Anyone tried this....?

[ILbandit]

Just curious of anyone has ever tried this Mod on the RS antenna, and if so, would it improve reception?

http://www.strongsignals.net/access/image/antennas/bearwires.gif

 

[N_Jay]

Just curious of anyone has ever tried this Mod on the RS antenna, and if so, would it improve reception?

http://www.strongsignals.net/access/image/antennas/bearwires.gif

Is there any explanation as to WHY those lengths were chosen?

I would ASUUME (Yes, I know) that the antanna was designed to work with the lengths as shipped.

Why is this better? What is the rational? :roll: :roll:

 

[scanjunkie]

It enhances low band performance. The stock antenna is resonant around 50MHz. The Mod changes the resonance to around 40MHz or so. Just depends on what you are listening to as to whether or not you want, or need, to do it.

Enjoy!
Mark

 

[ILbandit]

Is there any explanation as to WHY those lengths were chosen?

I would ASUUME (Yes, I know) that the antanna was designed to work with the lengths as shipped.

Why is this better? What is the rational?

I've never done it, just found that info, and was curious to the reasoning behind it also, I figured that by increasing the length it dropped the resonance, just didn't know if it would actually make enough difference to take the time to do the mod?

By taking it down to 40MHz, would that throw off everything on the mid bands, and 800's also?

 

[N_Jay]

It enhances low band performance. The stock antenna is resonant around 50MHz. The Mod changes the resonance to around 40MHz or so. Just depends on what you are listening to as to whether or not you want, or need, to do it.

Enjoy!
Mark

The original antenna 'should' have been somewhat resonant at several frequencies (At lease somewhere in each band).
Wondering where each resonant point is after the mod.

 

[ILbandit]

Wondering where each resonant point is after the mod.

That's what I'm curious about also.

Anyone ever put a stock one on a meter and checked it out? I know what they "claim" it to be, But who knows if it actually is there.

Maybe it isn't centered correctly, and that's why someone came up with this mod?

 

[N_Jay]

Wondering where each resonant point is after the mod.

That's what I'm curious about also.

Anyone ever put a stock one on a meter and checked it out? I know what they "claim" it to be, But who knows if it actually is there.

Maybe it isn't centered correctly, and that's why someone came up with this mod?

Most hobbiests would not have the tools to do this well.

At a minimum you would need a calibrated RF generator, good RF Selective voltmeter , and a reference antenna

A spectrum Analyser (calibrated) and a traking generator would be even better.

 

[ECPD279]

The way I understand it, the stock antenna is made resonant on 54, 144, and 440 MHz, as Radio Shack advertises that you can transmit on those ham bands. What the mod does is bring the antenna into the normally monitored scanner bands by making it resonant on 45, 155, and 460 MHz, as well as shortening the 800/900 MHz element a bit. I did the mod about six months ago, and it seems to work better on VHF Lo and Hi, about the same on UHF and UHF-T, and much better on 800/900 although it is still not by any means a stellar antenna. If you have the time and the spare rod laying around, and you don't want to use this as a ham antenna (who would?) by all means do the mod. It certainly didn't HURT the performance that this mediocre antenna achieves.

If however you want an antenna that will work MUCH better across the board, I use a Larsen NMO 2/70 dual band ham antenna which works beautifully from VHF-Lo right on up to 900 MHz. Strange that a 2M/440 ham antenna can outperform a scanner antenna across all bands, but it does.

 

[ILbandit]

I use a Larsen NMO 2/70 dual band ham antenna which works beautifully from VHF-Lo right on up to 900 MHz. Strange that a 2M/440 ham antenna can outperform a scanner antenna across all bands, but it does.

Do you think it out performs most of the "tri band" antennas in that price range out there?

i.e. Valor,Antenex,Antenna Specialist,etc.

 

[K5MAR]

I use a Larsen NMO 2/70 dual band ham antenna which works beautifully from VHF-Lo right on up to 900 MHz. Strange that a 2M/440 ham antenna can outperform a scanner antenna across all bands, but it does.

Do you think it out performs most of the "tri band" antennas in that price range out there?

i.e. Valor,Antenex,Antenna Specialist,etc.

I can tell you my experience. I used a Larsen commercial dualband version (NMO 150/450) as a scanner antenna and was fairly well satisfied with it, although it was lacking on VHF-low. Then I bought an Austin Spectra, and boy, did that make a difference! Both VHF-low and 800 MHz (the bands the Larsen wasn't designed for, of course) were much improved.

I've got the Spectra mounted on the headache rack behind the cab of my truck, connected to a Radio Shack Pro-2067. I'm planning a switch to a Uniden 780, and threw it into the truck for a road trip last week, connected to the same Larsen dualband referred to above, which is mounted on the left front fender opposite to the factory AM/FM radio antenna (hardly a prime location). The reception by the 780 was noticably better than the 2067, I can hardly wait to get it connected to the Spectra! :lol:

Mark S.

 

[ECPD279]

I use a Larsen NMO 2/70 dual band ham antenna which works beautifully from VHF-Lo right on up to 900 MHz. Strange that a 2M/440 ham antenna can outperform a scanner antenna across all bands, but it does.

Do you think it out performs most of the "tri band" antennas in that price range out there?

i.e. Valor,Antenex,Antenna Specialist,etc.

My second antenna is a Larsen NMO 150/450/800 scanner antenna, and I get better performance on the NMO 2/70. I also use a Radio Shack mag-mount 7db cellular antenna on the patrol car with surprisingly good results on VHF-Hi and UHF, although VHF-Lo is poor as you would expect. I haven't tried many other scanner antennas.

 

[nd5y]

I tried to modify a RS mag mount several years ago.
I measured it with a my MFJ antenna analyzer and
it read real bad everywhere. I thought there was some
weird problem so I took it to work and checked it on the HP network
analyzer and it was still bad everywhere. The mount and coax are junk.

I ended up taking it apart and built a better one using a good
Cushcraft NMO mag mount with low loss coax, a Larsen NMOQ mount
and some old Larsen whip pieces. I only used the top coil of the
RS antenna because I could not find rods of the proper size to fit
the Larsen mount and the bottom coil.

So anyway, I cut the bottom whip section about 19" and I used several
top whips of about 18 to 36" to cover whatever section of low band I
was interested in at the time.

The top coil acts as a center loading coil for low band and has enough
inductance to act as choke at high band, UHF and 800 MHz so that you
effectivey just have a 19" whip at those higher frequencies.
The top whip is cut to whatever lenght you need on low band
and doesn't seem to affect the higher frequencies.

You end up with a short loaded 1/4 wave on low band, full size 1/4 wave
on high band and 3/4 wave on UHF. I thought it worked really well.


Tom

 

[unitcharlie]

hi tom: could you post your mesaurements for the various rods.... i have a few useless rat shack antennas laying around.... might be able to get something out of them....

 

[nd5y]

Right now I have a 18.5" bottom rod and 21" top rod and
if I remember right the the 2:1 SWR bandwidth was about
150 - 160 MHz and 46 - 48 MHz.

I never measured or recorded the others and have long since cut them
up for other projects.

Tom

 

[unitcharlie]

thanx tom... i am always looking for things to do with my new rat shack antennas that don't work or stay together... but the 20 year old antenna works like a charm....

 

[scanjunkie]

I have the stock RS 20-032 mounted on an Antenex MON 51 base load and then mounted on a NMO mag mount...Works amazingly on all bands...best all band antenna I have ever used.