Dedicating a Discone to 800 MHz

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WeldGuy

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I have a Tram 1411 Discone antenna that looks to be primarily set up for 11 meters from Tram. As a lifelong "tinkerer" I was wondering if it could be repurposed as a dedicated 800 MHz receive only antenna. I know, there are better antennas out there for 800 MHz, but I thought it would be a worthwhile challenge.
I would start by getting rid of the vertical 11m section and the two, adjustable radials extension. I have a NanoVNA to use to measure the effect of any changes I make.
What do the antenna gurus think? (Be nice) LOL
After this, I'm thinking of making my 20 HP mower engine into a 1,000 HP race engine!!! (Kidding of course)
 

prcguy

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I don't think its worth messing with. That basic Discone without the whip works from a little over 100MHz to about 800MHz but somewhere around mid band or 400-500Mhz the radiation pattern starts pointing above the horizon and at 800MHz its really bad. You would have to cut the antenna down to about half size and then you might see as much as a 10dB improvement at 800MHz. Another problem is the SO-239 connector is not that great at 800MHz. If it were an N type I would say cut it down but not with an SO-239. Just buy one of these and enjoy the improved 800 reception for cheap $$. TerraWave 800-2500MHz 3dBi Omnidirectional Antenna M4030030O10006T - 800088423 | eBay
 

ScubaJungle

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I agree it's not worth it considering the extremely cheap alternatives that would work significantly better.
another option is this:

Its cheap and may seem questionable, but it blows away my Tram discone on all bands, hands down, and is telescopic so the element lengths can be tuned for different frequencies. It rivals my 800mhz yagi but is all around better since it isnt as directional as the yagi. Use the smaller elements, halfway - fully extended for best performance at 800mhz.
 

ScubaJungle

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You have to be kidding.. that is a very old TV Rabbit Ear antenna.
@cmdrwill
So because you associate this antenna with something you know is old, it has to be bad?
Well, if you researched basic antenna theory then you'd know that dipoles are effective antennas.
If you dont believe me, fine, but dont bash it without trying it.
I've logged 197 frequencies between 450Mhz and 467Mhz, alone, with no help from the DB, with this antenna in the past three months - dozens which arent in the database that have active licenses.
Again, feel free to think what you want, but dont make judgements with no basis.

Edit: by logged, I dont mean I got a hit on it - I mean I got site/system #/IDs, color codes, LCN/RAN/CTCSS, etc, TG &UIDs,
and this was all done using this antenna with DSD+, so manually, not running a scanner on autopilot 24/7 - all of these were signal I manually picked on DSD+ waterfall. Everyone loves to laugh this thing off, but nobody wants to give it a chance, even though the findings speak for themselves
 
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mmckenna

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@cmdrwill
So because you associate this antenna with something you know is old, it has to be bad?
No. I think what he is saying is thats overpriced for what it is.
Yeah, a dipole will work, but you can make your own antenna that will outperform it pretty easily.
 

ScubaJungle

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No. I think what he is saying is thats overpriced for what it is.
Yeah, a dipole will work, but you can make your own antenna that will outperform it pretty easily.
Hey, Im open to suggestions! But I dont think youll find a balun alone, like this, for very cheap. For $18, if you can show me something cheaper, thatd be awesome. The only baluns I could find that were comparable were from $30 - $300 though. Check out my thread about it, I wanted to build my own but it wouldve cost twice as much
Also, I dont know much more than the basics of antenna theory and wavelength theory, etc, but this thing literally competes with my Wilson yagi on 800mhz. When I first got the kit, I almost threw it out, and then I figured, well, might as well try it out - when I find the "sweet spot" length for the elements, it amazed me.
The two elements pretty much act as two antennas working together


 

Ubbe

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The two elements pretty much act as two antennas working together
That's correct and are the principal of a dipole antenna. Each element recieve the signal and are then added in the balun. A 1/4 with groundplane have only one active element and the groundplane are only for pulling the directivity down more to the horizon. If you have weak signals then placement of antenna are important and your yagi might be sitting in a bad position, but you probably have nowhere else to put it.

/Ubbe
 

jonwienke

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@cmdrwill
So because you associate this antenna with something you know is old, it has to be bad?
Well, if you researched basic antenna theory then you'd know that dipoles are effective antennas.
If you dont believe me, fine, but dont bash it without trying it.
I've logged 197 frequencies between 450Mhz and 467Mhz, alone, with no help from the DB, with this antenna in the past three months - dozens which arent in the database that have active licenses.
Again, feel free to think what you want, but dont make judgements with no basis.
Dipoles will beat a discone near their resonant frequency, but they are poor performers across wide frequency ranges. If you sweep them, you'll see spikes of good performance with large gaps in-betweeen where performance is abysmal. You can fill in coverage gaps by connecting multiple dipoles tuned differently in parallel, but the interaction between elements gets messy.

Get one of the cheap VNAs from Amazon, and sweep your antenna. It's probably tuned to the 450-467MHz range and performs well there, but go much above or below that, and it will be terrible.
 

WeldGuy

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I really think the proximity of her house to that cell tower is killing 800 MHz reception. I placed my 436 on the window sill yesterday while double checking all the exterior antenna connections. During the 1.5 hours I was there, not one MARCS call was heard on either radio.
In the most basic explanation, she is attempting to receive a "thimble" of signal with the cell tower dumping a bucket of signal on top of it. I think the exterior antenna is even providing a "funnel" for that bucket of cell signal.
Next step... directional antenna.
 

WeldGuy

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Dipoles will beat a discone near their resonant frequency, but they are poor performers across wide frequency ranges. If you sweep them, you'll see spikes of good performance with large gaps in-betweeen where performance is abysmal. You can fill in coverage gaps by connecting multiple dipoles tuned differently in parallel, but the interaction between elements gets messy.

Get one of the cheap VNAs from Amazon, and sweep your antenna. It's probably tuned to the 450-467MHz range and performs well there, but go much above or below that, and it will be terrible.
I used my NanoVNA to confirm the antenna and cable connections. The 750 MHz - 800 MHz SWR reading wasn't spectacular, but should work OK if not for the cell tower.
 

ScubaJungle

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Dipoles will beat a discone near their resonant frequency, but they are poor performers across wide frequency ranges. If you sweep them, you'll see spikes of good performance with large gaps in-betweeen where performance is abysmal. You can fill in coverage gaps by connecting multiple dipoles tuned differently in parallel, but the interaction between elements gets messy.

Get one of the cheap VNAs from Amazon, and sweep your antenna. It's probably tuned to the 450-467MHz range and performs well there, but go much above or below that, and it will be terrible.
Thanks, I will try that.
This makes sense - there are gaps, most notably the milair band and below 140mhz.
450-467 is shockingly good, VHF-high is good, VHF-low is average-ehh, and 800mhz is good.
But for the price and ease of use, the performance on UHF alone, is worth it. Not many antennas can rival the performance this does with that big range, even considering the gaps. No antenna is going to be perfect for all bands, either, otherwise we would all have it.
I will try to get a VNA to show tangible results.
 
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