If you want to roughly calibrate your receiver for AM, find a station not too far from your operating frequency that is a few miles away, with known output power, and uses a single quarter-wave tower. A 1 kW output at one mile will produce about 190,000 uV/m field intensity. Field intensity is proportional to the square root of output power, and is inversely proportional to distance.
Suppose that the station you are using for calibration is five miles away and has an output power of 5 kW. The field strength at your location is roughly [SQRT(5) x 190,000]/5 = 85,000 uV/m. Note the reading in dBu on your receiver. This is your calibration point. For measuring other field strengths, make the conversions between dBu and uV as I explained in my previous post.
This calibration is VERY rough (it doesn't take into account ground attenuation vs. distance, for example), but it will give you some idea about the magnitude of the field strength you are measuring.
I think I'm going to print
up your last few posts.
I think both my kids
have scientific calculators
around here somewhere.
Thank you for taking the
time to explain these different
ways to "measure" RF.
Best Wishes,
Bruce, DOGGRADIO STUDIO 2
Ermie's suggestions are also applicable to measuring CC!
RFB
It's about fifty dollars on Amazon.
For that amount you get a very
interesting radio.
It actually is not as sensitive on
the AM BCB as a lot of other radios.
The reason seems to be that
the internal loopstick is very small.
Really serious AM DXers have put
replacement loopsticks inside or have
attached them to the outside of the
radio. I understand the loopstick had
to be small as to keep it away from
the internal circuitry.
You do get a lot of radio for the price.
The DSP makes it a very selective AM receiver.
The FM is good, too, but not as good as some
other radios I've seen. It also gets a bunch
of the shortwave spectrum up about to 21 or
22 MHz. No BFO, but you can always make an
outboard BFO. There is a kit BFO on the market
that is made by Ten Tec (sp?).
The ergonomics are good. The DSP really works,
but it does have a few odd quirks. (I don't
mind the quirks - not for a 50 dollar radio.)
When the ionosphere is cooperating,
I don't have any problem at all hearing the 555 kHz
station (ZIZ?) in the Caribean. All of my other good
radios get that station too, though. My HQ-140X
hears the 555 station. (By the way, the 555 kHz
station is the last AM BCB split operating in
the Caribean. There were others, but they have
all been turned off.)
I haven't yet found any of the calculators around
the house yet that are capable of handling
scientific functions. But I will keep looking.
I will then be able to try an outside test with
my C Crane transmitter and see if this radio
could be of any use.
And you're right RFB, it seems that the radio
could be good for CC use. (I sure could it for
my CC experiments - if the PL-380 turned out
to be a proven performer.)
It does seem to me that the radio would have
to be compared to a real commercial field
strength meter before you could really use
it for something.
Thanks for reading this,
Bruce, DRS2
I just took a good look at your
comments again regarding the
conversions and the rough calibration
using a known AM station.
Bruce, DRS2
Bruce,
An on line calculator for conversions can be found here:
http://transition.fcc.gov/mb/audio/bickel/findvalues.html
Neil
OK. I can't do it today, but
tomorrow or the day after, I'll
take the C Crane, plunk it down
in the back yard, and try to take
some readings with the PL-380.
This will be interesting.
Thank you!
Bruce, DOGGRADIO STUDIO 2
This panel of part 15 members has somewhat failed to arrive at a consensus or much of a resolution regarding the original project of setting standards for equipment reviews.
Anyway, I have ordered the parts for a PhilB "dummy load" which will be fun to have, and this year for sure the vertical with radials will go into an area of the yard that needs a lot of clearing.
I might try to write something but my prejudice could get in the way. I believe in part 15 and would not find it easy to give the equipment a bad review. I am more of a propaganda writer.
"This panel of part 15 members has somewhat failed to arrive at a consensus or much of a resolution regarding the original project of setting standards for equipment reviews."
Perhaps the methods used by Bill over at HB can resolve the matter. It seems to work for them..why not here?
Problem really is this..you cannot have a standard when TX's themselves do not follow a standard...ie output impedance standard.
At least for accuracy sake, one size dummy does not fit all no matter what the assumed loading will be. The dummy load does not give us real world applied tests nor does this dummy load account for those variables in other TX's, just one, and I will say it now, that dummy load is obviously selected in value for the AMT5K's advantage. In other words, the value of that load was calculated to the AMT5K's load impedance and then spread out like butter on bread to apply to another transmitter with a totally different output network and final.
If there is going to be reviews, then it must be done in a manner that the units were intended to operate under, be it a wire or 3 meter long rod or holding your fingers on the output.
Rigged reviews don't fly very well with me and I will raise a red flag every time one is slapped up here.
RFB
...that dummy load is obviously selected in value for the AMT5K's advantage. In other words, the value of that load was calculated to the AMT5K's load impedance...
Do you know this for a fact?
Your assessment of the effect of the choice for a bench load is true in that it can affect the efficiency data. During the design of my transmitter and also in my experiments with the Ramsey AM-25 I varied the load resistance from 21 to 120 ohms and indeed observed the efficiency varied with this resistance.
