Railfan Technology > scanner antenna suggestions

Friend figured out the antenna on my RELM scanner was bad. Need a new one for RR frequency. BNC mount.
Suggestions for what and where to get one?
Handheld....

Posted from Android



Edited 1 time(s). Last edit at 02/10/15 22:05 by SD45X.

First off, be sure it is the antenna rather than the connector.

Set the scanner to a weak but readable NOAA weather frequency and
attach the suspect antenna. Then, remove the suspect antenna and
replace it with 16" of wire into the center of the BNC connector.
If there is an improvement. the original antenna is likely defective.

As a replacement, I have measured a significant improvement with the
MFJ 1717 series of antennas. The BNC connector version is MFJ1717.
The downside is that the antenna is @16 inches long and if you carry
the scanner on your hip, it will slap you in the side as you walk.

I am not a fan of "Smiley" antennas, some of their claims are "optimistic"
in my view.

Be Well,

Tim Colbert K3HX

Celebrating 50 years in amateur radio.

30+ years in the 2-way radio industry.

I've been using a 'gain' antenna but it has an SMA mount, should be a similar model with a BNC though. Bought it from Antenna Farm in Montana, found it using Google and digging through some websites:

Vertex ATV-10C
VHF 10.5" High Gain Antenna, 155-165MHz (Blk) VX-160/180/230/350/410/420/820/920 Series Portable Radios

A problem with 'gain' antennas is the potential for Intermod reception, that pager-type noise, or hearing somebodies Plumber service. Had trouble with it in Denver and around Colorado Springs. The increase in range/reception may be worthwhile. You can't really call it a 5/8 wave antenna since it's a coiled up rubber duck construction, so they use the phrase 'gain antenna'.

Also found a 'Gain' antenna at Fry's that worked well on the Bearcat I have for a backup, cost about 20 bucks but improved performance noticeably. Also has a more flexible whip. Look for the frequency range, connector type and the word 'gain'. Otherwise there's plenty of 'wide-band' or 'tri-band' antennas that are good replacements without the intermod potential. Antennas are often around 20 bucks so it doesn't hurt to have a spare, or trade them around if you have a problem.

First thing, Everything Tim, K3HX said it true. The MFJ1717 is a good antenna and Smiley tends to stretch the specifications on their antenna.

Often there are comments about some of the antennas being a "5/8 wave antenna." You are not going to like a 5'8 wave antenna on a handheld scanner. In order for it to be a 5/8 wave antenna for the railroad frequencies it's going to have to be about 40 inches long. There are some rules that you just can't ignore. A 1/4 wavelength at 161 MHz is roughly 16 inches. Anything shorter than that is a compromise of some sort. You can coil the antenna up and make it work but it's a compromise. It isn't going to work as well as a piece of straight wire, 16" long. You can't make it 9" or 3 inches and call it a 1/4 wave antenna. Likewise, you can't shorten a 5/8 wave antenna to 15" or even 9" and expect it to work like a 40" long antenna. 12 ounces isn't a pound. 7" isn't a foot. 37 minutes don't make it an hour. You just can't change some things.

Besides the MFJ antenna, Diamond makes a similar antenna, the RH77CA, I think. It cost a buck or two more than the MFJ antenna but electrically it is virtually the same. There may be some slight mechanical differences.

Here's some links to both antennas:
http://www.mfjenterprises.com/Product.php?productid=MFJ-1717
http://www.diamondantenna.net/rh77ca.html

Both companies have shorter antennas if you're just looking for a replacement.

IMPORTANT NOTE: While looking up the web addresses I came across a note by one supplier. Due to the work stoppage at the West Coast ports, some of these products may be delayed if you order them. One company said they had two containers sitting in the ports and another one at anchorage waiting to dock.

John

That's a very strange thing to say about a 5/8 wave antenna. I'd suggest the most important thing to do is find some antennas and try them out.
...

Actually there is an extendable or telescoping antenna with a BNC connector, it can be extended to a 1/4 or 5/8 wave, I've seen them at Radio Shack. The gentleman that had it was an old Air Force Tech of some sort, it worked pretty good in both modes. But the radio did fall over a lot.



Edited 2 time(s). Last edit at 02/11/15 23:19 by TCnR.

TCnR Wrote:
-------------------------------------------------------
> That's a very strange thing to say about a 5/8
> wave antenna. I'd suggest the most important thing
> to do is find some antennas and try them out.
> Somebody asked so somebody offered some
> suggestions. I can't think of a 5/8 wave antenna
> with a BNC at the base that would attach to a
> radio. That's some pretty creative sarcasm, in my
> experience it's pretty typical sarcasm for
> somebody with a call sign. If you get a chance go
> ahead and join the human race.
>
> Actually there is an extendable or telescoping
> antenna with a BNC connector, it can be extended
> to a 1/4 or 5/8 wave, I've seen them at Radio
> Shack. The gentleman that had it was an old Air
> Force Tech of some sort, it worked pretty good in
> both modes. But the radio did fall over a lot.


