your Subject line so it is more specificthan "Re: Contents of hfsig digest..."Today's Topics:   1. Re: 20m WSPR shield for Raspberry Pi (John, W9DDD)----------------------------------------------------------------------Message: 1Date: Sat, 23 Mar 2019 14:29:53 -0500From: "John, W9DDD" <w9ddd at tapr.org>To: hfsig at lists.tapr.orgSubject: Re: [hfsig] 20m WSPR shield for Raspberry PiMessage-ID: <dcfdb486-6eca-e59e-d85a-6dead1b8e325 at tapr.org>Content-Type: text/plain; charset=windows-1252; format=flowedI want one of those antenna analyzer kits.John, W9DDDOn 3/23/2019 2:23 PM, Bruce Raymond wrote:> Hi Keith,> > You've obviously picked the ultimate in terms of getting rid of hum - > using a battery (I didn't read the original post carefully enough). > You've hit on all of the fixes I can think of.> > 120 Hz implies full wave rectification of 60 Hz. Unfortunately, 60 Hz is > all around us, so that doesn't help much. Another relatively obvious > thing is to question the test equipment, although that's a real long > shot. I don't see how you get mixing products from a spec an or a scope. > I suppose an easy test for that would be to look at a known clean > signal, like from a signal generator, and look for mixing products. This > whole direction seems like a real long shot.> > You've got more power coming out of the transmitter than we would > expect. That probably means that the MOSFET bias voltage is fairly high > relative to its threshold voltage, so the bias current and gain are > high. It's possible that you're generating much stronger harmonic > components from the MOSFET than you otherwise would, raising the > harmonic content of the output.> > OTOH, 30 dB down means ~3% of the amplitude relative to the carrier. I > doubt this would have any impact on a WSPR receiver's ability to decode > the signal.> > > I originally put together a 30m WSPR transmitter kit. I sent ~45 of the > kits to John/TAPR. These are sold out. I redesigned the unit to use > surface mount parts and had 200 units assembled and tested, and > delivered to John. There should be plenty of these units available.> > 73 Bruce> > P.S. I'm working on an idea for an automatic antenna analyzer kit for > HF. It will scan a range of frequencies and find the resonant point and > VSWR at resonance (actually min VSWR, not necessarily resonance), and > 2:1 VSWR bandwidth. This will be a kit with no surface mount parts and > no case, but will have mounting holes so you can mount it in your choice > of cases. It will probably sell in the ~70 range. Does this sound like a > worthwhile project?> > > > Keith Wilson wrote on 3/23/2019 1:02 PM:>> Hi Bruce, and thanks for the generous response!>>>> My power measurement was made with a good 50 ohm load so maybe I have >> a nice hot MOSFET!>>>> As mentioned in my previous email, the testing was with a USB power >> bank battery, and I still have the 120 Hz apparent mixing products.? I >> tried a separate antenna (my SOTA antenna) so I was not attached to >> the station ground.? (My station ground is bonded to the household >> power ground) So I shouldn't have any way for 60 Hz power to get into >> the Pi or USB battery.? Still puzzled by the presence of these >> apparent mixing products.? Because they are down 30 dB, I probably >> won't get double decodes by receiving stations.>>>> Last question, TAPR is out of the 30 m boards.? Are they still available?>>>> 73,>> Keith - KE4TH>>>> On Fri, Mar 22, 2019 at 9:14 PM Bruce Raymond <bruce at raymondtech.net >> <mailto:bruce at raymondtech.net>> wrote:>>>>     Hi Keith,>>>>     I have to agree with Bryan (well, I suppose I don't *really* have>>     to agree with him, I just want to :-). The 20m transmitter is>>     Zoltan's design, but very similar to my 30m transmitter. The final>>     is an MMBF170 powered by 5 volts.>>>>     1. The power output is approximated by the formula?? P = V^2/2*RL.>>     The power supply is roughly 5 volts and assuming a 50 ohm load>>     (RL), P = 5^2/(2 * 50) = 0.25 watts.>>>>     It's reasonable to expect some losses and the safest way to list>>     the output power is to say you'll get at least 200 mW. Also, if>>     the supply voltage is higher than 5 volts then you'll get more>>     power. It's unlikely that it would be *that* much higher; it would>>     take 6? volts to give 360 mW. Another possibility is that your>>     antenna impedance is less than 50 ohms. If your antenna impedance>>     is, say, 35 ohms, then P = 5^2/(2 * 35) = 360 mW. The last (and>>     most probable) thought is that the MOSFET in your transmitter is>>     hotter than typical and gets driven harder, producing more output.