Out side antenna

[Voyager]

I am in a dense RF area, but I'm using $500 worth of Par notch filters to mitigate that problem, the same filters I used for the discone.

I suspect those filters don't do anything for strong in-band signals that desense the scanners. Yours sounds like a case where the reason you don't see improved performance is because your scanners are already saturated with signals.

Well, you'd think if the ST-2 actually had that much gain that Antenna Craft would have touted it proudly. Instead we get a spec sheet that looks like this:

They likely never did any testing on the gain, and that's why it's listed as Not Available. It's actually admirable that they admit it's not known rather than publish some exaggerated figures like 6 dB gain at VHF for an antenna that is 12 inches tall.

 

[SOFA_KING]

If a "rubber duck" worked better than your discone, I have to conclude you might have had a connector problem with the feedline connected to that discone. Maybe water in a connector is causing that "wet noodle"?

Another thing about discone antennas I discovered is that metal objects around them can detune them. Other antennas around them the same. I measured it with a TDR and was surprised it was effected that much. Even from 15 or so feet away I could see detuning. You have to mount them in the clear. A lot of people side-mount them, and even put other antennas next to them. That has a bad effect on antenna performance.

And when you have a testbed with RF overload issues, you really can't compare antennas under that condition. On my GRE scanners I do have an FM broadcast overload issue on VHF (hi and low). Not so on my Uniden scanners, so they are my preferred test radio. I too purchased a PAR FM trap to put in front of my Stridsburg multicoupler, but at my interfering FM broadcast frequency I was only getting -20 dB of suppression, and that was not enough for my GRE gear. I looked at the Stridsburg FM trap specifications and noted it offered an additional 15 dB of suppression, so I got it. That did the trick. Nice and quiet on my VHF noise floor now. The PAR now resides in my SUV.

This ST-2 antenna may very well be a good antenna. I don't know it, but would like to try it one day. Looking at it, I can only guess that it is similar to ham radio multi-band antennas that use coil traps to stack elements and tune sections of a band. You don't know how good or bad it can be until you sweep all the claimed (entire) bands with a TDR. Coils work where specifically tuned, and bite you beyond that. I did TDR testing on all my antennas. The hammy antennas did ok in the ham bands, but completely fell apart outside of them. That is the first thing I would do with an ST-2...sweep test it. Even the discone has some bad areas, but is far wider than any other antenna I have seen (no coils). One of my discone antennas works for TX on 220 (not supposed to), so something around it must have effected it to my advantage. I'll take that!

Now, since the Diamond discone has that mounting screw on top, I wonder how much better you could get 800 MHz to work on it with an 800 gain antenna mounted up in that spot (like a mobile curly Q whip). ??? That might be worth experimenting with. I'm betting that it would do VERY well. You have all that ground plane under it, so I can't see any reason it wouldn't. It would probably have to be tuned a bit, and checked with a TDR or VSWR meter (if your allowed to TX there), but that is easy enough. You lose low band, but some people don't need low band. I like low band, and use it for skip listening...even as an excellent 6m omni antenna, so I would not sacrifice my main discone 62 3/4" element, but maybe my "auxiliary" discone could try that 800 idea. Food for thought. :scratching chin:

And for those with LSM issues that need a yagi pointed at one site, you do know you can diplex (combine) you 800 antenna with another antenna to get multi-band coverage, right? Just shop for the appropriate ham radio diplexer. Look at the specs carefully, as some may not cover all the areas of the bands you might want to cover. I use a lot of these things. I have only 4 antennas on my house (not including my Jerrold Suburban VU TV antenna), and feed 10 radios covering 3 MHz to 1300 MHz. HF (homemade multi-band 6 element fan dipole), 6m, P25 radios, DMR radios, and 4 scanners, I got it covered! Although I could use another V/U antenna for my new Fusion radio. NXDN is next, so then what do I do? All these different digital format radios eat up my VHF/UHF antenna capacity!

Phil

 

[sparklehorse]

I suspect those filters don't do anything for strong in-band signals that desense the scanners. Yours sounds like a case where the reason you don't see improved performance is because your scanners are already saturated with signals.

