[Amps] nylons

R.Measures r at somis.org
Wed Mar 16 06:35:45 EST 2005 

Not bad, not bad.

On Mar 15, 2005, at 11:52 AM, David Kirkby wrote:

> R. Measures wrote:
>
>>
>> On Mar 15, 2005, at 1:04 AM, David Kirkby wrote:
>>
>>> RICHARD GEORGE wrote:
>>>
>>>>  There are two hydrogens atoms in a water molecule.
>
> One hydrogen atom says to the other "I have lost an electron".
> The second hydrogen atom, says "Don't be silly, you have not lost an 
> electron.".
> The first one then says "Yes, I have lost an electron -  I'm positive."
>
>>> So if a plastic had a lot of water
>>> in it, it would get hot if fed with 2.4GHz.
>>
>>
>>  I have melted nylon with 7MHz RF, but I never tried it at 2.4GHz.  
>> However, D-factor typically increases as freq. increases.
>
>
> I make no claim about the losses of nylon at RF, since I do not know 
> its properties.  I'm only saying that testing at one frequency does 
> not tell you much about losses at another frequency.

And if the sample is small it won't get hot at all -- even though the 
D-factor is bad news.
>
> In any case, there are different types of nylon. Perhaps with a search 
> of the internet, one might find some properly measured data, but 
> unless you know the exact source of the nylon, testing it yourself at 
> the frequency of interest is probably the best way.

Been there done that.  Went to the local plastics emporium and got the 
data sheet.  Nylon is good for D. C.
>
> I think you are right in saying loss does tend to increase with 
> frequency for solids at RF, although that graph for water clearly 
> shows the relationship is far from simple - for water at least.

Agreed, but water is weird.  It expands below 4º C and it can even sink 
ships.

> It may be simpler for plastics at radio frequencies. But I think this 
> idea of relying on a microwave oven in unlikely to be a very valid 
> test, especially given it is around 100 to 1000x higher in frequency 
> than your HF amp.
>
> G8WRB
>
>
>>>  There's a graph below
>>> showing hpw the loss of water changes by a factor of 10000000000
>>> depending on frequency!! (This viable to very short microwave
>>> frequencies, but the same applies elsewhere Ignore all the text - 
>>> just
>>> look at the graph, and not both axes are logs).
>>>
>>> http://www.lsbu.ac.uk/water/vibrat.html
>>>
>>> But other materials loss peaks will not necessarily cause heating at
>>> 2.4GHz.
>>>
>>> Light travels through water relatavily easily - you can see through
>>> light pretty well.  600 nm (5 10^14 Hz) or so would be a green light 
>>>  (if
>>> I recall correctly). Yet lower the frequency by a factor of 5 or so 
>>> to
>>> get to 3um (10^14 Hz) and water is *highly* absorbing. So water 
>>> absorbs
>>> the low frequency less than the high one. In fact, water has a lot
>>> absorption peaks, where it is highly absorbing, as that graph shows.
>>>
>>> Put a transmitter at one of those frequencies and any water will get
>>> very hot. Yet it is very low loss at about 400um (ultra violet).
>>>
>>> You can see that the absorption of water varies from 10^6 cm-1 to 
>>> 10^-4
>>> cm-1. Those two are a factor of 10000000000 apart!!!
>>>
>>> Other materials are the same - they will have absorptions that 
>>> depend  on
>>> frequency. Something that is poor at 2.4GHz where the microwave 
>>> works  is
>>> not necessarily poor at some other frequency.
>>>
>>> An example is PTFE. Most people know that as a good dielectric with 
>>> low
>>> loss at RF. But move to light and it is pretty absorbing - you can't 
>>>  see
>>> trough more than a couple of mm of it.
>>>
>>> The hemoglobin in blood is another example. This fact is used by the
>>> pulse oximiters that clip on your finger and are routinely used to
>>> measure blood oxygenation in hospitals. The absorption changes  
>>> depending
>>> on whether it is oxygenated or not.
>>>
>>> Perspex is another. Clear in the optical region (around 450-700nm), 
>>> but
>>> highly absorbing at 10.7um (where a C02 laser works). I know a  
>>> colleague
>>> who worked on C02 lasers said they used perspex goggles, as they  
>>> perspex
>>> started melting if the laser was hitting them, and you would know 
>>> this
>>> before it melted enough to damage your eyes. (You can't see 10.7um 
>>> with
>>> your eyes).
>>>
>>> So I don't think the fact a material does or does not absorb at the
>>> specific frequency of a microwave oven tells you that much about how 
>>> it
>>> will work at a very different frequency.
>>>
>>> YOU NEED TO KNOW THE LOSS AT THE FREQUENCY WHERE YOU INTEND YOUR
>>> TRANMITTER TO WORK - NOT AT SOME FREQUENCY THAT IS FAR REMOVED FROM 
>>> IT.
>>>
>>>
>>> Just my opinion,
>>>
>>> Dr. David Kirkby, G8WRB.
>>>
>>>
>>>> K6KWQ Dick "12 Volt radios are for wimps, real radios can kill you" 
>>>>  Still can't make it go QRO with "More Power"
>>>>  ----- Original Message -----
>>>>  From: John Irwin<mailto:crazytvjohn at yahoo.com>
>>>>  To: amps at contesting.com<mailto:amps at contesting.com>
>>>>  Sent: Monday, March 14, 2005 3:54 PM
>>>>  Subject: [Amps] nylons
>>>>
>>>>
>>>>  dudes
>>>>
>>>>  a large ace hardware store opened here last week , One block away. 
>>>>   I have noticed a lot of nylon items that look a lot like the 
>>>> ceramic  standoff insulators, they come with a hole in the 
>>>> center,and some are  taped for 6-32  or other simular sizes.  
>>>> lenght every 1/8 inch or  so,diameter 1/4 to 1/2 inch
>>>>
>>>>  How does nylon act in rf?    Like in a amplifier as used to 
>>>> support  variable capacitors or inductors? Next to the plate choke.
>>>>
>>>>  Anyone put some in the pi coil and see if it holds up. or does it 
>>>> go  up in smoke?
>>>>
>>>>  thanks
>>>>  john kb9tc
>>>>
>>>>
>>>>
>>>>
>>>>  ---------------------------------
>>>>  Do you Yahoo!?
>>>>   Yahoo! Small Business - Try our new resources site!
>>>>  _______________________________________________
>>>>  Amps mailing list
>>>>  Amps at contesting.com<mailto:Amps at contesting.com>
>>>>   http://lists.contesting.com/mailman/listinfo/amps<http:// 
>>>> lists.contestingcom/mailman/listinfo/amps>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>> -- 
>>> Dr. David Kirkby,
>>> G8WRB
>>>
>>> Please check out http://www.g8wrb.org/
>>> of if you live in Essex http://www.southminster-branch-line.org.uk/
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>
>>
>>
>
>
> -- 
> Dr. David Kirkby, G8WRB
>
> Please check out http://www.g8wrb.org/ of if you live in Essex 
> http://www.southminster-branch-line.org.uk/
>
>
>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

More information about the Amps mailing list