RFB was there guiding me through the setup of a carrier current system, and I had crystals for 570 and 670 kHz, also believing that lower was better as many think.
The first baffling thing was that my system would not match into the 220VAC power, which is the classically normal way of doing CC. I got ridiculous standing waves and was unable to match up.
Turning to the neutral injection method it matched up so well that I almost never needed to re-tune, except when prolonged dry or unusually wet conditions occurred.
But I ended up on 970kHz, partly because it was more out-in-the-open than the lower frequencies, but also because the system efficiency went way up at this mid-frequency location. Much less power needed to achieve good results.
Neil, are the ground radials bare or insulated? What gauge? Thanks, John
What a great completed project! I'm interested in how things changed over the winter when the leaves dropped around the antenna, and the results of any range tests you might have done.
Also, how did you modify your Ramesy kit transmitter for high efficiency, a different final?
This reminds me of an antenna I saw that uses hardware store piping parts, like a section of wide PVC for the coil, reducers and couplers on each end, and a 10 foot copper water pipe for the antenna, more expensive than what you just built with found pieces.
John,
The wire is 12 gauge insulated. No special reason for using #12 except that's what I had on hand.
Nate,
Here's a link to a thread in which I report my observations as the weather and seasons change.
http://www.part15.us/blogs/radio8z/weather-effects-antenna-performance
The AM-25 modification involved removing the final FET and the output filter network and replacing this with a BJT and new filter toroids and caps. I found that the type of core Ramsey used was lossy. These changes boosted the output power quite a bit while maintaining the legal 100 mW input power. I will try to dig out my notes on this and post them later.
I also found by experimenting that PVC is not a good material for a coil form. It absorbs RF power and reduces the coil Q and output power to the antenna. In fact, the original weather shield was a PVC pipe and this noticeably reduced the output power from the transmitter to the antenna. This was replaced with a salvaged ice cream bucket and things went back to what they were with no shield installed.
Neil
TNX Neil
Nate,
I had forgotten that I had posted the modifications I made to the Ramsey AM-25. The link is below. The thread is a bit long and there were documentation errors but the attached PDF explanation for "Mod 4" gives the best results.
I believe I also change out L4 but I am not sure. This has been off my bench for a while and I will have to look at the unit and let you know.
http://www.part15.us/blogs/radio8z/modifications-increase-efficiency-ramsey-am-25-transmitter
Neil