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Strange antenna results

R

radioman148

I just purchased an Sstran amt 3000. Instead of using the supplied wire antenna I tried my own vertical which I thought might work a bit better. When I first connected the vertical the results were no better. Then I noticed if
I pulled out the RCA connector just a bit from the transmitter and kept it connected on an angle instead of firmly connected to the sstran the results were vastly improved. I also tried using a different RCA connector in case my first one was bad & the results were the same.
Can anyone explain why a looser connection on an angle would work better than the plug placed firmly in the antenna socket? Could I be achieving some sort of ground that I didn't have before?
 
No electronics wiz kid here, BUT I have had the same experience with some connections on other items. You probably did achieve a better ground and thus the greater range.. I cant wait to get an AM xmitter. I currently have a great RAMSEY and I love mine.. I get great range and results.. Its a great way to run a PT15 fm station...
 
I've noticed that certain combinations of RCA connectors will short out if pressed in firmly, that is if the female opening is too small (now now!) and the plug has a "rivet" like expansion at the base of the pin, this expanded portion will short the socket if pressed firmly.
 
Thats right Radioman, RCA plugs do indeed short out sometimes. I used to have that problem with my very first "part 15" way back when: the RCA's shorted out to the mixer board; the sound got way better when I pulled them out a bit.

If you are having difficulty with the antenna: write me; I build the sstran antenna/parts.
Maybe your coil isn't right.
Carl @[email protected]
 
radioman148 said:
I Instead of using the supplied wire antenna I tried my own vertical which I thought might work a bit better. When I first connected the vertical the results were no better. Then I noticed if
I pulled out the RCA connector just a bit from the transmitter and kept it connected on an angle instead of firmly connected to the sstran the results were vastly improved. I also tried using a different RCA connector in case my first one was bad & the results were the same.
Can anyone explain why a looser connection on an angle would work better than the plug placed firmly in the antenna socket? Could I be achieving some sort of ground that I didn't have before?
Click to expand...

The performance difference between the wire and a vertical antenna should be negligible for the same length. Antenna routing relative to nearby ground or other conductive surfaces will have an effect on antenna tuning and performance. You will need to re-peak the trimmer capacitor whenever you change or move your antenna. The RCA plug includes a ground wire for the outer connection terminal. By pulling the plug out, you are likely disconnecting the ground wire. This will change the antenna characteristics a lot depending on where you connect the ground wire. If the signal increases with the plug pulled out a bit, then I suggest you investigate the ground wire connection. Sometimes the signal inside a house will actually improve with no ground connection due to the low RF impedance of the wall adapter coupling RF to the AC wiring and acting more like a "carrier current" system. RF will then be radiated by the AC wiring.

My experience with RCA plugs and jacks is that very old, cheap plugs and jacks did indeed cause bad electrical contact after many plug-unplug cycles. The modern versions don't do this. They have better diameter tolerance and better plating.

If you are seeking serious range, the solution is to use the base loaded antenna shown at: http://www.sstran.com/pages/sstran_buildant.html This antenna is is much more efficient than just connecting a whip antenna to the AMT3000 because the big loading coil on the external antenna is many times more efficient than the tiny inductors on the TX circuit board. The on-board inductors are fine for in-home broadcasting, but not for best range. These inductors are bypassed by switch settings when you set up the TX for the base loaded antenna.

PhilB
 
I've looked at the Sstran website & seen the antenna that Carl designed--especially the new one which he recommends sticking in the ground. My problem is I live in a very residential area with homes close together.
The bad news for me is I have no good place to put the antenna in the ground. Anyplace I put it would be either too close to my house or too close to trees. Can this antenna give good results on the roof?
I have a tower which holds a 3 element ham radio antenna.
I know it's not legal but I ran a 10 minute transmission from the Sstran through this antenna for experimental purposes only on a clear frequency during the day on the extended band.
I achieved about a quarter of a mile radius maybe a half mile in some directions.

Given my yard limitations can I expect to get considerably better coverage with a coil antenna stuck in the ground? I'd be very happy with a one mile radius but I don't know if it's possible with my yard limitations.
 