Why would you suspect that? That is exactly what those filters are designed for. I just said that I was receiving good signals from stations 50-70 miles distant with either antenna. Does that sound like the filters are not working? I don't think so. I added those filters because ALL of my newer Uniden radios, and the Whistler, were practically deaf at VHF-Hi. I based that on 14 years of using a BC780XLT with a rooftop antenna and a single FM trap filter. The 780 could receive those distant stations from 50+ miles at nearly full quieting, the 996 and other newer units struggled to get a peep beyond 25 or 40 miles. The newer radios simply don't have the nearly bulletproof front end of the 780. So one by one I started adding notch filters until finally I had ALL of the radios performing on VHF at very nearly the level I had enjoyed with my 780 for many years. Hence the comment that I was using filters to mitigate the problem.

I'm not trying to pick a fight here. I was just adding another users experience with a discone that happens to be contrary to yours. For whatever reason we've just gotten different results. Oh well.
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[sparklehorse]

They likely never did any testing on the gain, and that's why it's listed as Not Available. It's actually admirable that they admit it's not known rather than publish some exaggerated figures like 6 dB gain at VHF for an antenna that is 12 inches tall.

Making antennas was their only business. You can bet they tested every model. If you look at the spec sheets for their TV antennas they all include gain specs. Just sayin'.
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[Voyager]

Why would you suspect that? That is exactly what those filters are designed for.

Because if those filters filtered out strong in-band signals, you would not hear the in-band signals (or their strength would be greatly reduced). I'm sure they were made for adjacent band rejection, and not the bands you are trying to receive.

I'm not trying to pick a fight here. I was just adding another users experience with a discone that happens to be contrary to yours. For whatever reason we've just gotten different results. Oh well.

Understood. Same here. I'm just trying to understand why so many see much improved reception with the ST-2 over the Discone, but some see the exact opposite.

In almost every case, those who see stronger signals on Discones are in dense RF areas. So signal strength has to have something to do with it.

 

[Voyager]

If a "rubber duck" worked better than your discone, I have to conclude you might have had a connector problem with the feedline connected to that discone. Maybe water in a connector is causing that "wet noodle"?

Remember - there were three Discones involved. The feedlines swept good and worked fine on other antenna designs. The tests were done immediately upon install, so there was no chance there was water involved.

Another thing about discone antennas I discovered is that metal objects around them can detune them. Other antennas around them the same. I measured it with a TDR and was surprised it was effected that much. Even from 15 or so feet away I could see detuning. You have to mount them in the clear. A lot of people side-mount them, and even put other antennas next to them. That has a bad effect on antenna performance.

All were top-mounted on a pole with no other antennas within about 25 feet. In fact, no other obstacles. One or two had the stinger. At least one did not. The only exception to this is my current Discone which had an ST-2 added below it to test based on similar reception locations (trying to eliminate as many variables as possible).

And when you have a testbed with RF overload issues, you really can't compare antennas under that condition. On my GRE scanners I do have an FM broadcast overload issue on VHF (hi and low). Not so on my Uniden scanners, so they are my preferred test radio. I too purchased a PAR FM trap to put in front of my Stridsburg multicoupler, but at my interfering FM broadcast frequency I was only getting -20 dB of suppression, and that was not enough for my GRE gear. I looked at the Stridsburg FM trap specifications and noted it offered an additional 15 dB of suppression, so I got it. That did the trick. Nice and quiet on my VHF noise floor now. The PAR now resides in my SUV.

I am far enough away from any FM transmitters they are not an issue. In fact, I can hear stations 25 miles away on my GRE scanners that I cannot hear within 5 miles of the transmitter sites. (because those sites are in dense RF areas).

But, I suspect that the RF Overload is what is causing the reception issues with the higher gain antennas like in Sparkle's case.

Par and Stridesberg - quality products there.

This ST-2 antenna may very well be a good antenna. I don't know it, but would like to try it one day. Looking at it, I can only guess that it is similar to ham radio multi-band antennas that use coil traps to stack elements and tune sections of a band.

There are no coils on the ST-2 except for inside the balun.

One of my discone antennas works for TX on 220 (not supposed to), so something around it must have effected it to my advantage. I'll take that!

I thought they all worked on 220.... That's one advantage of the Discone - they load just about everywhere.

And for those with LSM issues that need a yagi pointed at one site, you do know you can diplex (combine) you 800 antenna with another antenna to get multi-band coverage, right?

