That was an interesting article, especially the bit about the point made in regard of the negative gain not being any impediment in the frequency range of these long wire direction antennas due to the limitation imposed by the high background QRN levels typically experienced in this part of the radio spectrum.
The only serious omission I thought, was reference to its close cousin, the Rhombic array, a sort of balanced version with actual gain making it suitable for transmitting signals as well as receiving them, unlike the Beverage which is suited only for receiving signals in that part of the radio frequency spectrum typically plagued with high levels of QRN.
Not really, that was "hard" enough IMO. :-)
I think your posts could be a lot more persuasive if you could only learn to lighten up a bit. You can achieve more with a kind word and a gun than with a gun alone (especially when there's no justification for "Going in, all guns blazing."... IMO).
You forgot to add "IMHO" or "IMCO" or just "IMO"... imo. :-)
Again, you forgot to add the all important "IMO". You seem to be rather forgetful about making it clear that your sage comments are just opinions. Perhaps you're presuming on your audience a little too much to insert all those missing "IMO"s that your postings are so woefully lacking. That's just sheer laziness, IMO.
Why? It can be any convenient impedance ranging from 100? through to
1200? (or even higher - let's not allow ourselves to be limited by 'mere convention'). :-)
I suspect you decided this random impedance value because of it being the standard 'notional' impedance of balanced transmission lines used by the telephone companies and used to calibrate the 0.775v 0dBmW reference on LMS kit and adopted by the audio industry for all those VU meters that adorn recording studio mixing desks and domestic tape recording equipment et al. I do believe this statement was crying out for yet another "IMO".
That's a rather sinister interpretation (IMO) of the point of AMDX's post which I think (also IMO) is more a cry for help from others more experienced and/or knowledgeable with/about the problems he's having with his (not unreasonable, IMO) quest to build a directional MF antenna for his DX SWL activities.
Only in your opinion (considered or not). :-)
In my opinion, I think AMDX is simply being a little more ambitious than the more typically laid back "DX SWL" enthusiast. He's been asking all the right questions about a subject that can seem more 'art' than 'science'.
op, i think someone else already said this but your issue is not the coax.
Your issue is the input circuit to the radio.
Make sure the input terminal that you connect the shield of the coax to is a good ground for the radio, I don't mean you need a ground rod there I mean it must be the RADIO ground.
There has been a lot of talk about my radio. I don't believe the radio is the problem. I'm using an Icom R-71A, driving the 50 ohm input.
Connecting a 75 ohm cable to a 50 ohm input for receiving is not perfect, but in most cases it won't be noticed. I'll be running a twist pair maybe today, That is pretty close to
100 ohms, I will try that with and without a 2 to 1 matching transformer.
A BOG antenna has an impedance from 200 to 350 ohms. A transformer matches the antenna to the feedline. I may or may not match the feed line to my 50 ohm receiver input. I may inductively load my BOG anf that can raise the impedance much higher. Calling for a different transformer.
Hi Johhny, I understand your wanting change to Phil, but he has been here a long time and with his deficient interpersonal skills. No amount of feedback has made any difference. And besides if you did correct his way, you'd spoil all the fun! Mikek PS. IMHO!
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 225 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 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
** "amdx" is an incorrigible troll with a one track mind, has been for nearly 20 years. Be a crime to encourage him.
** I did not forget - demonstrable facts need no such qualifications.
** What is NOT absurd about it ??
There are way to many absurd people posting ratbag notions here.
You seem to be rather
** I see you cannot tell the difference.
Makes you a "troll feeder".
Where does it say " crackpots welcome" here ??
** My point was about the need for "well balanced" - 600ohms will likely work well.
** He obfuscates, fails to reaveal his purpose and trolls on a NG that has nothing to do with his mad obsession so he can waste the time of others.
That's sinister enough.
** I have no idea what "amdx" is really after and he never reveals it.
He ought to find a NG with like minded folk and post there.
** Shame how a twisted, balanced signal line does not work unless the termination is well balanced.
** Now you sound like a lunatic, a couple of grades up from a mere ratbag.
Since using a CM choke on the _mains_ cable changes the coaxial leakage, it is not just a question if the coax cable in isolation, but the whole system seems to have an effect. Knowing the whole system makes it possible to give meaningful comments.
After installing a twisted speaker wire, connecting it to my 300ft Beverage On the Ground, and with an approximately 250 ohm terminating resistor. I tested a little last evening. Here's a short video of one frequency while I switch between the BOG, Longwire and Mini Whip antennas.
This WCKY 600 miles N of me, which is approximately the direction the antenna points.
You can clearly see the BOG has directional characteristics. Still more to do, rewind the transformer with a different core and ratio, install a vactrol to allow remote adjustment of the termination and install loading coils to make the BOG look longer.
Have you ever measured the input impedance vs frequency of a wide coverage receiver input? I have and it's awful. If you have an MFJ-259/269 or equivalent analyzer, it's easy to do. Don't worry about blowing up your receiver RF stage. The MFJ analyzers don't generate very much RF. You might be lucky and find that it's somewhere near 50 ohms at 1MHz, but I suspect that it will not even be close.
Incidentally, I've also measured the output impedance of various transmitters (using a different method) and found a similar problem. The output impedance is also nowhere near 50 ohms.
I do it all the time. If lazy, I just ignore the 0.2dB mismatch loss. If I'm trying to make accurate measurements, I use a minimum loss pad (-5.71dB):
I hope you mean CAT5 cable. It should work if you do everything possible to keep the line balanced. That means fairly straight runs, wide curves, and keeping the cable away from objects. The problems are usually keeping the line balanced when it goes through a hole in the wall, or when just laying on the ground. At 1 MHz, you should be ok with being a little sloppy.
