Need suggestions to reduce signal pick up of coax cable.

I was wondering something along similar lines, and so wondering the effect of an attenuator on the receiver input (as posted earlier), and if the noise went down disproportionately.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

Nope, I ran an 18 gauge twisted speaker wire. From a previous post,

With my 200+ft of coax I received 13 stations. One had a signal strength of 5.5 S units, 2 had 3 S units, 4 had 1 or 2 S units, and 6 had zero S units but were audible. Ran my 237 ft of twisted speaker wire, connected it to the 50 ohm input of my radio through a 1 to 1 transformer. I now only have 4 audible stations (vs 13) 3 with Zero S units and 1 that bounces up to 0.5 S units. Hooked it up to the BOG and it works, However bad day for any testing, lightning all around me. My conclusion, twisted speaker wire is a winner with respect to signal ingress. Mikek

Well, no, that ignores on your grounding. The coax long line was taking in signal on its shield, and because of ground-at-both-ends, that made a ground loop. The inner conductor was doing inductive pickup (it's an accidental transformer) of pickup by the loop.

Any scheme for making a much lower ground loop current, like ground-isolation at both ends, would make the coax a good receiver-of-small-signals shield. Tricky possibilities include putting power onto the coax and preamplifying at the antenna end, which would help the impedance issue.

I tried it without ground on either end and an isolation transformer.

Quite a clear demonstration of the directionality of the "BoG" which I initially assumed was simply strung out on supporting poles a few feet above the terrain as per the standard Beverage antenna setup.

Can you confirm that your BoG is simply 300 foot of insulated wire laid straight onto the ground with its far end terminated with a 250? non inductive resistor connection to a grounding rod?

I had to look up the word "Vactrol". :-)

I'm not so sure adding loading coils will improve your BoG antenna. Using loading coils to make an antenna look electrically longer reduces efficiency. A loading coil to bring a short whip antenna to resonance to improve its matching, results in greater current flow which increases the I squared losses in both the coil and the whip and ground resistances.

Far better, I'd have thought, to extend the antenna length if you can, especially when the directional properties seem to be essentially a function of actual, rather than electrical length in this case.

Still, I have no expertise in the matter of such end fed long wire arrays due to lack of real estate in which to lay one out, so I may be overstating the loading coil issue.

--
Johnny B Good

It is 300ft + /- a few, the wire is army field wire like this,

Note it is actually 2 conductor wire, but I have tied them together at each end. (I have thought about removing one of the wires, if I got good info that it would make any difference I would do it) I laid it on the ground as best I could, This is somewhat of a pine woods, so lots of pine needles and decaying vegetation on top of the dirt. I have 3 non inductive resistors in series (I didn't have the proper value) with a pot across them for the termination. I expected to make adjustments and test, but since I started we have had rain and lightning storms around, makes for tough listening. A 5 foot copper pipe driven in to the ground at each end. For the transformer I used a 35T0501-10H toroid with I think? 8 and 16 turns. This is probably not a good design, I started with wanting to be able to receive 200kHz beacons, so it has more turns than needed. I have the recommended Material 73 binocular cores on order to make a better transformer. I don't have an ideal property, There is a a wooded area behind my house. I spent several days clearing brush and plants for a straight line through the woods. Part of it is a drainage area and gets water that drains through when it rains hard. The wire is straight, but terrain is not level, the wire follows the terrain.

I learned about them 15 years ago when I built a rotatable Flag antenna with variable termination. I still have it and the power supply I used for the adjustment.

I am a little perplexed by the info I read that says the BOG is a inefficient low signal antenna. I'm not finding that. If you look at the video again, you can see the S meter needle shows only 1 to 1- 1/2 less S units than the 150ft longwire. Re: the loading coils, here's where I got that.

He does not mention inductors specifically for a BOG only a beverage, and I think being on the ground already slows the VP. I don't think efficiency is something to be to worried about with a BOG. The article even references low Q inductors. I'm thinking a BOG will need less inductance than a regular beverage to get to the optimum. Anyway, it's an experiment for the future.

Surge impedance is mentioned in the article, is this different than just plain impedance?

I'm boxed in on one end by a neighbor's fence and by a 5 lane road on the other.

I've been searching for more info, but didn't find any.

Mikek

Power vs. noise match s an issue at UHF and up, but not an issue at 1 MHz with huge band noise.

snip.______________________

You are killing yourself by laying the antenna on the ground. Try picking it up off the ground by 10 feet or so.

