Does anyone know if use of PVC pipe to encase transmitter and antenna within is a bad idea?
My concerns are signal propagation and interference from the PVC itself.
Considering building a transmitter stick out of a decent sized piece of PVC. Say 10 feet in length. Transmitter and gear are within the PVC pipe as well as the large wire antenna. Ends are capped and sealed.
Audio and power feeds available through drilled connector ports.
Idea is to have this ready to go stick and be able to walk it around and mount it instantly with various methods (hooks and connectors also bundled on the PVC pipe).
It's for "field testing" but could see this becoming a series of signal repeater nodes (given I can find all pieces that will fit in standard system pipe).
As stated in your other thread, THIS site has a perfect little unit you could build. It is the first unit on the page and doesn't use any PVC pipe at all, which would be better anyway than to encase the radiator (wire or whip) inside a PVC pipe. The author/builder notes that the radiator rod is just a salvaged fireplace screen rod and is a little short even for the 219 3 meter length limit, but that does not mean you cannot substitute that short fireplace screen rod with a 102" CB whip.
RFB
I wouldn't be afraid to encase the transmitter and possibly the loading coil inside a PVC pipe but encasing the antenna would make me nervous.
check out this thread though. the last response thinks PVC does not attenuate at HF.
https://www.eham.net/ehamforum/smf/index.php?topic=38828.0
"PVC does not have any loss til you get to VHF and above frequencies."
I see lots of plastic for all sorts of antennas out there. Unsure of exact type of plastic, but probably the most common thing for wifi and other 2.4Ghz and above transmitters. (That's where I got the idea from)
Wondering what sort of losses if any. Always something to consider..
A problem with PVC or any plastic pipe is the weight of the pipe will tend to make it difficult for it to be self supporting in the vertical direction.
I once built a coaxial co-linear antenna for 2 meter work and the smallest diameter pipe which would self support was 1-1/2 inch PVC.
Someone here once suggested using a fiberglass pole with the wire inside. The strength per weight is higher than PVC.
Maybe consider a fishing pole with the wire going through the loops?
"Maybe consider a fishing pole with the wire going through the loops?"
Good idea, cept those fishing poles with the loops are often metal loops, which might produce irregular inductive effects especially when the whole works is doused with rain water or collects snow (if environment conditions presents those factors).
Find a fishing pole with nylon or heavy plastic loops. Those metal ones will in effect create small chokes along your radiator wire.
RFB
I was thinking about 3-4 inch PVC and supporting the pipe with weighted down tripod.
3-4 inch was size to fully enclose transmitter and other gear in the pipe as well as the antenna.
Not incredibly hard to transport, but perhaps not totally ideal.
It still seems like that a 10' hunk of 3" or 4" PVC is way heavier and unwieldy than what you need. If you used a much shorter length (like 1 foot) with endcaps to house the just the transmitter; then glue in a female fitting that you could screw in a 102" whip antenna and another fitting on the bottom for power and ground connections. This would be much more portable.
Well, the 10ft piece seems to be hard to manage. It's a valid point.
Concept is a system that is fully contained with minimal external connectors, if any being used (antenna port maybe, perhaps external 12v power for charging the stick). Most of the length is to house a full wave wire antenna.
I am on the fence over more rigid whip antennas. Find them bulky in length and since so thin often visually lose track of them when moving gear around. Which ends up with whip smacking into things and even getting slightly bent.
If I reduce the wire antenna length, then lesser lengths of PVC become viable. Question is with a wire antenna, how much a reduction to a 1/2 or 1/8 antenna length will make on signal strength.
Other evolving idea is to divide the transmitter and associated hardware into it's own enclosure pipe (example: 1 ft length pipe with much wider diameter). Then on the top of that enclosure provide the antenna connector to interface with whatever antenna. Could see one pipe connected to other via a short coax jumper.
General concept beyond field testing is for installations that are blended into environment. Think urban/suburban front yards. Places where an outright equipment box and whip would stand out, might cause curious to touch or even steal such.
PVC is invisible, has no scrap value and can be blended easier. Most notable example would be in conjunction with existing flag poles.
"I am on the fence over more rigid whip antennas. Find them bulky in length and since so thin often visually lose track of them when moving gear around. Which ends up with whip smacking into things and even getting slightly bent."
You could make a sectioned whip or radiator element by having threaded ends and simply screw the two or three sections together, and unscrew them when time to move the works.
RFB
@RFB, do you know if anyone sells sectioned 3m whips?
Unsure if a DIY project like this is doable. Glad to follow plans if available. I don't do any real metal working (unfortunately).
...All the more interesting because if you scroll down you'll find a copper pipe loop antenna (magnetic as opposed to electric). I wonder what kind of range it would have.
The field strength of a loop antenna depends on the area enclosed and the number of turns and I don't recall the exact relationship but a while back I looked up the equations and did a back of the napkin calculation for a loop with a 3 meter circumference operating at 1600 kHz.
The calculation showed that about 300 turns of wire would be needed to get a FS about the same as given by a 3 m loaded vertical at 80 mW input. If this is accurate then the self inductance would be a problem.
It could very well be that I erred in my calculation and in doing so missed a chance for fame and fortune so if anyone wants to check this have at it because I could be wrong.
Neil