Looking For A Base Antenna For 39.3 - 39.6 Range

[951ryan]

Hey Guys,

Newbie here but been hosting live audio feeds for many years now. I'm struggling to pick up our local Highway Patrol on 39.680 with my discone antenna and would like to find something to give me my strongest chances at picking up the signal for me to stream to Broadcastify. Antenna sits on a 10ft pole on my 2nd story balance but its a somewhat hilly congested area. Would like to stay under $300 if possible on this one.

Any ideas?

 

[nd5y]

You can build a ground plane or dipole for way less than $300.

 

[spongella]

And mount it vertically.

 

[Ubbe]

If your discone have a top element you can try and replace that with a 1/4 wave element of 1.8 meter lenght, or 72 inches. You probably have to attach some non metallic guy wires to the top of that element as it would otherwise break the insert to the discone when the wind blows. My local hardware store have twice that long $10 aluminium rods that could be used so it should be pretty easy to find one and figure out have to attach it to the discone.

/Ubbe

 

[NC1]

Back in the days, in my old hometown, the FD and PD were both on VHF Lo like you are trying to receive. I know the frequencies were around 37 MHz and all the FD volunteers, along with off duty police used the old stainless steel 102" CB antenna. A few people cut them down a tiny bit to be on frequency but the rest just left it as-is and nobody could discern a receive difference between the two.

As far as the ground plane is concerned, I do not remember any specific style if any were even being used. I do recall a few people attached the coax braid to the metal mast and it worked just fine. You might want to try that first as a very effective alternative to messing with the discone.

 

[K5MPH]

I have use a A-99 Antron CB antenna for VHF Lo band and always seem to work good,NC1 idea might work also if you are in need for space concerns for mounting a bigger antenna like the Antron 99 sounds like you need a antenna with gain for that band area.....

 

[bharvey2]

If you're looking to receive VHF low band only, consider a quarter wave ground plane antenna or maybe a vertically mounted dipole as suggested above. Either could be fab'd up quickly and inexpensively. Rough dimensions on your elements would be just under 6ft in length for a 1/4 wave ground plane.

 

[prcguy]

If your Discone has a top whip I would consider lengthening the whip leaving the base loading coil in place. The base coil helps to decouple the whip on higher frequencies and will also shorten its length for 39Mhz. Since most top whips on Discones are tuned around 50MHz, you would only have to lengthen it around 1 to 1 1/2ft to resonate around 39MHz.

If your discone have a top element you can try and replace that with a 1/4 wave element of 1.8 meter lenght, or 72 inches. You probably have to attach some non metallic guy wires to the top of that element as it would otherwise break the insert to the discone when the wind blows. My local hardware store have twice that long $10 aluminium rods that could be used so it should be pretty easy to find one and figure out have to attach it to the discone.

/Ubbe

 

[ko6jw_2]

I am using a 48" whip on my Diamond discone and that brings the low band resonance to about 42Mhz. The whip is 0.10 inch and is available from various suppliers in different lengths. This one happened to be a whip off of an old RS 5/8 wave mag mount.

Arrow Antenna will custom make ground planes to your specification. I am think of ordering one for CHP. Not very expensive.

The discone, even though it can be tuned with a longer whip, is not a very efficient low band antenna.

 

[NC1]

The discone, even though it can be tuned with a longer whip, is not a very efficient low band antenna.

Exactly. Once you start messing with it, everything will be thrown out of whack.

You could try it, but you will eventually get around to realizing a dedicated low band antenna is the only way to go.
There is no getting around physical length, loading coils are just a compromise that will attenuate and degrade reception.

 

[Ubbe]

The base coil helps to decouple the whip on higher frequencies and will also shorten its length for 39Mhz.

Good point, but a shortening coil means that it also reduces the signal you want to receive as the effective element to pick up the radiosignal are shorter. I think that the OP wants to concentrate on the 39MHz feed and optimize that as much as possible.

