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Re: Which Dual Band FM Rigs for AO-27



    Could someone post a link or some info on which dual band mobile rigs
    (if any) are best suited
    to AO-27 FM type operation. I will be using small AZ-EL  CP steerable
    beams and preamp for
    the antenna end.

I've worked 25 states/provinces mobile with Yaesu FT-5100 and a omni-
antenna (mostly a 2 meter quarterwave because of its pattern at 70cm)
I would presume that whatever Yaesu says is the successor to that line
work fine. It was recommended to me specifically because it can receive
AO-27 without a pre-amp (although you may need a directional antenna in
some urbanized areas).

I've also used an Alinco DJ-G5TH, which seems to be at least as sensitive.
(I even made a couple of contacts using its stock rubber duck with a chain
link fence as a reflector, just as an experiment.)  It is sufficiently
sensitive that they have a button that switch in an 6dB attenuator on
receive for use in high-intermod areas.  I only infrequently use it, even
in the S.F. Bay Area, but it does solve many of the problems that a friend
of my complains bitterly about on his IC-W32A (which he has worked AO-27
with).  With an antenna similar to an Arrow, it works great and either 
should do well in your scenario.

One feature that's especially helpful for both is the ability to transmit
on the opposite band while being able to quickly change the receive
frequency.  You're probably going to be adjusting doppler 'by ear', so
this feature is almost essential.

    Anyone contemplating a dual band radio should consider the new Dual Band
    HT coming out soon that includes all of the following features:

	<amazing list omitted>

    I have seen it do a 9600 Baud PACSAT downlink with a handheld 3 el beam!

And that should be even better with the antenna you're considering or with
something comparable to what i'm using.  Yet, i don't know about you, but 
i don't think my budget is ready for this one yet.

    I use an Icom Z1A. About the only thing I did different with it from
    normal terrestrial FM was to set the frequency change resolution down to
    the minimum. I can now tune from 435.8 to 435.9 in 5 KHz increments. Not
    really sure even that was necessary.

You definitely want 5 KHz steps, but that's fairly standard now.

    1) tunes 430-440 MHz (mandatory)  2) full duplex operation (manadatory) 

Agreed.  You might be able to do without (2) on an occasional basis, but
please, make sure you can hear the downlink to some degree, even if you
can't hear yourself very well.  On AO-27, you're not so much listening
for your own downlink as hearing when someone else is talking over you.
Indeed, a modest amount of QRM on AO-27 is from people trying to make
sure they can hear themselves.  Don't worry, just put out your call when
you can copy other people's callsigns and someone will get back to you.
Really.

    3) can tune 70cm band (for doppler adjustment) while transmitting on 2M. 
    (many dual-band FM rigs make the "main band" for TX also the "main band" 
    for tuning)  

IMPORTANT, as previously noted.  If you have a choice between an HT with
that feature and a mobile without it, take the HT.  It's that significant.

    5) separate VHF and UHF antenna jacks, or use a diplexer so the preamp
    doesn't get hit with RF.  Preamps with rf-protection/switching help for
    the day when you accidently transmit on the feedline you would NEVER, EVER
    do that on.

That's one of the reasons i suggest something comparable to of the two rigs
that i'm using -- it can avoid the complexity of a diplexer; but that's only
relevant if you're using a true dual-band antenna as i'm doing. (And a 2m
quarterwave tuned for good SWR at 436.8 qualifies.)  The Arrow is normally
supplied with separate VHF/UHF cables, so it's better if you rig has that.
But that may be pretty rare among dual-band FM rigs and you'll probably be
using a diplexer.  I'm very happy not to be using a pre-amp (and rather by
getting gain thorough the antenna), as i know that someday, i'll forget.
(I just happy that my rigs have so far been able to transmit briefly into
an open circuit...)  So, an RF-switched pre-amp is what you'll want, and if
you can't afford that, think about the combination of your transciever and
antenna choices.  

    Separate radios are VERY practical, esp. on a bird like AO-27 where the TX
    frequency is fixed.  Note that some older used 70cm rigs that only tune
    430-440 MHz can be had for less $ becuase they don't cover the US FM
    repeater band.

Indeed, as then you can use separate antennas and not have the 70cm side
de-sensed by the 2m side while transmitting.  You're also less likely to
damage your pre-amp if you can run 70cm rig without a microphone connected.

			-- KD6PAG  (Networking Old-Timer, RF newbie)


P.S.  I've got a new QTH!  A large stack of cards will go out as soon as
i get settled, but send me e-mail if you want it sooner.  If you've sent
me a card and i haven't replied, please send me e-mail in case the card
was lost in the mail; those will go out within 24 hours.
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