grundig: UKW Bandwidth expansion - 5040W/3D

Dear Colleagues,

After some research into the UKW (FM) bandwidth, I am perplexed as to how difficult it might be to slightly "increase" the 100Mhz (or 104 Mhz) within the European radios to avoid the use of an add-on FM converter or FM expander.

While stationed in Japan from August 1965 until August 1968, in order to receive the Japanese FM stations on US made radios, there were small FM converters sold which covered the 76 - 90 Mhz range, and had circuitry to produce the IF 89Mhz (+/-500khz). The unit was powered by 6 UM-2 (1.5v D-size batteries) and used three transistors. Power consumption was 1VA.

I realize the above explanation relates to a decrease in the FM bandwidth - my question relates to a slight increase.

Would the additional modifications to the present circuits be sufficiently difficult to increase the FM reception range by 1 or 2 Mh??

Respectfully,
Robert

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Dear Robert,

I hope i understand Your Question correctly. If You want to hear Your favorite Station at i.e. 102 MHz, while the Radio only works between 87 and 100 Mhz there are two ways, worth a try.

Our Favorite Station Classic Radio is at 101.3. On Grundig Musikgerät 1099, Nordmende Elektra
( 1959 ) and Loewe Opta Planet , all only 87 - 100 Mhz, i made the Alignment as follow:

I set the Radio to 100 MHz, and tuned the Oszillator to recieve 101,3. then i tuned the
other CAP for maximum Sensitivity.

This works fine for my 3 Radios, and the Reception was good on the whole FM scale, but it was impossible to tune to Stations below 88,5 Mhz ( this is, because the whole scale is shifted. )

I would expect, that the limit of variation is about 2 Mhz, so if Your favorit Station is at 107.5 this won't help.

The other Way is, to realign the whole FM Tuner. You will need to realign the Coils and the Caps. The Question is, what the limit of variation is, and if it is possible at all. The other question is, what the Sensitivity looks like across the whole FM Range. You only can align 2 points, low end with coils, high end with caps. whats in between is taken care of when the circuit is designed, and will only be valid, for the original Frequecy Range.

If You want to try the first way, i can try to give You instructions, how to do, step by step.

Best Regards,

Henning Oelkrs, Berlin, Germany

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Dear Henning,

Thank you so very much for your prompt response. Essentially the "shift" of frequencies will be completely adequate, since 2 of the local stations transmit mostly excellent Diversified and Classical selections (with some public service announcements) respectively on 89.3 and 90.1 - but some very nice Top 40, Jazz, and Golden Oldies are transmitted on 100.5, 100.7, and 101.5. . . . .

For another excellent Jazz station (on 107.5), I will be content to enjoy those offerings on the Grundig 5490St/U. . . . .the export model with full 88-108Mhz.

My overriding doubts concerned the tolerances normally expected on the 100Mhz side of the band. I had presumed the typical maximum to be less than 1.0 Mhz.

I recently finished repairs on a Saba 300 Automatic 9T (US export model), and realized that the band could be shifted slightly; however, the shifting was from within the middle frequencies and they were off not much more than 1 or 1.5 Mhz.

I shall try the procedures first on the Nordmende Othello, and the Imperial 6024W . If I have no problems, then I will "shift" them up on the Grundig 5295 with the Wunschklang register.

Mit Freundlichen Grüße,
Robert

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Liebe Henning,

I have received 3 email requests - from 2 US members and 1 other Bavarian radio enthusiasts to PLEASE ask Herr Oelkers to provide a detailed step for the "FM shift" technique. Radio models they identified were Graetz, Nordmende, Philips, and of course, the popular Grundigs.

One gentleman was hoping to hear some words from Herr Knoll, but I assured him it would be a very minor task. He has a nice Telefunken Opus 55, and believes the procedure would be wonderful if he could receive the Classics 101.5 station

Thank you so very much,
Robert

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I've done this to lots of valve radios since there is a Swedish transmitter slightly above 101 MHz that people wants to hear,and I have never run into ny problems as long as the frequency shift is as small as this.Only when it comes to maybe 3-4 MHz or more,could it be difficult with the trimmers.It's quite simple really,once you've tried it.Henning Oelkers explanation of how to do it is correct.Coils for the low end and trimmers for the high end.

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Dear Robert,

my Step by Step Procedure is as follows:

1. Find out, which Cap Trimmer is for the Oszillator, and which for "Vorkreis" ( 1. circuit ).
    - Tune to a Station near to 100 Mhz.
    - Put a little piece of Tape on the Dial Glass, and make a mark.
    - Put a second mark (i. e. 1,5 Mhz) below this mark. This is, where the given Station is to
      be heard after the Procedure.
    - Put little Marks at the Caps with Felt Tip Pen, to notify the beginning.
   - turn the Oszillator Cap Trimmer slightly, the station will go away. If you can tune in
      the  Station with the normal Tuning knob, then it was the right Cap Trimmer. If You find
     the Station moved nearer to the second Mark, then You turned the correct direction.
2. Go on trimming and tuning in little steps, until You reach the second Mark. If Your set is Equipped with 180 Deg Ceramic Trimmers, note that they have no turning limit, and after reaching minimum Capacity, they go again to maximum  
3. To observe maximum Sensitivity across the whole UKW Scale, You schould tune to a Station
    in the 97 Mhz area, and tune the other Cap Trimmer for maximum Sensitivity.
 
4. Check the Tuning Results across the Whole UKW Scale. Depending of the Design of the Circuit, it may be difficult or impossible to reach the full Sensitivity.


If You are not shure, which trimmer is which one, it would be needed, to have the Exact Model in RM, Circiut Diagram, and a detailed Picture of the UKW Unit.

Please remember: Observe always Your personel Safety Precautions. 

Hope this will Help You ( and Your Colleagues ).

If You like or need Instructions for a Specific Model, please POST from the Model Page.

Best Regards,

Henning Oelkers,

Berlin 

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Dear Henning,

I hope the gentlemen who inquired of the specifics are viewing your specific instructions............I personally like the idea of a separate converter that uses a dedicated IF of approximately 99Mhz; and then the target receiver is left completely unmodified, and the tuning on the "converter" allows the full range from 100Mhz all the way up to 108Mhz.

Those converters were generally available only in isolated locations; and are extremely rare.

My ISP (Earthlink.net) has been having intermittent and sporadic problems on some Web based services today, and I am unable to access my WebMail.

I am sure there will be some appreciative readers.

Once again, thank you for the detailed instructions.

Viele Grüße,
Robert

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There is an even better and simpler solution than making a converter with a fixed IF: Mix the antenna signal with a fixed 10MHz crystal oscillator, using a high quality double balanced mixer, like a SRA-1 or similar. A simple fixed tuned preselector filter with two tuned circuits, stagger tuned to cover 100-108 MHz, is added ahead of the mixer 'black box'.

Without this circuit the radios receives 88-100MHz as usual. With it the radios tune 98-110MHz. The only downside is that the sensitivity will drop by a factor of 10 or thereabouts. If one is driving the fixed converter from a domestic cable network, then this should be less of an issue. Alternatively a simple preamplifier could be added, but this will be more problematic to build properly for persons with less experience in VHF circuitry.

I intend to build one of these, as I already have the needed parts in the junk box.

Hope this helps a bit.

Frank.

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