UHF antenna - wire or fibreglass?

Hi, My RFI 6.6 db antenna can't give the range required in the flat country, so I am looking to replace the whip with an at least 8 db one. RFI has a fibreglass one (with wire wound around inside I assume) that's about 2m long, & Benelec & GME have wire only ones that are about half that length (& price!).

For the same db, is one type as good as the other? Is the screw threads the same between brands? The RFI 8 db option has some new type of quick release attachment - is it compatible with their older type?

Cheers :-)
Back Expand Un-Read 0 Moderator

Reply By: Robin Miller - Tuesday, May 20, 2014 at 15:37

Tuesday, May 20, 2014 at 15:37
Probably not quite that simple Mike.

Your looking to go up 1.6db when as per another recent radio post i made radios can have up to 4 to 6 db difference in gain (not including those with non legal 25w output).

It quite possible that you can get that gain by taking trouble to put in fatter better cable.

You may know that your antenna has to be keep pretty straight to achieve its 8db gain and then will only give that gain when it is not obstructed , this means base of antenna needs to be above the level of the windows , particularly if windows have the film tint on them.

Many people then have roof racks which obstruct them further.

Even when achieved the antenna becomes directional.

One thing I suggest to anyone with some of these issues is to get a cheap 1/2 wave antenna from Jaycar etc which comes complete with cable and attach it up high (maybe on side of roof rack if have one - but not connected with metalbracket for first 6 inches).

Use this aerial as a reference , its often better than 2m bullbar mounting ones and also suffers from less directionability, and will not break as easily.

Robin Miller

Member
My Profile  Send Message

AnswerID: 532820

Follow Up By: Member - fawkesp - Tuesday, May 20, 2014 at 19:05

Tuesday, May 20, 2014 at 19:05
Robin, with regard to your comment on 1/2 wave antennas, do you mean one like this - http://www.jaycar.com.au/productView.asp?ID=AR3260

If so, it appears from the image that it has a metal screw base, how does this line up with your comment "not connected with a metal bracket for the first six inches"?

I only ask because a DIY person I'm not, but I am preparing for a Simpson trip in July and I would like to have a well-prepared UHF radio installation.

Peter.
1
FollowupID: 816134

Follow Up By: Robin Miller - Tuesday, May 20, 2014 at 20:13

Tuesday, May 20, 2014 at 20:13
Hi Peter

You made me look and I couldn't find it in that reference , maybe jaycar no longer stock , also brought one from Dick Smith but haven't checked that site.

However this is a link to same thing from mobile one site, but
I bet you could get them from Watco or similar for less than $45 (mine $29).

http://www.mobileone.com.au/antennas/2f_477mhzcoax.html


These antennas are very uncritical of what they are mounted on , don't need ground plane and are short and flexible.

However you cannot mount them close to say a metal roof rack , it doesn't matter if you mount them on top of rack with a few inches of metal bracket, but no metal to the sides of the antenna.

They are a great accessory , we always carry one as a back up and they can be quickly hung from the top to a tree and act as an extended range base antenna.
Robin Miller

Member
My Profile  Send Message

1
FollowupID: 816139

Follow Up By: Member - fawkesp - Tuesday, May 20, 2014 at 20:38

Tuesday, May 20, 2014 at 20:38
Thanks Robin, I'll have a look.

Peter.
1
FollowupID: 816143

Reply By: olcoolone - Tuesday, May 20, 2014 at 17:05

Tuesday, May 20, 2014 at 17:05
How much range do you want?...... antenna dB gain if great for adding distance if both parties are a constant.

There are too many variables involved as it relies on how well each radio transmits and receives.

Going up 1.6dB may in fact give you bugger all difference and may not be worth the extra time, money and hassle...... if you had a 4dB antenna and you went up to a 9dB you may see a noticeable difference under some circumstances.

There is way way to much emphases put on antenna dB gain in most mobile UHF CB situations that involves other parties you have no control over.

