<div dir="ltr">Bruce, I think there would be interest in an antenna analyzer kit at that price point, especially if it comes with its own display. I use a RigExpert model that has been very handy, but not very cheap!<div><br></div><div>For the 20m WSPR board testing, I'm using a Flex radio / PC as my signal analyzer. I have a sampling arrangement that reduces the signal by 80-90 dB.<br><div><br></div><div>Will the 30m WSPR board work with the same WsprryPi software the 20m version uses?</div><div><br><div>73,</div><div>Keith - KE4TH </div></div></div></div><div id="DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2"><br>
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</table><a href="#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2" width="1" height="1"></a></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, Mar 23, 2019 at 1:30 PM John, W9DDD <<a href="mailto:w9ddd@tapr.org">w9ddd@tapr.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I want one of those antenna analyzer kits.<br>
<br>
John, W9DDD<br>
<br>
On 3/23/2019 2:23 PM, Bruce Raymond wrote:<br>
> Hi Keith,<br>
> <br>
> You've obviously picked the ultimate in terms of getting rid of hum - <br>
> using a battery (I didn't read the original post carefully enough). <br>
> You've hit on all of the fixes I can think of.<br>
> <br>
> 120 Hz implies full wave rectification of 60 Hz. Unfortunately, 60 Hz is <br>
> all around us, so that doesn't help much. Another relatively obvious <br>
> thing is to question the test equipment, although that's a real long <br>
> shot. I don't see how you get mixing products from a spec an or a scope. <br>
> I suppose an easy test for that would be to look at a known clean <br>
> signal, like from a signal generator, and look for mixing products. This <br>
> whole direction seems like a real long shot.<br>
> <br>
> You've got more power coming out of the transmitter than we would <br>
> expect. That probably means that the MOSFET bias voltage is fairly high <br>
> relative to its threshold voltage, so the bias current and gain are <br>
> high. It's possible that you're generating much stronger harmonic <br>
> components from the MOSFET than you otherwise would, raising the <br>
> harmonic content of the output.<br>
> <br>
> OTOH, 30 dB down means ~3% of the amplitude relative to the carrier. I <br>
> doubt this would have any impact on a WSPR receiver's ability to decode <br>
> the signal.<br>
> <br>
> <br>
> I originally put together a 30m WSPR transmitter kit. I sent ~45 of the <br>
> kits to John/TAPR. These are sold out. I redesigned the unit to use <br>
> surface mount parts and had 200 units assembled and tested, and <br>
> delivered to John. There should be plenty of these units available.<br>
> <br>
> 73 Bruce<br>
> <br>
> P.S. I'm working on an idea for an automatic antenna analyzer kit for <br>
> HF. It will scan a range of frequencies and find the resonant point and <br>
> VSWR at resonance (actually min VSWR, not necessarily resonance), and <br>
> 2:1 VSWR bandwidth. This will be a kit with no surface mount parts and <br>
> no case, but will have mounting holes so you can mount it in your choice <br>
> of cases. It will probably sell in the ~70 range. Does this sound like a <br>
> worthwhile project?<br>
> <br>
> <br>
> <br>
> Keith Wilson wrote on 3/23/2019 1:02 PM:<br>
>> Hi Bruce, and thanks for the generous response!<br>
>><br>
>> My power measurement was made with a good 50 ohm load so maybe I have <br>
>> a nice hot MOSFET!<br>
>><br>
>> As mentioned in my previous email, the testing was with a USB power <br>
>> bank battery, and I still have the 120 Hz apparent mixing products. I <br>
>> tried a separate antenna (my SOTA antenna) so I was not attached to <br>
>> the station ground. (My station ground is bonded to the household <br>
>> power ground) So I shouldn't have any way for 60 Hz power to get into <br>
>> the Pi or USB battery. Still puzzled by the presence of these <br>
>> apparent mixing products. Because they are down 30 dB, I probably <br>
>> won't get double decodes by receiving stations.<br>
>><br>
>> Last question, TAPR is out of the 30 m boards. Are they still available?<br>
>><br>
>> 73,<br>
>> Keith - KE4TH<br>
>><br>
>> On Fri, Mar 22, 2019 at 9:14 PM Bruce Raymond <<a href="mailto:bruce@raymondtech.net" target="_blank">bruce@raymondtech.net</a> <br>
>> <mailto:<a href="mailto:bruce@raymondtech.net" target="_blank">bruce@raymondtech.net</a>>> wrote:<br>
>><br>
>> Hi Keith,<br>
>><br>
>> I have to agree with Bryan (well, I suppose I don't *really* have<br>
>> to agree with him, I just want to :-). The 20m transmitter is<br>
>> Zoltan's design, but very similar to my 30m transmitter. The final<br>
>> is an MMBF170 powered by 5 volts.<br>
>><br>
>> 1. The power output is approximated by the formula P = V^2/2*RL.<br>
>> The power supply is roughly 5 volts and assuming a 50 ohm load<br>
>> (RL), P = 5^2/(2 * 50) = 0.25 watts.<br>
>><br>
>> It's reasonable to expect some losses and the safest way to list<br>
>> the output power is to say you'll get at least 200 mW. Also, if<br>
