In a message dated 29.11.99 18:19:55 Pacific Standard Time,
<< There are advanced AVC circuit requirements for DXers that allow working
300/hr on CW in contests. The 1000MP has a modification just for that and
I use a 1000MP, can you tell me where I can locate the info regarding the
mod you mentioned in your post?
I've had several requests for this information. I got it from Dennis
K7BV. He's the editor of NCJ and a contester on CW. He mentioned that the
1000MP was a contest CW receiver with an AVC mod. I asked if Yeasu knew
about it and he said they did. It would seem logical that if you want to
know if the factory knows and who should want to know--ask them. I asked
Dennis if the mod would help in SSB piles ups and he thought it would. His E
mail is email@example.com.
There are many variations of AVC action other than fast, medium & slow.
W7wjp was telling me that with on receive if you switched to an off band
antenna the voice volume stayed the same. With another receiver the voice
One DXer was monitoring another and noticed he was missing certain
letters on SSB. They switched receivers and problem went with the receiver.
This would not have been known without a side by side check by top operators.
Years ago a W6 DXer pulled a prank on his friend by inserting a 10 dB
attenuator in the antenna lead to his 75A4. In LA during a contest there is
enough RF floating around to burn out the antenna coils in the receiver.
Even off band signals raised the AVC voltage so that weak ones can't be
heard. The 10 dB loss was just enough to keep the average AVC voltage down
enough so that he heard more weak ones than his prankster friend. He removed
it from the receiver coax later and didn't tell him about it. He would have
never heard the end of it.
Reducing the RF gain a bit can be helpful at times.
RF Preamps that have gain controls could be very useful. They some times
have too much gain. Using one properly can have the affect to further filter
of off frequency signals.
In the 40's Millen came out with a RF Pre-amp with plug in coils for 20,
15, 10 & 6M. It had input and output variable Xc's for tuning each tank
circuit. It had a screen voltage control to vary the gain and an in&out
switch. It worked but the plug in coils had tuning slugs in them which
lowered the Q. I intend to increase the size of the wire and see what the
difference is. I plan to make an adapter that allows me to plug in KW tank
In those AM transistor pocket radios I noticed one had an in phase
feedback capacitor (regenerative style) of such value in a single IF stage
that it gave more gain and selectivity thereby requiring only 1 IF stage. I
thought that would be a great idea for a RF pre-amp. They all used
individual tank circuits for each band. I have a couple of these R9er's and
other RF tube preamps to work over. R9er's are available at flea markets for
usually $15 with coils.
Then much to my embarrassment a CBer told me of such a circuit in QST
about 25 years ago that he built. It works. The circuit is so efficient
that it used only 1 tank circuit for 20, 15 & 10. This variable in phase
feedback increases the stage gain and selectivity until it breaks into
oscillation. I would use an attenuator between it and the receiver so that
the reveiver works with a S9 or weaker signal no matter how strong the
initial signal is.
For some great reading, read the QST's and Radio Mags from the 20's &
30's. A 39 QST had an article on a 5M RF Pre-amp with Hi-Q tank circuits.
It used a 1/4 WL length of 4" copper tubing and copper center rod as the tank
circuit for the grid and plate circuit. This should be very Hi-Q and
selective. I picked up on this idea real fast and immediately zipped to the
conclusion page to see what they would claim for performance. It claimed 7
S-Units gain where 2 were noise and 5 were signal. If true or close to it
this needs to be made up which I will do when I get back to SD. I will make
these plug in copper tube 1/4 WL tank circuit so I can plug them into the
Millen R9er. If it works on 6M I'll make it for 10 and lower next. This
circuit should also reject off frequency signals for the over loadable so
called modern receivers with untuned mixers. This should help reduce
overloading on any receiver and suck those weak ones out.
I have those Converters that RME made for 10-2M. They have a tuneable
tank circuit in the 1st RF stage and by the time it comes through these
circuits and being beat down to say 10M it should be real clean. I've heard
that 6M transceivers about 8 years ago would overload in the F layer
openings. One could work 100 J's in an hour with 10W from the NW. There is
a RME tunable RF pre-amp for .5 to 40 MHZ that I have. I'm just waiting for
the piles ups on 6M this cycle. There are now more on 6M with bigger
antennas and Linears. Hams will be creating their version of HARP
I have a SX-88, 75A1 with 3 kc filter and a KP-81 I will be comparing
front end selectivity's to the modern ones. The passive preselector that was
in CQ is the best circuit I've seen and will try and find it.
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