Barrett wrote:
One last question. Is the diameter of the traps at different frequencies
that important and why?

They tend to be larger towards top band.

More inductance is required on the lower frequencies
as inductive reactance decreases with frequency.
Inductance increases with coil diameter. If the
choice is lots of coax for small diameter coils
vs a lesser amount of coax for larger diameter coils,
the latter is preferable because of lower losses.
--
73, Cecil http://www.w5dxp.com

"Barrett" wrote in
. uk:

One last question. Is the diameter of the traps at different
frequencies that important and why?

They tend to be larger towards top band.

You really need to read a text that systematically develops an
understanding of the operation of a trapped antenna. It helps to understand
the operation of an untrapped antenna.

Unfortunately, lots of articles in ham mags aren't very reliable, so you
will need to read many articles and try to understand the underlying
principles to filter out the misconceptions that find their way to
publication.

By all means, ask questions about things you don't understand... but your
questions seem more like guessing your way to a solution and plugging the
gaps as they become apparent to you.

Owen

Thanks all for your time and help. Now I have enough information about the
traps I can now look and read up and give it ago.

73 to all


"Owen Duffy" wrote in message
...
"Barrett" wrote in
. uk:

One last question. Is the diameter of the traps at different
frequencies that important and why?

They tend to be larger towards top band.

You really need to read a text that systematically develops an
understanding of the operation of a trapped antenna. It helps to
understand
the operation of an untrapped antenna.

Unfortunately, lots of articles in ham mags aren't very reliable, so you
will need to read many articles and try to understand the underlying
principles to filter out the misconceptions that find their way to
publication.

By all means, ask questions about things you don't understand... but your
questions seem more like guessing your way to a solution and plugging the
gaps as they become apparent to you.

Owen

Barrett wrote:
Some one sent me an email and said these will do the job. Ceramic capacitor
disk 10KV/1000pF. Do you think these would work?

Depends on the dielectric material. There are some 10kV 1000pF caps out
there that have a fair amount of loss at RF and a fairly big temperature
coefficient, so as they get hot, the tuning will change.


What you want to know is how much current is flowing through the
capacitor. Then you can look up the capacitor ratings and figure out if
it will explode, melt, or work just fine.

Think about what that trap is doing, too. At frequencies above the
resonant frequency, any current will be flowing through the capacitor
(because its reactance is smaller, while the inductor's reactance is
larger), but, the current might actually be pretty small. Say you have
a 10-20 meter antenna with a trap. On 10m, you want the trap to "turn
off" the 20 meter extension, so it's roughly at the "end" of the 10m
dipole. That's where the current is lowest.

At frequencies below the resonant frequency, the capacitor's reactance
is higher, and more of the current flows through the inductor.

Cecil Moore wrote:
Barrett wrote:

Some one sent me an email and said these will do the job. Ceramic
capacitor disk 10KV/1000pF. Do you think these would work?


I don't know about those particular ones. Some ceramic
capacitors are meant to be DC biased for bypass service.
I once tried to use disc ceramic caps across my ladder-
line. They caught on fire because they were not rated for
AC service and lit up the night sky.

Someone told me the ceramic insulator was actually
trying to physically vibrate at the RF frequency and
friction heated it up.

That's basically what's going on. It's actually the ferromagnetic
domains doing the vibrating in the ceramic (i.e. there's no physical
displacement), but it's the losses in that vibration that's responsible
for the dissipation.


I don't know if your capacitors
are rated for AC operation.

A friend of mine used silver mica capacitors for his
traps and they worked fine.

Silver mica works fairly well at HF (assuming you stay within the
ratings).. mica is a low loss dielectric

http://cgi.ebay.com/68pF-6kV-Doorkno...QQcmdZViewItem

Good one., from eastern front....

Best regards. Bob

"Barrett" wrote in message
.uk...
Thanks all for your time and help. Now I have enough information about the
traps I can now look and read up and give it ago.

73 to all


"Owen Duffy" wrote in message
...
"Barrett" wrote in
. uk:

One last question. Is the diameter of the traps at different
frequencies that important and why?

They tend to be larger towards top band.

You really need to read a text that systematically develops an
understanding of the operation of a trapped antenna. It helps to
understand
the operation of an untrapped antenna.

Unfortunately, lots of articles in ham mags aren't very reliable, so you
will need to read many articles and try to understand the underlying
principles to filter out the misconceptions that find their way to
publication.

By all means, ask questions about things you don't understand... but your
questions seem more like guessing your way to a solution and plugging the
gaps as they become apparent to you.

Owen