Preselector Question
sam
85' (or so) inverted L. I've read that a passive preselector is what
I need to resolve the overload. MFJ has a few:
* MFJ-956 (.15-30 MHz LW/MW/SW Preselector/Tuner) $49.95
* MFJ-1048 -- Transceiver Passive Preselector 1.6-33 MHz $$119.95
Has anyone done a comparison of these (or the 956 and the 1046)?
Aside from the difference in frequencies that are covered (both get
the vast majority of the shortwave bands, right?) what are the main
differences? Why is one over twice the price?
I know that I could shorten the antenna, but on a shorter antenna I've
not been able to pull in some of the more weak/distant signals. I'm
hoping that a passive preselector will allow me to block out the
impeding signals without having to whack away half of my antenna.
Thoughts?
Thanks,
-sam
Philip
--
pb
"sam" <adon...@yahoo.com> wrote in message
news:5147a47d.02082...@posting.google.com...
Mark S. Holden
Hi
Not familiar with the specific models other than what's in the catalog but here's some observations:
The 1048 is made for folks who transmit and receive.
They also have a 1046 that's receive only and it's about $100.
All of these units cover all of the shortwave bands. The more expensive ones apparently filter out the AM Broadcast Band. This
won't help if you're chasing distant AM BCB signals, but it'll probably do a lot to reduce or eliminate your overload problems
when you're listening to shortwave frequencies.
I expect/hope the more expensive ones would also have better build quality.
Diverd4777
adon...@yahoo.com (sam) writes:
>
>* MFJ-956 (.15-30 MHz LW/MW/SW Preselector/Tuner) $49.95
>* MFJ-1048 -- Transceiver Passive Preselector 1.6-33 MHz $$119.95
>
>Has anyone done a comparison of these (or the 956 and the 1046)?
>Aside from the difference in frequencies that are covered (both get
>the vast majority of the shortwave bands, right?) what are the main
>differences? Why is one over twice the price?
>
I live in a very RFI heavy environment.
I've owned both;
the MFJ 1046 hasn't ever overloaded.
I think they should have pictures of both on their WEB site.
( But yes, try using the attenuator first..)
DAN
Ron Hardin
transmitting as well need to carry more current so the parts are
heavier duty.
I have a couple 956's that I use sometimes to take out intermodulation
in following broadband amplifiers. They're trivial circuits but
probably would cost you $50 in parts and chassis and scrounging
around time to duplicate.
It's like buying a MW loop instead of building one. It actually
saves you money and is neater in the end.
--
Ron Hardin
rhha...@mindspring.com
On the internet, nobody knows you're a jerk.
WA6LZH
difference. I don't think the MFJ units will do you any good if overload
is your problem. In fact they may very well be worse.
Tony
sam
Yes, I've had good success with the attenuator, and the strong signals
come in extremely well when attenuated. I'm hoping a preselector will
enable me to bandscan weak signals without the interference from the
overloading.
"Philip" <pl...@earthlink.net> wrote in message news:<Udsa9.701$N%4.6...@newsread2.prod.itd.earthlink.net>...
Diverd4777
> I don't think the MFJ units will do you any good if overload
>is your problem. In fact they may very well be worse.
>
How so ??
Mark S. Holden
A passive preselector won't add gain.
It's a tunable bandpass filter - it attenuates signals that are away from the frequency you want to listen to.
A simple attenuator will also attenuate weak signals that I presume he's trying to get.
WA6LZH
designed "Front End" to combat intermodulation from strong signals
within a band. I find it difficult to believe someone can design such a
circuit and sell it for 50 dollars. Especially MFJ. It is even harder to
believe when you consider that this device is operating full on and
without the AVC action of the receiver it is connected to. I am speaking
of course to the "Active" type and not the "Passive". I think a passive
device would add some front end selectivity and help the intermod
situation. I've used an antenna tuner on 160 meters with an NC-300 and
all but completely eliminated the Broadcast Band "Ghost" signals that
prevented 160 meter reception almost entirely.
Tony
WA6LZH
principle I suppose. It eliminated Broadcast Staion "Ghost Signals"
almost completely. I don't hink I'd spend too much for just a tuned
circuit though.
Tony
CW
--
CW
KC7NOD
"WA6LZH" <tang...@lucent.com> wrote in message
news:3D6AC543...@lucent.com...
CW
circuit.news:3D6AC412...@lucent.com...
Al
news:3D6A9D...@mindspring.com...
> It's like buying a MW loop instead of building one. It actually
> saves you money and is neater in the end.
Ron, you must have had some bad experiences here! I feel the same way about
winding toroids. The d*mn wire never stays where I put it. Oh well, it's a
good way to vent some aggravation!
