RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > Scanners, Receivers and Related Equipment Forums > Antennas and Associated Hardware > Build Your Own Antenna


Build Your Own Antenna - Discuss topics for building your own antenna.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 05-30-2018, 11:22 AM
Member
   
Join Date: Jun 2012
Posts: 8
Default UHF or BNC Panel Mount for Ground Plane Antenna?

Hi all,

I would like to make a ground plane antenna to monitor my local P25 system which is at 772 MHz. The signal comes in okay, but the transmissions break a lot and is very difficult to follow the conversations (my antenna is indoors). The broadcasting antenna is only 10 miles away, so an outdoor antenna would definitely improve the reception, but I still want to build my own antenna that may be mounted on the roof or attic.

I have looked at quite a few designs, but most of them use UHF/SO-239 mount even though the connectors are only good up to 300 MHz. Will that limitation have an impact on the antenna's performance near 800 MHz? If so, should I use a BNC mount instead since they are good to a much higher frequency?

I found this five pack of BNCs for a really low price: https://www.amazon.com/uxcell-Female...HTTTP5STGWFD2Y


Here is one of the websites I took a look at to make the antenna: https://m0ukd.com/calculators/quarte...na-calculator/

By the way, I am using two SDRs with Unitrunker and DSD+ to monitor the P25 system.

Thanks!
Reply With Quote
Sponsored links
  #2 (permalink)  
Old 05-30-2018, 1:44 PM
ko6jw_2's Avatar
Member
  Premium Subscriber
Premium Subscriber
Amateur Radio Operator
Amateur Radio
 
Join Date: May 2008
Location: Santa Ynez, CA
Posts: 620
Default

I would suggest a Yagi if you are primarily interested is in a single site. The gain over a ground plane will be significant.

As for the connector, I doubt that there will be much difference. An N connector would be a better choice. BNC's are not really intended for this type of use. The bayonet connection is not as mechanically sound as the screw on type connectors.

What kind of coax are you going to use? The loss in bad or lossy coax will out weigh any theoretical loss in the connector.

Finally, when buying BNC's remember that they come in both 50 and 75 ohm versions. The impedance factor is important, but there is also a difference in the diameter of the center pins. Buying connectors on Amazon etc. is problematical. A bargain generic connector may not meet the design specs. Same with cheap coax.
Reply With Quote
  #3 (permalink)  
Old 05-30-2018, 5:38 PM
Member
   
Join Date: Jun 2012
Posts: 8
Default

Thanks, I will take a look into something other than BNC.

I started making a Yagi last year, but I ended up pausing/giving up on it. I still have everything, just never finished it. I was planning to do the ground plane since it is so simple to make. Then later down the road finish the Yagi.

For the coax, I was thinking I would be okay with just using RG6. Luckily the attic is right above me, so all I would need is a short run of cable up the wall and I am right there. At most I would need 15 feet of coax.

Where do you recommend buying components?
Reply With Quote
  #4 (permalink)  
Old 05-30-2018, 7:23 PM
Member
   
Join Date: Sep 2006
Location: Southern California
Posts: 153
Default

Mouser Electronics sells top quality Amphenol connectors https://www.mouser.com/
Reply With Quote
  #5 (permalink)  
Old 05-30-2018, 9:22 PM
ko6jw_2's Avatar
Member
  Premium Subscriber
Premium Subscriber
Amateur Radio Operator
Amateur Radio
 
Join Date: May 2008
Location: Santa Ynez, CA
Posts: 620
Default

Quote:
Originally Posted by matters View Post
Thanks, I will take a look into something other than BNC.

I started making a Yagi last year, but I ended up pausing/giving up on it. I still have everything, just never finished it. I was planning to do the ground plane since it is so simple to make. Then later down the road finish the Yagi.

For the coax, I was thinking I would be okay with just using RG6. Luckily the attic is right above me, so all I would need is a short run of cable up the wall and I am right there. At most I would need 15 feet of coax.

Where do you recommend buying components?
Since you are only receiving RG-6 will probably be OK. However, it is generic and the home improvement store RG-6 is not the same and the type sold by say DX Engineering. Get the good stuff. DX Engineering is a good place to buy stuff.