CAT5e and CAT6 have a big advantage. The cable has 4 pairs of wire, all of which are about 100 ohms, with different twist rates to minimize crosstalk between pairs. They do this with slight changes in the wire gauges. My failed plan was to build a 4 element doppler direction finder with no electronics in the antenna assembly. Maintaining balance proved to be difficult, so the design reverted to using 4 coaxial cables, which was both more expensive and messy because all 4 cables had to be cut from the same roll. We eventually convinced the customer that some electronics in the antenna was necessary.
However, if you don't need direction finder type precision, CAT6 still might work for a directional AM BCB antenna project. Something like this: but with no remote RF amps and using CAT6 instead of coax.
Good luck.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Tuning a receiver input for optimum noise matching will nearly never happen at max. power matching, and power matching a generator will guarantee an efficiency < 0.5.
200 ft of coax will introduce losses by itself. One solution may be to add a preamplifier at the antenna to drive the coax. Add matching network at the receiver as needed.
Very impressive reviews, including a few by operators who rated it better than the professional/commercial communications receivers they were using alongside of it. The pictures suggest the use of a steel case so any thoughts of it allowing stray high field strength signals leaking past the input screening can be pretty well set aside.
However, that doesn't preclude the possibility of mains borne interference being conducted into the receiver via its power supply connections. Testing with a 12v SLA is an effective way to remove such potential interference sources from the equation. Not only does it eliminate ingress via the power supply connections, it also eliminates the possibility of interference being conducted onto the outer braid of the co-axial feeder where it can then reach the antenna feed point and so appear as an interference signal received by the antenna.
Very true, even in the case of a transceiver where it is of some significance to the Tx output filter, feeding a 75? line from a 50? filtered Tx output is normally not that much of an issue in practice (especially if a high vswr protection circuit has been included).
If you're referring to the turns ratio of the matching transformer, don't forget that a 2:1 turns ratio results in a 4:1 impedance transformation ratio.
Conventional transformer winding construction practice for mains and audio frequencies doesn't work so well at MF and HF frequencies due to the leakage inductance issue so such transformers are normally made up using bifilar and trifilar windings (perhaps even quadrifilar and quintifilar in more extreme cases) to minimise leakage inductance. The consequence of this is you rarely see such MF/HF transformers used to obtain impedance ratios outside of the common 1:1 and 4:1 options.
The classic balun transformer used to connect a 75? co-axial feeder (orthogonally) to the 72? centre fed half wave antenna is a trifilar wound 1:1:1 auto-transformer with all three windings in series phase aiding. The result is an auto transformer with two taps at one third and two thirds the way along from either end.
Working from left to right, the connections used for the antenna are LHS and Tap#2 with the feeder braid connected to Tap#1 and the co-ax inner to the RHS end connection. This provides antenna connections that are balance with respect to the braid connection (centre tap of the section between the LHS and Tap#2) and a 1:1 turns ratio between the feeder connection (Tap#1 and the RHS connection).
If you're using a centre fed folded dipole with a 300? feedpoint impedance, you could use an even simpler bifilar wound balun with your
75? co-axial feeder.
A better option may be to replace that 100? speaker wire with a 300? balanced feeder connected to a bifilar isolating transformer which provides a galvanically isolated link to a conventional 2:1 bifilar wound balun feeding the Rx antenna socket. If you can arrange for the feeder impedance to be 200?, the Rx will see a 50? impedance instead of the 75? in the 300? feeder case. However, the exact impedance value as you stated before, is far from critical for an Rx only setup.
The real benefit of using a balun and isolating transformer in this case will be to remove galvanic connections between the feeder and the station and antenna grounds and thus attenuate any interfering signals which may be polluting the station's local grounding point from travelling along the feeder as a common mode signal voltage to be injected into the antenna connection.
Mirroring the 1:1 isolation transformer and 2:1 balun setup at the station end will provide even greater attenuation to any such interference arising on the station's local grounding point (a balun will be required regardless). In this case though, you'll need your balun's unbalanced port to be a much higher impedance than the 50? or 75? impedances used at the station end of the circuit.
It's *so* not easy to achieve all of that in one step that I'd recommend the use of a third transformer to translate the notional 75? output of the balun into either a 300? (simple 2:1 bifilar wound auto-transformer) or else a 675? (3:1 trifilar) impedance match.
Attempting to get a better impedance match with non-standard broadband matching transformer ratios is unlikely to improve the situation. As is so often the case, compromise rules the day. Impedance matching in this case is secondary to achieving a galvanically isolated balanced transmission line setup to minimise unwanted signal pick up. Since the impedance of the Beverage antenna is expected to lie somewhere between
300? and 800?, it seems to me that you'd be better off testing both 2:1 bifilar and 3:1 trifilar transformers and choosing the least worst one.
Keep in mind that if you're going to replace a co-axial feeder with a balanced line feeder, unless you're using shielded twisted pair cable, you'll need to support it clear of any ground influences that might upset the balance, particularly true with the classic 300? ribbon cable transmission line. Regularly spaced support posts with insulated carriers to keep the ribbon cable at least a foot or so clear of the ground and any patches of long grass should suffice, not forgetting to transpose at every supporting point through a 180 degree rotation for good measure.
If you're using a high enough number of supporting posts along the line route, it might be better to transpose through either a consistent clockwise (or anti-clockwise - pick one or the other and stick to it) 90 degrees rotation at each support point along the route. If eliminating unwanted signal pickup is the name of the game, then transposition isn't optional, it's demanded (at least in the case of open wire or ribbon cable feeders).
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