I know that, and use such devices in my mobile installations, but for home use I generally use one antenna = one scanner or one antenna = multi scanners, and dedicate others scanners to other bands.

 

[sparklehorse]

In almost every case, those who see stronger signals on Discones are in dense RF areas. So signal strength has to have something to do with it.

The RF desense argument would have merit if the ST-2 provided a LOT more gain than the discone. Let's say it's in-band signals causing desense as you surmise. Let's say your gain assessment is correct and the ST2 has 6 dB gain on VHF Hi over the discone. Notch filters typically provide -25 to -50 dB rejection in the bands for which they're designed. Because dB's are logarithmic, the difference just between -6 dB and -25 dB is HUGE. So even if the discone was -6 dB from the ST2 I doubt that would make much difference in apparent performance due to overload. It seems far more likely that the differences people notice are down to the usual suspects, like type of coax, damaged coax, etc. But unless someone takes some proper measurements of the ST-2's gain performance we will never know for sure.
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[SOFA_KING]

The RF desense argument would have merit if the ST-2 provided a LOT more gain than the discone. Let's say it's in-band signals causing desense as you surmise. Let's say your gain assessment is correct and the ST2 has 6 dB gain on VHF Hi over the discone. Notch filters typically provide -25 to -50 dB rejection in the bands for which they're designed. Because dB's are logarithmic, the difference just between -6 dB and -25 dB is HUGE. So even if the discone was -6 dB from the ST2 I doubt that would make much difference in apparent performance due to overload. It seems far more likely that the differences people notice are down to the usual suspects, like type of coax, damaged coax, etc. But unless someone takes some proper measurements of the ST-2's gain performance we will never know for sure.
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All good points. I would love to sweep one and check return loss across all the bands. Maybe if I see one for sale at a ham fest, I'll buy it. But I love my discones so much I'm thinking of taking my TV antenna down to put up another one in its place. Then I could put some of that 1 5/8" hardline I have stored in my garage to good use (laughs), as it would have to run over to the other side of the house where feedlines enter. That would be a long trench! I also TX on many bands, so I get a lot of uses out of one of these things when I split off all the different bands with diplexers and triplexers.

Aren't antennas a lot of fun?

Phil

 

[Voyager]

So even if the discone was -6 dB from the ST2 I doubt that would make much difference in apparent performance due to overload.

Well, 6 dB is enough to cause issues, but your point is taken.

There are a few other factors involved which could make the situation even more dramatic:

1. Is the gain of the Discone really 0 dB or is it actually less than that? I am sure that on Low Band, for example, it is much less than unity gain simply due to the size of the elements. Even on High Band the radiators are about 1/12th wave (6")?

2. The radiators on a Discone are horizonally polarized. That alone can account for a 10-20 dB drop in signal strength.

3. The gain of the ST-2 is focused on the horizon. The Discone is not focused anywhere, but I suspect the angle of radiation (reception) is well above the horizon.

So, on the horizon there may be a much greater than +6 dB advantage of the ST2 - many multiples of that, in fact.

 

[sparklehorse]

Well, 6 dB is enough to cause issues, but your point is taken.

There are a few other factors involved which could make the situation even more dramatic:

1. Is the gain of the Discone really 0 dB or is it actually less than that? I am sure that on Low Band, for example, it is much less than unity gain simply due to the size of the elements. Even on High Band the radiators are about 1/12th wave (6")?

2. The radiators on a Discone are horizonally polarized. That alone can account for a 10-20 dB drop in signal strength.

3. The gain of the ST-2 is focused on the horizon. The Discone is not focused anywhere, but I suspect the angle of radiation (reception) is well above the horizon.

So, on the horizon there may be a much greater than +6 dB advantage of the ST2 - many multiples of that, in fact.

From Wikipedia:

>>> A discone antenna is a version of a biconical antenna in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath.

Omnidirectional, vertically polarized and with gain similar to a dipole, it is exceptionally wideband, offering a frequency range ratio of up to approximately 10:1. The radiation pattern in the horizontal plane is quite narrow, making its sensitivity highest in the direction of the horizon and rather less for signals coming from relatively close by. <<<


IIRC the radiation pattern varies with frequency. I don't know how much.
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[Voyager]

Well, if Wikipedia says it, it must be true. LOL

But, maybe they are counting on reflections from the radials into the radiators because they are most definitely horizontal.

