For Lab Use Only
To NOT transmit
on 15 Meters until after a 'spur' fix has been found
In the interest of finding a fix for the spur at 15 Meters, I will be giving a very limited number of passwords out to people with the needed skill, experience, and equipment required for this task.
Please see if you can build on the experience/experiments of others. I will not comment on the inputs, so you will need to sift for content of value. Please keep us posted as to your progress. It would be great to be able to modify these radios to operate from 10 through 15 Meters. Thanks for your help. Keep us informed as to any success/findings.
11/20/98
yes thanks, the password worked,
i will be sending the priority bd stuff to you next week. alll the testing
worked out with the replacement chip.
scott
11/19/98
Input from Marcin
I have no problem with sinchronism
of PLL but I can't to use password frequency because my chip don't accept
this password I have no idea why. This simple
modification like added capacitor and adjusted filters on PLL board I was
made on first after I changed chip. The main problem is with not accepting
password freqency, maybe there are special conditions to set the password
frequency - maybe I have to set every memorys (now I have programed only 3
maybe 4 channels). I promise I'll study papers from you and I'll try to set
my chip on frequency below 24.800. I, of course, will keep conntact with
You.
It would be helpful to me if you could describe what you had planned to do to the PLL board as my 2600 won't go below 23 MHz. I increased the freq spread of one PLL by padding the varicap coupling cap with 150 pf. The main PLL does not like to go below 34 MHz.
It looks like, in my case, that the main PLL will require some work. Probably additional varicaps and changes to the integrator. It would save me some time if someone else has already solved this problem.
The spur at 2*10.69MHz is present all the time! I will table the PLL work and concentrate on the spur.
24 MHZ Broadband instructions for your HR2510
These instructions are to broadband your radio if you have the 24.000Mhz mod or the ChipSwitch installed.
MOD #1
#1. Take the four screws out of the speaker cover on the radio.
#2. With the radio upside down and the PLL board facing you, Remove the four screws in each corner of the pll board.
#3. Loosen the four screws on the sides of the radio that hold the PLL tray in the radio. Loosen them all the way before they come completely out.
#4. Pull the PLL board out towards you so the bottom of the PLL board is upside down.
#5. Look at the diagram below and locate C304, C326, & C327. At the point where they connect together, you will place 1 leg of a 50V 220pf capacitor (Radio Shack P/N 272-124) and the other leg to Ground of the board.
#6. Check your work and make sure you did not short anything out and that you placed the capacitor in the right place.
#7. Reassemble the PLL board and connect power to the radio.
#8. Connect a watt meter and a dummy load to the antenna jack.
#9. Put the radio on 29.500.Mhz and peak L310 for maximum output power.
#10. Now put the radio on 25.500Mhz and peak L319 for maximim output power.
#11. Reassemble your radio and your ready to go.
MOD #2 A simpler method...
Here is a simpler method of increasing the VCO coverage on the HR2510. If your HR2510 is Chipswitched, but doesn't lock on 12 Meters, this mod will take care of the problem without having to access the underside of the synth PCB.
Remove the four screws from the bottom cover and remove the cover.
On the PLL board locate L307 (TP306).
Install a small ceramic capacitor between the long lead of L307 and ground. Any value between 180 and 220 picofarad (pf) will do. There is a convenient ground loacted just behind L307. this locationis a plate-through hole (it looks like a shiny solder dot showing through the silk screening.)
The set should now lock from 24.800 to 29.900Mhz without further adjustment.
If you have access to a scope, the radio can easily be broadbanded for better performance in this new frequency range. to broadband, monitor the output at J311 and adjust L310 and L319 for equal output at the upper and lower limit of your operating range.
More information to be added soon so come back often.
If you have any Questions or Comments, you can E-Mail me at Rogerbird
Yes my 2600 has been operating on 12 meters for several years. I applied the password -- the PLL will not work below 24.8 MHz. Both loops break into oscillations. Must expose a pole in the loop. Looking in to fix.There is inadequate bypassing on the PLL board. The various oscillator and amplifier sections are not separated by chokes, etc. The LO is "spur city". Breaking up the power distribution is going to be a chore due to SMT design. Still analyzing to determine what and where new bypassing would be required. I'm sure others have been down this path before. Feel free to pass along my EMail address to any other folks who have been working on this problem. Our collective heads surely should come up with something.
The following is a typed copy of a letter Chipswitch sent out to all
interested parties on August 28, 1991.
-----------------------------------
An open letter to all CHIPSWITCH customers; August 28,
1991
As you may already know, the CHIPSWITCH engineers have uncovered technical
problems with the Low Frequency Modification Kit design, and this has delayed
our getting the product to market. The problems occurred because of 2
factors:
1. The slight variations in component / circuit performance from one radio to
the next.
2. The limited bandwidth of the VCO and transmit mixer filters.
Both of these obstacles were overcome in mid July and the first prototype
kits were produced and installed in a few "alpha test site" radios for
evaluation. All of these radios worked extremely well, giving full transmit
power and excellent receive sensitivity over the full 20.9 to 29.9 MHz
bandwidth the kit was designed to provide.