>>     I've played with this on the 30m transmitter and have gotten power>>     outputs in this range by biasing the MOSFET on more. The threshold>>     voltage for a MMBF170 MOSFET is between 0.8 and 3.0 volts with 2.1>>     volts being a typical value. The 20m transmitter has a voltage>>     divider putting 2.3 volts on the gate. If your MOSFET is fairly>>     hot then it would be biased on more and likely put out more>>     output. The end result is *yes* the output is real. => Watch for>>     the MOSFET getting hot. If it does, you might want to add a heat>>     sink or change the gate bias resistor (R2) from 1.2K to something>>     larger, say 1.5K. <=>>>>     2. Power supplies - in the words of Socrates, suffering an>>     learning are two names for the same experience (I don't know that>>     Socrates actually said that, but I like to say he did). I have>>     learned through hard experience that inadequate power supplies>>     cause a whole bunch of problems, and they're usually very>>     difficult to troubleshoot because the problems are either>>     intermittent or just not something I'd normally suspect of a power>>     supply. The power supplies normally used for the Raspberry Pi are>>     usually marginally adequate. I'm very impressed with the job the>>     designers of the Pi did, but they cheaped out on the power supply>>     filter on the board (electrolytic capacitor).>>>>     Now we compound the problem with trying to run a transmitter off>>     of the same power supply in addition to running the Pi. This>>     doesn't help things. In the beginning I bought a bunch of cheap>>     5V/2A power supplies from China that worked with my Pi/30m>>     transmitters. I had a bunch of weird problems, such as the>>     software getting corrupted during normal operation. At first I>>     thought the problem was cheap SD cards or some problem with the>>     operating system/software. I now believe the problem was power>>     supply glitches causing the Pi to get confused and do bad stuff. I>>     switched to bigger power supplies and my problems disappeared.>>>>     My recommendation is to get a 5V/3A power supply and make your>>     measurements again. 120 Hz sidebands sounds like AC bleeding>>     through the power supply, even if it seems that the power coming>>     off the supply is clean. It could also be some sort of interaction>>     between your antenna ground and your power supply ground. You>>     might try a different power supply and/or an isolation transformer>>     for a test. This might be similar to hum problems direct>>     conversion receivers have that are associated with grounding.>>>>     73 Bruce Raymond/ND8I>>>>>>>>     Bryan Corkran wrote on 3/22/2019 4:22 PM:>>>     I had a lot of trouble with power, in the end I bought the>>>     ?official? 2.5 amp adapter and had no trouble after that.>>>     Keith is right the shield is designed for the V1 board hence the>>>     little slot in the middle for the display port. I had problems>>>     with the shield fouling on the heat sink I?d added on a 3b board>>>     so I used a GPIO extender to raise it a small amount.>>>>>>     Bryan, VK3KEZ>>>>>>     On 23 Mar 2019, at 5:36 am, Keith Wilson>>>     <keith.wilson.pcs at gmail.com <mailto:keith.wilson.pcs at gmail.com>>>>>     wrote:>>>>>>>     I have the 20m WSPR shield working on a new Raspberry Pi 3 B+. >>>>     I see apparent mixing products in the output, 120 Hz away from>>>>     fundamental, when using a USB power bank to power the Pi.? Since>>>>     these are not coming from a switching power supply, where are>>>>     they coming from?? These products start at about 30 dB below the>>>>     fundamental.>>>>>>>>     Also, with a scope I measure the voltage output at 12V peak to>>>>     peak into quality 50 ohm dummy load.? This is 0.36W, higher than>>>>     the 20dBm (0.10W) specified.? Is this too good to be true?>>>>>>>>     Note the shield was not designed for the Raspberry Pi 3 B+ so it>>>>     can't be fully inserted on the 40 pin GPIO plug, but seems>>>>     stable enough partially inserted.? Getting WSPR reports from>>>>     across the USA and occasional overseas reports too.>>>>>>>>     Keith - KE4TH>>>>>>>>     <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon>>>>>     	Virus-free. www.avast.com>>>>     <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link>>>>>>>>>>>>>     _______________________________________________>>>>     hfsig mailing list>>>>     hfsig at lists.tapr.org <mailto:hfsig at lists.tapr.org>>>>>     http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org>>>>>>>>>     _______________________________________________>>>     hfsig mailing list>>>     hfsig at lists.tapr.org <mailto:hfsig at lists.tapr.org>>>>     http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org>>>>     _______________________________________________>>     hfsig mailing list>>     hfsig at lists.tapr.org <mailto:hfsig at lists.tapr.org>>>     http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org>>> > > > _______________________________________________> hfsig mailing list> hfsig at lists.tapr.org> http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org> ------------------------------Subject: Digest Footer_______________________________________________hfsig mailing listhfsig at lists.tapr.orghttp://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org------------------------------End of hfsig Digest, Vol 40, Issue 3************************************
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