From: Vadim Kogan (vadim@XCF.Berkeley.EDU)
Date: Fri Mar 18 2005 - 10:39:24 PST
(subject change, but reference to the original thread kept)
So, the consesnus is that nobody has tried to modify the AS-1729 itself, but
people have modified the MX-6707's elements for 30-33 MHz band to bring SWR
down to usable level.
So far, there is indication (from Jim) that there exists a more or less
detailed analysis/modification procedure in an article in some old MV
magazine. He might be able to find it, but possibly somebody else could.
Also, so far we don't know what actual inductors/capacitors are needed for
the base (let's assume the base is gutted and we're just putting in the
elements that are needed for low SWR on 27.205), nor do we know much about
the antenna itself... For the interested parties, here's the schematic of
what's inside the MX-6707: http://vadim.berkeley.edu/AS1729Sch.pdf. Note
that it has no values for any of the inductors or capacitors, so if somebody
has this information, I'd be very happy to have it (and put it up next to
the schematic).
We know the antenna is a center-driven vertical dipole with the top whip
being effectively a single-element pole, and the bottom whip being a coax
wrapped in a single-element pole? We don't know the lengths of the poles,
except that we hope they're the same length, possibly 2.2-2.3 m. I'm stupid,
so I don't really understand the purpose and operation all the 3 contacts
that go to the top part of the MX-6707.
One is the RF signal, which has in parallel an inductor or a capacitor. The
fact that there is only one position with the coil and the rest is with the
capacitors suggests to me that the coil is for the 30-33 MHz band and the
antenna itself is probably happiest around something near 33 MHz (or a bit
higher). Hence the suspicion that each part has about 2.2-2.3 m worth of
wire coiled up on it. Somebody should correct me :-)
The other two I'm a bit puzzled. I'd think that one of them would be pure
ground, but it isn't. I'm not very clear on the use of WHT/BLU line and the
inductors there. Somebody please enlighten me.
I really have no idea how bad is the antenna at 27.205 and whether there are
any modifications to increase the percentage of power it radiates.
Also, I wonder what people would recommend for a CB radio. RCI-2950/2970?
RCI-6900? Something else? Although I think I'll start with something used,
so if it walks away I will not cry too much (if somebody has something to
offer, please do so, MV list beats eBay). But eventually I'd like to have
something good (and one day get a HAM license).
Vadim.
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