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Re: [IRCA] How to phase BOG's? (Jim Glover)
Jim...a few comments about your test and my experiences.
First of all, the fact that when you placed your hand on the rx and the signal level went up significantly raises all sorts of red flags. I have been DXing from the truck or car using BOGs, Bevs, low Bevs and mini-Bevs for two decades and the only time I have ever experienced that is when the cable from the phasing unit to the rx has been loose or damaged. Most of this DX has been with the rx connected to the vehical battery by the cigarette light connection or accessory connection.
Currently I am DXing domestics using the E-1 sitting in my lap propped up against the steering wheel. It is run off its own batteries and the antenna input is the cable coming from the Quantum Phaser. I don't notice any difference when I set the E-1 down on the seat next to me. Tonite I'll make a test by setting the rx down, getting out of the truck and disconnecting the head phones to make 100% sure that I have no contact with the rx and if there's any change in null or signal level I'll report back.
My opinion is that your entire directivity test may be invalid due to this hand effect. What I suggest prior to going out next time would be to toss out a hundred feet or so of wire on the ground at home and then see if there's the hand effect when run of rx batteries and when run off car battery and when run off rx batteries but with the rx grounded to the chassis as you, IMHO, really don't want this effect.
I realize that some of what I will now say is different from what has been said by others as will as different from "theory" and may get my burned at the stake for sacrilege. However, they are my experiences with BOGs since I first layed one down in Nov 2001.
The lack of transformer has just about nothing to do with your measured lack of directivity from my experiences and testing since you are running the BOG into your car and compared to being directly on the ground, there's only the slight upslope to get under your car door. Since I am unsure how much is picked up inside my truck, I place the phasing unit on the seat next to me rather than the dash board to reduce any vertical effect. Lack of transformer also has minimal effect on any lack of gain. Typical BOG impedance is about 250 ohms. The 5:1 SWR caused by inputting directly into 50 ohms is not going to destroy signal levels. My measurements years ago showed the expected db or two loss..ie no big deal for AM.
A 500 ft BOG is long enough to show significant directivity and especially on the high end of the band. I would prefer 900 feet or so for the low end, but much beyond that I noted quite significant losses due to ground and a reduction in directivity on the high end.
Longish BOGs have significant F/B even unterminated due to ground losses. I presume this is because the back end signal is reflecting off the far end and travelling further to the rx than the incoming wave. I have also observed this effect on very long Bevs...like a mile or so long the couple times I've been fortunate enough to use them. Here is my detailed article about the F/B of an unterminated BOG. http://www.dxing.info/community/viewtopic.php?f=17&t=371 I also tested this effect in Grafton WI on a 480 footer aimed ENE/WSW. As an example, aiming ENE I get the Holland MI TIS on 530 and aiming WSW it is the TIS near Madison in bad 540 slop.
Lack of termination is also not causing poor side nulls. Termination will definately help reduce back end QRM, but I have never been able to get good termination that is broadbanded across the entire BCB. I also have been unable to do the same across the BCB for classic elevated Bevs. Some of this is because the back null depths vary as a function of wavelength.
Rather than worrying about transformers for a quicky DXped to the park, don't bother. I honestly think that I last used a transformer on a BOG over 5 years ago. Now if I was cabling them back into a building, then of course I'd use one so that the cable would be a cable and not part of the antenna. What would you use for the ground for the transformer anyhow ?
What would you use for the ground for a termination in the park? ie..don't bother and just phase a pair.
I don't have time to write a huge detailed post about all the details of phasing BOGs until later this week so here's a quick primer. But for now, go here http://www.dxtools.com/PRODUCTS.htm and buy the Quantum Phaser and battery pack (so you can use it mobile). Perhaps there are better phasers, but I've done OK with this one and it sb quickly available.
All you then need is about a football field worth of land and without tall weeds, grasses and undergrowth..ie so the wires are on the ground. Something like 325 ft //195 will jaw drop you on the upper third of the band as you'll have a pattern like a small yagi with good F/B. 350 ft would be a good length to // that 500 footer. If you buy a new 500 foot roll of wire you can try 575 ft // 425 ft at the park. When you pick the wire up, use cord winders as it is very easy and they cost about 7 bucks.
Different lengths are used so that there is a decent ammount of signal left over after phasing. If you phase two BOGs that are // and the same length you'l null about everything on the channel. Staggered BOGs ..ie staggered feed points and ends should work even better, but then you need transformers, cables and grounds and I haven't tested it bit am certainly happy with my method.
