Project: Product Reviews on Part15.us

... Does reviews and testing all the time:

http://www.xrqk.com/RADIOBRANDYNET/

http://www.radiobrandy.com/RBpart15am.html

http://www.radiobrandy.com/

It seems, from reading the many "review" posts here, that the two main interests regarding part 15 AM transmitters are "How far will the signal go?" and "How good is the audio?".

With this in mind, bench testing could provide a predictor but a more useful test may be on a standard antenna test range. This could be done by someone with access to some clear acreage upon which a "standardized" radial system could be installed and each device under test (DUT) would be tested with the manufacturer's recommended antenna working against these radials. Perhaps a near field relative field strength and a far field relative field strength at specified distances could be used as comparative performance measurements among the various DUTs. For consistency, all tests would need to be done on the same antenna range.

Relative field strength could be done with a "poor mans" meter by using an AM receiver modified to measure received signal strength.

I do not think bench tests will be as useful since the antenna loading would have to be simulated. A DUT which supplies X mW into a load may not provided the same with an actual antenna. A claim of "X% output transistor efficiency", for example, by itself does not predict the power which will be delivered to an antenna.

In summary, I think the most meaningful comparison for range will result from the use of an actual transmitting environment which is the same for each DUT.

This is how I would approach the subject of review.

Neil

Neil, your suggestion of a standard radial location is very sensible and I only have these questions to further understand it...

Would the time of day make a difference for getting comparable results?

Do relative conditions matter, such as moisture and temperature?

What are some variables that haven't been mentioned?

(My eye situation rules our my
participation in this current venture.)

HOWEVER, I am going to disclose
something that I have never told
you guys.

In the early 1980s (as a ham)
I worked for a magazine in
Newington, Connecticut for a
place called, The American Radio
Relay League. It was 30 years
ago, and I lived down the street,
and was a ham. I knew some guys,
and they got me in there.

The magazine is called QST, as many
of you guys know.

A lot of people like the ARRL, and a lot
don't. I can understand. But I think
the headquarter's staff has always tried
to do their best to help ham radio.
And, I really do have a soft spot for
the place. For a guy with a disability,
they were just SO GOOD to me there. The
kindness from the people there - well -
I will never forget it.
And, hey, I was just trying to pay for
my apartment and for some food to eat.
I was just working there, you know. What
a weird stroke of luck. (And I did meet
some of the most amazing and talented
people I have ever met in my life.)

Anyway, I ACTUALLY WROTE a product review
for QST! Who would have believed it? It
was for the Radio Shack DX-302 HF
communications receiver. Some of the
guys knew that I was also an SWL, and
they figured I would get a kick out of it.
That's when I found out that I didn't have
any skill for writing, but they helped me
out and the review got into QST. Like
the ARRL or not, these dudes were REALLY
nice guys, and I got my 15 minutes of
radio fame. (By the way, the DX-302 was
a really weird receiver, but I wouldn't
mind having one for old time's sake.)

ANYWAY, those guys had (and still have) a lab,
so they could take a ham rig, and test
for various transmit and receive parameters.
You know. The standard stuff.

But, THEN, a person took whatever it was he
was reviewing out into the field, and actually
used it for a while. Sometimes a guy would
keep a radio for several months until it
was given back to the manufacturer. If it
was a mobile radio, they'd throw it into
a car and drive it around for a few months.

So, some stuff was done in the lab, but
then things were done out in the field.

I think there are 3 things that are
of great interest to us dudes at Part15.us.

(I could be wrong at this, so feel free to
chime in at any time.)

1) The first question I think is -
what is the best Part 15 AM
transmitter/antenna combination,
is it legal, reliable, how far
does it go, and how is the
customer service if anything goes
bad.

2) What kind of software will help
my Part 15 station? I can't say too
much about this, because I don't
see computers very well. But there is
programming software, automation software,
audio processing software, and streaming
software (if you're into that.)

3) Can I get an audio processor of some
kind to perhaps increase my AM transmitter's
coverage range, by using the audio most
efficiently.

So, I think somebody has got to take some
lab parameters of whatever is being tested,
and then somebody has got to use it for
a while. Is this second item achievable?

I don't know. In the case of the SS Tran
AMT-5000, it should be tested over SOME
period of time. All of us who have had
neighborhood Part 15 radio stations - on
the AM BCB - know that coverage conditions
are not the same every day. Heck, I was
testing my station (when it was on 1690 or
1700) every day. I drove my wife crazy,
because she would have to drive the car
all around town all the time. (For those
who don't know - I can't drive a car because
of lack of vision.) I know there is SOMEBODY
out there who is using an AMT-5000 with an
optimized outside antenna system. We just
don't know who they are, and they don't know
us.

Anyway, that is my story about writing a product
review ONE TIME for a magazine with a circulation
of about 150,000. They did testing in a lab, and
then in the field.

