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RS Model 20-006 Center-Loaded Telescoping Whip Antenna

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subter

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Just got a BCD396T a couple weeks ago. I was in Radio Shack over the weekend and they had a sale going so I picked up this antenna. It got mixed reviews on their site, love it or hate type reviews. Most complaints were regarding the plastic piece at the base. 99% of it is metal and it has a small plastic ring above the BNC connector but it appears to be of solid construction overall. I can't see this breaking easily if you handle your scanner with care.

So far it seems to be slightly better than the stock rubber ducky in the 800Mhz range. There are three different lengths you can extend it for that range so it probably takes some trial and error. I can pick up transmissions from home that I could only pick up at work (closer to the transmission). It's adjustable depending on what freq. range you want so it seems like a pretty good all around antenna. I'll update when I test out some more ranges.
 

kb2vxa

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Hi Sub and readers,

That plastic piece is simply the insulator but since it supports the whip I would handle with care like any other, they're all made that way and not to be manhandled.

No, not three, possibly not even two lengths for 800MHz unless it can go down to 3" below the center load. 3" is 1/4 wave and 9" is 3/4 wave, only those will be resonant and present a 50 ohm impedance to the antenna input. Not that it matters all that much but 6" being 1/2 wave (also resonant) presents several thousand ohms it's way out of line.

There is that one certain difficulty with such an antenna, 800 is the oddball so with the whip so adjusted it's out of line with VHF Hi Band, the length for that being 19" and then it's out of line for 800. With the upper section fully extended (if it's adjustable) the load coil roughly resonates it on VHF Lo Band so what's under it makes little difference. For optimum performance it has to be adjusted for the band in use and you can't walk and chew gum at the same time with this one.
 

subter

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Thanks for the more technical explanation, I'm still learning in some areas. Let me clarify: the bottom section adjusts to 5 3/4" (same as stock antenna for BCD396T), 7 3/4" and 9 1/4". The top extends out to several more legnths So kb2vxa, what would be the optimal length for the 800 range?
 

subter

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Can anyone comment on the optimal length to extend this antenna for the 800 range?
 

subter

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Well I found my answer elsewhere. The formula for computing proper length in inches on a whip antenna is 2800/frequency in Mhz.
 

Al42

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Except that you're not taking the coil into account. You can't adjust a loaded antenna with a ruler, you need an antenna bridge or experimentation. (Or measurement of the inductance of the coil and a few formulas.)

BTW, both the top and bottom are infintely adjustable - you don't have to only use the antenna with any particular piece fully extended. The adjustment is any length from shortest to longest for that part of the antenna.
 

MB

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subter said:
Can anyone comment on the optimal length to extend this antenna for the 800 range?
Did you read the instructions that came with it?

They say to only extend 1 to 3 lower section for 220 - 1296 MHz.

So for 800MHz I would experiment with only extending 1 lower section.
 

wogggieee

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I've found that with the antenna all the way retracted i get pretty good all around coverage on VHF, UHF, and 800. If i have the bottom section (below the coil) i get better on VHF and UHF and 800 seems to pick up very slightly. I really seem to get good performance in most configurations. Though i think alot of the signals here are fairly strong.
 

gcgrotz

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I have that antenna, I once hooked it to the Anritsu Site Master antenna analyzer and played with various lengths while watching the sweep. If I get time I'll dig out the Anritsu and try it again. I don't think I was really interested in 800 at that time. I bought it for Lowband fire around here but they have moved to 800 sooo...

BTW, I've had it for years, I used it to monitor mil-air on the morning of Sept 11. It has held up very well but just dont whack it hard because it would probably snap right off.
 

user786

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I also have this telescoping Radio Shack antenna and would LOVE to get ACTUAL results from someone doing an antenna sweep.
I would be interested in knowing EXACTLY where is the best adjusted length for these frequencies:

860 Mhz
470 Mhz
170 Mhz
150 Mhz
130Mhz
125 Mhz.

I know I am asking a lot if I am just asking a favor BUT what the heck I'll ask anyway. If someone could help I would greatly appreciate it. If you can't then that's fine also :)

Either someone will reply and possibly benefit a lot of us or someone will think I am a real jerk who should go out and buy my own sweeper.

Thanks in advance for any responses.
 

W4KRR

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To expand on MB's answer above:
The instructions are very general in nature, they say for 25 thru 136 MHz to extend all nine sections; for 138 to 174 MHz extend only the upper four sections, and from 220 to 1296 Mhz extend only one to three lower sections. You could probably fine tune the adjustment if you had test equipment.
 

gcgrotz

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OK OK, I get the hint... I'll get er done sometime in the next day or 2 I promise. Don't worry about your own sweep gear, mine belongs to my employer and they paid a sweet chunk for it. Check out Tessco for Anritsu products.
 

user786

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Any updates for us gcgrotz ?
Heck you are darn lucky to have access to that kind of euipment.
 

gcgrotz

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It is sitting on my desk right now. If my phone doesn't ring making me have to go out and actually work, I will do it in a few minutes (soon as I finish browsing RR - gotta have priorities)!
 

gcgrotz

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Test results

Ok here is an attached excel spreadsheet. I had to zip it so it would post. I picked frequencies where the best SWR values could be found, they are close to the requested frequencies.

This antenna, from an SWR point of view, kind of stinks. But then so do most scanner antennas. The good news is that since it is mounted on a handheld, there is no feedline loss due to the high SWR. Note that a low SWR does not necessarily mean better reception, a dummy load for instance. I don't want to start that discussion!!!

Best SWRs at high end of VHF band around 170 and in the mil-air band from 250 to 315.

Pretty decent on low band - surely better than a stock rubber duck

800 MHz is not great but I noticed BIG changes in both SWR (generally better) and resonant frequency (goes higher) when I put my hand on the connector at the base. If you do a lot of 800 listening, maybe 3 or 4 wires about 3" long secured to the connector would give you a ground plane of sorts. Keep the scanner vertical at this freq, cross polarization losses can be 15-20db. Not quite so critical at VHF/UHF.

For the money, if you can't put up an outside antenna, at 800 MHz the best deal is a cellular mag-mount on top of a file cabinet or refridgerator.

It is cool to have access to this test equipment. The calibration 50ohm load costs as much as a decent scanner! I have spent many long all-nighters going around doing annual system sweeps. We can't take sites down before 00:00 to disconnect lines. That part isn't cool. I only wish it covered 2-30 MHz too! It can measure feedline losses and distance to fault, great for testing that old coax in the junk box.

Ya'll have fun!
 

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user786

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Thanks gcgrotz. That info is excellent!
Wonder why Radio Shack couldn't have done that ?

One clarification I need is which section you are referring to when you say bottom section and top section. I already know the top sections are referring to the sections above the black center load and the bottom sections are referring to the sections below the black center load.
What I need clarification on is when you say 1 bottom section extended and 0 top sections extended....which one of the bottom sections is extended ? The one closes to the BNC end or the one closest to the black center load ?
And same for the top sections...when you say 1 top section extended and 0 bottom sections extended....which one of the top sections is extended ? The one closes to the TIP end or the one closest to the black center load ?

It makes a difference for sure as the sections are of differing lengths so I just wanted to know which ones you used in your testing.

Thanks again
 
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