I've used Phased BOG Systems with the wires as close as a foot and they work great. You can also hold one spool in one hand and the other in the other and the spacing will be fine as you walk out.
73 KAZ
-----Original Message-----
>From: Neil Kazaross <neilkaz@xxxxxxxxxxxxx>
>Sent: Sep 29, 2009 7:35 AM
>To: neilkaz <neilkaz@xxxxxxxxxxxxx>
>Subject: Fw: [IRCA] How to phase BOG's? (Jim Glover)
>
>
>----- Original Message -----
>From: "Jim Glover" <psykey@xxxxxxxxxxxx>
>To: "Mailing list for the International Radio Club of America"
><irca@xxxxxxxxxxxxxxxx>
>Sent: Tuesday, September 29, 2009 6:18 AM
>Subject: Re: [IRCA] How to phase BOG's? (Jim Glover)
>
>
>There is no internal ferrite bar antenna. My guess is that I was
>giving the antenna system a ground plane. The BOG was simply
>inserted into the center of the chassis SO-239. I'd made no
>connection to the outer section of the SO-239 (ground). Under
>other circumstances--e.g. if I'd been powering the transceiver
>from the car battery--my transceiver would have been grounded to
>the car. But since I was powering the transceiver from its
>internal battery, there was no "other side" of the antenna. By
>placing my hand on the metal body of the transceiver, I was
>probably creating a capacitive coupling between my body and the
>transceiver. My body was also capacitively coupled to the car.
>The result was probably that the car's body became a "ground
>plane" or "counterpoise" or whatever you want to think of it,
>providing the antenna with an "other side".
>
>In a future test, I will try grounding the transceiver to the
>car body to see if I get the same type of result. If I do,
>that will, IMO, strongly suggest that I'm barking up the right
>tree here.
>
>I'm thinking there are two big factors limiting the Beverage-ish
>performance of my BOG. One is that 500' at 530 KHz to 1700 KHz
>is relatively short, in terms of a wavelength. Even if you
>allow for the antenna ending up much longer electrically by
>virtue of its proximity to ground, it still doesn't get long
>enough to become directional off the end. The other big factor
>is probably good soil conductivity. I had already been wondering
>about this factor--then Bruce Conti (replying on the NRC-AM list)
>mentioned that BOG's perform better over soil with low conductivity.
>According to the maps, the soil conductivity around here is on the
>high side.
>
>On Tue, Sep 29, 2009 at 03:50:15AM -0700, Russ Edmunds wrote:
>> There has to be some explanation for why there was so little difference
>> between the car radio and the BOG. Part of that is the length, part is no
>> termination and part is no matching transformer. But it seems as if there
>> should be something else.
>>
>> That thought is magnified by the increase in signal strengths by putting a
>> hand on the receiver, although since I'm not at all familiar with the
>> receiver in question, if it has an internal ferrite bar antenna, that
>> could partially explain it.
>>
>>
>> Russ Edmunds
>> Blue Bell, PA ( 360' ASL )
>> [15 mi NNW of Philadelphia]
>> 40:08:45N; 75:16:04W, Grid FN20id
>> <wb2bjh@xxxxxxxxx>
>> FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
>> AM: Modified Sony ICF 2010 barefoot
>>
>>
>> --- On Tue, 9/29/09, Jim Glover <psykey@xxxxxxxxxxxx> wrote:
>>
>> > From: Jim Glover <psykey@xxxxxxxxxxxx>
>> > Subject: Re: [IRCA] How to phase BOG's? (Jim Glover)
>> > To: "Mailing list for the International Radio Club of America"
>> > <irca@xxxxxxxxxxxxxxxx>
>> > Date: Tuesday, September 29, 2009, 12:51 AM
>> > On Mon, Sep 28, 2009 at 06:30:57PM
>> > -0400, Gil Stacy wrote:
>> > > Jim, Dave:
>> > > Dave, I doubt if Jim's car antenna was coupling with
>> > the BOG.
>> >
>> > I can rule it out. I rolled the BOG up, and then
>> > checked many
>> > of the stations again on my car radio. The BOG was
>> > now once
>> > again a spool of wire in the trunk of my car, and the
>> > sations
>> > were still rolling in.
>> >
>> > Thanks, Gil, for the additional information about phasing
>> > these things. I don't really need to spend another
>> > C-note or
>> > two on one of these phasers ... but oh my, it is tempting.
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>>
>>
>>
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