As for antenna choice..... it's personal preference driven by cost, looks and function.
AnswerID: 532826

Reply By: Member - PJR (NSW) - Tuesday, May 20, 2014 at 17:19

Tuesday, May 20, 2014 at 17:19
Something to remember about the propagation of a vertical radio signal. And I will use an analogy so that it can easily be understood. Now grab a stick in the middle and hold it straight up and down. ie vertical. Now walk along with one end touching the ground. Just imagine that after a while it will eventually wear out and fall over

Total signal loss. Sure a stronger or higher wattage would mean that it would go further but you really have to make it thick or much greater power and just going from 5 to 25 watts is not a big jump.

So to improved the "reach" we clean up the signal before it even leaves the car. Firstly get it mounted higher. On the roof is best but watch for carports, garages and underground car parks.

Then just as Robin said, get some better quality cable. Make sure there aren't any kinks in it. Kinks or sharp bends will knock it back very quickly. Now make sure all terminations are done properly. No dirty or dry joints etc. If crimped then don't use the bench vice to crimp it.

Then get a VSWR meter and check it.

Personally for UHF I suggest that unless you are competent with high reliability soldering and clean work space practices, I would pay to get done and tested with a VSWR meter.

The installation in the car is where more problems exist and where errors are made. The VSWR test is a good guide.

Now if you want more then go and put a big stick on the car but I think you should be happy with the improvements done by cleaning up your installation.

Side story:
I run a 9.6 db , 5 element yagi on a 50 foot high tower for hf bands. It's called a Wilson System one. Not the biggest hams station in the world by a long shot. But I had a spotless installation, technically that is. No connectors crimped with pliers nor any soldering done with a gas flame etc. But the best thing that I ever did was use extremely low loss cable that I purchased after a "special" Defence site was demolished. With that set up I reached Burbank California on 0.75 watts on 28 Mhz. A record. The others around me weren't heard at that power and only one local station could hear the California station. I have also been told that I had the biggest signal out of Australia during contests. And without any power amp and just running 100 watts I have won several international contests.

Most of this success with my home station and providing base comms for Australia wide car rallys etc, I attribute to my meticulous technical aspects of the installation. I did it professionally back in those days before computers. Sure I am blowing my own trumpet but I have the trophies and awards to prove it. Australian HF Champion several years.

I had a "clean house". Just as we are recommending that you do. The try a larger antenna if you really wish.

Phil
AnswerID: 532829

Follow Up By: Robin Miller - Tuesday, May 20, 2014 at 22:12

Tuesday, May 20, 2014 at 22:12
Love your side story Phil , used to do much the same but on VHF, every competition meant we were off to a new mountain top an this first got me into exploring , then the fun of chasing pirate 27mhz operations , dx hunts hanging out the car window with a 3 element Yagi (144mhz)

Your preparation sounds better than mine though , I relied on new technology to win , like a new thing on VHF called a transistor, making the first contact Melb to Adelaide and while it didn't always work I still remember the excitment today and understand how you could generate such a enthusiasm for the hobby.

We could probably swap stories for a long time around a campfire !
Robin Miller

Member
My Profile  Send Message

2
FollowupID: 816145

Follow Up By: Member - PJR (NSW) - Tuesday, May 20, 2014 at 22:30

Tuesday, May 20, 2014 at 22:30
No doubt we could. 2073 in the 1989 CQWW from here. 1st Asia/pacific. One of many.

Catchya
1
FollowupID: 816148

Reply By: Cybermike - Tuesday, May 20, 2014 at 17:29

Tuesday, May 20, 2014 at 17:29
Distance required is up to 60km across the plains to a base station when camping out. A directional antenna for temporary setup could be an option. Unfortunately there is no repeater around.
AnswerID: 532830

Follow Up By: Bob Y. - Qld - Tuesday, May 20, 2014 at 18:43

Tuesday, May 20, 2014 at 18:43
Thanks for clarification, Cybermike.

How high is base station antenna? Do you camp out in one spot, or in different places?

As you say, a Yagi might be the go as they are light to pack, and give a very directional signal. Think you need some sort of mast, say 20' - 40' high, with either a 12dB base antenna, or a Yagi.

In another life, when we lived on a station down the Diamantina River, we had 2 repeaters, but occasionally we had to use simplex on scramble, for, shall we say, sensitive issues. At those times, we would use a simplex channel, and would park vehicle on a high ridge, and talk to the base, usually after dark.