Al
KA5JGV
WA6LZH
help. I paid much less for my Yaesu FC-901 antenna tuner at a flea
market and it handles 300 watts. Do MFJ if you like but I'm sure you can
find a simple circuit for a tuner on the net and with a receive only
power requirement you can get away much, much cheaper than 49.95 and
probably have a better made piece of equipment. I've found the simple L
network with alligator clips using a homemade coil and an old broadcast
variable makes a fine tuner. The internet is a fine place to do a search
for schematics, instructions etc. Don't be too dissappointed if you
don't achieve all the results you ask for. If the 7600GR is one of those
portable SW receivers that uses a telescoping antenna you may be. It
was designed for that antenna or the active antenna that is it's
accessory. Putting a long wire on it may be the source of your problem
but you are right in thinking a tuner may help. It may. In my day a
preselector was an amplifier. A tuner was a tuner. But men were men and
women were women. It may be that all we old farts are not worth
listening to but listen anyway yu never know what might turn up.
So we all adapt.
Tony
Diverd4777
> It may be that all we old farts are not worth
>listening to but listen anyway yu never know what might turn up.
>
>So we all adapt.
>
Tony:
" Growing Old isn't for Sissies"
( Betty Davis )
- or maybe it was Ernest Hemmingway
sam
It may be that all we old farts are not worth
> listening to but listen anyway yu never know what might turn up.
Tony, great reply and advice. I definitely appreciate your insight. Thanks!
-sam
starman
As I mentioned earlier, a passive preselector completely removed the
intermod's caused by connnecting my Sony-2010 to a fairly long
inverted-L antenna, so I have every reason to believe the results would
be similar for the 7600GR.
If you're going to build a passive preselector, the inductors (coils)
should be made with ferrite cores to provide a high 'Q' which will make
the tuning quite sharp. Ideally the coils should have adjustable ferrite
cores (slugs) so they can be aligned for each tuning range. Using a
variable capacitor of about 365-pf, you can cover the entire shortwave
spectrum (3-30 Mhz) with two coils. They need to be switched into the
tuned circuit, one at a time, typically with a rotary switch.
*****
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sam
Unfortunately, setting up my antenna taxed my mechanical abilities,
and I doubt I could figure out how to 'roll my own' unless is was
really easy and required no knowledge of electronics - at least not
without some handholding. Thus my question, which probably should
have read "can someone recommend a passive preselector that I can buy
that's not $100" (which sounds expensive).
starman <sta...@tech.net> wrote in message news:<3D6C5D8A...@tech.net>...
WA6LZH
I'm not sure that a ferrite core coil or torroid has a higher Q
than an air wound coil. In fact if memory serves me I think the air
wound coil is best. It certainly is more easily constructed. A coil with
a ferromagnetic core will certainly be smaller, have less "Mutual
Coupling" and may have an acceptable Q. From an internet search:
What are the advantages of an air core coil?
* Its inductance is unaffected by the current it carries. This
contrasts with the situation with coils using ferromagnetic cores whose
inductance tends to reach a peak at moderate field strengths before
dropping towards zero as saturation approaches. Sometimes non-linearity
in the magnetization curve can be tolerated; for example in switching
converters. In circuits such as audio cross over networks in hi-fi
speaker systems you must avoid distortion; then you need an air coil.
Most radio transmitters rely on air coils to prevent the production of
harmonics.
* Air coils are also free of the 'iron losses' which affect
ferromagnetic cores. As frequency is increased this advantage becomes
progressively more important. You obtain better Q-factor, greater
efficiency, greater power handling, and less distortion.
* Lastly, air coils can be designed to perform at frequencies as
high as 1 Ghz. Most ferromagnetic cores tend to be rather lossy above
100 MHz.
http://www.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html
At any rate I wish the fellow with the intermod problem good luck in
obtaining a "Passive Preselector" at a modest cost and I hope it
resolves his problem.
Tony
RHF
.
For a Pre-Selector / Antenna Tuner, you may wish to consider the Yaesu
FRT-7700 for its extra filtering for the AM/MW band.
.
I have used the MFJ-901, 1020, 1040, and 959 and prefer the Yaesu.
The FRT-7700 is small and compact but packed full of features. It has
a both a High-Z (Push-Terminal) Antenna Input and a Low-Z SO-239
Antenna Connector. The outputs are two mini-coaxs: one for the AM/MW
and the other for the SW bands. Front panel controls: ON-Off; A-B
Antenna; Output DX/BCB & SW; Attenuation 0-60dB; Band Switch LW, MW,
SW-4; Matching 1-4; and Tuning. I use mine with a MW 'Un-Tuned' Loop
Antenna and Random Wire Antenna for SW. Works well with my Kenwood
R-5000, and I do not have to change set-ups each time I go from MW to
SW. They can be found 'used' in the $50-$75 price range on eBay.
