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Project: Product Reviews on

Hi Everyone, one of the lively conversations that go on here at that recently caught my eye was a discussion about a product review for the amt 5000 (you can read the product review conversation thread here). Now it caught my interest because one of the projects I wanted to get going this year was to have product reviews on - rather timely! I added my comments to the thread but thought it would be best to start a new thread to capture interest going it is! I have pasted my thoughts below: Submitted by jpjanze on April 23, 2012 - 08:28. Very interesting discussion thread and one dear to my heart. One of the things I wanted to work on this year for was to integrate product reviews into the site and from the looks of this thread, it would appear that this would be a 'welcome' addition. I put some thought into how this might work and have some ideas - treat this as a starting piont: 1) we need people to 'do' the reviews 2) we need a process to follow to 'do' the reviews so they are objective were necessary and subjective where necessary 3) we need the 'test gear' to 'do' the testing 4) we need 'products' to test 5) we need to document and publish all of the above. First off, let me know if anyone supports the idea Second, I know I can arrange for #4 and #5 After figuring out what #3 is, I could certainly start working on getting it If the idea is supported, know anyone that would be interested in 'doing' the reviews? I imagine, if interested, this group could pull together a reasonable 'test suite'? Let me know what your thought are? - Am I crazy? (wait a minute, don't answer that) Cheers! Jon Paul

Radio Brandy

All the best, Ken N. KF7PLC

Review Criteria

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.


Questions About It

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?

Carl Blare

I Never Thought I'd Tell You Guys This, But

(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

(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

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

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

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,

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.


Slightly Off

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."

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

Carl Blare

SWR Meter

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 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?!!


Enemy of Imagination

Logic and reason is an enemy of imagination.


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.

Carl Blare

I don't know if this applies, but

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/



Interesting Point

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.

Carl Blare

I Really Don't Know

Hi Carl!

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

Best Wishes,


Feeble Help

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.

Carl Blare

Lite Brite

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!


Thank You 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


Twice the Rice

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.


Charter Member - Association of Low Power Broadcasters

Member Station - ALPB

Flea Bulbs

Remember that milliwatts used to light the bulb are milliwatts not producing a signal. They also change the load on the transmitter so if only used in setup and removed things probably have changed. Probably good for experimenting but I would hesitate to use them for constant monitoring.


Constant Loading

Indeed Neil. The setup would constantly be absorbing some of the energy and robbing it from the radiator. It would take quite a bit of experimentation to find a coupling point where a meaningful indication is obtained while trying to prevent too much of the signal being absorbed and turned into heat/light.

A much more fancier and elaborate monitoring system would need to be constructed, one with voltage amplifiers to boost the very loosely coupled signal of forward and reverse so as to provide isolation and enough coupling to obtain a sample signal in both directions, then feeding either a dual meter setup or single meter or set of bulbs. Problem with that approach is the calibration and matching. However with a general range field of the VSWR meter, perhaps a "ball park" range could be built into the meter system with a range adjustment control to compensate for the various setups out there.

Pretty much all VSWR meters have a calibrate control to set the reflected meter. Maybe this concept can work as well with the proposed flea meter here.


Flea Power SWR Meters

Holy thread drift, Batman! But that is what makes things interesting.

RFB is on the right track. We have two very common types of SWR meter pickups which essentially differentiate between forward power and reverse power. A simple type uses pickup loops in a coax line or stripline. The second uses toroid transformer coupling. Both rely on diodes to produce DC indications to drive a meter.

The two limitations I see for very low power use is the forward voltage drop across the diode and the very small energy available to move the meter indicator. Expanding RFB's comments, amplification most likely is the key here.

There is a rather simple op-amp circuit which simulates a nearly perfect diode producing near zero forward drop with no appreciable reverse leakage current (Many op-amp references have this circuit schematic). I have used this circuit for some instrumentation applications, the most recent being in a high speed (tens of nanoseconds rise time) peak detector. To get this to work at this speed and presumably at RF requires very high bandwidth and slew from the op amp. The amps I used have (Unity Gain) BWs upward of 50 MHz and slews of hundred of volts per microsecond. These are readiably available and not too expensive but I don't have the numbers at hand as I post. If anyone is interested in experimenting with these let me know and I will dig out and post the part numbers.

