Batboard

I have updated my original doc to include missing pictures of the VCO disassembly, and a new section on the transmitter output filter mods for full power up to ~ 54 MHz.

I also added info on the P200 and the LCD display radios along with what software to use for the various radio models.

You can pm me or go to yahoo RadioModifications or Yahoo MOTOROLA-USER and find the new copy in their files section.

It is in Microsoft Office Word 2007 format.

As of this day repeater Builders still has the old copy so don't go over there for the new doc.


Just received an e-mail from Kevin at repeater builders and he should get the updated doc in soon.


Mike

Mike,

Any problems with rx sensitivity?


David Epley, N9CZV

on several radios converted most were around .3 uV all the way up to 53.99, some would only do around .35 at the upper end but still usable.

why what are you measuring ?


If I had an actual schematic of the radio to work from I could probably come up with some better receiver mods if needed.

.9 is the best I get

How are you injecting the generator signal in and is the receive channel the same as your old 53.41 frequency that used to be on Greens Peak ?

I have that channel in 1 of my HT's and it measure ~ .335 uV, another thought is what sensitivity are you measuring at around 52.525MHz, this will give me an idea if its the L/C matching components directly at the antenna connector or somewhere else.

Are you doing the antenna connection to RF generator the way in the article with a small pigtail connector directly at the antenna connector ?

Hopefully so and if your getting good TX power across the band with the same output connector then it very well could be one of the matching components farther back in the receiver stage or as I said the match right at the antenna connector, especially if your not using any high end transmit channels in which case it may not show up easily.

I had a similar problem with a down banded MT1000 from the ~approximate 36 to 42 MHz split down to 29 MHz it would not do better than about .8uV until I changed a lot of parts farther back in the receiver chain and evn then best it did was ~.4 uV.

Also Is there any chance that you your problem radio is a mid split radio that was reprogrammed as the high split version this would show up as poor RX all across the 50 to 54 band.

Mike

Dave,

Some more information from some radios that I worked on a couple of years ago.

Coming off of the antenna connector there is a shunt capacitor to ground at the antenna connector end, this capacitor is marked H1 so it is 20 pf, in some of my radios converted for another ham my notes mention that I had to add a 10 pf to 15 pf 0805 or 0603, 50 to 100 volt, NPO chip capacitor in parallel with the existing capacitor.

There is also an inductor coming from the antenna connector end and going to the Hybrid antenna switch module and this inductor is 8 turns.

This inductor is clearly visible from inside the radio towards the antenna connector, I had to spread open wide 3 of the 8 turns on this inductor to enhance TX power and receive sensitivity at the upper end of the 6 meter band.

I would first try and spread this inductors turns while measuring RX sensitivity and if you reach a limit then try and parallel a 10 to 15 pf chip capacitor, or maybe even a small trimmer capacitor from the antenna connector to the adjacent ground plane and then go back and re-adjust this inductor and the capacitor to see what effect this has on RX and TX performance.


When I find my digital cameras software I'll take some pictures and pass them along and also include these notes to a revised document.

Also I'm still looking for a schematic for this radio and then maybe I can go ahead and further optimize the RF section some more.


Mike

Anybody have any views on aligning the RX front end of a 29MHz MT1000?

I've searched around but cannot find any info on front end alignment - such as which pots to tweak

I'm aware that RSS Service Mode is only for SQ and Dev - front end is manual pots.

Anybody got any alignment extracts from the service manual?

My 30-36MHz MT1000 works great on 29.6MHz - with no RSS HEX editing you can program down to 29.5Mhz. I'm finding RX sensitivity on 29.6MHz is good - I can copy the NY 29.62 MHz repeater OK on the helical - but maybe I can actually improve RX sensitivity by realigning front end?

Thanks

there really weren't any tuned slugs in any of the coils for the pre-selector so adjustment of the front end is pretty much up to sweeping the preselector and coming up with new cap and inductor values.

I'm thinking that those who don't have a network analyzer/sweep generator and spectrum analyzer could use something like an MFJ-259 or similar analyzer to look at the receiver pre-selector tuning and play around with the front end coils and the pre-selector components if they need to improve the RX performance.

When I down banded my 36 to 42MHz radio to 10 meters I used a network analyzer and swept each stage of the receiver to come up with new cap values, unfortunately I only planned to do 1 radio and I didn't document the changes at all.

I too am looking for a schematic of either the MT1000 or the P200 low band radios, if anyone can help out with a schematic then I'll model each radios receiver stage and try to come up with some better component changes.

And yes I did try google and everything listed as having a valid schematic or service manual came up as not having it anymore once I contacted each source.


Mike

Thanks mike m

Its useful to know that there are no tuning slugs in the Low Band MT1000 front end coils - which is also the case with my 29MHz Maxtrac.

RX sensitivity at 29.6MHz using my 30-36MHz MT1000 is OK- so I will probably leave it as is!!!

