Looking for a multi-band mobile antenna covering VHF low

[HappilyRetired]

I am looking for a quality multivand mobile antenna preferably with an MMO mount covering 42 MHz, all of the VHF airband up through CALFIRE/US Forest Service (118 - 173 mhz) and 700/800. I know that's a lot to ask since VHF low band is pretty much not in use. But the California Highway Patrol is there and they have no intention to moving. I have learned that I can do it with a diamond mx2000 triplexer that is reversed but then I will need three separate antennas and I don't want to do that. I'm a retired cop and I don't want to look like a cop.

 

[prcguy]

What you are looking for doesn't really exist with VHF air band, if you compromise that the old A/S MON series will cover 42MHz (after tuning) plus roughly 150-174, 450-512 and 800. So will the Austin Spectra although in my field testing the A/S works better in the VHF lo and UHF ranges. VHF air on these is about like a random coat hanger wire.

Here is some info with a gain chart comparing the A/S and Spectra to a broad band military antenna but VHF lo through UHF, no 700 or 800.

30-50 mhz antenna?

Years ago I did an article for Monitoring Times magazine comparing a 9ft military broad band antenna to the Antenna Specialists MON series and an Austin Spectra. On the chart below I used the Shakespeare military antenna as a reference (green trace) and compared the other two antennas with it...

forums.radioreference.com

 

[HappilyRetired]

What you are looking for doesn't really exist with VHF air band, if you compromise that the old A/S MON series will cover 42MHz (after tuning) plus roughly 150-174, 450-512 and 800. So will the Austin Spectra although in my field testing the A/S works better in the VHF lo and UHF ranges. VHF air on these is about like a random coat hanger wire.

Here is some info with a gain chart comparing the A/S and Spectra to a broad band military antenna but VHF lo through UHF, no 700 or 800.

30-50 mhz antenna?

Years ago I did an article for Monitoring Times magazine comparing a 9ft military broad band antenna to the Antenna Specialists MON series and an Austin Spectra. On the chart below I used the Shakespeare military antenna as a reference (green trace) and compared the other two antennas with it...

forums.radioreference.com

I am not able to locate the mon52 or the replacement mon752. It looks like the only thing available is the Austin Spectra but $160 is a bit much. My plan believe it or not was to simply place it on a magmount on a file cabinet in my office. Right now I'm on the third floor and getting miserable low band performance. I haven't tried high band or 800 yet. I'm told that 800 goes through walls quite well compared to low band. That was the reason why CHP went to 700 MHz portables. Basically I either need to spring for the Spectra or go with plan B.

Plan B was to get copper alarm tape that normally goes on windows and the connectors used to wire them to the alarm system and go up 48 in with a slight break beneath it and then down 24 in and then connecting a 300 ohm balun a 75 ohm output. From there to the scanner. Right on the wall. If it doesn't want to stick I can use push pins to hold it in place. I don't know how well that's going to work especially since I don't know what's in the wall as far as wires and whatnot to mess with this antenna that was referred to me on this site. There's only one other option left.

I spring for the Spectra and mount a metal plate in a clear spot in my office on the ceiling - no fluorescent lighting - and the Spectra suspended upside down. I read about this on a another website and I'm pretty positive based on what I read that it'll work upside down or right side up. It's not like it's a gain antenna that narrows the beam? My intention is VHF low band for CHP, Air Band, VHF for fire, 470-512 for LA County Fire and then San Bernardino County fire at 800.

I'm not always the sharpest tool in the shed but I'm trying to learn. What would be the most productive method to pull in a good signal? I'm kind of leaning towards the copper tape on the wall which is a pretty inexpensive way of going about it. But the inverted Spectra seems like the better choice all the way around.

 

[ind224]

You said NMO so I was going to stay quiet but then you said you thought about mag..... the old rat shack 2 coil mag mount mobile covers everything you want 42 being the compromise. Been running those for decades replacing the tiny coax that won't bite a screw on BNC w RG6 when needed and using old CB antenna or speaker magnets when the stocker has had enough drop testing.

 

[popnokick]

Before you stick anything to the wall try one of these very portable antennas to locate the best spot on the wall or in a window. Scroll down the page to see the all-wire version you can hang anywhere. They work on VHF low band by also using the coaxial cable as part of the antenna. Once you find the “sweet spot” for reception you can make one out of copper tape per the specs in the article (one leg 48” and one 18”)

Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

wiki.radioreference.com

 

[prcguy]

I am not able to locate the mon52 or the replacement mon752. It looks like the only thing available is the Austin Spectra but $160 is a bit much. My plan believe it or not was to simply place it on a magmount on a file cabinet in my office. Right now I'm on the third floor and getting miserable low band performance. I haven't tried high band or 800 yet. I'm told that 800 goes through walls quite well compared to low band. That was the reason why CHP went to 700 MHz portables. Basically I either need to spring for the Spectra or go with plan B.