I've found anything over 40-50 clicks is stretching the performance, of a mobile to base, unless you can elevate the mobile. In UHF, "Height is might"

Bob.

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 816130

Follow Up By: Echucan Bob - Tuesday, May 20, 2014 at 18:47

Tuesday, May 20, 2014 at 18:47
CM
If you aren't mobile then a high mounted directional antenna would give the best results. I made a Yagi for use on the 3G 850MHz band using a bit of poly pipe and some aluminium tubing from Bunnings. The poly pipe mast enters a "T" piece connector and the front and back of the beam emerge from the other ports. The hardest part was the accurate drilling of the holes for the elements. For a 470 MHz Yagi the elements are going to be a decent length and the unit won't look as silly as my 3G unit.

Just Google 470 MHz yagi for the measurements. There are even retail ones made by talented Chinese artisans.

Remember that each 3 dB of gain represents a doubling of signal strength. So a 14 dB yagi will give a useful increase in gain over your basic dipole.

Bob
1
FollowupID: 816131

Follow Up By: Bob Y. - Qld - Tuesday, May 20, 2014 at 19:33

Tuesday, May 20, 2014 at 19:33
Had to stir the memory cells a bit, can't beat a rib fillet, salad & chips to help :-)

To further improve Tx/Rx in your situation, get some Heliax cable, LDF-4 was the stuff we were "given", and it makes a vast difference to signal/sensitivity. Not cheap!!!

Otherwise, RG-213 cable and some good quality connectors will help.

Andrews Communications, in Sydney, have heaps of "stuff" on their website. No affiliation etc

Bob.



Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 816136

Follow Up By: olcoolone - Tuesday, May 20, 2014 at 20:20

Tuesday, May 20, 2014 at 20:20
The only real way is with height or yagi or both.

Expensive coax and some you bute connectors will only improve your reception and transmission very marginally at an uneconomical cost....... A yagi and or height will give big results.

The other option is to run a keyhole antenna set up using a vertical and horizontal antenna....... That gives you the best of both worlds.

We have used two 5 watt handhelds running 2 watts to transmit and receive 104 kilometres, we had height on our side.
1
FollowupID: 816141

Follow Up By: Bob Y. - Qld - Tuesday, May 20, 2014 at 21:07

Tuesday, May 20, 2014 at 21:07
olcoolone,

Thought I'd already mentioned height as a pre-requisite?

Googled keyhole and found an informative screed on www.houseofradio.gr with more info than I need, or could absorb. They recommend "expensive coax etc" over ordinary RG-58/59.

When we installed the exxy stuff, we had an immediate Tx simplex radius increase of 15-20 clicks, which in our situation was good value for the expense. As it was a workplace(albeit rather large at 4,200 sq. kms), welfare of staff was paramount. The OP may well have the same issues?

Yeah, you can often get some unreal distances, even with handhelds. Some of the staff once talked to a pilot, over 70 nM away, just to test how far the h'helds would transmit.........and receive.

Bob.

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 816144

Follow Up By: Member - PJR (NSW) - Tuesday, May 20, 2014 at 22:21

Tuesday, May 20, 2014 at 22:21
Commercial yagi for AU UHF CB. Scroll down to TDJ-400B. Put it on a pole as high as you can handle and point it back to the base. Use good coax as well. I would also try to keep it on one side of the pole or make the top few feet out of a strong plastic pipe.

Link: Radio Specialists

There will be more. I wasted a bundle of time ear5lier but that is the nature of forums. I hope I didn't bore you.

Phil
2
FollowupID: 816147

Follow Up By: olcoolone - Wednesday, May 21, 2014 at 09:36

Wednesday, May 21, 2014 at 09:36
QUOTE [Thought I'd already mentioned height as a pre-requisite?]

Didn't know I wasn't allowed to say that again....

Keyhole antenna systems have been used for years where you want to increase transmit and receive in one direction but still want to transmit and receive off axis.