I'm sorry if I insulted anyone or seemed sarcastic. If I upset anyone, I'm truly sorry. As far as having a "call sign," I took my test to get that in the presence of an FCC examiner. I have also held the First Class Radiotelephone License with a Radar Endorsement until the FCC converted all First Class Licenses to General Class. That doesn't make the the smartest person on this forum but it probably means I have proven to the government that I have enough knowledge to work on any radio transmitter in this country, including radar and microwave installations.

Finding antennas and trying them may not be all that easy, depending on where someone lives and what they have access to. As a ham I have access at ham radio conventions to try several antennas if I want to but most people don't have that luxury. Maybe they might check with a friend and try the antenna the friend is using. Generally, a 6" rubber duckie is a 6" rubber duck is a 6" rubber duck. The two antennas I mentioned previously are virtually the same size and offer the same performance. A 2" or 3" stub might be OK for a NASCAR event or other small area but I wouldn't want to use one for rail fanning.

I expressed my comments because it seems that every time the subject comes up, someone will claim that their 16 or 18 inch long antenna is a 5/8th wave antenna and that's just not the case, and of course, I wouldn't expect to see anyone walking around with 40 inches of antenna on the end of a BNC connector on their scanner. Antenna theory is a pretty complicated subject, much too complicated and lengthy to fully discuss on this forum. There are complete books on just this subject. Some manufacturers tend to exaggerate their claims in their advertisements. You can also have trouble comparing apples and oranges. Some manufacturers compare their antenna gain to a 1/4 wave or 1/2 wave antenna. Others compare theirs to the hypothetical "isotropic radiator." A perfect 1/2 wave antenna has 2.15dB gain over the isotropic radiator. A properly mounted 1/4 wave antenna is virtually the same as a 1/2 wave antenna due to the image antenna below the ground plane. The gain of a 5/8 wave antenna is sometimes hard to pin down because of how it can be measured but 3.5dBi is generally accepted. Sometimes that is misrepresented as 3dB over a 1/4 wave antenna but that's not correct. The installation of the antenna can alter that also. The lower angle of radiation is a major factor. The 1/2 wave would be idea for use with a scanner if it were not for the impedance at the feed point and the angle of radiation. A 1/2 wave, end fed antenna has an extremely high impedance, that is, maximum voltage and minimum current. This can be a safety issue when using it on a transmitter. The 5/8 wave antennas we use on cars has a load coil in the base, effectively a transformer that allows it to match an odd impedance at the antenna feed point to the impedance of the radio. The transfer of power from the antenna to the radio is maximized when the impedance of the antenna matches the impedance of the radio, typically 50 or 52 Ohms. A 5/8 wave piece of wire or telescoping antenna does not exhibit the properties of a properly designed 5/8 wave antenna.

If you really want to understand these characteristics, there are several resources on the net. The American Radio Relay League has some books that are intended for the non-engineer, non-PHD community.

Again, I did not intend to insult anyone.

John



Edited 1 time(s). Last edit at 02/12/15 00:29 by wa4umr.

Well, I'm K6KMJ from back in February, 1958, and my crusty opinion is
that if the antenna is attached and it works, you'll be happy; I cannot
get too excited about a DB or two difference between antennas. I do
favor a Diamond RH205, which is a 1/4 wave 2 meter whip that I connect
to my Icom IC-V82. The nice thing about this antenna is that it
extends to 5/8 wave, which for me means that I can extend it when
listening to weak signals... It does make a difference.

John.

The OP already determined the antenna was bad and then asked for an antenna to purchase. Both threads open with how to troubleshoot a bad antenna.

Anybody taking a ham exam or a Commercial license exam has to deal with with a Government official, contractor or bureaucrat of some sort. There all over the place, RR employees deal with FRA inspectors, electrical contractors deal with permitting and inspectors, it's endless. There's even Federal employees monitoring TrainOrders.

But the O.P. asked for an antenna.

Why do both suggested antennas show as 144/440 MHz?
RR is 160-161 correct?

Posted from Android

Those are HAM Bands, sounds like an OEM antenna. The Vertex is 155-165MHz.

-------------------------------------------------------
> Why do both suggested antennas show as 144/440
> MHz?
> RR is 160-161 correct?
>
> Posted from Android


I also have tried a 160/460 (approx) to cover the EOT's with a Yeasu FT-60R, the antenna didn't work out too well. Empirically, the two bands seem to numerically related and a standard 160 MHz antenna seems to allow enough EOT signal into the receiver to be useful.

found the Vertex link:

http://www.theantennafarm.com/catalog/vertex-atv-10c-5033.html

*this is an SMA connector, pretty useless to the O.P. I'm noticing Vertex seems to only make SMA connector antennas, try googling the specs and a BNC option should be available from another manufacturer.