I guess being only 400KHz "out of band" will not result in much loss of performance. It was the same with my Maxtrac which was only 100KHz out of band as the Maxtrac officially covered 29.7 - 36 MHz. With the Maxtrac, RX sensitivity was still OK at 2 MHz out of band - RX sensitivity was about 3-4dBm down at 2 MHZ out of band but still very useable.

With the 29.7-36 MHz Matrac, I was thinking that it might be possible to add either ferrite or brass slugs to the "empty" coil cans to peak performance on 29 MHz??

Brass slugs or screws in the MaxTrac front-end coils will raise the usable frequency a few MHz. To lower it, you'd want ferrous metal slugs or screws, #6-32 size, about 1/4 inch long, but only if you need to move more than 2 MHz. For a few hundred kHz you won't gain any noticeable improvement (3dB is noticeable, and you might get 0.25dB gain).

The MaraTrac radios uses the same RF boards and would have identical characteristics.

Bob M.
======

--> Mike M: Check your PMs. <--

For anyone needing some more 6 meter receiver and TX improvement on a P200 or MT1000 low band radio go to this link and down near the bottom download the following PDF's.

http://www.repeater-builder.com/motorol ... index.html

Document 1: Radius P200 Low-band RF board information <Schematic

Document 2: Radius P200 Low-band Alignment Procedure <Service manual

Don't forget to download the following PDF so you won't have to do the convoluted programming in the original document.
Document 3. Modifying the low-band P200/MT1000 RSS to cover the 6-meter and 10-meter bands

I'm still working on more in depth tx mods but here some quick fixes for low sensitivity above 53 MHz and low power above 52 MHz, this will improve power in the 52-53 MHz range, I'm still addressing some >53 MHz issues but I figure most 6 meter TX use appears to be below~ 52.54 MHz.

I am also presently analyzing the Remote/Standard hybrid antenna switch module U103 to see how much it is rolling off and if I find that it is effecting performance then I may remove and bypass it but this is still a TBD mod.

These component designators are the schematic ref designators from the manual that you will download above for 6 meter only. I'm still working on the 10 meter fixes.

These changes should be done even if there were any similar changes in a 2nd or 3rd revision document that I may have previously posted on other user groups in which some of you may have performed.

1. Locate capacitor C8 on the receiver back end filter and replace it with a 68 pf chip cap of the same size
2. Locate capacitor C2 on the receiver front end amp and replace it with a 100 pf chip cap.
3. Locate capacitors C131 and C130, which are lumped 1/4 wave line components on the T/R switch and replace each with a 51 pf cap of the same size.
4. Locate C126 on the antenna side filter and replace it with a 20 pf chip cap.
5. Locate capacitor C127 on the antenna filter and replace with a 39 pf chip cap
6. Align the receiver across your operating range by the method in the 2nd document, basically tune L12 and L13 for best sensitivity across your operating range.

If you are using the remote antenna sense connector then perform these mods.

1. Locate chip capacitors C125 and C124 and replace with 51 pf chip caps of the same size.


Transmitter mod to get more power above 52.0 MHz

You can do the 2 capacitor TX component changes if desired or just mod L120 and then go directly to the align stage and simply tune C115 and C159 to see what improvement you gain.

If you really need more than ~ 6 1/2 watts above 52.5 MHz or your radio is till sagging above 52.5 MHz under 5 watts then do the 2 capacitor parts changes also but remember that power will still roll off more above 53MHz.

1. Locate C117 on the TX low pass filter and replace with a 75 pf chip cap, (a 82 Pf cap could work if you can't find the 75pf value) of the same size and preferably a 100V rating. A high Q cap is recommended here.
2. Locate C116 and replace with a hi Q type 130 pf chip cap, this extends the tuning range of C115 so you can peak tune above 52 MHz.
3. L120 should be an 8 turn inductor of approximately 150 nh, as it was originally it is 9.5 turns so remove 1.5 turns.


Align the transmitter using the procedure in the 2nd document, tune C159 and C115 and please use a long insulated tool when tuning C159.

I did not notice any differences in peaks of the two tuning caps so go ahead and tune C159 for best power at your highest TX frequency and then adjust C115 for best balance of TX power across the band while staying between 6 and 7.8 watts (mine was 51.11MHz low to 53.0 MHz High on TX).

Also be aware that your maximum Tx current will be just over 2.1 amps due to the power transistors efficiencies degrading above 50 MHz.

I was able to get 6.0 to 7.8 watts across my operating range from 51.11 low to 53.0MHz High on Transmit.

Due to some stability issues with resonances in the collector chokes of Q101, Q102 and Q103 I did not want to push for more power above 53 MHz than around 6 watts and this is an issue that I'm working on now.

I have a newer document with these changes and some prior ones that never were posted and when I finish wish the stability issue I'll submit this one.


Mike