2 antennas, same mast?

[STTScott]

I'm building my base station using a BTech 50w mobile unit. (For the time beiing, I'm currently using an 8w Baofeng F8HP with a Nagoya UT-72 mobile anenna, magnetic mount, until all my equipment gets delivered.) So here's a techy question: I have 2 Ed Fong anrennas that i'll be using -- one UHF built especially for GMRS frequencies and one VHF built especially for Han Frequencies.

 

So -- would there be a technocal/performance problem if I lashed both antennas to the same mast -- AND/BUT I'm not using them both at the same time? Correct me if I'm wrong, but it seems to at if you have 2 antennas (one UHF and one VHF) and you're using one as active and the other inactive/no use/no TX or RX/basically dead), it seems to me that the 2 antenna/1 mast will work out OK.

 

OTOH, it wouldn't surprise me if an engineer person out there would advise against UHF'ing using a dead tree limb as some sort of redneck jerry-rig. But the  again, I dunno. That's why I'm here.

 

So what say y'all?

[gman1971]

First off, in case you were thinking about it, you cannot legally link GMRS with VHF Ham frequencies...  it is not allowed.

 

But, should you decide to crossband, the two radios you have will desense really bad due to the missing front end filtering on both CCRs, at least if you use this two antenna approach, that is.

 

Then, if the two antennas don't have enough vertical separation, you'll certainly incur in radiation pattern issues for the lower antenna...  as in: the lower antenna might not radiate in all directions equally, so it might create dead zones, both in elevation and bearing... in layman terms: range will suck, aside from the fact that those radios reception range for simplex already sucks... so it will suck squared.

 

You're better off with a dual band antenna and a diplexer, but again, given the radios you have, I'd keep my range expectations low... If range is what you seek, for personal use, without requiring infrastructure put in place by others (eg, repeaters) you'll have to do it the same way they did it. Which means you'll need a lot of Batwings (Motorola) and a lot of Greens ($$$$) Range in radio doesn't come cheap... My wallet knows this very well...

 

G.

[mbrun]

I'm building my base station using a BTech 50w mobile unit. (For the time beiing, I'm currently using an 8w Baofeng F8HP with a Nagoya UT-72 mobile anenna, magnetic mount, until all my equipment gets delivered.) So here's a techy question: I have 2 Ed Fong anrennas that i'll be using -- one UHF built especially for GMRS frequencies and one VHF built especially for Han Frequencies.

 

So -- would there be a technocal/performance problem if I lashed both antennas to the same mast -- AND/BUT I'm not using them both at the same time? Correct me if I'm wrong, but it seems to at if you have 2 antennas (one UHF and one VHF) and you're using one as active and the other inactive/no use/no TX or RX/basically dead), it seems to me that the 2 antenna/1 mast will work out OK.

 

OTOH, it wouldn't surprise me if an engineer person out there would advise against UHF'ing using a dead tree limb as some sort of redneck jerry-rig. But the again, I dunno. That's why I'm here.

 

So what say y'all?

Multiple antennas may be mounted to same mast, but things get more complicated quick. Take a look at almost any commercial antenna tower and you will notice lots of them.

 

The prime spot is almost always at the top and is reserved for your most prized and important service antenna. All others are mounted below it. Others are mounted lower to avoid one antenna from negatively affecting the other without very, very expensive equipment. But when you mount them lower you now have additional considerations that result in the need to mount the antennas on stand-offs out to side of the tower and away from conductive surfaces (metal tower) and the feed lines serving antennas high up to the tower. When the lower antenna is too close to the tower or a feed-line, the antenna impedance and radiation pattern of the antenna will be materially impacted.

 

I soon will be doing this myself. Currently I will be using a GMRS collinear antenna atop a 45’ HD fiberglass mast and will be mounting a similar design dual-band amateur antenna off the side part way up. While the fiberglass mast negates concerns of a conductive tower, I still need to add separation from the vertical feed-line serves the upper antenna.

 

Antidotally speaking, I can tell you that I tried hanging two Ed-Fong antennas from a common hook at the same elevation at my home, one for GMRS, one for amateur. Both receive and transmit range was noticeably degraded. I would easily tell because I am on the fringe of multiple repeaters in both services and my transmit and receive performance was immediately decreased. Separated them horizontally by a wavelength and seemingly back to normal.

 

If you will search the internet would will find a variety of calculators that will inform your vertical and horizontal placement decision.

 

Good luck.

 

Michael

WRHS965

KE8PLM

 

 

Sent from my iPad using Tapatalk

[gman1971]

Yes, absolutely, Michael... hopefully I didn't convey it cannot be done, just the fact that placing two antennas on top of each other is not as simple as just placing one atop the other and letting it rip... 

 

Your comment about how commercial antennas are installed is spot on... but doing things like commercial installations means $$$$ and time...  and then you need a lot of height, a good fiberglass mast, good feedline, using lateral extension to avoid feedline from messing with pattern... etc.

 

I think the OP is better served by a dual band with a diplexer than going through all the hassles of a two antenna installation.

 

Eager to hear about your results in your GMRS installation... what antenna do you have in mind?

 

G.

 

Multiple antennas may be mounted to same mast, but things get more complicated quick. Take a look at almost any commercial antenna tower and you will notice lots of them.

The prime spot is almost always at the top and is reserved for your most prized and important service antenna. All others are mounted below it. Others are mounted lower to avoid one antenna from negatively affecting the other without very, very expensive equipment. But when you mount them lower you now have additional considerations that result in the need to mount the antennas on stand-offs out to side of the tower and away from conductive surfaces (metal tower) and the feed lines serving antennas high up to the tower. When the lower antenna is too close to the tower or a feed-line, the antenna impedance and radiation pattern of the antenna will be materially impacted.

I soon will be doing this myself. Currently I will be using a GMRS collinear antenna atop a 45’ HD fiberglass mast and will be mounting a similar design dual-band amateur antenna off the side part way up. While the fiberglass mast negates concerns of a conductive tower, I still need to add separation from the vertical feed-line serves the upper antenna.

Antidotally speaking, I can tell you that I tried hanging two Ed-Fong antennas from a common hook at the same elevation at my home, one for GMRS, one for amateur. Both receive and transmit range was noticeably degraded. I would easily tell because I am on the fringe of multiple repeaters in both services and my transmit and receive performance was immediately decreased. Separated them horizontally by a wavelength and seemingly back to normal.

If you will search the internet would will find a variety of calculators that will inform your vertical and horizontal placement decision.

Good luck.

Michael
WRHS965
KE8PLM


Sent from my iPad using Tapatalk

[STTScott]

Thank you all for the enlightening answers. For now, I'm using a Baofeng handheld until my mobile (using it as a base) comes in, at which point I'll use the handheld for mobile. I basically asked my question to cut down on things becoming a small antenna field since I'm a renter -- even tho the 2 antennas  would't be used at the same time. I kinda figured things would get sketchy mounting 2 antennas on the same mast, but didn't know for sure. Again, thanks for the added knowledge.