>> the supply voltage is higher than 5 volts then you'll get more<br>
>> power. It's unlikely that it would be *that* much higher; it would<br>
>> take 6 volts to give 360 mW. Another possibility is that your<br>
>> antenna impedance is less than 50 ohms. If your antenna impedance<br>
>> is, say, 35 ohms, then P = 5^2/(2 * 35) = 360 mW. The last (and<br>
>> most probable) thought is that the MOSFET in your transmitter is<br>
>> hotter than typical and gets driven harder, producing more output.<br>
>> I've played with this on the 30m transmitter and have gotten power<br>
>> outputs in this range by biasing the MOSFET on more. The threshold<br>
>> voltage for a MMBF170 MOSFET is between 0.8 and 3.0 volts with 2.1<br>
>> volts being a typical value. The 20m transmitter has a voltage<br>
>> divider putting 2.3 volts on the gate. If your MOSFET is fairly<br>
>> hot then it would be biased on more and likely put out more<br>
>> output. The end result is *yes* the output is real. => Watch for<br>
>> the MOSFET getting hot. If it does, you might want to add a heat<br>
>> sink or change the gate bias resistor (R2) from 1.2K to something<br>
>> larger, say 1.5K. <=<br>
>><br>
>> 2. Power supplies - in the words of Socrates, suffering an<br>
>> learning are two names for the same experience (I don't know that<br>
>> Socrates actually said that, but I like to say he did). I have<br>
>> learned through hard experience that inadequate power supplies<br>
>> cause a whole bunch of problems, and they're usually very<br>
>> difficult to troubleshoot because the problems are either<br>
>> intermittent or just not something I'd normally suspect of a power<br>
>> supply. The power supplies normally used for the Raspberry Pi are<br>
>> usually marginally adequate. I'm very impressed with the job the<br>
>> designers of the Pi did, but they cheaped out on the power supply<br>
>> filter on the board (electrolytic capacitor).<br>
>><br>
>> Now we compound the problem with trying to run a transmitter off<br>
>> of the same power supply in addition to running the Pi. This<br>
>> doesn't help things. In the beginning I bought a bunch of cheap<br>
>> 5V/2A power supplies from China that worked with my Pi/30m<br>
>> transmitters. I had a bunch of weird problems, such as the<br>
>> software getting corrupted during normal operation. At first I<br>
>> thought the problem was cheap SD cards or some problem with the<br>
>> operating system/software. I now believe the problem was power<br>
>> supply glitches causing the Pi to get confused and do bad stuff. I<br>
>> switched to bigger power supplies and my problems disappeared.<br>
>><br>
>> My recommendation is to get a 5V/3A power supply and make your<br>
>> measurements again. 120 Hz sidebands sounds like AC bleeding<br>
>> through the power supply, even if it seems that the power coming<br>
>> off the supply is clean. It could also be some sort of interaction<br>
>> between your antenna ground and your power supply ground. You<br>
>> might try a different power supply and/or an isolation transformer<br>
>> for a test. This might be similar to hum problems direct<br>
>> conversion receivers have that are associated with grounding.<br>
>><br>
>> 73 Bruce Raymond/ND8I<br>
>><br>
>><br>
>><br>
>> Bryan Corkran wrote on 3/22/2019 4:22 PM:<br>
>>> I had a lot of trouble with power, in the end I bought the<br>
>>> “official” 2.5 amp adapter and had no trouble after that.<br>
>>> Keith is right the shield is designed for the V1 board hence the<br>
>>> little slot in the middle for the display port. I had problems<br>
>>> with the shield fouling on the heat sink I’d added on a 3b board<br>
>>> so I used a GPIO extender to raise it a small amount.<br>
>>><br>
>>> Bryan, VK3KEZ<br>
>>><br>
>>> On 23 Mar 2019, at 5:36 am, Keith Wilson<br>
>>> <<a href="mailto:keith.wilson.pcs@gmail.com" target="_blank">keith.wilson.pcs@gmail.com</a> <mailto:<a href="mailto:keith.wilson.pcs@gmail.com" target="_blank">keith.wilson.pcs@gmail.com</a>>><br>
>>> wrote:<br>
>>><br>
>>>> I have the 20m WSPR shield working on a new Raspberry Pi 3 B+. <br>
>>>> I see apparent mixing products in the output, 120 Hz away from<br>
>>>> fundamental, when using a USB power bank to power the Pi. Since<br>
>>>> these are not coming from a switching power supply, where are<br>
>>>> they coming from? These products start at about 30 dB below the<br>
>>>> fundamental.<br>
>>>><br>
>>>> Also, with a scope I measure the voltage output at 12V peak to<br>
>>>> peak into quality 50 ohm dummy load. This is 0.36W, higher than<br>
>>>> the 20dBm (0.10W) specified. Is this too good to be true?<br>
>>>><br>
>>>> Note the shield was not designed for the Raspberry Pi 3 B+ so it<br>
>>>> can't be fully inserted on the 40 pin GPIO plug, but seems<br>
>>>> stable enough partially inserted. Getting WSPR reports from<br>
>>>> across the USA and occasional overseas reports too.<br>
>>>><br>
>>>> Keith - KE4TH<br>
>>>><br>
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>>>><br>
>>>><br>
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