30-50 mhz antenna?

[bobruzzo]

I was wondering if I'd be able to hear anything on those old lowband freqs. So I put radio into custom search, connected an old Antron-99 cb antenna, and I can hear Norwich Fire (Ct) all the way here in Cranston (RI) Thats about 37.5 miles. Also hearing many other stations (fire, rescue) out in Connecticut. The ground around new england is not very conductive like in Kansas, lots of rocks! I realize the cb antenna is far from 30-50 mhz resonance and I am losing some signal. The antenna was cut to work on upper portion of 10 meters. I looked all over for a specific 30-50 mhz base antenna but nothing out there. I could make a simple vertical dipole but no way to hang it and get it up vertical and high enough. I also have a Diamond Discone but even with its top vertical element, the cb antenna is probably better. Anyone have different ideas? A cheap commercial antenna?

 

[prcguy]

A military OE-254 bicone works fantastic as does a Cobham COM-201B and they cover roughly 30 to 88MHz continuous with no tuning. Both show up on eBay surplus for various prices. There are some large military Discones that cover 30MHz to past 100MHz but those are very scarce and pricy. I need to get rid of one but have to think about what its worth. These are huge at about 8ft tall and 8ft across at the base.

 

[bobruzzo]

A military OE-254 bicone works fantastic as does a Cobham COM-201B and they cover roughly 30 to 88MHz continuous with no tuning. Both show up on eBay surplus for various prices. There are some large military Discones that cover 30MHz to past 100MHz but those are very scarce and pricy. I need to get rid of one but have to think about what its worth. These are huge at about 8ft tall and 8ft across at the base.

Wow those things get huge. I remember when I was a kid we used to go to a place called Beavertail on the island of Jamestown in Narragansett bay (RI) There was a huge abandoned military complex and there were fields of huge antennas. I remember seeing those gigantic discones. The place was razed in early/mid 70's. But I will look on ebay for the antennas you mentioned.

 

[markclark]

At the bottom of this page you can order a very solid low band antenna. It is made of solid, heavy rod with a machined mounting bracket. I have one and I'm impressed with both the workmanship and performance for my CHP monitoring.

Arrow Antenna Arrow Plane

 

[Ubbe]

But I will look on ebay for the antennas you mentioned.

The cheap alternative could be to get a normal size discone that works from 100MHz and upwards and then extend every element to 3 times their length. You would have to support the ends by steel wire or something and twist two turns around each end to form a ring. Best are to solder that to the elements but glue could also work. It doesn't matter if it has electrical contact or not but it shouldn't rub metal to metal as that creates RF interference. The top elements, also supported by a steel wire, probably need something to hold them up as well so they don't break off at the center crown. A circle of some hard plastic laid on top with a cut out for the middle crown might work, having the steel wire going thru it at each element. Or just two wooden planks in a cross with a hole in the middle for the crown.

/Ubbe

 

[Ubbe]

At the bottom of this page you can order a very solid low band antenna.

It doesn't seem suitable. " This Antenna will have a bandwidth of about 0.5 MHz near the low end of that range"

/Ubbe

 

[dragonball]

i have a wmm 460 antenna from whistler

 

[bearcatrp]

I still have my old Antron 99. Haven’t used it in 20 years. If I recall, there are ring toward the base allowing you to adjust frequency range. I don’t remember how much it will adjust. Search for that info to check. The Antron 99 is one of the best cb antennas I have ever owned.

 

[KinkedCoax]

A military OE-254 bicone works fantastic as does a Cobham COM-201B and they cover roughly 30 to 88MHz continuous with no tuning. Both show up on eBay surplus for various prices.

I find the COM-201B to be the best compact performer for low band VHF. You can't go wrong with this battle proven unit. Speaking of which, I just picked up the vehicular mount variant on Ebay. The seller accepted my offer which was almost half the Buy It Now asking price. As of this posting there are 3 more available. If someone else doesn't snag them I probably will .

 

[p1879]

I have had good lowband vhf results with the Antron as well as another "cb" vertical. Even though coax loss is not high at these frequencies, the Belden 9913 cut out a lot of noise. If you have that antenna up it might be worth working it out for awhile.

We are happily entering a good period of more frequent propagation events for this band. If you have an old scanner that you can devote to low band, perhaps try running some of the frequencies reported in loggings on this forum. At local dusk especially, but also at other times, you might encounter the famously strong Ft. Hood TX range control frequency of 30.450.

You might like to hear it before the Ft. name gets cancelled--and witness another loss of our national history.

 

[markclark]

It doesn't seem suitable. " This Antenna will have a bandwidth of about 0.5 MHz near the low end of that range"

/Ubbe

That number is for transmitting. Reception across the band will work well.

 

[prcguy]

Antennas like this are reciprocal, whatever they do on transmit they do the same on receive. Meaning if they have narrow BW and suck on transmit 5MHz from resonance, they will suck on receive to the same extent.

The problem I encounter all the time with antenna reviews is the reviewer has nothing to compare their antenna with, so they might say "it works great" when in reality it doesn't compared to an antenna that actually does.

That number is for transmitting. Reception across the band will work well.

 

[p1879]

One could note that forum member "KKN50", who posts some great vhf low-band loggings--many are good "skip" catches--uses a 10M dipole antenna.

