2 meter J-Pole question

[NWI_Scanner_Guy]

A while back, I purchased a copper tubing J-pole antenna off of eBay (2 Meter VHF J Pole Base Antenna Heavy Duty Amateur Ham Radio Scanner 144 148MHz | eBay) to use with my 2 meter rig.

Well, just recently I purchased a dual band rig, the Yaesu FT-7900R. Great radio, but I've only been using it on 2 meters so far. Don't have an antenna tuned for 70cm. However, I decided to do a little investigating, and saw on the above referenced link that although the antenna is pre-tuned for 144 - 148, it also says it can be used on 70cm.

My question is...how effective would this antenna be when operating on 70cm? I'm thinking about buying a dual band mobile antenna and mounting it up in my attic, but would rather not if the j-pole would be somewhat effective on 70cm and not do any kind of damage to the radio itself.

Thanks in advance for any information provided.

 

[teufler]

do you have an swr meter. if so, on low power first, key up 445.000, see what it says, if acceptable, less than 2.0, try mid power. I think it will "listen" fine but transmitting, best stay to low power. There are several clone dual band antennas, that at hamfests, sell for around $55.00.

 

[NWI_Scanner_Guy]

do you have an swr meter. if so, on low power first, key up 445.000, see what it says, if acceptable, less than 2.0, try mid power. I think it will "listen" fine but transmitting, best stay to low power. There are several clone dual band antennas, that at hamfests, sell for around $55.00.

No, I don't have a SWR meter. Since I want to get more serious with my radio activity, I guess it'd be a good idea for me to invest in one.

On the page I linked to, the gentleman has a picture of a SWR plot for 70cm. He doesn't say what the power setting was, but at 445.000, the SWR was 1.0 and from 440 to 445 as a whole, the SWR was 1.5.

Might be going to a hamfest this coming weekend, so if I do go, I'll look to see what antennas are available.

Thanks for the info teufler, I appreciate it.

 

[LtDoc]

A 2 meter 'J'-pole can certainly be -usable- on 70 cm but how can you gauge 'effectiveness'? And while SWR isn't affected/determined by power, the meter used to measure it certainly can be...
- 'Doc

 

[nanZor]

For the most part, a 2 meter J-pole used on 70cm that has a reasonable swr can be certainly used for that purpose.

However, the radiation pattern is basically a cloverleaf at uhf instead of the classic doughnut as seen on a half-wave radiator. At 70cm, the cloverleaf pattern appears due to the long-wire effect. This means that instead of looking out towards the horizon, it is looking upwards.

This may not be an issue for local repeaters if you can hear them clearly, and make up for the upward-looking lobe by just using more transmit power.

This is good to know if for some reason you decide to get a purposely-tuned uhf antenna that has a lower radiation lobe, such as if you run into trouble doing simplex work or need to reach repeaters that need a lobe down near the horizon to hit.

 

[teufler]

There are clone antennas of the diamond "style" antennas. 2 or 3 section fiberglass, with the radiating wire inside. Basically assemble and go. No tuning. I've had 3 for about 20 years. 2 section, 4.5 dbd gain, while the 3 section is 6.5 dbd. I use them for events as i travel around the county. The brand is workman, several ham dealers carry them. They have not handled high wind well, on water towers, the wind has beaten them pretty bad. But on 20-30 poles, on the sides of houses they have held up fine. Basic difference between the diamond brand and the clone brand is diamond has alittle more brass in the cuplings and the cuplings have alittle finer threads. I believe the brackets that come with the antenna that you would attach to a mast, are a bit stronger..