Edit to Add: The op amps are the AD841, AD843, and AD847 types. The precision diode circuit is shown in the left half of the schematic in Fig. 29 of this data sheet:

Edited again to add more: Another approach which might be better (from the circuit stability perspective) and cheaper is to use lower performing op-amps to boost the signals from the pickups and then use conventional diodes and meters to process the amplified signals.


More Thoughts

The loop pickup coax or stripline SWR pickups are easy to build but probably will not give a satisfactory signal at BCB frequencies. This is because the coupling is a combination of magnetic and capacitive effects with the capacitive effects being small at these frequencies. The lowest frequency pickup of this design I have seen operates down to 3.5 MHz but possibly the design would work at BCB frequencies. It could be tried to find out.

The other more complex design with the toroid transformers uses only magnetic and direct voltage taps and would work well at BCB frequencies with the proper toroid material such as type 2.

Just thinking out loud.


Then What

If such a two-tiered device were built, showing forward RF and reflecting RF, and added, say, to an AMT3000, what is it that would get adjusted to optimize the SWR? Selecting taps above or below peak on a loading coil?

Carl Blare


Adjust for minimum reflected power.


Let Neil do the review!

If the new owner is willing to buy an AMT-5000 kit, I suggest that Neil would be about the best man for the job of doing a review. He is a moderator of this site, he has already made an AMT-3000, and he is an EE and a professor. What beter qualifications would you want?

A few problems ...

if a rice bulb is used, it will not register actual numbers of any kind, plus, it doesn't show, as mentioned, reflected energy ratios.

With that in mind, I'm still working on what might be called a near-field coupler, with which I could certainly use some expert advice. It will consist of a loop antenna with appropriate diode, cap, and resister (which I will likely eliminate) device which is measured with a digital multimeter.

The digital multimeter I have can measure down to two decimal places of microvolts. I used in in conjunction with a similar device when I tuned my antenna on the boat. The thing is, although they are meaningless units (because the loop antenna, or short whip with a few turns on a wood dowel, won't produce actual broadcast voltages, and are affected by distance and interference ... of course), it can still give you readable numbers, and more useable than an analog meter ... because analog meters are slow to react and readings don't show small numbers, making it difficult to detect peaks.

In the end, the one I used still took several afternoons of work climbing up and down (plus backing away from it to help eliminate body proximity effects) to adjust length, and peaked in the line width of one relatively new Sharpie pen (either side of it, the numbers started going down). It worked quite well at the time, but lately I have perceived some signal degradation ... which could be due to weathering of the antenna and loading system, seaweed buildup on the ground plate. etc.

In fact, if such a device could be reasonably calibrated using a borrowed one-time professional measuring device, such as the FCC uses in the field, and keeping the test parameters equal, it could be used over and over for the same test (except for changes in parts/component wear). xx uV measured @ 1M.

All the best, Ken N. KF7PLC

Great Idea

Not a bad idea Ken! But I think that with such elaborate build of a meter to measure these low power levels would take the meter well beyond the scope of hobby and Part 15 budgets. Having such a meter matched up to a professional device no doubt would raise the cost of such a meter, probably beyond most people's budget.

I believe also that such a meter should be kept simple for those who are not vested in translating numbers from a DVM to mW and uV. Using the bulb approach, if doable, provides the basic indicator in both forward and reverse, and very simple to tune by making the forward bulb bright, and the reverse bulb dim. No calculating, no conversions, no need for external metering with test leads dangling causing inductive changes to the antenna system.

The meter should be designed to fit within the enclosure of the antenna system..become a part of it full time. Everyone knows that even the slightest influence by a leaf off a tree or a bird perching on the top hat will shift that antenna's resonance big time. Not to mention the headache of tuning it while avoiding your own body's inductive influence on the thing.

Fun fun fun!! :)



"Let Neil do the review!"

Why not! I have a masters in EE and over 30 yrs in the radio and television broadcast engineering field. And I have the proper test gear to boot. But what I do not have is an open area suitable for an outdoor antenna system and part of the reasons why I run a CC AM station instead of a 219 setup. Too much clutter nearby along with neighboring homes and fences, which no doubt would hamper the testing results.

Neil has my nomination!


Another Approach

Perhaps using the same technique for measuring audio can be used here to measure VSWR..meaning the combination of Ken's op-amps and say a 5 step or more LED driver chip for the indicator. Have two segments, one LED segment showing forward, the other reverse.