Sure quality coax and connectors do help but it's like using a cheap run of a mill halogen driving light and using expensive cabling, plugs and relays and expect them to work like HID driving lights...... when it would of been cheaper to just buy cheap run of the mill HID's at the start.

There are many different grades of RG58 cable from the cheap and nasty up to better quality Belden or Heliax.

RG59 is not a coax I would advise to use as the RF resistance is much higher...... great for dual antenna setups but not for one...... or you want to watch a movie.

2
FollowupID: 816158

Reply By: Member - William B (The Shire) - Tuesday, May 20, 2014 at 18:14

Tuesday, May 20, 2014 at 18:14
Hi Cybermike,
I can not comment on the merits of db ratings of UHF antennas.
I can comment on steel or fiberglass.
I have had steel antennas before and each one has snapped off due to no flex, especially if travelling along corrugated roads.
I have a RFI fiber glass one now and it wobbles around a lot but stays intact.
Hope that helps.
William
Always planning the next trip. VKS-737 mobile 1619

Member
My Profile  My Blog  Send Message

AnswerID: 532831

Follow Up By: Bob Y. - Qld - Tuesday, May 20, 2014 at 19:10

Tuesday, May 20, 2014 at 19:10
Agree with William. Stainless steel whips plus corrugations = new whip required!

Bob

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 816135

Follow Up By: Member - Scott M (NSW) - Tuesday, May 20, 2014 at 20:33

Tuesday, May 20, 2014 at 20:33
Agree x 2 - had a fibreglass spring based antenna I bought from some bloke who makes them in Cessnock of all places off Flea-bay. (see photo)

Got great reception and it was bashed within an inch of it's life up the Canning last year and came up trumps.

We met a group of three coming south around well 48 ( so they were barely into the trip) and they driving up and down asking questions as to whether we'd seen vehicle x or vehicle y ... turned out they all had those metal spring centre join antennas, all three had snapped off already

1
FollowupID: 816142

Follow Up By: Member - Phil G (SA) - Wednesday, May 21, 2014 at 09:23

Wednesday, May 21, 2014 at 09:23
Can I suggest that corrugations + bullbar mounts + heavy aerial or elevated feed are not a good combination.

I have used a roof mounted antenna on a knock down bracket (aerial swings down when hit). It is common in SA - never seen a broken antenna with this setup and in very overgrown country or in the city, just use a stubbie aerial. Roof mounted transmits best.


3
FollowupID: 816156

Follow Up By: Member - Scott M (NSW) - Wednesday, May 21, 2014 at 11:34

Wednesday, May 21, 2014 at 11:34
Phil - looks good - our spring loaded survived OK though :-)

One thing a trip up or down the Canning give you is you become an instant expert on which antenna or sand-flag set-ups work and which don't...
1
FollowupID: 816173

Reply By: Bob Y. - Qld - Tuesday, May 20, 2014 at 21:11

Tuesday, May 20, 2014 at 21:11
C'mike,

Re thread query, think all aerials use a 5/16" thread, unless they're the ones that screw onto a SO-239 base.

Bob.

Seen it all, Done it all.
Can't remember most of it.

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 532850

Reply By: Iza B - Wednesday, May 21, 2014 at 06:00

Wednesday, May 21, 2014 at 06:00
Fibreglass has no effect on the performance of an antenna. A fibreglass antenna is simply using the material to support the active antenna element, the wire. An antenna that uses a ground plane will normally give better performance in any given situation. High mount, free from closely placed vertical interference elements, will give best performance for a given antenna.

Iza
AnswerID: 532861

Reply By: Cybermike - Monday, Jun 02, 2014 at 23:15

Monday, Jun 02, 2014 at 23:15
There's a lot of info here - thanks to all. Yes - it is while working out at a large outback property. To get a yagi with enough increase in dB would be a lot to lug around & I already have too much gear to pack! It sounds like the go is to have a 1/2 wave antenna hoisted over a tree branch. I'm onto a supply of Heliax L4A cable which I'll get a radio technician to solder. I'll also get the mobile 6.6 dB antenna reconnected with this, & remounted from the bullbar to the roof. Cheers, Mike.
AnswerID: 533631

Sponsored Links

Popular Products (13)