Hello all,

I was just doing some more reading and came up with a few more
questions. It seems that I failed to take into account adding a
harmonic filter between my antenna and RF amp. However, in regards to
low power transmission (100W), would I still need harmonic filters?

I saw a design for a 1kW AM system and it had several huge harmonic
filters. I think the total weight was about 60 lbs. I want to keep my
system as small as possible.

Is there an alternative setup to get rid of the harmonic filters?

Thanks!

use a decent radio and you shouldn't need extra filters.

"CD" wrote in message
ps.com...
Hello all,

I was just doing some more reading and came up with a few more
questions. It seems that I failed to take into account adding a
harmonic filter between my antenna and RF amp. However, in regards to
low power transmission (100W), would I still need harmonic filters?

I saw a design for a 1kW AM system and it had several huge harmonic
filters. I think the total weight was about 60 lbs. I want to keep my
system as small as possible.

Is there an alternative setup to get rid of the harmonic filters?

Thanks!

What sort of system are you building? Amateur radio? CB? Pirate AM
broadcasting?

Roy Lewallen, W7EL

CD wrote:
Hello all,

I was just doing some more reading and came up with a few more
questions. It seems that I failed to take into account adding a
harmonic filter between my antenna and RF amp. However, in regards to
low power transmission (100W), would I still need harmonic filters?

I saw a design for a 1kW AM system and it had several huge harmonic
filters. I think the total weight was about 60 lbs. I want to keep my
system as small as possible.

Is there an alternative setup to get rid of the harmonic filters?

Thanks!

It's a radio system use for missionary work in third world countries.
We are not too worried about breaking FCC rules since we will be using
them outside the US. My concern with the harmonic frequencies is mainly
protecting the transmission system and also not interfere with other
sister stations. From what I've read so far, some harmonic frequencies
might couple to the transmitter input and that can affect the output.

I guess what I really don't know about is how exactly harmonics affect
the system... and if a DSP based transmitter would also need these
bulky harmonics filter.

Hmm..also, wouldn't the harmonic filters normally be part of an antenna
tuning unit?

"CD" wrote
My concern with the harmonic frequencies is mainly
protecting the transmission system and also not interfere with other
sister stations. From what I've read so far, some harmonic frequencies
might couple to the transmitter input and that can affect the output.

The usual mechanism is when the 2nd harmonic of an active transmitter (F1)
mixes with the fundamental of a nearby station on F2 to produce an IM
product at 2*F1-F2. This can occur in a nonlinear output stage of F1, and
harmonic filters normally have no affect on the in-band IM product that is
generated.

The control is to filter the external fundamental signals from entering F1's
output stage via the antenna connection, so they are not present there to
generate spurs.

Hmm..also, wouldn't the harmonic filters normally be
part of an antenna tuning unit?

It is more closely connected with the harmonic "signature" of a given tx,
and so is usually supplied as part of the tx system. The tx OEM has to
certify that his tx meets specs for harmonics and spurs, and couldn't do
that unless the performance of the filtering network was under his control.

RF

Visit http://rfry.org for FM transmission system papers.