WSKY567

That whole experiment was a total bust, lol. First, you were spot on about the Great Stuff. I had a little more time than I thought I would this morning so I did some investigating. The two ends of the PCV were solid with foam. I did an SWR test and was floored. 17:1!!!!! I pulled the antenna out of the tube and all of the foam in the center of the tube had degraded to goo along the inner surface of the pipe. No foam. Needless to say no more Great Stuff. Tested the antenna and still 17:1. Pulled the plexiglass spacer out from between the elements and Voila! 1:1.5. I don't know if the RF was riding the filaments of the plexiglass or if the plexiglass was acting as a dielectric increasing inter-capacitance, or both, or something else? I then tried some foam (like you get inside a case) and that was better but still bad, around 1:7. Next was masking tape only, which yielded 1:3. You nailed it, anything I did messed with the antenna. Still don't know the effect of the PVC tube as I had bigger fish to fry. The foam was just nonexistent so that was a systemic bust. So...... Enter controlled experimentation. One change at a time. Time to get serious with this little enigma. One thing that came up in Google was the material used in a tie wrap. I am going to try drilling two holes in a tie wrap and sliding that over the elements, only impacting the elements with the thickness of the tie wrap (capacitance) while providing the rigidity needed. Kelvar cord just went on the list of things to try as well. I have found that Google interprets RF transparency only in regard to RF loss passing through a material it does not consider interaction. I get it as most folks are only interested in getting a signal through a barrier. I am also not willing to wade through endless white papers to get the answers I need. Makes my head hurt. Can't express how much I appreciate the coaching you are providing. I'm confident you have cut years off my learning curve. Not sure when I will get back to the work bench but by Monday if not sooner. Right now it's time for a mad dash to work.

Sincerely appreciate that! Inexpensive experiments. The materials are nothing. The tools are killing me, lol. Saving grace is that you always have the tool. I added the foam in a few applications. Not by plan but because of the way the foam deposited in the tube with a lot of gaps using the can foam. I'm working today and tomorrow but first of the week I'll test the antenna specs. Next build, I'm thinking about using two end caps, drilling one for the coax exit point and using a little JB weld to affix the coax to the cap. Going to try to concentrate the foam to two points, top and bottom of the antenna just to establish a stable position within the tube. Obviously this depends on how the current build tests. If the foam causes too much deviation in specs I think I'll try two rubber disks to stabilize the antenna. One point where I'm lacking is understanding when to cut and when to add. Right now I'm starting long and cutting until I see an adverse effect. Watching the Tubers is not helping much so far. I'm convinced that half the tubers haven't a clue and the other half are engineers trying to impress me with their prowess. Net result so far is I'm wasting a lot of time on YouTube. One Tuber elaborated on a vector analysis of phase relationships which may be nice to explore down the road but he gave no sense of what is acceptable. Right now I'm simply interested in SWR, resonant frequency, and loss. I'm familiar with phase relationships in the audio world but have no idea of the ramifications on a carrier frequency. PS.... One big reason I'm "kicking butt" is that I'm retired and only work a couple times a week at a gun range to get out of the house. It's obviously winter so I have a lot of time to entertain myself with indoor hobbies. These radios are hitting the spot for that entertainment.

Final step: Bought 1" PVC pipe. (Actual ID just over 3/4") Filled with Great Stuff spray expanding foam insulation to secure antenna in tube. Put a cap on it. Left about 1' of extra length on bottom of PVC for mounting. Pig tail extends from bottom of tube about a foot. I feel no need to post a pic as it is just a chunk of PCV pipe. Now I will spend the next 1 to 3 days picking dried Great Stuff off my hands. Think I'll use the antenna for a field base station with a hand held.

Length of both elements are from the inside edge of the base. Width and connection points are from inside edges of the wire. These measurements are from the bare wire build. That one has a better SWR than the insulated build.

Ok, Short element is 6.5" Long element is 18.75" Spacing = 12.76mm Connection point = 14.54mm I put the antenna on the oscilloscope but due to the limited horizontal resolution (1ns), I can't get an exact frequency measurement but it is very close. I'm getting about 2.2 units and 462mhz is 2.16ns. I was testing for 462.500 MHZ.

That would be great!!! I'll grab some measurements tomorrow. I can't get the to elements exact (limits of micrometers) but I can get the connection point and spacing exact.

Wondered if the insulation would have an impact. An analyzer would be nice. How would you rig that up? Use another antenna to feed the analyzer as a receiver? I have an oscilloscope so maybe I'll tap the antenna at the feed points and see if I can get a decent resonant frequency read. It won't work well as a spectrum analyzer. If I do use another antenna as a receiver, that antenna may also cause variation in frequency, is that correct? I guess I could get a frequency generator and use that as a comparison but every option is $$$$$$$$. Not sure I'll make too many more antennas. It's fun to do but I don't see putting them to good use.

The first build, the one with bare wire was 1:1.2 but the second build with insulated wire was 1:2, so you read right.

A couple more pics of original build: Stand-Off or spacer Spacing at bottom of antenna and connection point

I'll go shopping at some point. Have to get a long drill bit anyway to get the LMR-400 through the outer wall. It would be great to have a rig I could tune that way. Something I would wait till spring to do as interference from things in the house can probably have as much influence as minute tuning. I sense that tuning below 1:1.2 is going to be very fine tuning. I put another pigtail on the original and it reads 1.2 on the low side and 1.4 on the high side of the band. For the first time I got a real good solid solder on the PL connectors. That 300W did the trick.

Ok, so I decided to start over. OooooPs. This time trimmed too much and ended up around 1:2 . I promised a pic. It doesn't look like much, but here it is: Have electrical tape on the bottom to keep the coax from moving around and electrical tape holding the plexiglass stand-off while the glue dries. Probably will just leave it on. On a brighter note have the soldering problem solved. Got a monster Weller D650 with 300 Watts of heating power. Solder is flowing like water. Beautiful soldering job. Might try a 3rd build just to see if I can do better but this one is solid.

Thanks! I like these. Trying to avoid the expense of the crimp and die set although I'm starting to rack up some expense trying to get a soldering gun/iron that will provide enough heat for the mass I'm trying to heat.

Appreciate this. I do have one I use for cooking. I have always enjoyed sweating copper pipe of all things. I'll have to practice a little to make sure I don't melt or burn off the insulation in the coax.

I'll check that tomorrow when I go back to work on it and let you know.

Soon my friend. As soon as I clean up my bench and the solder joints a little. Probably sometime tomorrow. It really doesn't look that special. Just a bent copper wire with a chunk of coax soldered to it, lol.