Antenna Specialists VHF 1/2 wavelength

[AZDon]

Does anyone have a cutting chart for an old Antenna Specialists, VHF 1/2 wavelength antenna. I actually have two, one will be used as a mobile antenna and the other will be used in a base station application.

Does anyone out there have a copy of the cutting chart? Mine has disintegrated.

 

[AZDon]

Cutting chart

someone, some place has to have a copy of this cutting chart.

 

[rwier]

I have no knowledge if the lengths are antenna brand/model specific. I am posting this for the formulas at the bottom.

Ham Radio HF/VHF Antenna Lengths

GOOGLE search "Antenna Specialists VHF 1/2 wavelength" returns

http://preview.tinyurl.com/h2pu5a2

 

[mmckenna]

Well, try a bit longer than half a wavelength at whichever frequency you plan to use it on, then trim accordingly. Since this is the "Scanner/Receiver Antenna" forum, I'm going to guess you are using it for receive only, so that makes the precision even less critical.

1/2 wave antennas are fairly broadbanded, so it doesn't have to be exact.

 

[AZDon]

Thank you, but that wasnt what I needed. Hopefully, someone might be able to help me out. I have an old base coil that closely resembles an old mobile cb antenna. The coil of my antenna is about 4" in length and about 3/4" in width. It is gray in color. Antenna Specialist sold a ton of these 1/2 wavelength, VHF Hi band antennas. My cutting chart is gone, so I can only hit and miss by trial and error. Thank you again for your response.

 

[AZDon]

Actually intend to use it in the 2 meter ham band until I can afford to get something else for the ham band. Then I plan on using the 1/2 wavelength antenna for the 156 Mhz band. Question, did you once live in the WDC area?

 

[mmckenna]

deleted post. Let me try again.

 

[mmckenna]

No, never lived in DC area.

I have a Laird half wave for the 2 meter band. Whip length is right about 38 inches. That should get you pretty close. For 156MHz, you'll shorten it a bit.

I might be able to help you find the cut chart for the Laird. I probably have it in my shop somewhere, but I won't be back there for a few weeks.

 

[mmckenna]

Here's the online version of the cut chart for the Laird:

http://cdn.lairdtech.com/home/brandworld/files/ANT-DS-B1442N 111114.pdf

I found it to be off by a bit. I cut my antenna for 146MHz, which shows as 42.5 inches on the chart. I put it on the analyzer and had to cut about 2 inches off.
Exactly where and how it's mounted (with or without a ground plane) makes a bit of a difference, so if you can follow up with an SWR meter or an antenna analyzer, it would be a really good idea.

 

[markclark]

The attached file is most likely one of the antennas you have. An ASPS177 is 49" and the ASP553 is 51.5" longest length by default. I can't find a cutting chart but those whip lengths at will get you started.

 

[mmckenna]

That's a 5/8th's wave. That will make the whip too long.

 

[AZDon]

Back in the day, Antenna Specialist manufactured a wide range of antennas, am sure they made a 1/2wl mobile antenna and probaly produced a 5/8wl mobile antenna as well, both of those coils looked almost identical. At this point I have no option but to believe the brochure provided by markclark is provides the correct lengths for the antenna coil that I have. The coils depicted in the brochure look identical to mine, later today I will run a test with an element measuring 51.5" to see if it matches. In the event I am in possesion of a 5/8wl coil then the Laird cutting chart will get me provide me with a good place to start. I appreciate the assistance provided by both of you.

 

[AZDon]

The Antenna Specialst brochure shows a gain of 3db, if memory serves me correctly the A/S 1/2 wavelength antenna had 2.5db gain with more bandwidth in comparison with the 3db gain provided by a 5/8th wl antenna with a little less bandwidth. Regardless, going to work with the numbers both of you provided.

 

[mmckenna]

Right. A half wave will have 2.4dBd with a perfect ground plane. Without any ground plane, they have 0dBd, AKA Unity Gain, or the same as a quarter wave with a ground plane.

Let us know what you figure out.

 

[cmdrwill]

Most Antenna Specialist base coils were 5/8 designs using a 49" whip in the commercial part of the VHF band, 150-170.
So to get down to ham, the whip has to be longer.

Is there any number on the inside edge of the bottom of the coil?

 

[AZDon]

Not sure, will check on that tomorrow.

 

[AZDon]

Mystery Solved

Took a close look at the inner part of the antenna mount and stamped on the outer edge of the metalic thread was 130-174 but nothing else to describe the model number or the design of the antenna. Placed the antenna on a mag mount and started tuning on the ham bands, my trusty Daiwa SWR meter determined that this antenna loaded pretty well on 2 meters across the band, which tells me that this is a 1/2wl VHF antenna as compared to a Larson 5/8wl antenna that I have.

Dug in a little deeper and searched the patent number of the antenna coil, took a little time because one of the digits was missing. Within minutes I located a patent that was issued August 16, 1966 for a half wave vehicle mounted antenna with impedance matching transformer.

Now that it has been determined what type of antenna coil I have I can again proceed with finding a cutting chart for this design of antenna or just trim away.

Question, anyone know if I trim a VHF 1/2wl antenna mounted on a mobile mount to a specific frequency if it needs to be retuned if its placed on a base mount with radials? Seems as if you are suppose to add 1.5" to it. Guess I will start figuring that one out to. If anyone out there has a cutting chart for a 1/2wl VHF antenna let me know.

 

[prcguy]

If it truly is a 1/2 wave could it be one of their no ground plane types? I've seen them with a white coil and fiberglass whip but not sure about a grey coil and metal whip.
prcguy

Took a close look at the inner part of the antenna mount and stamped on the outer edge of the metalic thread was 130-174 but nothing else to describe the model number or the design of the antenna. Placed the antenna on a mag mount and started tuning on the ham bands, my trusty Daiwa SWR meter determined that this antenna loaded pretty well on 2 meters across the band, which tells me that this is a 1/2wl VHF antenna as compared to a Larson 5/8wl antenna that I have.

Dug in a little deeper and searched the patent number of the antenna coil, took a little time because one of the digits was missing. Within minutes I located a patent that was issued August 16, 1966 for a half wave vehicle mounted antenna with impedance matching transformer.

Now that it has been determined what type of antenna coil I have I can again proceed with finding a cutting chart for this design of antenna or just trim away.

Question, anyone know if I trim a VHF 1/2wl antenna mounted on a mobile mount to a specific frequency if it needs to be retuned if its placed on a base mount with radials? Seems as if you are suppose to add 1.5" to it. Guess I will start figuring that one out to. If anyone out there has a cutting chart for a 1/2wl VHF antenna let me know.

 

[AZDon]

VHF 1/2wl mobile antenna

Both of these coils consist of grey plastic coils. If I recall, I obtained one of these coils back in the early 70s as part of an A/S base and the other in the early 80's as a mobile antenna. The original patent was obtained September 1959 then aparently modified or renewed in 1966. Under the origninal patent the antenna was designed as a VHF 1/2wl mobile antenna. The original inventor, Arthur Finke seemed to be employed by Antenna Specialist at the time the original patent was filed.

It remains to be seen if there is really any differance in vertical element length depending if its used as a base or mobile antenna, time will tell.