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Author Topic: Multi-band Antenna with Counterpoises for City Apartments  (Read 715 times)
KD2BNT
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Posts: 1




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« on: November 02, 2017, 09:00:24 AM »

Greetings fellow hammers,

I'm new to the hobby despite being granted a license back in 2012.  I'm back now and just received my general license and I'm studying for the my extra examination.  As I rediscover radio, I've been tinkering with antennas and new ideas.  I would appreciate if anyone could help me with the following:

I'm experimenting with using a multi-band antenna (Comet UHV-6) in a city apartment setting (on the second floor), and my goal is to be to operate my rig on HF bands in addition to VHF/UHF.  The antenna is mounted on a mag-mount attached to a window-mounted air conditioner.

During an initial test run, my base radio didn't show any high SWR (I don't have an antenna analyzer yet) and my VHF/UHF transmissions seemed to be suspect when i used my handheld to test my base transmissions, however, i was able to make a contact successfully without any complaints.  My receiving seems to be excellent VHF and UHF.

As for grounding, I plan to ground my rig to a MFJ-931 (artificial ground) grounded to the building old cast-iron heating system (the type with the large radiators made from a large hunks of irion that release steam), and possibly ground the antenna mount to it too since it's only a few feet away from the window.

I've been reading about using counterpoises in apartment settings to improve SWR and transmission-reception issues, however, they need to be cut to size by using the equation 468/freq/2 in order to match your operating band.

My question is: can you add many counterpoise wires to a multi-band antenna to balance your antenna to work with the different bands the antenna is designed to operate in? 

David Garcia KD2BNT




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WB6BYU
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Posts: 17070




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« Reply #1 on: November 02, 2017, 09:40:34 AM »

Quote from: KD2BNT

... and my VHF/UHF transmissions seemed to be suspect when i used my handheld to test my base transmissions, however, i was able to make a contact successfully without any complaints...



This is quite common:  your transmissions overload the HT.

Consider what happens when you are talking through a repeater and listening on your HT.
Typically you are listening to the output frequency of the repeater.  When you transmit
on the input frequency using another radio nearby, your HT is overloaded by the RF and
sensitivity is greatly reduced on the output frequency, so you can't hear the repeater.
You don't hear the signal on the input frequency because you aren't tuned to it.

Typically you can hear your transmitter in that case when your HT is tuned to the repeater
input frequency (or on simplex) but  you usually can't hear the repeater well due to overload.




Quote
 

As for grounding, I plan to ground my rig to a MFJ-931 (artificial ground) grounded to the building old cast-iron heating system...



Probably work better if you just ground it directly rather than using the MFJ-931.

I've actually had good results using aluminum window frames for a ground, as they
were all tied together.




Quote

My question is: can you add many counterpoise wires to a multi-band antenna to balance your antenna to work with the different bands the antenna is designed to operate in? 



Yes, you can.  They may not "balance" the antenna, but they will work as counterpoises.

I tend to be pragmatic about such things:  I might, for example, add radials for 40m and 20m,
then try the antenna on various bands to see if that is enough.  If not, I add radials for any
problem bands and try again.  You don't always need separate wires for each band, but it
doesn't hurt.
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WB2WIK
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Posts: 21753




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« Reply #2 on: November 02, 2017, 10:58:33 AM »

A have a UHV-6 (several years now) which I purchased long ago intending to use it for some portable operations with it installed above the roof of my RV, which had all aluminum skins so I used a large 3-magnet type mag mount and duct tape (!) to literally tape the legs/magnets to the roof, creating a bond that would work when parked.

IMO it's not a good antenna.   Almost anything worked better on HF.   (On VHF it works fine.)

One thing I bought shortly afterwards which did work better and quite a lot better was the MFJ "Super Hi-Q Loop" model MFJ-1788:  https://www.mfjenterprises.com/Product.php?productid=MFJ-1788

This is a small loop antenna (about 3' in diameter) that works best (in my experience) when installed "vertically" and not horizontally and can be placed in a window opening or almost anywhere.   It is very sharply tuned and only operates over a few kHz of each HF band, however it's tunable remotely using the supplied controller and once you get the hang of that (tuning takes only seconds and it's very obvious when it's "tuned") it works remarkably well.

It doesn't use or require any sort of ground connection or counterpoise.
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