 

[sparklehorse]

But, maybe they are counting on reflections from the radials into the radiators because they are most definitely horizontal.

I think that is sort of how it works. With a discone the disk radials work in concert with the cone radials. The disk is not the only part of the antenna that radiates, the whole thing does.

A snippet from Radio-electronics.com:

>>> The way in which the discone operates is relatively complicated, but it can be envisaged in a simplified manner. The disc and cone elements sufficiently simulate an electrically complete disc and cone from which the energy is radiated. As a result the greater the number of elements, the better the simulation, although in reality there is a balance between performance, cost and wind resistance. Often around six elements are used, but the number is not critical.

In operation energy from the feeder meets the RF antenna and spreads over the surface of the cone from the apex towards the base until the vertical distance between the point on the cone and the disc is a quarter wavelength. In this way it is possible for the energy to be radiated or received efficiently. <<<

More here:

Discone antenna :: Radio-Electronics.Com

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[SOFA_KING]

Voyager..You really don't understand a discone and how it works. And if you put a low band radiator on top, like I did, it does great on low band. At least as good as a low band ground plane. Talking to Canada and northern NH multiple times from Florida with only 100 watts doesn't happen by negative gain and bad radiation angles. The opening was mediocre at best during the last VHF contest, so it wasn't just good conditions either. I even worked a few Idaho stations on a double hop last summer. Got the logs to prove it. That's proof to me.

And that is the thing that I can't understand about your posts. You keep showing how much you don't know, but you always try to come off as an expert...and never wrong about anything. Come to think of it, that is a good question. Can you admit you are ever wrong about anything? If so, what?

Sometime it is just better to quit while you are, well, not looking so unknowledgeable.

EDIT: And I'm going to admit I'm wrong about the ST-2. I thought that was that fiberglass covered vertical someone posted earlier. I had one of these (ST-2, but called something else...I think) way back in the day. I think Channel Master used to make it. It is nothing more than a series of dipoles like a VHF/UHF version of a fan dipole. I have a bigger version of that between two pushup poles on my roof right now. It's my HF fan dipole. 6 dipoles covering 75m to 6m tied to a single feedpoint. Covers all ham bands from 75m to 6m. Real good and wide on 75m, 60m, 40m 20m, fairly good on 17m, ok on 15m, needs a little help on 12, great on 10m and ok on 6m. My Discone is much better on 6m. If I had more space, I would run more elements to increase bandwidth. I could use a set for 30m and 12m. So, yes, I was wrong. I know exactly what an ST-2 is and how it works.

P

 

[NDRADIONUT]

You can put an 18" whip on the disk and improve vhf if you have no low band around you....

 

[SOFA_KING]

You can put an 18" whip on the disk and improve vhf if you have no low band around you....

Have you done that? I swear my low band whip, which is 3/4 wave on the VHF government band, helps my VHF reception. I like that!

P

 

[NDRADIONUT]

Oh ya it makes a difference... You can also do a 6" for uhf which makes an even bigger difference on that band....

 

[SOFA_KING]

Oh ya it makes a difference... You can also do a 6" for uhf which makes an even bigger difference on that band....

I believe it. The reason I keep saying 62 3/4" is because that is the magic length to tune 6m and cover the whole band with 1.7:1 VSWR on the ends (flat at 52), which is hard for me to understand, as most ground plane antennas can't even do the full 4 MHz. Is it acting like an off-center fed dipole or ground plane antenna? The ground radials are short, and the radiator long (normally 56" for each), so that makes sense. I also wonder if that lowers the angle of radiation. I wish I still had access to the /\/\ antenna test range down in Plantation (if it even exists anymore).

P

 

[NDRADIONUT]

The fatter the radiator is... The wider the bandwidth you will get... So maybe your 62" rod is pretty thick....

 

[prcguy]

I guess I'll chime in here and stir things up a little, hope it doesn&#8217;t take up too much space. To start I basically agree with most everything in post #13 of SOFA_King for general info on antenna systems, excellent info. Except adding a full 1/4 wave whip on top of a Discone unless you really need the improvement on 6m and wish to give up performance somewhere else.