Just tossing ideas.


Gain With SWR

The very interesting paper that was linked earlier (On the Topic of SWR - MRAM 1500) said something that impressed me. It said that (if) a reflection comes back to the transmitter and makes a quick u-turn and joins the transmitted RF IN PHASE, it will actually add to the resulting antenna power. I presume this is known as "antenna gain."

That might also be a condition worth achieving.

Carl Blare

Thanks, but....

I appreciate the confidence but I can't commit to such a review project. Though I have access to 90 acres of farm land it is 100 miles away and it wouldn't be feasible to do a range there given the changing environment with crops growing 8 months of the year in the fields.

I tend to agree with RFB's point about getting meaningful numbers which would be useful in predictions about other installations. Maybe a field test comparing several different transmitter types would have some predictive value, but maybe not. Suppose brand A demonstrated 30% better range (however that is determined) than brand B. Would that be useful?

If someone wants to do the field work and take data that is fine and I am available to advise.


Sensible Moment

Usually my brain is too cluttered to reach the crisp clarity that I feel is just out there ready to be grabbed. But Radio8Z's note just now gave that slight nudge that might be a ..... well, there, I've already blabbed on until I'm confused again. Maybe I can still say it.

We have certain givens with AM part 15.

The input to the final may not exceed 100mW. If we can obtain that measurement FROM ANY TRANSMITTER, we start on an even playing field.

The next stage is the efficiency of the final stage. If we could calculate that factor for EACH transmitter you would know who was ahead in the race.

Now comes antenna matching, to a tried-and-true 3-meter vertical with ground radials.

The transmitter that did best in all three departments will probably provide the best result.

At a moment like this it seems simple.

Carl Blare

A proposeal for simple RF measurement for reviews

Product reviews typically repeat features which are already available from manufacturers' web sites, followed by installation experiences and subjective evaluations of audio and range performance. I have never seen results of audio or range tests comparing two or more different AM transmitters performed with exactly identical installations, so meaningful comparisons of various brands is just not available.

Even exotic, expensive test equipment won't provide meaningful comparison information unless all tests of various transmitters are done under identical, controlled and repeatable conditions.

No transmitter manufacturer has ever published any information about RF output level, which is what any serious Part 15 broadcaster really wants to know when making a purchase decision. The input power is always 100mW, but that doesn't mean much except that it is legal.

I suggest that RF output testing of a transmitter under review be done in a way that is independent of any actual antenna/ground system installation. Instead of an antenna system, the transmitter should be tested with an antenna simulation circuit. In the old days the simulation circuit was called a "dummy load" and was just a 50 ohm resistor, but all the major, serious part 15 transmitters (Rangemaster, Procaster, Talking House, AMT5000) won't work when connected to a load resistor. They must be connected to a short vertical antenna which is effectively a capacitor in series with the ground resistance. The antenna capacitance is the C part of an LC series-tuned resonant circuit along with the L provided by an inductor located inside the transmitter. Likewise, conventional SWR and RF power meters won't work because they assume a 50 ohm near resistive impedance.

I suggest that RF output evaluations be done with the antenna disconnected and replaced by a capacitor and resistor in series between the TX antenna connector and the TX ground connector to simulate the antenna system under controlled conditions. TX output power can be calculated from the RF RMS voltage measured across the resistor. The RF voltage can be measured with a decent scope or RF voltmeter, either of which can be had for a few hundred dollars on Ebay (watch for the ones that say the unit has been tested and is operational).

A " standard" antenna simulation circuit can be defined by forum consensus (I suggest a 30pF 500V 5% mica capacitor and a 30 ohm 1/4 watt 5% carbon composition resistor).

Also, a " standard" measurement procedure and calculations could be published for all reviewers to follow. It will be easy to set up and measure two or more different transmitters under the same simple controlled conditions, and there is even the opportunity to get meaningful comparisons of different transmitters by different reviewers because the test conditions are acceptably simple and repeatable.

As an additional bonus, using a scope across the resistor also allows display of the modulated RF waveform to evaluate modulation level as part of the review of the transmitter audio performance..


Hi From Sean

Hi I am the one who brought up the rf meter,and SWR.
Not sure where that post went to,but there is a really good meter
not for much money that can read down to 5 mw and show SWR also.

Please look at this site for the meter. It really does come in handy and it is

You guys will really love this meter.



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