Dual Band Antennas (1 Viewer)

[bronc076]

Is there some magic to a dual band antenna? I have a Yeasu FT2980 2M radio and when I bought it I got an antenna I cut to length for the frequency I use and an NMO base, I picked the middle of the 2m band, like 146MHz if I remember what I did. Now I'm looking at dual band radios (Icom 2730A) which will transmit on both 2M and 70cm. I'm looking at dual band antennas and I have not done the math regarding their length. But what frequency are they resonant to? Or is it a factor, clearly a piece of wire 3' long will be a fraction of a waive for several frequencies, but I just don't know enough about this stuff to understand how a dual band antenna works. Is there some magic happening in the base I don't know about? I've been looking around on the interenet but I can't seem to find an explanation. They all seem to be pretty short so I'm thinking I'm comprimising my 2M performance. Still researching but I thought I'd ask you guys. What if I just use my 2M antenna, will it just be crap for 70cm? Guess I need an SWR meter.

A full waive at 440MHz is (2ft. 1 - 17/32in. or 0.648 M)
3/8 wave at 146MHz is (2ft. 4 - 7/8in. or 0.733 M)

courtesy Amateur Vertical Antenna Calculator - http://www.csgnetwork.com/antennaevcalc.html

So it is just a comprimise that works everywhere but not well, or again, am I missing something?

Thanks
Rob
KJ7JDB

 

[1911]

So it is just a comprimise that works everywhere but not well, or again, am I missing something?

Bingo. No, you're not missing anything.

I have a Larsen dual-band antenna on my 40 that is 1/2-wave on 2m (with a bottom-loaded coil) and I don't remember what on 70cm; it works well enough on 2m and I hardly ever use 70cm, but when I've tried it, it worked there too. I bought it when I got my dual-band radio, but if I were doing it again I would probably just get the best 2m antenna I could since I rarely if ever use 70cm.

 

[bronc076]

Thanks!

 

[JLH]

A quarter wave at 146mhz will also show a decent match at 450 but the takeoff angle is high. Simple, small and rugged though.

 

[Bunga]

Agree with chupacabra. I got a spectrum analyzer and was really shocked how bad (inefficient) a lot of dual band antennas are. Pick your main freq and get a matched antenna. Don't get me started on HT antennas.

 

[Pskhaat]

Agree with chupacabra. I got a spectrum analyzer and was really shocked how bad (inefficient) a lot of dual band antennas are. Pick your main freq and get a matched antenna. Don't get me started on HT antennas.

This is one of the reasons we stopped trying to come up with a dual-band radome antenna. Like in Oz, lots of folks are running two single bands with a band pass switch with better performance.

 

[DaveInDenver]

This is one of the reasons we stopped trying to come up with a dual-band radome antenna. Like in Oz, lots of folks are running two single bands with a band pass switch with better performance.

You pick your poison to some extent.

Say you're running a pair of monoband antennas that you combine using a diplexer. You have insertion loss and an extra layer of connectors.

If you use a switch instead of passive filters you can reduce some of the loss but then you can't work both bands simultaneously.

I have antennas done both ways, a plain Larsen dual band (I like the NMO2/70) and two monoband coupled with an MFJ-916. Both work. But then again I don't see any particular issue with my Larsen mounted on an NMO punched in the middle of my roof (this is not an insignificant detail). SWR sweep shows nothing concerning and the on-the-air performance meets expectations.

Honestly, there's more important things to worry about than this. Using a dual band from a major brand that doesn't make ridiculous claims is going to work fine. The dual or more band antennas that claim super gain and have several coils are probably going to disappoint, though.

But there's nothing wrong with the basic concept of an antenna covering multiple bands. Cellphones and WiFi devices rely on the principle of using collinear coils to make an antenna work on multiple bands.

 

[Kofoed]

A dual band is 1/2 wave length on 2m and does not need a grounded mount

 

[Pskhaat]

Say you're running a pair of monoband antennas that you combine using a diplexer. You have insertion loss and an extra layer of connectors.

Yup, there is absolutely loss through the switch/diplexer. As much as the attenuation in a dual-band antenna? Or course depends on the resonating bands for sure.

The dual or more band antennas that claim super gain and have several coils are probably going to disappoint, though.

The gain game is weird. We keep the inductor low (yes, with drawbacks on that) but don't coil along the radiating length.

 

[DaveInDenver]

Yup, there is absolutely loss through the switch/diplexer. As much as the attenuation in a dual-band antenna? Or course depends on the resonating bands for sure.

