I am trying to find/build a simple antenna to transmit in the 20-30 MHz
range. I have an HP RF signal generator with an N-type RF output
connection. I purchased an antenna from RadioShack but it only goes
down to 121 MHz for transmitting.

On the receiving end I have a scanner. I looked up info online for
building a zip antenna for receiving (I take it the built-in antenna
with my scanner, a Realistic Pro-2021, will not be adequate), but I
can't find any simple info on the best way to construct a simple Tx
antenna for 20-30 MHz that I can plug into my RF signal generator. Any
advice?

In case you are curious as to what I'm doing, I'm using the signal
generator to send out sine wave audio tones to various frequencies (as
in the Spiricom experiments), and have been successful at frequencies
above 121 MHz, but I don't have an antenna that goes below that
frequency.

Thanks in advance for any help.

PS I was able to pick up 121+ MHz frequencies on my scanner with the
built-in antenna even though I had to constantly readjust my Tx antenna
to transmit at various frequencies. Why did my scanner pick up those
frequencies without me having to readjust the antenna length, and will
a SWR with its own antenna be sufficient for picking up any SW signals
I transmit, or do I still need to build a receiving antenna?

grav