Antenna Setup for base scanning?

[w4wxp]

Currently I have a Antcom/Powerwerx Wideband VHF/UHF Base Antenna ( https://powerwerx.com/base-station-wide-dual-band-antenna ) that I've been using for my RTL SDR, with LMR-400 going to it, about 25 feet up at the base or so.


I have a BCD436HP that is about to be on the way. Considering the frequency range, (That antenna alone will probably be deaf on 700, 800+ etc mhz, I'm guessing), would I be better off getting a diplexer and adding an 800-ish mhz wideband antenna? Or should I just pull the trigger on a DPD omni-x?

Suggestions?

 

[Ubbe]

It will probably work fine in the 800Mhz band. Any metal in the air will receive radio signals. One customer review says " Good SWR on public safety frequencies also."

The Omni-X hasn't any 800MHz specific antenna element and it's the VHF and UHF elements that receives the 700-900MHz bands.

/Ubbe

 

[w4wxp]

It will probably work fine in the 800Mhz band. Any metal in the air will receive radio signals. One customer review says " Good SWR on public safety frequencies also."

The Omni-X hasn't any 800MHz specific antenna element and it's the VHF and UHF elements that receives the 700-900MHz bands.

/Ubbe

My concern is that some lengths receive better than others - for example, my 160 Meter OCF Dipole is deaf on some ranges it isn't designed for (some of the maritime ssb bands, for example), unless I crank my preamp all the way up on my Icom 746.

 

[vagrant]

Your current antenna notes a frequency coverage of 145-162 MHz & 445-469 MHz. Whether it works well enough around 800-ish your dongle would be able to let you figure that out now. If not, a diplexer and the additional 800-ish antenna would help with some gain on those frequencies you want to monitor. Still, do you have a source for a diplexer that splits above/below 500 MHz? If not, the Omni-X may be more suitable.

I would love to see several SWR plots of the Omni-X on the frequency ranges it covers, or at least one big sweep. I will probably purchase one and sweep it myself one day. Consider this, the wide coverage of the Omni-X will typically have less gain versus a purpose built antenna for a limited range. Still, that may not be a bad thing as it depends on one’s needs. This is why a discone is a favorite as a 118-500 MHz single antenna. It will even receive above and below that with strong, or nearby transmitters.

Wide coverage, low gain, single antenna = Omni-X, Discone, Scantenna
vs
Narrow coverage, improved gain antennas using a diplexer or triplexer.
vs
Wide coverage low gain using a 118-500 discone and a 800-ish antenna using a diplexer with a split at 500 MHz.

…. or dedicate a scanner for each narrow gain antenna improving your chances of hearing a transmission in that range instead of scanning additional frequencies, or stopped on one. This last one is the best option, but has more cost and or multiple antennas in the air may not be feasible.

 

[Ubbe]

I would love to see several SWR plots of the Omni-X on the frequency ranges it covers, or at least one big sweep.

You can make antennas with perfect SWR but are still deaf. I had a Diamond X512 up and listened to some HAM repeaters and noted their signal strengths and also scanned all my usual frequencies between 70-470MHz. Then I took the antenna down and modified it by soldering jumpers over capacitors and change the bottom coil with it's capacitor signal dividing net to get all the "raw" signal out by taking the signal out from the top of the coil. I had done a sweep of the antenna prior to that and that looked good, but after the modification it was 3:1 at best and usually 6:1 in the HAM bands. When listening and checking the signal strengths from the HAM repeaters they where actually stronger, double up at some 3dB but the big difference where all other frequencies outside of the HAM bands that where up to 10dB stronger even with incredible bad SWR.

It's a matter of getting all of the signal to the receiver and not reducing it by losses in SWR matching circuits, if you do not need to use the antenna for TX. I wouldn't think that the Omni-X have any SWR matching but it's three dipoles in parallell and will make it look weird when looking at a SWR sweep, and the proper performance test would be to check the received signal strength compared to another antenna.

/Ubbe

 

[w4wxp]

You can make antennas with perfect SWR but are still deaf. I had a Diamond X512 up and listened to some HAM repeaters and noted their signal strengths and also scanned all my usual frequencies between 70-470MHz. Then I took the antenna down and modified it by soldering jumpers over capacitors and change the bottom coil with it's capacitor signal dividing net to get all the "raw" signal out by taking the signal out from the top of the coil. I had done a sweep of the antenna prior to that and that looked good, but after the modification it was 3:1 at best and usually 6:1 in the HAM bands. When listening and checking the signal strengths from the HAM repeaters they where actually stronger, double up at some 3dB but the big difference where all other frequencies outside of the HAM bands that where up to 10dB stronger even with incredible bad SWR.

It's a matter of getting all of the signal to the receiver and not reducing it by losses in SWR matching circuits, if you do not need to use the antenna for TX. I wouldn't think that the Omni-X have any SWR matching but it's three dipoles in parallell and will make it look weird when looking at a SWR sweep, and the proper performance test would be to check the received signal strength compared to another antenna.

/Ubbe

Yeah... a T2FD is a good example of that. Great SWR, but I think your erp is about 5% or something?

 

[vagrant]

Agreed, and a standard Diamond discone would be a good candidate many have experience with. While the results would obviously not be identical for everyone in a comparison at their location, it would be reasonable enough...of course the comparison testing would need to occur morning, noon and night. My Scantenna is definitely directional, so I might see an Omni-X sooner rather than later.

...and the proper performance test would be to check the received signal strength compared to another antenna.
/Ubbe