The discone, even though it can be tuned with a longer whip, is not a very efficient low band antenna.

Yes, but the discone are not used as such and only works as a groundplane at 39MHz for the top whip.

/Ubbe

 

[prcguy]

If the OP only needs a 39MHz antenna, then he should get a dedicated 39MHz antenna. If he needs VHF/UHF bands and 39MHz and there is a top whip on the Discone then I think lengthening the whip will make a worthwhile improvement.

 

[techman210]

I have been thinking of buying one of these Sirio antennas.

The price seems pretty reasonable.

Sirio GPA 40-70 Omni-Directional Base Antenna FASTEST SHIPPING | eBay

 

[prcguy]

Here is the same antenna but tunable from 27 to 45MHz. If this is for CHP you could tune the 39MHz through 45MHz channels.

Sirio GPA 27-45 Mhz ground plane base antenna | eBay

I have been thinking of buying one of these Sirio antennas.

The price seems pretty reasonable.

Sirio GPA 40-70 Omni-Directional Base Antenna FASTEST SHIPPING | eBay

 

[N4ANJ]

Check out the Hustler G-3754. 37-54 mhz, 8 ft tall, 6.4 db gain, you can adjust the lengths to set your frequency, about half your budgeted amount,and weighs 9 lbs.

 

[Ubbe]

The Hustler is a standard 5/8 GP antenna and are not even close to having 6.4dB gain.

My suggestion to add a full 1/4 wave element to the discone costs almost nothing as everything else needed are already supplied by the discone.

/Ubbe

 

[radioman2001]

Buy a cheap CB antenna and cut it down, as you are only receiving. You are going to lop off about a foot from the verticle the radials are not that important. Or you can take the dimensions of the VHF J pole and make them longer. Either way you are going to have use some math.

 

[NC1]

The Hustler is a standard 5/8 GP antenna and are not even close to having 6.4dB gain. My suggestion to add a full 1/4 wave element to the discone costs almost nothing as everything else needed are already supplied by the discone.
/Ubbe

The 5/8 is used only for transmit (there is a whole theory behind this that I am not going to get into), but the 5/8 is slightly off frequency for the receive. I would not suggest it for receiving purposes.

That 6.4 dB gain claim is assuredly bogus. Any magical antenna that only states "dB" should be summarily dismissed for the garbage that it is. Anyone half way legitimate will state either dBi or dBd. Even a 3.2dBi equals a 0dBd in the real world. Maybe it has a 6.4 db gain over a dummy load.

If you add a 1/4 wave element to the discone, then the remaining 1/4 (to make a 1/2 wave) is nothing more than a corkscrew. It's not going to do much in the real world. Also remember that the coil is already a compromise to accommodate both VHF and UHF, so the number of coil turns along with the spacing and wire guage are not really going to be ideal to begin with.

Best solution: old 102" CB whip (cut to frequency) mounted on a pole with a fairly decent cable as short as possible. Center conductor goes to the antenna, and braid gets affixed to the pole. I doubt anything else will outperform that setup by any decent margin.

 

[radioman2001]

Quote"
That 6.4 dB gain claim is assuredly bogus. Any magical antenna that only states "dB" should be summarily dismissed for the garbage that it is.

Manufacturers always like to use DBi as a comparison, hence you get the BS gain figures. Plus any antenna cut relatively close to correct frequency will work on receive, especially on low band. The old Plectrons and Installerts on low band used to work with a piece of #18 wire hanging out the back

 

[prcguy]

It can't be 6.4dB gain and I also see it rated as 4.25dBd gain, which is impossible. Its only about 1/4 wavelength long. Did Hustler somehow change the laws of physics?

Check out the Hustler G-3754. 37-54 mhz, 8 ft tall, 6.4 db gain, you can adjust the lengths to set your frequency, about half your budgeted amount,and weighs 9 lbs.