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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 20th Jul 2021, 2:15 pm   #21
G8BBZ
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Default Re: Redifon R550A

I stand corrected on the HEF4750/4751 - I remembered them as a Motorola part which highlights the dangers of relying on memory in old age.
I should perhaps also have mentioned that the R500 family was the first processor controlled equipment in the Redifon inventory.
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Old 20th Jul 2021, 9:40 pm   #22
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Default Re: Redifon R550A

Peter G8BBZ said:
Quote:
The R499 can be used with an external LO source simply by feeding the LO signal directly into the mixer - this was a factory option.
This is what I have been doing with a synthesiser into the mixer but it still only allows you to receive those frequencies that the front end filters are tuned to. My synthesiser doesn't have enough grunt but even if I put some amplification in to it, I would still be limited to the filter frequencies. Crystals are the real answer, only three required, but the money box isn't full enough!
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Old 20th Jul 2021, 10:56 pm   #23
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Default Re: Redifon R550A

The HEF4750 & 1 might deserve to be split into a thread of their own.
They were quite difficult to get your head around, to begin with, but once you understood them a bit more....

David-RW, I'm trying to recall Mike Underhill but it just won't come. I think perhaps I came to that party just a bit too late. Sorry if a bit OT.
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Old 23rd Jul 2021, 10:59 am   #24
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Default Re: Redifon R550A

Pat Hawker, G3VA, briefly mentioned the R499 receiver in his Technical Topics column in the April 1968 issue of Radio Communication.

Mike Underhill, G3LHZ, worked for Mullard / Philips for many years, working on frequency synthesizers, including the HEF 4570/1 and other things. He later went to the University of Surrey. Many years ago (late 1990's ?) he caused something of a controversy over the efficiency of small transmitting loop antennas. Google is your friend on this one.

The HEF4570/1 were used in the design of a synthesized communications receiver which was published in the first issue of Ham Radio Today, ie the January 1983 issue. The article mentioned Terry Giles, G4CDY, and indicated his involvement in the design of the integrated circuits. He also wrote a technical note:
T. G. Giles, Versatile LSI frequency synthesizers system, Mullard Technical Note 142
I think that I may have a copy, but at the moment I am not in a position to check.

I am curious to know what the phase noise performance of the HEF4750/1 was like in HF receiver applications.

HTH and 73

John KC0G / M0KCY
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Old 23rd Jul 2021, 11:27 am   #25
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Default Re: Redifon R550A

Thanks John for the info regarding Mike Underhill. I used to have that article you refer to. I seem to recall the main thing about the HEF4750 (the PLL) was it had two phase detectors, allowing two loop bandwidths, one for fast lock, the other one slow to maintain it. It switched between them as lock was approached/achieved. That might make it quite good?

In the Pye MX290 series of PMR radios the HEF4751 was not used. The divider was something else from Plessey. It was serial loaded with the division ratio in 4x4 bit bytes. Maybe other manufacturers did this mix and match too?

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Old 23rd Jul 2021, 11:51 am   #26
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Default Re: Redifon R550A

Hi All,
I am not aware that any phase noise figures for the R500 were ever published by Redifon. However, the R500 was intended as a high spec receiver for use in demanding environments so I would expect that phase noise must have been a design criteria.
Also, the same synthesiser was used in the companion DU500 Transmit Drive and there was an increasing concern about the effects of transmitter phase noise on overall system performance when used with broadband RF Power Amplifiers in multi receiver, multi transmitter installations - as in Naval Integrated Comms Systems.
The digitally controlled, motor tuned FET RF amplifier used as in both the R500 and the DU500 was also packaged separately as the RFS11 Pre/Post Selector for use in situations where tight control of RF bandwidth was required - a well known application is the DWS Piccolo terminal using the Plessey receiver intended for Embassy deployment where the guys in the Embassy across the street may well be running kilowatts of power on their systems ( a lot like a Naval environment really)
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Old 10th Aug 2021, 10:02 pm   #27
John KC0G
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Default Re: Redifon R550A

Re. post #24, I am now back home and have found:
T. G. Giles, Versatile LSI frequency synthesizer system, Mullard Technical Note 142, TP1790, 1980
I made a typo in the original title. This is a 16-page printed document. On the back it states that is reprinted from "Electronic Components & Applications", Vol. 2, No. 2, February 1980.

It is an updated version of:
T.G. Giles, Use of LN123 and LN124 LOCMOS Devices in Frequency Synthesizer Systems. Mullard, TP1756, 1979.
These were the earlier part numbers of the HEF4750 and HEF4751. My copy runs to 43-pages in a type-written format. It includes notes on the (VHF) Synthesizer Evaluation Board.

Sadly I can find neither document online.

The HEF4751 is a universal divider. With external prescalers it can divide by 6.5 decades. The devices can be slaved, with an extra two digits per slave divider. The data sheet indicates that it has two outputs: a higher frequency output, with some phase jitter, and a lower frequency output with no jitter. I was not familiar with the rate multiplier techniques which are used to control the dual modulus prescalers. I had to work quite hard to really understand how it all worked.

The HEF4750 is a frequency synthesizer device. In comparison to the HEF4750 it is relatively straightforward. It does have two phase detectors to drive the single output. The higher speed one is a conventional phase / frequency detector. One it gets close enough, the output from the pahse / frequcny detector goes into a tri-state mode, and the sample and hold phase detector takes over

The synthesizer in transceiver described in the Jan 1983 issue of Ham Radio Today (see post #24) is a single loop design with 1kHz steps. It did state (page 15) that this could be reduced to 100Hz steps with the addition of two CMOS 4000 i.c.'s "with no sacrifices in performance". Details were to be published in a later issue. I have not found them, but have not looked very hard. The article also mentions a commercial communications receiver manufactured by Redifon used the same chip set to gives steps of 10Hz. I assume that this was multi-loop design.

73 John KC0G / M0KCY
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Old 10th Aug 2021, 10:52 pm   #28
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Default Re: Redifon R550A

Quote:
Originally Posted by John KC0G View Post
is a single loop design with 1kHz steps. It did state (page 15) that this could be reduced to 100Hz steps with the addition of two CMOS 4000 i.c.'s "with no sacrifices in performance"
I think that's enough to get me proper suspicious. There aren't any free lunches and the first trace of 'summat for nowt' is an indication that one or other of the things is not working to its proper capabilities.

David
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Old 27th Nov 2021, 2:10 am   #29
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Default Re: Redifon R550A

The attached article appears to refer to the single-conversion R500, although it was not mentioned by name.


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Old 1st Dec 2021, 4:28 pm   #30
John KC0G
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Default Re: Redifon R550A

Michael O'Beirne, G8MOB, was reported as making the same comment in the Technical Topics column in Radio Communication, March 1986, p.67.

The patent application, which is mentioned in the paper, for switched filter circuits was published as CA1162994 and US4385402. I have not found a GB or European patent.

The same paper was used as the basis for Chapter 5, "IF Amplifiers" by C.S. den Brinker and R.A. Barrs in "Radio Receivers", edited by William Gosling, IEE, 1986.

73 John KC0G/M0KCY

Last edited by John KC0G; 1st Dec 2021 at 4:30 pm. Reason: typo
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