Also Yaesu made the FRA-7700 Active Antenna that has the same
frequency range and only requires 9VDC to operate with any receive.
.
~ RHF
The O/M of the 'new' Kenwood R-5000 Yahoo Group.
* http://groups.yahoo.com/group/kenwood-r5000/
.
Jake Brodsky
wrote:
>At any rate I wish the fellow with the intermod problem good luck in
>obtaining a "Passive Preselector" at a modest cost and I hope it
>resolves his problem.
Umm, if you're getting IMD from modern powdered ferrite cores, you've
got bigger problems than most listeners on this news group can deal
with.
Keep in perspective what we're talking about here: Consumer radios
(not military) and we're talking about adding an preselector to limit
common wideband radio problems such as second order IMD products.
We're not trying for extraordinary Q, we're not trying to transmit
through these cores. Saturation is not much of an issue here.
73,
Jake Brodsky, AB3A mailto:fru...@erols.com
"Beware of the massive impossible!"
Robert F Wieland
WA6LZH
really easy to wind a simple coil, buy a capacitor and clip them
together thus rolling your own antenna tuner, save some money and learn
a bit in the process. Nothing wrong with buying a premade box, we've all
done it. I just wanted to point out a viable alternative. Oh OK and
maybe get a new recruit. I'm also really irked by any company that sells
a coil and a cap for 50 bucks.
Tony
gil
Gil
sam <adon...@yahoo.com> wrote in message
news:5147a47d.02082...@posting.google.com...
Ron Hardin
There's also input and output jacks, box, switch and several coils
and caps. Probably it's like a Huffy bicycle, cheaper to buy that
way than getting the parts individually, and it's already a bicycle.
If you already have all the parts in the junk box, it's another matter.
I didn't think there was a Lucent in Columbus any more. And why isn't WA6
California?
WA6LZH
feel any tremors lately though. I think my NNTP server may be in Ohio.
Well I can pick up a few feet of bare copper wire next to nothing, a
piece of plywood pretty cheap, an alligator clip probably in Berkeley
(Although sold for a different purpose) and a small variable from Radio
Shack. I can wind a coil on a piece of PVC or like I did when I was 9
yrs on an Oatmeal container and I have a pretty darn good L-network
antenna tuner. One that will provide an impedance match and out of band
rejection as well. Total cost maybe 5 or 10 I dunno maybe more maybe
less but I can say for sure lots of fun. The coil is connected one side
to the "Hot" antenna terminal on the radio, the other end to the
antenna. A short lead clips the alligator to one side or the other and
the cap goes from either end to ground. Start with maximum capacity and
clip up or down on the coil until maximum signal is heard then tune the
capacitor for a further increase.
starman
I agree that a properly made (dimensioned) air coil core can have a
decent 'Q', but as you point out, it would be considerably bigger than a
ferrite core coil for HF use. I assume that compactness' in a passive
preselector is a virtue.
I too am bothered by what they get for a small metal box with a handfull
of low cost componants, except perhaps for the variable capacitor.
*****
starman
He wants to use a longer antenna for weak signals without the
overloading problem. That's what the passive preselector does.
*****
gil wrote:
>
> For that radio, shorten the antenna.
>
> Gil
>
> sam <adon...@yahoo.com> wrote in message
> news:5147a47d.02082...@posting.google.com...
> > I'm getting lots of nighttime overloading on my 7600GR connected to an
> > 85' (or so) inverted L. I've read that a passive preselector is what
> > I need to resolve the overload.
Mark S. Holden
>
> 8/28/02
>
> I agree that a properly made (dimensioned) air coil core can have a
> decent 'Q', but as you point out, it would be considerably bigger than a
> ferrite core coil for HF use. I assume that compactness' in a passive
> preselector is a virtue.
> I too am bothered by what they get for a small metal box with a handfull
> of low cost componants, except perhaps for the variable capacitor.
> *****
The parts used in building something like this are probably a very small part of the actual cost to produce it.
When you're building something as a business, you need to set the price high enough to cover packaging, printing, labor,
insurance, taxes, the factory, advertising, warranty repairs, shipping, profit for yourself, and a markup for the retailer.
But I agree it seems silly that you can buy a bare bones portable SW radio for less than a basic antenna tuner.
A great reason for building your own is you can select a better grade of parts - for example, the preselectors I've tried would
be much nicer to use if the knob on the variable capacitor was replaced with a 3:1 vernier dial.