I would suggest buying a Yagi unless you have an antenna analyzer the works at 800Mhz and most of them don't.
Reply With Quote
Sponsored links
  #6 (permalink)  
Old 05-31-2018, 12:18 PM
Member
   
Join Date: Jun 2012
Posts: 8
Default

Well it looks like I might just buy a Yagi. Is there a manafuctuerer or one that you recommend? I found this one from the link posted above by bb911, but it is $75. I do not want to spent quite that much, because I still need to buy some coax and connectors/adapters on top shipping costs. https://www.mouser.com/ProductDetail...6K%2fsXA%3d%3d

I searched around online for a bit and found this one for $45. https://www.excel-wireless.com/700-m...ct-description

Do you think that is a good buy?

Thanks again for the help.
Reply With Quote
  #7 (permalink)  
Old 06-01-2018, 11:14 AM
Member
   
Join Date: Jun 2012
Posts: 8
Default

I found a few other Yagis online. I will link them here, excluding the two above, in case anyone else is looking for some.

https://www.solidsignal.com/pview.asp?p=301111
https://www.wilsonamplifiers.com/wil...z-band-301111/ (same model as above but from another dealer)
https://www.wilsonamplifiers.com/wil...-50ohm-314411/

I ran into a problem though, it is not all that easy/cheap to connect multiple scanners, or in my case SDR dongles, to one antenna. Again I am using two SDRs to monitor P25. It would be just as cost effective to buy a second Yagi versus a cheap di or multicoupler. That would start to become too pricey for me.

For some cheaper options, I can try to make some Yagis and/or ground planes, mostly with the supplies I have on hand, and see how they work (I would still like to make my own to have some experience). Otherwise, I may just buy a pair of 700/800 MHz whips and get them mounted up high.
Reply With Quote
  #8 (permalink)  
Old 06-01-2018, 5:45 PM
Member
   
Join Date: Sep 2006
Location: Stockholm, Sweden
Posts: 2,143
Default

As the transmitter site are only 10 miles away you can use any kind of antenna as long as it is on the roof or outside of the window. You say you have a signal inside the house but the conversations break up so it just needs a smidgen more signal to work.

The last antenna you refere to are a 2GHz 3G/4G antenna.

You can get a cheap radio/tv amplifier that have two output connectors for $25. https://www.ebay.com/itm/ViewTV-2-Po...a/153018998341 and there are also some surplus amplifiers at a very low price.

But start with RG6 cable and put any antenna you already have, or intend to build, outside on the roof and see what you get. Maybe the easiest thing is to have two coax cables connected to two different type of antennas and see what works best.

You can build a coax colliniar antenna from RG6 coax. https://www.balarad.net/ Calculate the lenght of each element to the 770MHz frequency (165mm) and do antennas with even number of elements, 4 or 6 can be tested first.

/Ubbe
__________________
TRX-2 BCD536 HP1 BCT15 BC246 BC346 BR330 UBC3500 Pro2006 Pro2042 Optocom OS545 Scout PCR1000 ICR2500 IC75 DX394 AR8200 IC-R2 IC-R10 UBC780 MD380 CS580 CS750 Pro96 Perseus ADCR25 AcecoSC1plus RTL-SDR
Reply With Quote
  #9 (permalink)  
Old 06-02-2018, 4:14 PM
Member
   
Join Date: Jun 2012
Posts: 8
Default

Thanks Ubbe. Good stuff there.

Yup the signal is just almost there. I hear about 50% of the conversations, but it is broken up so much you cannot make it out.

I ended up piecing a three element Yagi together. My signal increased by about a third. I will try adding some more elements later to see what I can do. Like I said previously, I started making a Yagi last year with some aluminum rods, but I never finished (I am horrible at soldering). Maybe I will give that another shot.

I also had some RG6 on hand so I went ahead and made the coax collinear antenna. That increased my signal by about 50%! I would say about 70% of the conversation was heard. I will be working on getting my antenna mounted on the roof or attic. There are solar panels on the roof. My guess is that those are not helping the signal inside.

As for the antennas, the coverage area and specs sheet states that it does cover 700-800, just with less gain compared to 2 GHz.

