Mobile antenna questions
Moderator: Queue Moderator
Mobile antenna questions
I have a VHF antenna on a 50 watt Orion radio and a tri-band antenna on a Kenwood TM-D700 ham radio. Both antennas are located on the roof of my vehicle with about 2 feet of space between them. My question is can I put an 800 mhz Phantom antenna in between those 2 antennas without any problems. The 800 mhz radio is a recieve only unit and doesn't transmit but I wanted to find out if there would be any problems doing this before I do it. Thanks in advance for any help.
With 2 feet of separation, even halved, you should have no problems with mounting the Phantom within that space, and should not have negative interactions with either.
Even 12" spacing is greater than a 1/2 wave at 800, so there should NOT be any coupling taking place from VHF or UHF.
The Phantom is small in height, and with 3", that does not have enough height to be affected by a UHF or VHF near-field RF signal, and the frequency separation also helps a great deal as well.
I run 65 watts on VHF, and 35 on UHF and have the dualband antenna spaced less than 10" from the 900 antenna connected to the GTX mobile, and aside from some desense on VHF, I have not detected any harmful signal levels geting back down the cable to the VHF radio from the 900 radio, or vice versa with high band.
The IFR could see a rise in the noise floor, with a few minor spikes above and below the 140-160 range, but nothing of a level that could harm either radio.
But for peace of mind, I rarely run 65 watts on VHF, mostly it's set at 25.
VHF: FT2800M
900: GTX
UHF: MTS2000 with homebrew amp (45 W. max)
900 antenna: Tuned 3 dB collinear, NMO
Diamond diplexer for UHF/VHF
Antenna: Radiall Larsen 2/70, NMO mount, 2.5Dbi on VHF, 4.5Dbi on UHF.
I attribute the desense to the wideband nature of the 2800, since the receiver is quite sensitive across a wide frequency range, this does cause near-field RF levels to interact and create noise in the front end, but not enough to cause any damage to the receiver.
Not to mention, the GTX is NOT running within factory spec when programmed for amateur use, although close, it still falls outside the tolerance, and will cause interference to a receiver placed in the near-field of its antenna, but at least the transmitter does not have the RF levels to cause physical damage to another radio placed close to its antenna, and would probably only damage one if fed directly from the GTX.
But nobody would do this, would they?
Even 12" spacing is greater than a 1/2 wave at 800, so there should NOT be any coupling taking place from VHF or UHF.
The Phantom is small in height, and with 3", that does not have enough height to be affected by a UHF or VHF near-field RF signal, and the frequency separation also helps a great deal as well.
I run 65 watts on VHF, and 35 on UHF and have the dualband antenna spaced less than 10" from the 900 antenna connected to the GTX mobile, and aside from some desense on VHF, I have not detected any harmful signal levels geting back down the cable to the VHF radio from the 900 radio, or vice versa with high band.
The IFR could see a rise in the noise floor, with a few minor spikes above and below the 140-160 range, but nothing of a level that could harm either radio.
But for peace of mind, I rarely run 65 watts on VHF, mostly it's set at 25.
VHF: FT2800M
900: GTX
UHF: MTS2000 with homebrew amp (45 W. max)
900 antenna: Tuned 3 dB collinear, NMO
Diamond diplexer for UHF/VHF
Antenna: Radiall Larsen 2/70, NMO mount, 2.5Dbi on VHF, 4.5Dbi on UHF.
I attribute the desense to the wideband nature of the 2800, since the receiver is quite sensitive across a wide frequency range, this does cause near-field RF levels to interact and create noise in the front end, but not enough to cause any damage to the receiver.
Not to mention, the GTX is NOT running within factory spec when programmed for amateur use, although close, it still falls outside the tolerance, and will cause interference to a receiver placed in the near-field of its antenna, but at least the transmitter does not have the RF levels to cause physical damage to another radio placed close to its antenna, and would probably only damage one if fed directly from the GTX.
But nobody would do this, would they?
Re: Mobile antenna questions
You could stop adding new holes to the roof and consider
using a tri-band antenna. Have installed a number of these
for use on a mobile command vehicle. They wanted more
radios and ran out of antennas and places to mount them.
In using the tri-band antenna, you also end up using
what is called a triplexer. This takes and band splits
the antenna signal into 3 different ranges. You end up
with 3 antenna ports for the radio side and one for the
antenna side. You have a port for VHF, a port for UHF
and a port for 800 MHz. The radios operate just fine.
It's lke you have an antenna for each of the bands
with only a single one on the roof.
Jim
using a tri-band antenna. Have installed a number of these
for use on a mobile command vehicle. They wanted more
radios and ran out of antennas and places to mount them.
In using the tri-band antenna, you also end up using
what is called a triplexer. This takes and band splits
the antenna signal into 3 different ranges. You end up
with 3 antenna ports for the radio side and one for the
antenna side. You have a port for VHF, a port for UHF
and a port for 800 MHz. The radios operate just fine.
It's lke you have an antenna for each of the bands
with only a single one on the roof.
Jim
I have a tri-band antenna on my Kenwood D700 now but I can't figure out how to get it to work with my 800 radio or I would. I still have my triplexer that I used to use with my UHF and VHF Spectras and the D700 but I no longer have Spectras so its in a box. If I use the triplexer with the D700 and the 800 radio how can I put them all together? The triplexer has 3 cables off of it for each band (UHF,VHF and 800 ) and one input for the antenna cable but the Dual band D700 only has one antenna jack and one on the 800 radio so if you can tell me how to do it I gladly will. It is probably something simple that I have overlooked. LOL I will definitely appreciate any other help.