For PhilB

Over 30 years ago when I ran my first part 15 in college I found that if I dropped about 100 ft of bellwire out the window and ran it strategically around the building I could easily get a half mile. So you are right about a long wire working as well as a vertical if placed correctly.
 
radioman148 said:
Can this antenna give good results on the roof?
I have a tower which holds a 3 element ham radio antenna.
Given my yard limitations can I expect to get considerably better coverage with a coil antenna stuck in the ground? I'd be very happy with a one mile radius but I don't know if it's possible with my yard limitations.
Click to expand...

You will get much better range with the base loaded antenna. You can mount it on your roof with a heavy gauge ground wire down the outside of the building for RF ground and lightning protection. The ground wire should be connected to an 8 ft copper-clad electrical ground rod. You can add horizontal radial ground wires fanning out from the ground rod for additional range.

You can also mount the antenna at ground level. I definitely recommend the ground rod and radial ground wires. You should use as many radials at the longest length possible for a ground level installation.

You could also mount the base loaded antenna on top of your tower. Don't mount it part way up. It's not good to have the antenna parallel to a nearby grounded tower. With the antenna at the top of the tower you probably won't have easy access to the transmitter for fine tuning. This is something to consider. If you can access the transmitter at the top, then you are OK. The tower should be well grounded (ground rod and radials).
 
Assuming I cannot put in on the roof, do you still think I'll get better results sticking it in the ground within 10 ft
of my house? I'd rather move it farther away but I can't.
Seems to me if it's that close to the house I'm going to lose lots of signal coverage in at least one direction with the building in the way.
 
radioman148 said:
R Fry, Is it in your opinion then to just use a 3 meter wire?
Click to expand...

IMO the best approach to minimize potential FCC problems with Part 15 AM systems is to strictly observe the 3 meter limit allowed for the maximum radiating length.

Physics shows that this includes at least the length of the conductor considered to be "the antenna," the conductor from the transmitter r-f output terminal leading to a loading coil (if used) or to the "the antenna" (if not), and the entire length of the conducting path from the transmitter ground terminal to a true r-f ground buried in the earth (not just the short wire next to the transmitter that some define as the entire ground lead).

From reading posts on Part 15 AM boards apparently many operators are using "elevated" systems with long, radiating ground conductors and have not been cited for that by the FCC. OTOH, some have.

The decisions about a given installation are up to each person, but best made with a clear understanding of Part 15 rules, knowledge of the physics of these systems, and their possible enforcement risks.

//
 
Well if I put the antenna in the ground as you recommend and being that I can only put it near my building--about 10 feet away, I'm going to get virtually no distance on the other side of the building am I?
 
radioman148 said:
Well if I put the antenna in the ground as you recommend and being that I can only put it near my building--about 10 feet away, I'm going to get virtually no distance on the other side of the building am I?
Click to expand...

That could reduce the signal somewhat in some directions, and maybe increase it in others, especially if the building has vertical conductors (downspouts, electrical wire, aluminum siding etc.

But MW signals travel through many structures without much loss. Otherwise licensed broadcast stations would be a lot more affected than they are.

In your case you'll have to make the best of what your circumstances permit, I guess. You should be able to cover your house and lot, and probably more -- which is about all one can expect from a compliant Part 15 system.

//
 
I can already cover that much area with the 3 meter supplied wire mounted inside my house.
So if I can't expect any better with a coil based antenna outside, I might as well not spend the time or money.
 
If you use a low-loss coil tuned to system resonance, and a good r-f ground, then other things equal, you will get better range than when using a 3-m wire, a poor r-f ground, and a lossy/incorrectly tuned coil.

//
 
radioman148 said:
How much extra range do you think I would get in a residential area?
I realize it's just a guesstimate.
Click to expand...

All we can say is that you will DEFINITELY get better range when compared to a 3 meter wire and using the internal tuning coils. A side-by-side comparison should yield about 25 times greater range. So if you get 100 ft with the wire antenna, you should get about 2500 ft with the base loaded vertical. This only an estimate for comparison due mainly to the better efficiency of the base loaded antenna. Actual range depends also on how well the antenna is constructed and how careful you are tuning it. Also your ground path is very important for range.

Bottom line is the base loaded vertical is definitely the way to go. What range you actually get with the antenna at ground level and 10ft from your house is really unknown. There is no way to predict the results and whether they meet your expectations.

Phil B
 
Phil--

in your opinion would the antenna be likely to work better in the ground next to my house than it would if I mounted it on the roof about 30 ft higher in the clear?
It certainly would be easier to mount on the ground. If the difference is insignificant or better on the ground it would be much easier to do that.
 
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