 

[markclark]

Antennas like this are reciprocal, whatever they do on transmit they do the same on receive. Meaning if they have narrow BW and suck on transmit 5MHz from resonance, they will suck on receive to the same extent.

The problem I encounter all the time with antenna reviews is the reviewer has nothing to compare their antenna with, so they might say "it works great" when in reality it doesn't compared to an antenna that actually does.

So you say that a ground plane antenna is narrow banded for receive? Unbelievable.

 

[MDScanFan]

A typical ground plane antenna (thin quarter wave whip over a ground plane) is narrow band when using a metric like efficiency. Sure it will receive signals across a wide range of frequencies but it will only be efficient across a narrow portion. A typical ground plane antenna tuned for 30 MHz will probably have 10-20 dB of loss at 50 MHz. Whether that much loss matters will depend on the situation.

So you say that a ground plane antenna is narrow banded for receive? Unbelievable.

 

[prcguy]

Yes, it will have a percent of band width like +/- a couple percent and the further you get away from the resonant point the worse it works. For example, a ground plane cut for 146MHz will have an ok match at 144 and 148MHz and you won't notice much if any difference in gain at +/- 2MHz. Go +/- 5MHz and it will start to degrade. Go +/- 10MHz and it can be down several dB in gain not to mention the match is getting pretty bad. Go +/- 20MHz and it can be 6dB or more down.

For a lower frequency antenna the same percentage of BW will give you a narrower useable range because the base frequency is lower. So a ground plane cut for 40MHz might work ok +/- 1MHz but get +/- 5Mhz away and your probably down 3dB and at +/- 10MHz probably a good 6dB down and possibly more. This works the same for transmit and receive.

Some of the broad band military antennas are a compromise in they may be degraded a few dB from a resonant 1/4 wave ground plane but they can be consistent over a very wide range like not much difference in gain from 40MHz to 90MHz. Many of the military units roll off some at 30MHz but over most of their range they will work much better than a resonant ground plane used way out of band.

So you say that a ground plane antenna is narrow banded for receive? Unbelievable.

 

[markclark]

Yes, it will have a percent of band width like +/- a couple percent and the further you get away from the resonant point the worse it works. For example, a ground plane cut for 146MHz will have an ok match at 144 and 148MHz and you won't notice much if any difference in gain at +/- 2MHz. Go +/- 5MHz and it will start to degrade. Go +/- 10MHz and it can be down several dB in gain not to mention the match is getting pretty bad. Go +/- 20MHz and it can be 6dB or more down.

For a lower frequency antenna the same percentage of BW will give you a narrower useable range because the base frequency is lower. So a ground plane cut for 40MHz might work ok +/- 1MHz but get +/- 5Mhz away and your probably down 3dB and at +/- 10MHz probably a good 6dB down and possibly more. This works the same for transmit and receive.

Some of the broad band military antennas are a compromise in they may be degraded a few dB from a resonant 1/4 wave ground plane but they can be consistent over a very wide range like not much difference in gain from 40MHz to 90MHz. Many of the military units roll off some at 30MHz but over most of their range they will work much better than a resonant ground plane used way out of band.

I appreciate what your saying, however, I think the OP just wanted to know of a good general use low band antenna for low band monitoring. And, I did compare the ground plane to two other professional grade low band antennas - and for a fraction of the cost the perfomance is impressive compared for receive only purposes.

 

[trp2525]

...I looked all over for a specific 30-50 mhz base antenna but nothing out there...Anyone have different ideas?...

Antenna Specialists made an excellent dedicated VHF-Low monitor antenna back in the day. The model number was MON-4 and it covered from 25-50 MHz (see 3 attached pictures). Although Antenna Specialists has been out of business for many years (unfortunate as they made some excellent monitor antennas from the 1970's to the early/mid 2000's), you can occasionally see them pop up on eBay, Craigslist, etc. Some of the antennas are even New-Old-Stock/New-In-Box.

 

[prcguy]

This is a good antenna but it only covers a few MHz of VHF lo at a time. You have to cut the whip to favor the needed part of the band.

Antenna Specialists made an excellent dedicated VHF-Low monitor antenna back in the day. The model number was MON-4 and it covered from 25-50 MHz (see 3 attached pictures). Although Antenna Specialists has been out of business for many years (unfortunate as they made some excellent monitor antennas from the 1970's to the early/mid 2000's), you can occasionally see them pop up on eBay, Craigslist, etc. Some of the antennas are even New-Old-Stock/New-In-Box. View attachment 121815View attachment 121816View attachment 121817

 

[trp2525]

This is a good antenna but it only covers a few MHz of VHF lo at a time. You have to cut the whip to favor the needed part of the band.

The Antenna Specialists Monitor antennas that covered VHF-Low back in the day were typically cut at the factory for the center of the band. With the antenna covering 25-50 MHz that made the center of the band at 37.5 MHz. If you wanted to optimize performance above 37.5 MHz they included a cutting chart to shorten the antenna for better resonance at the higher frequency that you desired. If you wanted to optimize performance for a frequency below the 37.5 MHz center of the band, you were out-of-luck as you couldn't "add metal" to the antenna's original factory length to make it longer.

I have the instruction manual for the Antenna Specialists MON-52 mobile monitor antenna and it includes the VHF-Low cutting chart. The chart shows the antenna cutting length for frequencies above 37.5 MHz. For frequencies below 37.5 MHz you leave the antenna at its original factory length.