I don't know if this is of any use. But it was
one of the best times in my life. I was young.

Best Wishes,
Bruce, DOGGRADIO STUDIO 2

P.S. It is really nice of you, Jon Paul,
to come in and talk about this project.
Hopefully, there will be people with the
time and hardware to do something regarding
this challenge.

This is slightly off the subject of product reviews, it's more in the way of product previews.....

Well, on this website we have talked about "wish lists" we might have of features we'd like to see. Recently somebody said they'd like to see an SWR meter (Standing Wave Ratio) built into a part 15 AM transmitter.

In previous posts we have shared fond memories of tube transmitters with their beautiful glow that gave a special magic to broadcasting.

I remember rattling on about building a scale model tube transmitter that looked like a toy version of an old-time AM transmitter, with rheostats and meters.

This whole stream of thinking came back into my mind when I saw Paul Thurst's engineering blog "Transmitters Used to Look Like Something."

http://www.engineeringradio.us/blog/

Right after that bit he has a good blog on Troubleshooting.

Though not impossible, it would be quite difficult to construct a VSWR meter capable of measuring these flea power levels and accurately measuring the return on a loaded 3 meter whip or rod.

Question would be..finding a meter capable of even indicating such low levels of signal..in either direction, and measuring it with enough accuracy to trust it, without having to build the thing with amplifiers that in turn would also need to be calibrated to represent what is actually there on the system.

Such a piece of gear would start to dive into expense vs practicality and in our case with the power levels involved, may not be such a great idea after all. But there are plenty of schematics on VSWR meters out there that perhaps one might be able to be modified and adapted.

Like others, I too am surprised one has not appeared on the scene over the years. Perhaps there is a reason why, like maybe what I have just described above eh?!!

RFB

Logic and reason is an enemy of imagination.

EDITOR HAS RETURNED:

After I posted the above, which credits RFB with reason and logic which disappoints our simple imaginary "SWR meter",

It has occurred to me that Albert Einstein said almost the opposite...

"Imagination is more important than knowledge."

Intelligence has a way of canceling itself out.

Hi Guys:

i remember on one of Carl's Low Power Hours - there
was a guy who used a "grain of wheat" bulb to tell
when his coil was tuned correctly. This was for his
Part 15 AM antenna tuning coil.

The coil was a bunch of turns of copper wire on a
form. That top of the coil (it was sitting on it's side)
was sanded, and a sliding contact was moved across
until the best signal strength was obtained. At this
point the little light bulb lit up. The bulb was actually
used for a tuning indicator.

I think these particular "grain of wheat" bulbs were hard to
find. He had to order them from somewhere outside of
the U.S. The bulbs of this type were really small and took
very little energy to run.

Just thought I'd throw that in. I guess it's not really an SWR
meter. but it might be of some use/

Bruce, DOGGRADIO STUDIO 2

Glad you remembered that bulb method, Doggradio 2.

Given all we've been discussing, it is a good question whether the bulb shows all output power, or whether it could be lit in part by back-flow, also known as "Standing Wave."

The simpler it gets the more complicated.

Hi Carl!

After doing experiments with
carrier current, I feel like
I don't know anything anymore.

Best Wishes,
Bruce, DOGGRADIO STUDIO 2

I join you Mr. Doggstudio2 in "not knowing anything anymore."

When this happens I begin studying a different subject, other than carrier current or short antenna differences.

The other subject is learning itself. How does one learn, as effectively as possible.

I am paging through "The Oxford Book of the Mind", an actual book, and may present the findings on a future radio show.

Perhaps the membership knows how to learn, they all seem to have knowledge, although they may have simply had good genes.

Remember those? Ahh..the hours spent creating different images with clear colored pegs...till the light bulb burns out.

Thing is with a rice bulb approach is that VSWR increases as the forward power is increased, which in a basic sensing device such as that rice bulb, will indeed indicate by brightness of the amount of signal passing through it.

Problem is this, Carl is spot on about the bulb indicating both forward and reverse voltages thus the bulb will indicate what is passing through it and in both directions.

It may be possible to use two low voltage diodes in opposite polarity and two rice bulbs, one to measure forward (+) voltage and the other to measure reverse (-) voltage. In such a setup, the tuning process would involve making the forward bulb bright and the reverse bulb dim when reaching the peak resonance.

The setup would need to be loosely coupled so as to minimize loading effects which if coupled too heavy will rob some of that power, but coupled enough to actually measure something in both directions.

Have fun!

RFB

It's a good thing you're here. (And a lot of
the other guys, too.)

I remember that "peg light thing." I never had
one, but I remember the TV commercials.

Since I've been experimenting with CC, my IQ
has dropped to about 65.

Bruce, DRS2

I recently read an article showing how to use two bulbs to show forward and reflected power. I believe the application was used with twin-lead lead in cable.

I have to find that article and post it here. We'll see if it's adaptable.