weird Tram

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AlphaFive

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I have been recently frustrated after moving my four discones around in my attic. I realized my Tram 1411, attached to a BCD536, had originally come with a long jointed top whip. I felt as though I was not utilizing the 1411 to it's fullest capacity.
1st problem, my attic mount height from floor base to top beam was only 5' 6". Far short of the discone with it's top whip. I researched for a period of time, I was able to piece together that if I wanted the best reception below 100 MHz. I needed to find a way to mount the top whip.
Well, I had been hanging the discone from the top beam with bailing twine, sans the top whip. I set down the discone into the recycled fiber insulation (which is supposed to be fiberglass free) . At that point height restriction only allowed the bottom half of the whip to fit into the top coil. Okay, lets try it. What occurred with the top whip on, and sitting in the fiber insulation was a degradation, in two places that should have not suffered. An A.T.I.S. at 120.200 had to have the squelch opened all the way to receive the voice modulation. A DMR frequency at 454 Mhz. suffered 1 to 2 bar loss if I parked my BCD536 on the freq.
I went back up in the 'crawlspace'.. took off the half whip, and rehung my 536. I was able to receive the A.T.I.S. at 120.200 on # 4 squelch with a decent voice modulation. My 454 Mhz. DMR went back up by 1 to 2 bars.
I cannot say what would have occurred if I had the ability to hang the discone insulation free, with a whip. But, I can say that without the whip, and hanging free, my V.H.F. above 100 and U.H.F. were improved. Don't know which was a deciding factor, insulation or the whip itself....odd
 

jonwienke

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Not odd, obvious.

Installing only half of the whip makes it resonate at frequencies higher than what it was designed for--frequencies normally only picked up by the discone itself. And the whip is out of phase with the discone, so the RF signal received by the whip is cancelling out some of the RF signal received by the discone. The degree of cancellation depends on the frequency; some frequencies will be cancelled out more than others.

When the entire whip is installed as designed, it resonates at frequencies below what the discone picks up, so phase cancellation is mostly a non-issue.
 

AlphaFive

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Tram

Very cool, this is why I ask.. I did not know that. Now that I read it, makes sense to me. Thanks for that, your help is always appreciated. Darn that blasted attic! I swear I'm going to move someplace where the Antenna Police won't haul me away for daring to put something outside..........
 

AlphaFive

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Tram

Address the issue strictly below 100 Mhz...
I am going to attempt to come to a conclusion here based on what information I can find. There appear to be two main varieties of discones produced. Those with a top coil, those lacking a top coil.
If I create a scale of 1 to 10. One being the absolute worst receiving ability, nothing but silence.
Ten being the absolute best, pulling in every signal within 30 miles.
The highest quality discone ever manufactured without a top coil, could only ever achieve an 8, compared to the highest quality discone ever produced that had a top coil, which would rate the 10..
I should conclude that simply because a discone has no top coil, it is by no means worthless. It is just made on a different grade of performance. It would be fair to say the question is as RG58 coax would be compared to 9913.
I am trying to figure this out due to the fact that I use three with no top coil, and one with. I have never even thought to examine the differences in performance. Both types are advertised as being set for 25 Mhz. to 1300 Mhz. End result, the differences are on a graded scale? Both will work, the top coil is just an added bonus to those who can afford it??
 
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jonwienke

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The size of the discone dictates the low and high ends of its usable frequency range. You could build one the size of a refrigerator that received well below 100MHz, but it wouldn't work as well for 800MHz.

Adding a vertical to the top merely extends the usable range on the low end a bit if it's sized appropriately..
 

AlphaFive

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Thank you, you've helped me understand a few more basics regarding discones. I never gave them a second read after I installed them, goofy on my part. Now I'm learning
 

AlphaFive

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Tram 1411 top coil

Okay. In reference to my Tram 1411. Height restrictions in my attic make inserting the top two sections of the whip into the top coil impossible. With that in mind.

1) Will having the top coil (black plastic) attached to the antenna, hanging from the attic beam, cause any degradation to my reception?
2) If.. the top coil is a problem, can it be removed? Doesn't appear so, looks as though it is manufactured to be part of the body. Thank you for your time.
 

jonwienke

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If you can't have the entire whip, don't have any of it. Or you'll continue to have issues.
 

AlphaFive

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whip

I've been comparing my reception in U.H.F. and V.H.F. with other units, my Pro 197, and even my old reliable Pro 2020. The other two units do a slightly better job. Also, when I place my 536 on a different whip-less(?) discone, the reception is a slight improvement. My instinct told me the whip was a problem, but I did not want to believe it. Thanks for your help, I believe your right.
 
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