Looks like everyone has a different view of what a Discone is and what its parts do&#8230;.A Discone is a type of aperture antenna that launches a vertically polarized wave from the feedpoint or intersection of the horizontal disc and the tapered cone and the disc elements cannot be looked at the same way as other types of antennas.

The ideal Discone is made from a solid disc and solid cone and not individual elements. It takes at least 16 disc and 16 cone elements to emulate a solid sheet metal Discone and less elements will be less efficient than a full sheet metal version. Many commercial and military Discones have 12 elements, some with 8 and most scanner versions only have 6 per disc and 6 per cone, meaning they are less efficient than what the designer had in mind.

With that said, a good quality Discone with 12 elements has about the same gain as a resonant 1/4 wave ground plane over most of its 8:1 frequency band width and those with only 6 elements are only slightly worse. I've had a RS Discone on an antenna range comparing to other types of antennas, so reports of a Discone being trumped by a rubber duck are a little disturbing to me.

From the lowest end of a Discone&#8217;s design frequency to about half way through it will have a pretty good low angle of radiation towards the horizon and on par with a cut to frequency 1/4 wave ground plane. For the typical DJ-130, RS and other Discones of the same size this would be about the lower end of the VHF air band through the UHF public service band.

Above that the lobes start to point upward and even though it has about the same gain at 800MHz it will be up in the air and at the horizon the useable gain will be down quite a bit and that&#8217;s where scanner Discones get a bad rap for 800MHz reception. If you need good 800 reception get a separate 800 gain antenna and a diplexer for your Discone.

The base loaded whips you see on some Discones are for roughly 50MHz reception and they are very sharply tuned to a narrow band around 6m, although they do improve much of the VHF lo-band a little. The base loading of the whip does two things, it shortens the whip from a full 1/4 wavelength of about 6ft at 50MHz, and more important for my part of the discussion is the loading coil helps decouple the whip from the Discone at higher frequencies. That last part is worth repeating, but instead just read it a couple of more times.

Otherwise if you put a 6ft tall full 1/4 wave 6M whip on top, that whip will now be active on higher frequencies and the Discone design and operation is out the window. At all frequencies the now full size 6ft whip will be active and in parallel with the Discone and RF currents will flow on both parts of the antenna. It will work great on 6M but on other freqs it will skew the pattern up and down and all over the place. If and where these lobes are in phase you will have some gain and where they are not you will have loss. Plus where the 6m whip is 1/4 wavelength or multiple resonant it will lower the feed point impedance of the Discones causing mismatch and further degradation.

Adding a whip for bands like VHF or UHF that that a Discone already covers?? Please don&#8217;t do that unless you want to wreck a perfectly good Discone.

In my opinion a Discone should be left as a Discone with no whip of any kind on top and if you need VHF lo-band get a separate lo-band antenna and a diplexer and don&#8217;t muck up your Discone with a whip.

One thing you can count on from a Discone is a good and fairly consistent match to 50 ohms across its entire 8:1 frequency range and usually much more. This is great for those that want to add a preamp (a separate topic) where the antenna presents a good match to the input of a preamp. An ST-2 or other multi band antenna may have a good match at a few specific frequencies but everywhere else it will be all over the map and this can send a preamp into oscillation.

I&#8217;ve experience this and have seen a wide band preamp oscillate on other types of antenna but not on a Discone. It&#8217;s mainly due to a crappy designed preamp but there are lots of them out there.

As for the Antenna Craft ST-2 and clones, I don&#8217;t own one but I can say it has no more gain than a 1/2 wave dipole at any frequency and probably less. It&#8217;s not possible to have 6dB or even 3dB gain over a dipole based on its &#8220;nest of dipoles&#8221; design. It will also be somewhat narrow band around its design frequencies, unlike a Discone which works the same everywhere except for the pattern skewing at higher frequencies mentioned above.
prcguy

 

[sparklehorse]

Wow, very informative post prcguy, thanks for that! I've only nibbled around the edges of learning how discones work, but you've helped me understand them better. Now I know why mine was disappointing at 800 MHz. I think your idea of the discone, plus an 800 MHz antenna and diplexer sounds like a potentially great setup. I might just have to pull my discone out of the basement and try that out. Thanks.
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