Keep the wire you have and tie both leads together on both ends as you have done. Take the far end to ground through a few hundred ohm carbon comp (old school) resistor. Nothing about this antenna is in any way critical.

Are you interested in the tropical bands (60, 90, 120 meter bands) ?

For medium wave (200 to 600 m) reception, the Beverage should be at least 600 n long,

Surge impedance is a rather old-fashioned way of saying what we call Zo or the transmission line characteristic impedance.

An open circuit long transmission line reads infinite ohms on a plain 'ol DC VOM but to a step (aka surge) in voltage a brief current will flow which divided into the step voltage would equal the surge impedance. HTH

piglet

Lack of ingress could also be due to higher losses :)

Is the twisted speaker wire insulated with PVC? PVC is remarkably lossy even at LF/MF. CAT5/6 UTP has the advantage of low loss dielectric, the disadvantge of high resistance thin conductors can be offset by paralleling pairs.

piglet

Is there a way I can measure the surge impedance of the Bog at the end of my tested pair? If not, how can I do this with portable home brewed test equipment at the BOG wire start? The only portable test equipment I have is an MFJ-259. Thanks, Mikek

I'll leave this as a possibility, with the caveat that, I'm surprised at the high signal level of the supposedly Lossy BOG antenna. The two don't seem compatible.

CAT5/6 UTP has the advantage of low loss dielectric,

I'm working towards an antenna system with four phased antennas using Cat5 to carry the signal and DC for amps. I have got a mixed messages about shielded Cat5, some say grounding a shield is no necessary others have done it.

I hadn't thought about paralleling a couple pairs, that would give approximately a 50 ohm impedance. Interesting.

Actually I did thing about paralleling, but for the DC carrying wires. Thanks, Mikek

That is exactly what the MFJ-259 is built to do!

I do not have one but I think the only MFJ-259 limitations may be that it doesn't go lower than 500kHz and that it won't read impedances higher than 700 ohms - in all other respects you should have a great tool for the job. I think the MFJ manual even mentions Beverage antenna somewhere?

piglet

OK, so surge impedance is another way to say characteristic impedance of the cable. I measured it a 1800kHz, (that's a low as it goes) and I get just a little over 500ohms, but the scale is very crowded up there so It could be 400 to 700ohms. This is with a 250 ohm termination at the end of the wire. I also have an LCR meter, I measured at* 120Hz, 1000Hz, 10kHz and

100kHz, got about 660 ohms on all but 100kHz then it said 12,000pf capacitance. Again, with a 250 ohm termination at the end of the wire. *those are the only choices

I had a time constraint, I should have looked for a resonance also, next time. This evening I'll add some inductance to the MFJ-259 oscillator, and get the frequency range so I can cover 500kHz to 1700kHz, and retest. As I know it, if I get that end termination to be the correct value then I can adjust frequency up or down and the R measurement will stay constant. I don't know how any impedance of the line will affect that. That could take several 600ft trudges through the woods getting that adjustment right. Is there a way to take several measurements at different frequencies and calculate that. Thanks, Mikek

Maybe I can bring out a couple of wires from the R meter on the MFJ-259 and measure it on my digital meter. so I can see the changes.

I've been looking at TDR videos and one has a pulse generator circuit. I'm not above carrying my scope out in the woods dragging an extension cord or 3. Mikek

No, I'm doing just fine, a little ache in my knee, but otherwise OK. The antenna is good also. Do some reading on BOGs and beverages. Here's a start, >

I think the biggest receiving advantage is that being on the ground reduces the VF, making the antenna seem longer than it is. It also is less susceptible to noise. All the info I get says it is a low signal antenna, but I only note

1 or 2 S unit difference. However last night I measured the impedance of at the radio end of the feedline and noted about 130 ohms. S I rewound my isolation transformer and now the long wire and BOG are about the same. I think my BOG may have a little higher output because, It is in a wooded area with lots of dead vegetation and pine needles, so I'm not really directly on the dirt. I may get out and clear a line several inches wide and see how getting it right on the dirt affects operation. I'm still working on a way to get an actual measurement of the wires impedance, it is to high for the MFJ-259 to measure accurately. I did get the MFJ-259 frequency down so I can measure in the AM broadcast band. I had to use a tapped inductor and use a switch to do it in two steps. About 480kHz to 1Mhz and 870kHz to 2Mhz. Mikek