There would be no attenuation unless something is broken or not tuned. Depending on how a diplexer is made the losses would be similar to those in a matching or phasing elements.

If a multiband whip isn't tuned then it will show attenuation across your frequencies of interest. That's a design or construction issue, not a technical or theoretical one. As you go from one to two to more bands of coverage your margin of error for getting everything right is smaller. But a simple dual band with a coil in the middle intended to make a loaded whip on 2m (perhaps 1/2λ) and collinear or phased elements (perhaps two 5/8λ) on 70cm is well understood.

The antenna itself usually has enough gain to offset loses and ideally is slightly positive. No SWR sweep can tell you this overall performance. It can only show network losses or lack of them and antenna impedance, which ideally matches your expected impedance.

The special gain case would be a 1/4λ monopole that is considered unity gain. Any matching losses could be viewed as mathematically attenuation. But this antenna is actually 2.15 dB of gain over an isotropic antenna, so has gain in the real world depending on your reference (2.15 dBi vs 0 dBd).

The gain game is weird. We keep the inductor low (yes, with drawbacks on that) but don't coil along the radiating length.

That's a simplification, but generally yes loading coils should be at the feedpoint or center of an antenna with capacitance at the end, if you wish to use it.

 

[jackhossross]

Stumbled upon this thread, so something like this (to boost my AT&T and Verizon signals), is not worth it?

I was thinking of pairing this GME Antenna with a cell booster ..

 

[1911]

Stumbled upon this thread, so something like this (to boost my AT&T and Verizon signals), is not worth it?

I was thinking of pairing this GME Antenna with a cell booster ..

Are the cell phone frequencies here the same as used in Australia? Because your antenna wavelength needs to be some resonant multiple for the frequencies you are using, or it won't do you any good. There are companies that make cell phone boosters and antennas for here in the U.S.

weBoost | Cell Phone Signal Boosters for Home, Cars, RVs & More - https://www.weboost.com/

 

[Pskhaat]

wavelength needs to be some resonant multiple for the frequencies you are using

We have been looking at releasing cell/data antennas. It gets a lot more complicated with 5g now. The frequency bands are literally all over the spectrum. From way down low 600 MHz on legacy bands, all the way up to 40 GHz. The radome antennas that we produce which are similar in concept to GME's, are single-band and could be made to resonate only kinda well on a couple, but no way to get the full spectrum.

 

[1911]

The radome antennas that we produce which are similar in concept to GME's, are single-band and could be made to resonate only kinda well on a couple, but no way to get the full spectrum.

The nature of the beast and the inherent problem for all multi-band antennas everywhere in every/any frequency band. Physics can be a bitch at times.

 

[jackhossross]

Are the cell phone frequencies here the same as used in Australia? Because your antenna wavelength needs to be some resonant multiple for the frequencies you are using, or it won't do you any good. There are companies that make cell phone boosters and antennas for here in the U.S.

weBoost | Cell Phone Signal Boosters for Home, Cars, RVs & More - https://www.weboost.com/

Per GME's website the wavelength's that work on the multiband antenna I linked do match with the 4G/3G frequencies here in the states for AT&T and Verizon.

No clue on 5G - not really worrying about 5G at this stage.

 

[jackhossross]

We have been looking at releasing cell/data antennas. It gets a lot more complicated with 5g now. The frequency bands are literally all over the spectrum. From way down low 600 MHz on legacy bands, all the way up to 40 GHz. The radome antennas that we produce which are similar in concept to GME's, are single-band and could be made to resonate only kinda well on a couple, but no way to get the full spectrum.

I have been watching your developments, but it seems your stock is difficult to grab when its available. The reason for me going somewhere else.

 

[Pskhaat]

I have been watching your developments, but it seems your stock is difficult to grab when its available. The reason for me going somewhere else.

Well we just provided a huge lot out to those on our wait-list. We are releasing the rest to the store tomorrow

 

[Pskhaat]

No clue on 5G - not really worrying about 5G at this stage.

Research question:. Would you all be interested in NON 5g radomes?

 

[jackhossross]

Research question:. Would you all be interested in NON 5g radomes?

I am not sure I am the best person to sample, I just need something consistent - which when away from people, generally 5G just isn't as accessible as other connections.

So figured I would be fine targeting 3G/4G for my purposes of connecting to zoom and safety access/request.

 

[Pskhaat]

I am not sure I am the best person to sample, I just need something consistent - which when away from people, generally 5G just isn't as accessible as other connections.

So figured I would be fine targeting 3G/4G for my purposes of connecting to zoom and safety access/request.

By default, you don't really choose the band if your phone supports it. It's a tough step to crack.