Plan B was to get copper alarm tape that normally goes on windows and the connectors used to wire them to the alarm system and go up 48 in with a slight break beneath it and then down 24 in and then connecting a 300 ohm balun a 75 ohm output. From there to the scanner. Right on the wall. If it doesn't want to stick I can use push pins to hold it in place. I don't know how well that's going to work especially since I don't know what's in the wall as far as wires and whatnot to mess with this antenna that was referred to me on this site. There's only one other option left.

I spring for the Spectra and mount a metal plate in a clear spot in my office on the ceiling - no fluorescent lighting - and the Spectra suspended upside down. I read about this on a another website and I'm pretty positive based on what I read that it'll work upside down or right side up. It's not like it's a gain antenna that narrows the beam? My intention is VHF low band for CHP, Air Band, VHF for fire, 470-512 for LA County Fire and then San Bernardino County fire at 800.

I'm not always the sharpest tool in the shed but I'm trying to learn. What would be the most productive method to pull in a good signal? I'm kind of leaning towards the copper tape on the wall which is a pretty inexpensive way of going about it. But the inverted Spectra seems like the better choice all the way around.

In some recent testing the Austin Spectra did poorly on some bands and the MON series did better. You can make a bent up dipole or similar in a window out of alarm tape but why would you use a TV balun?

 

[HappilyRetired]

In some recent testing the Austin Spectra did poorly on some bands and the MON series did better. You can make a bent up dipole or similar in a window out of alarm tape but why would you use a TV balun?

"Antenna impedance is a significant parameter influencing the performance of communication systems. Matching the antenna impedance with the system impedance is critical for maximum power transfer, as an antenna transmits or receives maximum power when the impedance is matched."

this is no different than when we had roof-mounted TV antenna is it had to have a TV balance so that you could connect cable TV coax and bring it down to your TV set that also had a coax TV connector. I think it was called the f connector. Otherwise you ran ladder line, that brown stuff, and then you had to use a converter at the back of the TV set so that it would plug into the 75 home receptacle.

 

[prcguy]

"Antenna impedance is a significant parameter influencing the performance of communication systems. Matching the antenna impedance with the system impedance is critical for maximum power transfer, as an antenna transmits or receives maximum power when the impedance is matched."

this is no different than when we had roof-mounted TV antenna is it had to have a TV balance so that you could connect cable TV coax and bring it down to your TV set that also had a coax TV connector. I think it was called the f connector. Otherwise you ran ladder line, that brown stuff, and then you had to use a converter at the back of the TV set so that it would plug into the 75 home receptacle.

TV antennas with screw terminals are usually 300 ohms balanced and require a 300 to 75 ohm matching transformer to feed coax. This is due to the particular log periodic design they use that results in a higher impedance feed point. Most any antenna you would make for VHF low band like a dipole or ground plane would be low impedance and would not require a matching transformer For direct connection to 50 or 75 ohm coax.

 

[mmckenna]

I am looking for a quality multivand mobile antenna preferably with an MMO mount covering 42 MHz, all of the VHF airband up through CALFIRE/US Forest Service (118 - 173 mhz) and 700/800.

One option would be to use a diplexer and two antennas:

1 antenna would be a VHF High band 5/8th's wave. That would give you good performance on VHF high band. It would act as a base loaded 1/4 wave on VHF low band. some amateur radio operators have done this with 2 meter/6 meter band installations.

Then a separate antenna for 700/800MHz.

May not be exactly what you are looking for, but would be an option. The VHF 5/8th's wave would stand out, but 1/4 wave 700/800MHz antennas are pretty short and would likely blend in well.

 

[prcguy]

One option would be to use a diplexer and two antennas:

1 antenna would be a VHF High band 5/8th's wave. That would give you good performance on VHF high band. It would act as a base loaded 1/4 wave on VHF low band. some amateur radio operators have done this with 2 meter/6 meter band installations.

Then a separate antenna for 700/800MHz.

May not be exactly what you are looking for, but would be an option. The VHF 5/8th's wave would stand out, but 1/4 wave 700/800MHz antennas are pretty short and would likely blend in well.