Recently, one of these radios was connected to a Hewlett-Packard model 8566
spectrum analyzer to evaluate spectral purity and spurious emissions during
transmit. It was then discovered that a "spur" (spurious emission) was
present in the transmitter output spectrum whenever the transmit frequency
was below 24.6 MHz. Analysis proved this spur (at 21.390 MHz and -23.5 dBc)
was actually the 2nd harmonic of the 10.695 MHz local oscillator circuit used
for both receive and transmit operations.
This was quite a surprise to our engineers as a properly designed double-
balanced mixer circuit (such as the one Uniden used in this chassis) should
offer at least 45 dB rejection of the high-level "switching" input
frequency. Apparently, the TA7320P mixer chip used in these radios does not
provide maximum rejection, and no external pins are provided to incorporate a
"balance adjust" circuit which might have improved the rejection to an
acceptable level.
After additional engineering efforts, we concluded that there were no low-
cost methods of reducing the spur to the -40 dBc level required by F.C.C.
regulations. Therefore, we decided to cancel production of the original 15
Meter Low Frequency Kit.
This caused a lot of disappointment among us at CHIPSWITCH as well as a lot
of ham operators who had been looking forward to having a low-cost 10, 12,
and 15 meter mobile rig.
Many of these operators urged us to provide the kit anyway, and their
argument went something like this:
CHIPSWITCH would not be breaking any laws by providing the kit since it is
the responsibility of the amateur himself to operate his station in a legal
manner. Since the spur would only be 0.2 Watt and was inside the 15 meter
band itself, the probability of interfering with another ham's operation was
small, and these hams would be willing to take that responsibility.
But for every ham who wanted the kit to be made available, there was another
who felt that if the spur could not be eliminated, the kit should not be
sold. A few heated arguments on local repeaters convinced us that we needed
to consult the A.R.R.L., the elected representatives of all American
amateurs. We explained the technical and ethical problems to them and
requested an opinion. Briefly, their position is that no radio should be
used by a ham operator that would inadvertently transmit a spurious emission
above the -40 dBc limit imposed by the F.C.C.. (A copy of their response is
enclosed on yellow paper.)
Therefore, the 15 meter Low Frequency Kit will not be offered as previously
announced. Instead, a 12 meter Modification Kit will be made available
sometime in the 4th quarter of 1991. Since this kit will only allow
operation from 24.8 to 29.9 MHz, the spur will no longer appear in the
transmit spectrum.
The following letter was sent in September of 1992.
---------------------------------------
12 Meter Kit Update
I am sorry to inform you that the 12 Meter Kit is not available for
shipping at this time. The kit has been designed and thoroughly tested on
numerous radios. The problem we are having, however, is that we are finding
it difficult to describe the process of removing the surface mounted
components on the backside of the pc-board in such a way that there is no
possibility the wrong component could be removed, or the wrong trace cut. We
have tried drawings and pictures of the backside, but still the hazard is
great. Those people who have been shown the procedure, have had no problem
installing the kit...it's just that 'first' kit. Many kits have been
installed, and there is nothing special about the components, they're mostly
'off the shelf'. It's just knowing where to install them, and how to safely
modify the backside of the pc board.
The following is a copy of the text of a letter from The American Radio Relay
League, Inc.
----------------------------
Dear Mr. Valentine:
The FCC specification regarding spurious emissions from an amateur radio
station is located in Part 97.307 (d) of the FCC Rules. It is as follow:
"The mean power of any spurious emission from a station transmitter or
external RF power amplifier transmitting on frequency below 30 MHz must not
exceed 50 mW and must be at least 40 dB below the mean power less than 5 W,
the attenuation must be at least 30 dB."
This rule is derived from the International Radio Regulations, which have
the force and effect of a treaty. Please be advised that the operator of any
amateur transmitting device that is violation of this specification, or any
other Part 97 rule, may be subject to possible enforcement action, including
monetary forfeiture.
During our recent telephone conversation you indicated that a Chipswitch
computer chip can be modified for 15 meters and installed in a Uniden HR-2510
or HR-2600 Transceiver. You further stated, however, that this modification
will result in a spurious emission being generated at 21.390 MHz that is only
-23.5 dBc. A spurious emission of this magnitude would render the use of
this transceiver on 15 meters to be in clear violation of the FCC rules.
We cannot recommend, and indeed we must actively discourage, the use of any
such amateur equipment that would be inconsistent with the FCC rules and
standards. This particular standard is a minimum standard and normally can
easily be met with current devices and technology. It is clearly in the best
interest of all hams to observe the rules regarding the amateur service and
to minimize unnecessary interference to other operators.
Please feel free to contact me if you have any further questions.
Sincerely,
---
Signed ---
Michael E.
Gruber
ARRL
Laboratory
As stated before............a password was install into the CHIPSWITCH IC
program to keep users from using 15 meters. We held out hope that a fix for
the spurs could be found, but no one has worked on this matter since.