Since the collinear is so simple to make, would you recommend making two of them and running two lengths of coax to my SDRs or use a TV amp?
Reply With Quote
  #10 (permalink)  
Old 07-03-2018, 2:33 PM
Member
   
Join Date: Jun 2012
Posts: 8
Default

Just an update. I recently realized that the P25 system I was trying to monitor is simulcasted. I installed SDR Trunk and the audio comes in great. Previously, I was using Unitrunker.

If anyone has similar problems like I stated in the first post, it might be a simulcast system. The audio comes in great 99% of the time, and I am still using the stock SDR antennas indoors.
Reply With Quote
  #11 (permalink)  
Old 07-03-2018, 6:27 PM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,944
Default

There is only one pin size for BNC, no difference between 75 ohm and 50 ohm and they are mechanically compatible and will mate just fine.



Quote:
Originally Posted by ko6jw_2 View Post
I would suggest a Yagi if you are primarily interested is in a single site. The gain over a ground plane will be significant.

As for the connector, I doubt that there will be much difference. An N connector would be a better choice. BNC's are not really intended for this type of use. The bayonet connection is not as mechanically sound as the screw on type connectors.

What kind of coax are you going to use? The loss in bad or lossy coax will out weigh any theoretical loss in the connector.

Finally, when buying BNC's remember that they come in both 50 and 75 ohm versions. The impedance factor is important, but there is also a difference in the diameter of the center pins. Buying connectors on Amazon etc. is problematical. A bargain generic connector may not meet the design specs. Same with cheap coax.
Reply With Quote
  #12 (permalink)  
Old 07-08-2018, 4:24 AM
trp2525's Avatar
Member
  Premium Subscriber
Premium Subscriber
 
Join Date: Mar 2010
Location: Massachusetts
Posts: 1,000
Default

Quote:
Originally Posted by matters View Post
Hi all,

I would like to make a ground plane antenna to monitor my local P25 system which is at 772 MHz...

I have looked at quite a few designs, but most of them use UHF/SO-239 mount even though the connectors are only good up to 300 MHz. Will that limitation have an impact on the antenna's performance near 800 MHz?...
A better choice would be to use an N connector chassis mount to build your 772 MHz ground plane antenna. See the attached picture. You can purchase one here: https://www.theantennafarm.com/catal...fn-1020-1-8304
Attached Images
 
__________________
trp2525
RCA 16S400, Regency HX1500, PRO-2006, PRO-197, TRX-2, BC950XLT, BCD996XT, BCD396XT, SDS100, Motorola Minitor II, Antenna Specialists MON731
Reply With Quote
  #13 (permalink)  
Old 07-08-2018, 6:34 AM
Member
   
Join Date: Sep 2006
Location: Stockholm, Sweden
Posts: 2,143
Default

Quote:
Originally Posted by matters View Post
Since the collinear is so simple to make, would you recommend making two of them and running two lengths of coax to my SDRs or use a TV amp?
When it comes to receive antennas the best solution are often to have an amplifier at the antenna, it will increase the antennas performance and make it more wideband and buffer the antennas varying impedance to the coax fixed impedance.

The amplifier will have some 10-20dB gain so you only have to fit a passive $5 splitter at the other end of the coax to feed several receivers and still have a lot of signal left. In fact it might be too much and a variable attenuator are in most cases needed to be able to get the best reception. If you are experimenting with antennas you absolutly want a remote feed amplifier with a bias-T and a variable attenuator and a splitter with the number of out ports that you'll need and it's often neccesary to use a FM broadcast filter.

The colliniar coax antenna are pointing its direction a bit too much in the sky, so it would help if you could attack ground elements to the bottom of it to make it work even better. A made one for 1090MHz, without ground elements, and it works better in the air VHF 118-136 range, and a lot of other frequencies, than a 125MHz 1/4 GP I put in its place for comparison.

/Ubbe
__________________
TRX-2 BCD536 HP1 BCT15 BC246 BC346 BR330 UBC3500 Pro2006 Pro2042 Optocom OS545 Scout PCR1000 ICR2500 IC75 DX394 AR8200 IC-R2 IC-R10 UBC780 MD380 CS580 CS750 Pro96 Perseus ADCR25 AcecoSC1plus RTL-SDR
Reply With Quote
  #14 (permalink)  
Old 07-08-2018, 7:29 AM
Member
   
Join Date: Mar 2002
Location: New Orleans region
Posts: 2,505
Default

Let me throw out a few comments that I don't think have been mentioned. The type of vegetation that is around you is going to play an important part in this game of signal strength and distance. If your out on the plains of the mid west, about the most your going to have to deal with is the rolling hills and some livestock wandering around. But if your in a heavy tree area, the ten miles might as well be 100 miles. You will have a major problem. This is especially true if you have long needle pine trees around you.