Perhaps the bench tests could be conducted with varying loads with the results reported, yet even this would not predict the performance with a real antenna of unknown impedance. The utility of a bench test is limited but if the limitations are understood these test can still be useful.
Neil
"Do you know this for a fact?"
No. But just going by the discussions from weeks and even months ago elsewhere on the forum about optimum tuning for the AMT5K (aka sweet spot), that sweet spot for the high efficiency spec is around the proposed 30ohm test load presented within this thread.
I do not argue that it is probably the most closest representation to an outdoor setup and a great start point for bench testing. But suppose that same test load connected up to a Procaster, where that Procaster's output tank is designed to push that 3 meter aluminum rod that bolts to the TX cabinet side and the test load itself has a negative effect on the Procaster's possible peak results?
Why not test the units as they are meant to be ran in real application along with the bench mark testing? And for the bench testing of units designed to run a 3 meter rod, then test it with it's 3 meter rod. By comparison in as far as grounding and nearby objects on the bench between a AMT5K pushing a piece of wire and the Procaster pushing its 3 meter aluminum rod, should be a pretty good even playing field for the units under test. Then after that, outdoors where it really counts?
Or perhaps categories should be created for reviewing. Specific test conditions for TX's designed to just push wires hung from the roof, and a category for units designed to be outdoors pushing 3 meter long rods over ground systems?
RFB
It's difficult to participate in an intelligent discussion about practical and meaningful methods of reviewing transmitters when RFB keeps interjecting extraneous comments that demonstrate his ignorance of basic circuit and antenna principles:
"... that dummy load is obviously selected in value for the AMT5K's advantage. In other words, the value of that load was calculated to the AMT5K's load impedance and then spread out like butter on bread to apply to another transmitter with a totally different output network and final".
As I said earlier in this thread, this dummy load will only work with transmitters having an integral series tuning coil, which include the Rangemaster, Procaster, Talking House and AMT5000 transmitters.
The 30 pf capacitor value was selected as an approximate mid-point between extremes of 25 pf for a 102" stainless steel CB whip and 34 pf for a 118" long 1/2" copper pipe. The capacitance calculation applies to short vertical antennas and depends only on the length and diameter. The formula is published in the ARRL Antenna Handbook and many other places. I would repeat it here, but math and detailed technical information seem to irritate some people.
The 30 ohm resistor value was selected to represent the average ground resistance of 30 ohms which has been tossed out most frequently on the forums over the years. I have no idea whether this is a real typical number, but it seems reasonable for a simple 4-wire radial counterpoise. Real ground loss resistance can range from about 2 ohms for an elaborate broadcast station radial system to maybe 100 ohms for a ground rod and no radials.
I also believe I said previously that the actual capacitor and resistor value for a "Part15.us" standard dummy load could be modified by consensus of the forum participants. (I should have said "... qualified forum participants").
This dummy load provides a way to measure the actual output power delivered by a transmitter under conditions presented by a "typical" part 15 antenna. The output power of any of the mentioned transmitters really depends predominantly on the Q of the series loading coil and not so much on the RF output transistor efficiency (assuming all the mentioned transmitters have a decent transistor efficiency in the range of 70% to 98%).
That's all folks. I think seeking a meaningful part 15 transmitter performance review process is a dead and street. It's not worth the effort when people like RFB are around to turn a straight-forward technical approach into Jell-O. I have better things to do with my time.
No need to run off peeved. I am merely pointing out the vast variables this testing proposal will encounter..as you are well aware of. I don't rule anything out of consideration because of what all of us do agree on..the unknowns of the various configurations out there.
I am also not trying to exclude your proposal Phil. So far it's the best one for the bench testing. I think I've said that a time or two. 😉
I just want to see fair reviews across the board, fair testing, under fair conditions that best represent the actual intended operation environment of the units themselves. I truly think that only outdoor testing, be it on an elaborate 3 meter antenna over a good grounding system, or mounted up to a chain link fence pole in a trailer park will provide what people are asking for. If any particular unit is only designed to run indoors off a wire, then test it under those conditions as it was designed for against others of the same type and intended operating conditions. If there is a modification to make those wire pushers become 3 meter rod pushers, then test those modified units with their outdoor counterparts.
Sorry if your getting the wrong vibe from what I post and say Phil. I am only looking for the same thing many others are..a real world comparative test of not just one particular unit, but all of them.
RFB
"No need to run off peeved."
"Sorry if your getting the wrong vibe from what I post and say..."
That's a real disconnect from reality! The true nature of the vibes are clear. Do you ever actually read what you post? I am still aggravated. A quick attempt at a nice-nice post won't cut it. You have too much history.
Bypassing my hesitation to say anything.. something aggravated me,,
I can't legibility pretend to have the experience or true knowledge pertaining to this discussion, to the degree of validly that I should interject my comments concerning it...
However, in my novice position; there is a solid echo in agreement that I too am "..only looking for the same thing many others are..a real world comparative test of not just one particular unit, but all of them."
Real world comparative test - and the results of those test, are what reach a genuine conclusion.