Heathkit

I've always used broad disclosure, myself. (I write my own patent specifica tions for the most part, and then work with a lawyer on the details of the claims. I learned what I know about claim-writing from a genius, the estima ble Stephen Kaufman, Esq. His claims somehow manage to seep into all the wh ite space left by the prior art. I'm not as good at as he was, but I learne d a lot.

I've seen all three of those situations in cases I've worked on as an exper t witness.

Re: enforcing your patent against the Chinese. If you've licensed your pate nt to a big outfit, it's not that unusual for them to defend it. You can al so go to the International Trade Commission, which runs cases super fast an d can order the Customs to stop imports of the infringing articles.

Cheers

Phil Hobbs

? 0.1?

I would use a vswr meter to adjust my matching to my antenna. Within reas on I do not care what the actual value is. I just want to get the best vs wr that I can. If the best is actually 1.1 or 1.5, who cares ( except for bragging rights ).

Dan

Worse. Is that 2% of full scale or 2% of indicated reading? Percent of full scale is how it's done on most RF wattmeters. Let's pretend the meter is on the 100 watt full scale position. If I feed it 100 watts, for 2% of full scale, the power could be anywhere between 98 and 102 watts. No problem there. However, let's reduce the input power to 10 watts. Now, the power could be anywhere between

8 and 12 watts, or +/-20% of the indicated 10 watts. Not so good.

For reference, the highly popular Bird Model 43 wattmeter is rated at

+/-5% of full scale. Commodity wattmeters are typically +/-8% of full scale. Examples:

Now, if one wants real accuracy, a calorimeter is needed: Accuracy varies from 0.5% to 2% depending on model. See chart under "Calorimeter Selection Chart".

At one time, Bird made a calorimeter type wattmeter for broadcast stations. Model 6080A/6081A. Accuracy is 3% of indicated power from 1 to 10,000 watts.

These daze, most digital RF wattmeters use wide dynamic range log detectors/amps, such as the ADL5513: See Pg 16 for "Error Calculations". My eyeball guess(tm) from the graphs is an error of about +/-0.5dB. 0.5dB is a power ratio of 1.12 times or 12% of indicated watts. If they're going to use such a chip to deliver 2%, it will probably need a calibration table lookup system for it and the directional coupler errors.

All this begs the question whether the average ham needs laboratory grade accuracy for their station. I don't think so, but I've been wrong before.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

It would be interesting to know how the ERP is measured. You need to get the antenna system losses into it, the reflection loss is not alone enough.

--

-TV

Agreed. The only thing a low VSWR buys you is that the transmitter output protection circuit, which is usually set to kick in at VSWR=2.0:1, does not complain.

There are also better ways to tune an antenna. My favored method for HF is using a remote field strength meter. It's located at the approximate height of what I would like to see for a takeoff angle (about 15 degrees), and as far away as practical. I adjust the antenna tuner for maximum field strength, double check that the VSWR is

to deliver 2%, it will probably need a

for it and the directional coupler errors

I've used the ring-down of an 80-MHz crystal to calibrate DLVA-type detecto rs of the sort you find in FM IF chips. You make a Colpitts XO running at t he series resonance, taking the output from the cold end of the crystal, th en use a PIN diode switch to ground the top of the tank on command. After a small jump, the output decays exponentially at a rate of about 1 dB per mi llisecond, which is quite convenient.

Then you just need a full-scale reference.

Heathkit may well be using an inexpensive DDS to generate a 2-D calibration table.

Bird didn't have that luxury.

Cheers

Phil Hobbs

There were some comments about "remote sensors" in the Heathkit product description. It is possible to calibrate these in terms of field intensity in Watts/cm^2, dBuV/m, etc. Measurement of this field strength/intensity/density is required for AM and SW broadcast stations and for measuring RF exposure. For example: Once the "remote sensor" is calibrated in terms of field strength, it should be possible to work backwards, using the path loss, and produce a number for the EIRP. Similar products already exist but are not intended for making accurate measurements, just monitoring:

The catch is that the "remote sensor" needs to be sufficiently far away from the transmit antenna to not be in the near field (about 10 wavelengths). Or, the calculations need to include some consideration for the near field, which requires that the E and H fields be measured separately.

Handy cheat sheet: I forgot from which book I stole it.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Maybe you take a picture of your antenna and upload it to the box and it uses some fancy image recognition/AI algorithm to make a guess!

That sounds something like how my various antenna simulation programs (NEC2/NEC4) operate. I stuff in some numbers and they produce a tolerable guess at to what the radiation pattern and frequency vs VSWR plot might look like under ideal conditions. However, when I actually visit an antenna range and measure what the antenna is really doing, the patterns look similar, but are far from identical. Usually, it's something I forgot to include in the model, such as the mounting structure, nearby reflectors, cars in the parking lot, chain link fence, power lines, position of the moon, etc. Given the choice of accepting a rather erroneous reality, versus dealing with a totally out of control but realistic model, most antenna designers take the easy way out, even if it's wrong.

Incidentally, a few months ago, I did almost exactly as you suggest. I took photos of an antenna, used a pair of dividers to extract the dimensions, and built an NEC2 model of the antenna. Using Photoshop to remove the parallax and distortion made it fairly easy. No AI. Just me doing all the midnight sweating and swearing.

With antennas, the uglier they look, the better they work.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

(snip)

I know you won't believe me if I say you are way off so see this:

Also, you could consult a Smith chart.

I don't see anything on the above web page that refers to power lost by reflection due to VSWR (4% power loss or a 0.18dB mismatch loss).

I use a Smith chart for calculating impedance matching and transmission lines. There's nothing on the chart that has anything to do with calculating reflected power.

Maybe try one of these online calculators: Plug in a VSWR=1.5:1 in any of the above and they will produce a 4.0% power loss by reflection, which means that 4% of the transmit power (assuming a lossless transmission line) is NOT available for delivery to the antenna.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Nice list... But, no impedance analyzer ?

boB

If it stays up the whole year, it is too small ...

--

-TV (OH2UG)

I've occasionally wanted one, but it would take up too much rack space. I h ave a nice HP four-post instrument rack that I bought from a guy in Mass wh o used to post here (ecnerwal), but those have become very scarce.

I make do pretty well with the Measurements 59 GDOs for LCs, the Smart Twee zers for ESR, and the Boonton 72s and AADE meter for small caps. The sampli ng scopes are OK for semi-quantitative stuff at really high speed.

When my ship comes in, I might spring for a scope/logic analyzer combo.

Cheers

Phil Hobbs

'fraid I beat you there, Phil. I managed to get around $2.5m worth of stuff for less than a thousand dollars. :P

Jeeps in Cosmoline? Growing weed?

Cheers

Phil Hobbs

Nope, just similar stuff as on that list you posted. Some of them have faults, but almost all of those are repairable and I quite enjoy the challenge of that anyway.

Well, you're one up on me there. I hate repairing stuff. Do you have a list?

Cheers

Phil Hobbs

I knew you'd ask that! No I don't. There's just too much. :P