<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head><body bgcolor="#FFFFFF" text="#000000">Hi Ed and Ricardo,<br>
<br>
Thanks for the feedback. Much appreciated. <br>
<br>
My concept for the antenna analyzer is to combine an Arduino (computer),
Si5351a board (oscillator, frequency set by the Arduino) and an LCD
diisplay. The oscillator drives a simple resistor bridge with the
antenna as one of the legs of the bridge. I'm using an AD8307 log amp to
measure the voltage across the bridge. I've attached a picture of the
prototype analyzer. <br>
<br>
The idea is to sweep a range of frequencies to find the resonant point
and calculate and display the VSWR at that frequency. <br>
<br>
Initially I thought that I could also measure the bandwidth where the
VSWR of the antenna is 2:1 or less. I wasn't able to get that to work.
After some reflection I realized that there are reactive components once
you get away from resonance that make measuring VSWR impossible with a
resistive bridge.<br>
<br>
I've tried to keep the operation simple. After turning the power on, you
turn the knob (rotary encoder) to set the center frequency of the
sweep; that's shown as "IN:" in the photo. Each click of the knob
changes the frequency by 1 MHz. Then analyzer sweeps from 0.5 - 1.5
times the center frequency. In the case shown (center frequency = 12
MHz), the analyzer sweeps from 6 MHz - 18 MHz. After you set the center
frequency you push the knob to start the sweep. It's fairly quick -
takes about 2 sec to do a sweep. The analyzer should work over a
frequency range of 1-30 MHz. It's possible that the range can be
expanded.<br>
<br>
My objective was to make something that's portable and relatively cheap,
sorta trading accuracy for money. I think it will be accurate within
5%-10%. Actually, the frequency measurement seems to be accurate within
10 KHz and the SWR within ~0.1 at resonance.<br>
<br>
This is an open source project, so I'm planning on releasing the source
code into the wild. I'm planning on shipping an preprogrammed ProMini
with the kit so that you don't have to do any programming or loading of
software.<br>
<br>
I have two AD8307 chips in the design. These are smd chips that I'm
going to have presoldered to the pcb so the builder doesn't have to do
that. Everything else is through hole/parts with leads. There are a
couple of other smd chips shown on the prototype. These were part of
another project (mag loop autotuner) and not part of the antenna
analyzer.<br>
<br>
I'm planning on having the analyzer available to show at
Hamvention/Dayton in May and have kits available through TAPR hopefully
in July - if I can get the documentation ready ;-)<br>
<br>
I'm interested in everybody's thoughts and comments. Any and all
feedback is welcome.<br>
<br>
73 Bruce/ND8I<br>
<br>
<br>
<br>
<br>
<span>supertech0491 via hfsig wrote on 3/24/2019 12:07 PM:</span><br>
<blockquote type="cite" cite="mid:md5:ih%2Fi8oPE7S6Vz+uHnVHzzA==">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<div><br></div>
<div>Reference mention of analyzer project lit, I'd be interested in
obtaining one.</div>
<div>73,</div>
<div>Ed K5KBV</div>
<div><br></div>
<div><br></div>
<div id="composer_signature"><div style="font-size:85%;color:#575757"
dir="auto">Sent from my Samsung Galaxy smartphone.</div></div>
<div><br></div>
<div style="font-size:100%;color:#000000"><!-- originalMessage --><div>--------
Original message --------</div><div>From: <a class="moz-txt-link-abbreviated" href="mailto:hfsig-request@lists.tapr.org">hfsig-request@lists.tapr.org</a> </div><div>Date:
3/24/19 11:31 AM (GMT-06:00) </div><div>To: <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a> </div><div>Subject:
hfsig Digest, Vol 40, Issue 4 </div><div><br></div></div>
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1. Re: hfsig Digest, Vol 40, Issue 3 (supertech0491)<br>
<br>
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----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Sun, 24 Mar 2019 11:29:56 -0500<br>
From: supertech0491 <a class="moz-txt-link-rfc2396E" href="mailto:supertech0491@yahoo.com"><supertech0491@yahoo.com></a><br>
To: <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a><br>
Subject: Re: [hfsig] hfsig Digest, Vol 40, Issue 3<br>
Message-ID:<br>
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Content-Type: text/plain; charset="utf-8"<br>
<br>
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.<br>
-------- Original message --------From: <a class="moz-txt-link-abbreviated" href="mailto:hfsig-request@lists.tapr.org">hfsig-request@lists.tapr.org</a>
Date: 3/24/19 11:00 AM (GMT-06:00) To: <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a> Subject:
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Topics:?? 1. Re: 20m WSPR shield for Raspberry Pi (John,
W9DDD)----------------------------------------------------------------------Message:
1Date: Sat, 23 Mar 2019 14:29:53 -0500From: "John, W9DDD"
<a class="moz-txt-link-rfc2396E" href="mailto:w9ddd@tapr.org"><w9ddd@tapr.org></a>To: <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.orgSubject">hfsig@lists.tapr.orgSubject</a>: Re: [hfsig] 20m
WSPR shield for Raspberry PiMessage-ID:
<a class="moz-txt-link-rfc2396E" href="mailto:dcfdb486-6eca-e59e-d85a-6dead1b8e325@tapr.org"><dcfdb486-6eca-e59e-d85a-6dead1b8e325@tapr.org></a>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 <a class="moz-txt-link-rfc2396E" href="mailto:bruce@raymondtech.net"><bruce@raymondtech.net ></a>>
<a class="moz-txt-link-rfc2396E" href="mailto:bruce@raymondtech.net"><mailto:bruce@raymondtech.net></a>> 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>>>???? <<a class="moz-txt-link-abbreviated" href="mailto:keith.wilson.pcs@gmail.com">keith.wilson.pcs@gmail.com</a>
<a class="moz-txt-link-rfc2396E" href="mailto:keith.wilson.pcs@gmail.com"><mailto:keith.wilson.pcs@gmail.com></a>>>>>????
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>>>>>>>>????
<a class="moz-txt-link-rfc2396E" href="https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon"><https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon></a>>>>>????
Virus-free. <a class="moz-txt-link-abbreviated" href="http://www.avast.com">www.avast.com</a>>>>>????
<a class="moz-txt-link-rfc2396E" href="https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link"><https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link></a>>>>>>>>>>>>>????
_______________________________________________>>>>????
hfsig mailing list>>>>???? <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:hfsig@lists.tapr.org"><mailto:hfsig@lists.tapr.org></a>>>>>????
<a class="moz-txt-link-freetext" href="http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org">http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org</a>>>>>>>>>>????
_______________________________________________>>>???? hfsig
mailing list>>>???? <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:hfsig@lists.tapr.org"><mailto:hfsig@lists.tapr.org></a>>>>????
<a class="moz-txt-link-freetext" href="http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org">http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org</a>>>>>????
_______________________________________________>>???? hfsig
mailing list>>???? <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:hfsig@lists.tapr.org"><mailto:hfsig@lists.tapr.org></a>>>????
<a class="moz-txt-link-freetext" href="http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org">http://lists.tapr.org/mailman/listinfo/hfsig_lists.tapr.org</a>>>>
> > > _______________________________________________> hfsig
mailing list> <a class="moz-txt-link-abbreviated" href="mailto:hfsig@lists.tapr.org">hfsig@lists.tapr.org</a>>
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