Edited 1 time(s). Last edit at 02/12/15 11:29 by TCnR.

While we are on the subject of antennas.... I recently searched this forum about magnetic mount antennas for a vehicle, and read a lot of stuff that is simply over my head. Sooooo, what I got out of it were positive comments about the traintenna and the Larsen antenna.

Any advice on which one would be better or are they similar? I had a radio shack magnetic mount that broke, and that wasn't specifically for RR frequencies so thought I'd upgrade to one that is.

Electrically the Traintenna and the Larsen antenna look very similar, visually the construction seems to be different. Mag mount antennas usually leave scratches on the roof. I think I've had Larsens, the Traintenna guys seem to be part of the RR crowd. Traintenna looks like it's been cut to the RR band, the Larsen looks like it needs to be measured and cut. I've had quite a few similar to the Larsens, so I'll add my $0.02.

Let us know what you decide and how they work out.

TCnR Wrote:
-------------------------------------------------------
> Electrically the Traintenna and the Larsen antenna
> look very similar, visually the construction seems
> to be different. Mag mount antennas usually leave
> scratches on the roof. I think I've had Larsens,
> the Traintenna guys seem to be part of the RR
> crowd. Traintenna looks like it's been cut to the
> RR band, the Larsen looks like it needs to be
> measured and cut. I've had quite a few similar to
> the Larsens, so I'll add my $0.02.
>
> Let us know what you decide and how they work out.

In that case I think I'll go with the traintenna, since I don't trust myself to cut it right especially reading about the best method to cut it.

I move the antenna between vehicles so that's why I like the mag mount, I'm rather careful taking it on and off to minimize scratching. Thanks for the advice, I'll post the results once I get one (and get out to use it).

I've seen good instructions on cutting a 5/8 wave antenna but can't find them, went to Google and found an excellent discussion about lots of 5/8 wave benefits, sure enough it's on TO:

http://www.trainorders.com/discussion/read.php?9,1369784

also a length chart, but it doesn't say where to start the measurement, the TO discussion does though (at the ground plane):

http://www.fireelectronics.com/cutting_chart.htm

Tim K3HX has some good instructions for cutting stainless steel antennas and doing it safely. One thing to note on cutting the antenna. There are differences in the base coil and if one manufacturer says to use 39.25 inches for 161 MHz, another might call for 40.125 inches. As long as you are not transmitting, it's not that critical but, if you're going to cut it for a frequency, you might as well get it as close as possible to the correct length. When I worked in a 2-way radio shop we would often cut the antenna an inch or two longer than called for. We would check the SWR and cut a half inch off and measure it again. We would repeat until we got a 1:1 or saw a slight increase. Usually we would end up pretty close to the recommended length but sometimes we ended up a half inch different. Not a big deal but if we were doing it, it only took a minute or two longer to get it right on the money.

John

I use the Diamond RH77CA on the handhelds, works great but rather weak mechanically at the connector. One drop on Donner and it was a goner. Still like 'em though, just carry spares! Nagoya makes a similar version only it's more noodle-style, it works well if you handle it with TLC, and doesn't slap your side as hard as the Diamond. And yes, the Smiley isn't the absolute best rubber duck out there, but it's not bad. Just watch that the duck doesn't unscrew from the base and connector. Lost one that way last year.

In the car, I use Larsen antennas whenever I can. Have used various models for 27 years and not one has gone bad or broken. And that's driving all over the West from Canada to LA, Missoula to Salt Lake, the Siskiyou line in Oregon with low hanging trees on the old stage roads over the passes. They just keep on workin'.

The Antenna Farm is a good source for antennas. I prefer the Laird EXH-160 series of antennas. They are tuned for the 160 mHz band and are pretty tough. Just order the one with the BNC connector. The optional high-gain antennas sold by Kenwood, for example, on their commercial portables are actually Lairds.

I also like the EXH-160-xxx for the 161 Mhz band, the BNC model is EXH-160-BN. They are only rated 10 MHz wide, so if you need to TX outside that range then look at the Larsen SPWB22150, it covers 136 to 174 and works almost if not as good as the EXH-1xx-xxx antennas. I run them both, but need TX on the ham band and 155 range so the Larsen is the one that gets used on those days.

Jim

WW Wrote:
-------------------------------------------------------
> The Antenna Farm is a good source for antennas. I
> prefer the Laird EXH-160 series of antennas. They
> are tuned for the 160 mHz band and are pretty
> tough. Just order the one with the BNC connector.
> The optional high-gain antennas sold by Kenwood,
> for example, on their commercial portables are
> actually Lairds.