Antenna switch relay

[KB3ZI]

I’m building a cb style antenna patterned after the hygain super scanner antenna but built for vhf receive…looking for suggestions for relays for the switch box…
thanks
kb3zi

 

[prcguy]

I’m building a cb style antenna patterned after the hygain super scanner antenna but built for vhf receive…looking for suggestions for relays for the switch box…
thanks
kb3zi

Do you know what the original relays were like SPDT, DPDT? The Super Scanner (made by Antenna Specialists) has about 3dBd gain at best, that seems like a lot of work for little gain.

 

[KB3ZI]

Do you know what the original relays were like SPDT, DPDT? The Super Scanner (made by Antenna Specialists) has about 3dBd gain at best, that seems like a lot of work for little gain.

The antenna was rated at 8.75 db gain directional and 5 Omni…corrected size and spacing of elements should do nicely on vhf receive….the control box used dpdt relays and was 110 volts but 5 volt relays will work for receive

 

[prcguy]

The antenna was rated at 8.75 db gain directional and 5 Omni…corrected size and spacing of elements should do nicely on vhf receive….the control box used dpdt relays and was 110 volts but 5 volt relays will work for receive

The gain numbers are an outright lie, no more than about 3dBd in directional mode. Look at most antennas from this period, they all have ridiculous gain numbers like the 1/2 wave center fed Shakespeare Big Stick shows 7.65dB gain. But its a center fed coaxial dipole which has right around 0dBd gain. That's why I'm saying its a lot of work for little gain.

 

[buddrousa]

The only antennas I knew that were good numbers and that was the Avanti Astro Beam, Moonraker 4 and the Moonraker 6 beams. There gain was very good and the Front to Back Ratio was very good.
I started with the Astro Beam upgraded to the Moonraker 4 and then to the Moonraker 6 beam in the late 1970's early 1980's.

 

[KB3ZI]

This post is not about how good or bad an antenna is…that’s my point of experimenting it’s about the electrical mechanics thank you

 

[MotoMOTRAC]

The gain numbers are an outright lie, no more than about 3dBd in directional mode. Look at most antennas from this period, they all have ridiculous gain numbers like the 1/2 wave center fed Shakespeare Big Stick shows 7.65dB gain. But its a center fed coaxial dipole which has right around 0dBd gain. That's why I'm saying its a lot of work for little gain.

SOMETIMES its not the gain, but rejection (directivity, though low to moderate) off the back/sides that's important, as well as being able to get a rough first bearing ... the super scanner allowed almost instantaneous bearing (though rough) determination. Just sayin ...

 

[KB3ZI]

SOMETIMES its not the gain, but rejection (directivity, though low to moderate) off the back/sides that's important, as well as being able to get a rough first bearing ... the super scanner allowed almost instantaneous bearing (though rough) determination. Just sayin ...

The arrl Antenna book has a 40 meter switchable 5 antenna setup steering is electrical by shunting the other 4 using reflectors that’s where I’m headed but vhf receive as soon as I get switching figured out…help with relays is what I need not construction or theory thanks all

 

[MotoMOTRAC]

The arrl Antenna book has a 40 meter switchable 5 antenna setup steering is electrical by shunting the other 4 using reflectors that’s where I’m headed but vhf receive as soon as I get switching figured out…help with relays is what I need not construction or theory thanks all

Have you ever seen the little TO-5 package relays? They use a transistor TO-5 can package ... I used one to switch an RCA 40673 dual gate MOSFET 2m preamp in and out of an RF path into receiver back in the late 1970s ...

Edit: Diodes could be used today, PIN diodes.

 

[KB3ZI]

Have you ever seen the little TO-5 package relays? They use a transistor TO-5 can package ... I used one to switch an RCA 40673 dual gate MOSFET 2m preamp in and out of an RF path into receiver back in the late 1970s ...

Edit: Diodes could be used today, PIN diodes.

Not good at designing a circuit but that’s where I’m headed….low power dc switching 3 antenna separately or all three active at once

 

[prcguy]

SOMETIMES its not the gain, but rejection (directivity, though low to moderate) off the back/sides that's important, as well as being able to get a rough first bearing ... the super scanner allowed almost instantaneous bearing (though rough) determination. Just sayin ...

Yes the rejection off the back of of a Super Scanner is useful which can make the gain seem higher. In the end a 3 element Yagi on a small rotor will have similar rejection and more gain and will be simple to implement.

 

[MotoMOTRAC]

Yes the rejection off the back of of a Super Scanner is useful which can make the gain seem higher. In the end a 3 element Yagi on a small rotor will have similar rejection and more gain and will be simple to implement.

The super scanner allowed almost instantaneous bearing (though rough) determination. Sometimes ALL you've got to work with are a couple of short transmissions (you been there, done that right?)

 

[KB3ZI]

Yes the rejection off the back of of a Super Scanner is useful which can make the gain seem higher. In the end a 3 element Yagi on a small rotor will have similar rejection and more gain and will be simple to implement.

But you miss the point that a beam is not Omni directional so you need two antennas and a rotor where with my antenna I have both in one and have found a switch design that will work

 

[prcguy]

But you miss the point that a beam is not Omni directional so you need two antennas and a rotor where with my antenna I have both in one and have found a switch design that will work

I guess it all depends on how much performance you are willing to give up. For VHF use a Super Scanner has neither good directional gain or good omni performance for such a complicated device. The only thing that works ok is the backside rejection and you only have three direction choices.

You can get a lot more omni performance with a good used VHF gain type antenna and much better directionality with a good 5 element Yagi with both on the same mast with a rotor. I’ve used a number of CB Supers Scanners in the 70s and was never impressed. Plus most of them failed after a couple of years due to relay problems.

As for getting an instantaneous bearing, not really because you only have three bearings available, you will never know the actual bearing. I do marine band RDF for the USCG and mostly use a handheld 3 element Yagi and a Doppler DF. You can get a very quick fix with the handheld Yagi like within 5 seconds. A Yagi on a rotor takes longer like 30 to 60 seconds but it will be accurate where a Super Scanner type will not. I’m just pointing these things out before the OP embarks on a complicated design and construction project that will give limited results.

 

[KB3ZI]

It’s not a complicated build…it’s three vertically dipoles cut for vhf receive and a switch box..I’ve been experimenting with antennas many years so if you just have criticism look elsewhere

 

[buddrousa]

All in one never beat designed for. I had 2 near real near to me and bot wished they never wasted their money. One copied my setup the other bought my old raker 4 setup.

 

[MUTNAV]

So to sum up, you're going to have to figure it out (and post the results of the relay stuff here please if you do experiments ).

If you're a ARRL member, QST magazine from Nov 2024
has a homebuilt high power HF antenna relay that has 1.4 to 1 SWR at 144 MHZ.

 

[RFI-EMI-GUY]

I’m building a cb style antenna patterned after the hygain super scanner antenna but built for vhf receive…looking for suggestions for relays for the switch box…
thanks
kb3zi

Even at 2 meters the wavelength is so huge that you really do not need any special relay. Watch out for stray capacitance and excessive wire lengths.

 

[MUTNAV]

Even at 2 meters the wavelength is so huge that you really do not need any special relay. Watch out for stray capacitance and excessive wire lengths.

I was kind of wondering about that. Home-made step attenuater can be done with regular slide switches.

I guess one could be made and then if really sensitive about SWR, swept with a SWR analyzer or equivalent

 

[KB3ZI]

Even at 2 meters the wavelength is so huge that you really do not need any special relay. Watch out for stray capacitance and excessive wire lengths.

Yep I’m aware…thinking of switch with diodes