actually, if you are going to use a BALUN, you might as well go for the 2:1 (yes, they do make these). It will match the 50 ohm line to the 100 Ohm terminating impedance that is the feed point of the loop. THis will also have 1 added benefit: the loop will become multi band. It might be closed enough to resonance to work well into the 2 meter band.
DE n7zzt Eric
On Dec 14, 2015, at 7:01 AM, Mike Keithley wrote:
> I also wonder if a 1/1 balun would help. I think it'll isolate the coax from the loop.
>
> ----- Original Message -----
> From: Tom Fowle <[log in to unmask]>
> To: [log in to unmask]
> Date: Sunday, December 13, 2015 6:50 pm
> Subject: Re: Report on 10M Loop Project, and Request for Feedback
>
>>
>>
>> Richard,
>> So far as I can tell, your math is correct. I aggree with others, fixing it
>> will most likely make no audible difference for RX.
>>
>> You should be able to remove pipe from only two opposite segments of the
>> loop, it will be a bit "squished" that way but much less work and again
>> shouldn't make any operational difference.
>>
>> but if you're being obsessive, go haead and cut some off all the sections,
>> what the heck! <GRIN>
>>
>> I wonder if placing a small varriable capacitor across the feed point would
>> let you adjust for a better match, but again, probably no difference on RX
>> and you'd have to have an analyzer available to fiddle with it.
>>
>> Tom Fowle WA6IVG
>>
>> On Sun, Dec 13, 2015 at 06:58:55AM -0800, Richard B. McDonald wrote:
>>> Hi!
>>>
>>>
>>>
>>> I want to report on my 10M full wave loop (FWL) project, and ask for
>>> feedback on it. My aim was a resonant antenna at 28.4 MHz for RX only on my
>>> TS-2000. I viewed this project as practice for the antenna I *really* want
>>> to make - an 80M FWL for both RX and TX (inspired by Ron).
>>>
>>>
>>>
>>> To make my loop, 14 gauge insolated stranded copper wire sits inside 1" PVC
>>> ~12' atop my wooden shack. It is in the shape of an octagon. I measured
>>> the length of the wire at 1005 / 28.4 = 35.39', which I rounded to 35.5'.
>>> There is a 25' run of 75 ohm coax (the kind for TV, which I was told is fine
>>> for RX antenna purposes like this) properly soldered to the ends of the
>>> wire.
>>>
>>>
>>>
>>> So, my friend from our ham club measured this antenna with his analyzer. It
>>> turned out to be resonant at 25.5 MHz : ( Now, only because I am obsessed
>>> with my project and by way of learning, I should like feedback on the
>>> following:
>>>
>>>
>>>
>>> 1) I am told that one thing affecting resonance is the "velocity
>>> factor" of the wire. Apparently, the insulation of both a) the wire itself
>>> and b) the PVC affects the velocity factor. I have no idea what "velocity
>>> factor" is, nor how it affects the calculated length of a wire for a FWL as
>>> per the above.
>>>
>>> 2) To bring the resonant frequency up to 28.4 MHz, I *think* I need to
>>> decrease the size of what I have built. Is that right? "Decrease" as in
>>> shorten rather than "increase" as in lengthen?
>>>
>>> 3) To decrease the size of my loop, I plan to cut 6" (0.5') off each of
>>> the eight sides of the octagons for a total of 4' (including obviously the
>>> wire therein). Check my math (reasoning) on this. 28.4 / 25.5 = 1.11;
>>> meaning I am too big by 11%. 0.11 * 35.5 = 3.9; say 4'.
>>>
>>>
>>>
>>> Incidentally, even though my loop is a little off, it seems to RX better
>>> than my 43' vertical does on 10M. Some have said that for RX only this
>>> resonance differential is insignificant. In other words, they say that even
>>> if I tune my loop precisely to 28.4 MHz, on 10M it would be imperceptible as
>>> to 25.5 MHz for RX. What do you think about this?
>>>
>>>
>>>
>>> 73,
>>>
>>> Richard KK6MRH
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