I had forgotten about a 5/8 wave VHF antenna working at roughly 1/3 the frequency as a 1/4 wave base load. Looking at the typical Larsen 2m 5/8 tuned to 146MHz and working well at about 52MHz. That is a ratio of about 2.808. If you tune a Larsen or similar 5/8 mobile whip to around 155MHz for commercial use it should then resonate around 55.2MHz, way too far from CHP freqs to be effective. Very unfortunate.

 

[mmckenna]

Good point on the 5/8th's VHF whip. Too far out to be much good.

As for CHP going to CRIS, I think that's going to be a slow transition.
We got a new chief a few months ago, and he came over from CHP. He was not a fan of the low band system.
Since CRIS is still being built out, any real widespread migration of CHP is going to take a while. Menifee will probably benefit from CRIS/CHP transition before a lot of the state. However, I suspect it'll be mostly/fully encrypted.
Still, there's a lot of regions of the state that will likely never have good CRIS coverage. I suspect low band will stick around in some form or another for many years to come.

Doing this all with one antenna would be a challenge. Two antennas would be much easier. A dedicated low band antenna would likely be your best option, and then add one of the tri-band antennas for everything else.

 

[RFI-EMI-GUY]

I am looking for a quality multivand mobile antenna preferably with an MMO mount covering 42 MHz, all of the VHF airband up through CALFIRE/US Forest Service (118 - 173 mhz) and 700/800. I know that's a lot to ask since VHF low band is pretty much not in use. But the California Highway Patrol is there and they have no intention to moving. I have learned that I can do it with a diamond mx2000 triplexer that is reversed but then I will need three separate antennas and I don't want to do that. I'm a retired cop and I don't want to look like a cop.

Trying to receive low band from within an office building is going to be a challenge with the noise from equipment inside competing with the desired weaker signal outside.

The idea about alarm foil is clever. I used to install burglar alarms and my seasoned partner Burt, told me that when he lived in NYC, a customer who sold transistor radios in the basement of a building needed coverage to demo the new fangled radios. So Burt put alarm foil around the top of the glass display cabinet, ran twin lead up to the roof and hooked up an FM broadcast antenna. It worked extremely well.

 

[HappilyRetired]

TV antennas with screw terminals are usually 300 ohms balanced and require a 300 to 75 ohm matching transformer to feed coax. This is due to the particular log periodic design they use that results in a higher impedance feed point. Most any antenna you would make for VHF low band like a dipole or ground plane would be low impedance and would not require a matching transformer For direct connection to 50 or 75 ohm coax.

I am going by this design posted on this website. It uses a 300 to 75 home balun. I do know a bit more about my issue though. I find that if I put the scanner on my chest with or without the bracket and using the provided with antenna the low band frequency comes in loud and clear. It is capacitively loading to my body for the ground side of the antenna. If I said it back down it gets crappy again. That tells me that I have a problem with a ground. This suggests to me that if I put anything up that has the vertical portion of an antenna in the ground I would be doing okay. A couple of days per person there are

Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

wiki.radioreference.com

 

[popnokick]

I am going by this design posted on this website. It uses a 300 to 75 home balun. I do know a bit more about my issue though. I find that if I put the scanner on my chest with or without the bracket and using the provided with antenna the low band frequency comes in loud and clear. It is capacitively loading to my body for the ground side of the antenna. If I said it back down it gets crappy again. That tells me that I have a problem with a ground. This suggests to me that if I put anything up that has the vertical portion of an antenna in the ground I would be doing okay. A couple of days per person there are

Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

wiki.radioreference.com

The "problem" is more accurately described as with the RF counterpoise "ground". As you've very correctly noted, your body is providing the counterpoise ground when you hold the radio, and it goes away when you put it down. Have you tried the Homebrewed OCFD yet? It may solve the counterpoise problem and is more likely not to rely upon you as the "ground".

 

[ind224]

Receive only correct?

 

[HappilyRetired]

The "problem" is more accurately described as with the RF counterpoise "ground". As you've very correctly noted, your body is providing the counterpoise ground when you hold the radio, and it goes away when you put it down. Have you tried the Homebrewed OCFD yet? It may solve the counterpoise problem and is more likely not to rely upon you as the "ground".

I sure don't want to have to hold the thing all the time to be the counterpoise. 🤣 I'm aware of the counterpoise. My Elmer has me reading a book on basic antenna theory for whatever that's worth. That's why I brought it up that if I put the scanner on my chest just using the included whip antenna yields good performance.