My second comment has to do with multiple scanners using the same antenna. Most scanners today have some IF leakage. This can cause one scanner to hear signals from the other scanner's radiated IF. In some cases, you might not have an issue at all. In other cases, one scanner will causes signals to be heard on the other scanner when it is receiving a signal. This bogus signal will not always show up on the same frequency, but will generally show up some place else. It might be just a ticking type signal or produce actual audio.

The best way to prevent this is to use an amplified multi port coupler that provide isolation between the different output ports. They cost more than a simple passive power slitter, but they do help to keep the different receivers from talking to each other.

An amp right at the antenna is a good move, but make sure it has a low noise figure for the highest frequency you will use it at. Then with multiple radios, you will need a low gain, multi port amp to feed the individual receivers.

As has been said many times before, in a simulcast system that your looking to listen to, it will take some homework to locate the nearest tower and use an antenna that has gain that will be able to null out the other towers around you. In some cases a yagi antenna may not be the correct selection. You may need to go to a corner reflector antenna to be able to null out a second tower to allow good reception.

Good luck on your efforts on your antenna system.

Oh one other comment about running your antenna cable down the wall. I try to run my cables inside the wall. But the fire code required that a fire stop be installed inside the walls after a certain date. That date is different around the country as each jurisdiction adopted the codes. But what it did was to put a 2x4 about mid way between the ceiling and the floor inside the walls.

So in order to run a wire from the attic to the normal 18 inch above the floor for an outlet box, you will need about a 6 or 8 foot drill rod shaft to drill a hole in the fire stop. It is extremely difficult to drill the hole, pull the drill rod out and then try to run a fish tape down, through the hole you just drilled and down to the hole for the outlet box. These long drills have a hole in the tip of the drill bit so you can run a wire or string through it and pull it back up. Most of them also have a hole in the drill shaft end that goes into your drill. This also allows you to attach a string to that end if the drill is not long enough to reach the hole 18 inches above the floor.

Just make sure you use a strong nylon string in your efforts. You will be some really pissed off if the string breaks and you loose the drill rod or it breaks on the lower end while trying to pull the wire up to the attic. Make sure you tape up the ends so the knot and wire don't come loose while pulling.
__________________
Jim

Last edited by jim202; 07-08-2018 at 7:36 AM..
Reply With Quote
  #15 (permalink)  
Old 07-08-2018, 3:51 PM
Member
   
Join Date: Sep 2006
Location: Stockholm, Sweden
Posts: 2,143
Default

The cheap $5 splitters that you have for sat dishes and the like with F connectors have 10-20dB isolation between ports in 1-2 splitters of different brands that I measured. Just the ticket you need to not let receivers interfere with each other.

A multicoupler like the Stridsberg probably use the exact same technique as cheap sat splitters as they state they have 20-25dB port isolation. There is one tranformer in the Stridsberg splitter that two ports share. Two other ports share another transformer and then those two transformer are connected to a common third transformer. If the interfering signal has to go up to the third transformer and down to the other transformer if will have a greater isolation compared to the ports that share a final transformer. So choose wisely which ports to use with any type of isolation splitter if you experiance interference while another scanner scans thru its frequencies.

Always use a variable attenuator together with an amplifier. Going +/-6dB usually makes a noticable difference in reception. Besides losing sensitivity with a too high signal level it also makes the scanner overload, which has its own issues that comes with that.

/Ubbe
__________________
TRX-2 BCD536 HP1 BCT15 BC246 BC346 BR330 UBC3500 Pro2006 Pro2042 Optocom OS545 Scout PCR1000 ICR2500 IC75 DX394 AR8200 IC-R2 IC-R10 UBC780 MD380 CS580 CS750 Pro96 Perseus ADCR25 AcecoSC1plus RTL-SDR
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 10:48 AM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2015 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions