Radio Shack Discone

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jthorpe

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I don't know why I did this, but I did. I despise Radio Shack and went in there anyways, buying their discone antenna. I haven't had a chance to check SWR on this thing yet. I'm going to do it tonight. Seems to do pretty well on low band and sucks horribly on 800. I'm curious if any of you know what frequency this thing is tuned for out of the box? I can't seem to find any information on that. Any help would be appreciated.
 

OceanaRadio

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jthorpe said:
I don't know why I did this, but I did. I despise Radio Shack and went in there anyways, buying their discone antenna. I haven't had a chance to check SWR on this thing yet. I'm going to do it tonight. Seems to do pretty well on low band and sucks horribly on 800. I'm curious if any of you know what frequency this thing is tuned for out of the box? I can't seem to find any information on that. Any help would be appreciated.
J,
The RS Discone has a vertical whip that used to be factory tuned for the amateur radio 2m band, and probably had about 2:1 or less SWR in the 144-148MHz range. The vertical whip on the discone could be shortened for lower SWR on higher frequencies, but should receive well throughout the VHF-high LMR band as-is. Presumably the horizontal and sloping discone components of the anternna are for the 800MHz and higher bands. The antenna was never a super performer there but mounting height usually accounts for more than particular antenna selection where receive-only is concerned.

Jack
 

prcguy

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Measure the length of the cone radials and they will be 1/4 wavelength at the lowest frequency, I believe its a little below 100MHz on the RS. A Discone has up to around 8:1 frequency range if designed correctly, which would put the RS technically out of band over 800MHz. They don't stop working above their 8:1 range, the pattern just gets really squirrelly and points way up or down with dead spots at the horizon. The whip on the RS, Diamond DJ-130 and others is tuned right around 50MHz, not 2m. The Discone operates more like a ground plane where the whip resonates.
prcguy
 

OceanaRadio

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prcguy said:
Measure the length of the cone radials and they will be 1/4 wavelength at the lowest frequency, I believe its a little below 100MHz on the RS. A Discone has up to around 8:1 frequency range if designed correctly, which would put the RS technically out of band over 800MHz. They don't stop working above their 8:1 range, the pattern just gets really squirrelly and points way up or down with dead spots at the horizon. The whip on the RS, Diamond DJ-130 and others is tuned right around 50MHz, not 2m. The Discone operates more like a ground plane where the whip resonates.
prcguy
prcguy,
Thanks for the update on RS's current discone. I did qualify my comment on factory tuned as "used to" (mine is about 15 years old now and does have a ~2m whip). I assumed they might still make that old 20-176 or the current product might be similar. I have mine installed in the attic now and connected to bench test equipment where it can transmit on VHF-Marine and receive anything from VHF to HF.
Jack
 

Skypilot007

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Just FYI.... my RS discone fell apart after about 4 years up on the mast. Hope you have better luck. It did perform ok for what I needed it for. There are better discones out there.
 

SAR923

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Jack,
Are you talking about the quarter wave ground plane that's still the RS 20-176 or the RS discone, part no. 20-043? I'm a little confused about which antenna you're using.
 

prcguy

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I have had RS Discones dating back to when they were forst sold, probably 20+ years ago and the top whips have always been tuned to 50MHz, I guess maybe yours has been modified. There would be no need to have a 2m (146MHz) whip because the active Discone range covers that already.
prcguy.
prcguy,
Thanks for the update on RS's current discone. I did qualify my comment on factory tuned as "used to" (mine is about 15 years old now and does have a ~2m whip). I assumed they might still make that old 20-176 or the current product might be similar. I have mine installed in the attic now and connected to bench test equipment where it can transmit on VHF-Marine and receive anything from VHF to HF.
Jack
 

OceanaRadio

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I have had RS Discones dating back to when they were forst sold, probably 20+ years ago and the top whips have always been tuned to 50MHz, I guess maybe yours has been modified. There would be no need to have a 2m (146MHz) whip because the active Discone range covers that already.
prcguy.
Its been so long since I bought my RS Discone I can't remember if I cut it or not. But the whip would have been quite long to be resonant on 50mhz and I don't recall trimming much if I did. The whip is over 3' long as I recall, and it provides a near 1:1 in the marine band. I made a couple repairs to the "cone" radials over the years but it survived at least 10 years service before I mounted it indoors.

I also have one of those old ground plane antennas, thanks Jim for the numbers on that v. the discone. One by one they were all replaced by marine antennas. Only my scantenna remains as a testament to my earlier scanning days, and when this third one (bought 3 for $9.99ea several years ago) finally bends in the wind, I won't put another scantenna up. Too fragile and can't transmit, but it sure is a damn good listener.

Jack
 

ka5lqj

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R$ 'Discone'

Hi,

There is no such 'animal' as an "all-band" (30-50/150-174/406-512/800-1.3ghz) antenna. What is
being passed off for a discone is really a poor ground plane. A true discone's top element is either
a metal disc, .7 the diameter of the lowest freq. and the "skirt" is a ¼ wave length of the lowest
frequency. If the antenna hears VHF Lo-band (30-50 mhz), it's NOT going to hear the 800 mhz
trunked freqs.

Depending on how far you are away from the intended reception, you need the best antenna you
and get or build yourself. If you live near by and don't have a lot of pager 'traffic', a simple ground
plane can be made from an SO-239, some #12 solid copper wire, some soldering or crimp lugs and
4-40 hardware. There are plenty of plans on the I-net. "Google is your friend", LOL!

If you need something more elaborate, then on-line reasearch is best. Just remember, there are a
LOT of antenna makers. Antennas are like fishing lures.....They catch more "fisherman" than "fish".

A lot depends on your individual circumstances...distance from station, antenna height, possible co-
channel or "bleedover" interference. If you live some distance from the stations a directional yagi or
quad (vertically polarized) maybe what you want. I prefer to "roll-my-own", as I've been an antenna
expirimenter since 1958.

Respectfully,
73,

Don/KA5LQJ
 

prcguy

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A 1/4 wave whip for 50MHz is about 5ft long and the RS Discone 50MHz whips have a loading coil at the base to shorten them to about 3ft. The loading coil is needed to help isolate the whip at higher frequencies (acts like a choke) and if you remove the whip the Discone will probably work better in the 100 to 800MHz range including marine. If you just stick a random whip on a Discone there will be unpredictable currents between the whip and normal Discone operation and performance will usually drop.
prcguy
Its been so long since I bought my RS Discone I can't remember if I cut it or not. But the whip would have been quite long to be resonant on 50mhz and I don't recall trimming much if I did. The whip is over 3' long as I recall, and it provides a near 1:1 in the marine band. I made a couple repairs to the "cone" radials over the years but it survived at least 10 years service before I mounted it indoors.

I also have one of those old ground plane antennas, thanks Jim for the numbers on that v. the discone. One by one they were all replaced by marine antennas. Only my scantenna remains as a testament to my earlier scanning days, and when this third one (bought 3 for $9.99ea several years ago) finally bends in the wind, I won't put another scantenna up. Too fragile and can't transmit, but it sure is a damn good listener.

Jack
 
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