As for the OCFD, that's what I was going to use alarm tape for. I have different measurements for it but I'll go with whatever has been found to be most effective. 48 inches up and apparently 18 inches down is what is recommended. It has a 300 ohm impedance at the center point to which a 300->75 ohm cable TV balun is attached and terminated at the radio. 75 ohms versus 50 ohms is nothing. Not for receive. Even on transmit it would only be 1.5:1. At home I use LMR 400 for everything but here in the office I've been using RG6Q. I even bought the stripping tool as well as the special compression tool to attach high quality connectors. I have three radios here at the office and I plan on using a cable TV three-way splitter to share one antenna. I've heard that someone makes a special splitter or coupler for scanners but I don't know the company name.

I have also read that I can use copper alarm tape and make a rectangle of it around the window in my office and see how that works. I think that that would make the antenna somewhat directional but I won't know until I try. It may work on low band but then what about 800? That's a rhetorical question and I know that I just need to experiment. I will report my results here. I have a application that will allow me to read the RSSI of the control Channel which is I guess the reading of the signal strength? I'm led to believe that the higher the number the better.

It may end up that I purchased the Austin Spectra on a MAG Mount and suspended from the ceiling upside down but on a piece of metal for the ground plane. I can't seem to locate an antenna specialist on 752. That's supposed to be the better antenna for low band and up into 800.

 

[HappilyRetired]

Trying to receive low band from within an office building is going to be a challenge with the noise from equipment inside competing with the desired weaker signal outside.

The idea about alarm foil is clever. I used to install burglar alarms and my seasoned partner Burt, told me that when he lived in NYC, a customer who sold transistor radios in the basement of a building needed coverage to demo the new fangled radios. So Burt put alarm foil around the top of the glass display cabinet, ran twin lead up to the roof and hooked up an FM broadcast antenna. It worked extremely well.

Unfortunately I don't have access to the roof or I would put up at actual antenna.

 

[prcguy]

I am going by this design posted on this website. It uses a 300 to 75 home balun. I do know a bit more about my issue though. I find that if I put the scanner on my chest with or without the bracket and using the provided with antenna the low band frequency comes in loud and clear. It is capacitively loading to my body for the ground side of the antenna. If I said it back down it gets crappy again. That tells me that I have a problem with a ground. This suggests to me that if I put anything up that has the vertical portion of an antenna in the ground I would be doing okay. A couple of days per person there are

Homebrewed Off-Center Fed Dipole - The RadioReference Wiki

wiki.radioreference.com

I wont give my honest opinion of the Wiki OCFD project but I will point out that by design it does not cover the VHF low band. Its lowest design frequency is around 85MHz and it operates on harmonics of that. Plus the typical TV transformer is being stretched to cover the original 54 to 806MHz and CHP frequencies are out of the specified range meaning more loss on top of the OCFD that does not cover low band.

 

[HappilyRetired]

I wont give my honest opinion of the Wiki OCFD project but I will point out that by design it does not cover the VHF low band. Its lowest design frequency is around 85MHz and it operates on harmonics of that. Plus the typical TV transformer is being stretched to cover the original 54 to 806MHz and CHP frequencies are out of the specified range meaning more loss on top of the OCFD that does not cover low band.

I don't know if this is going to work but I'll try it and report my findings. The formula for an ocfd antenna is 64/36. Using 42 MHz as my base frequency the following math applies:

468/42 = 11.1428571429
11.1428571429 * .64
= 7.1314285715
* 12 = 85.577142858"

468/42 = 11.1428571429
4.0114285714 * .36
= 4.0114285714
* 12 = 48.1371428568"

The math checks out if I add both Inches together which means I have to have a 12 ft tall ceiling which I don't have. I suppose I could try from floor to ceiling and just accept the best that I can get, or maybe put a preamp in line, but I'm not going to be in my office all the time. One website I read mentioned that went stressed for space the antenna does not necessarily have to be in a straight line which means I could do a z shape for both the top and the bottom and see what I get using copper tape. I have a headache now.

Another thought would it be to take some light angle iron and drill it out for animal mounts and put one for low, vhf, and 350 and above. That would match a diamond MX2000 triplexer. I've read that if you reverse it physics basically picks the correct antenna. But it's a cost of antennas I may as well just buy the Austin Spectra!

Damn! At this point I think someone should award me a PhD in antenna Theory. I must have read a hundred websites trying to find an angle on this.

 

[HappilyRetired]

I came across this antenna but for some reason I doubt it works on low band. Then again it may be a electrical equivalent to the Austin Spectra.

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